Apr 292014
This backup battery setup looks good, but there's one huge mistake the prepper made in developing it.  Do you know what it was?  The answer is at the bottom of the article.

This backup battery setup looks good, but there’s one huge mistake the prepper made in developing it. Do you know what it was? The answer is at the bottom of the article.

This is a further part of our series on solar energy.  Please also visit our sections on energy in general and solar energy in particular for more related articles.

There are two ways of developing a solar system for a retreat.  By far the simpler is to simply go out and buy the biggest bestest system you can afford, and whatever you end up getting is what you have, and you’ll adjust and survive as best you can with what you have and the energy it provides.  There’s little danger you’ll end up with ‘too much’ solar power!

The more complicated way is to work out how much power you need to live your life to a certain standard of comfort and convenience, and to buy sufficient power generating capacity to provide this.

If you’re just going to buy a system and hope for the best, we’d urge you to buy way more capacity than you think you might need, and way more than the sales people are telling you to get.  That’s an interesting reversal – usually sales people tend to oversell and you can buy less than they tell you is necessary, but in the case of solar power, the chances are the opposite may be true (we guess salesmen undersell because the true full costs and complications can become rather daunting).

Even if you’re just going to buy a system and hope for the best, you should still read through the rest of this and the associated articles in our solar power series, so you have at least some idea of the big gap between claimed power generating capabilities and the actual energy you are likely to receive (sometimes there can be a five-fold discrepancy), and can create some sort of realistic expectation for what you’ll actually be able to do with your system.

In our article ‘How Much Solar Generating Capacity Do You Need‘ we looked at some of the considerations needed to match your power and energy requirements (two similar but different things, as explained here) with what to expect from solar panels.  The big problem is that the output from solar panels varies more or less proportionately with the intensity of the sunlight shining on them, and the total sunlight each day can vary widely, depending on just on season, but on each day’s specific weather.

So although you can work out your average daily needs for power (probably with some seasonal variations) and similarly, you can work out your average daily power generation (again with seasonal variations) the problem is that your actual daily power generation will sometimes be much higher than average (well, that’s not a problem, is it) and on other days, will be much less than average (and there’s your problem!).

The other big issue with solar power is that at night, solar power reduces down to zero.  You need to supplement solar power either with another power source that does work reliably at night, or with a means of storing/saving energy during the day that you can then tap into at night – the most common example of which being batteries.

Clearly, you need to select a system with as much power as possible to keep you going on very low sunlight days.  But there is also a point at which you can switch strategies – by increasing your battery storage capacity, you can provide yourself with additional energy reserve by storing up surplus energy on sunny days, and using that stored energy not only at night, but on days with less than anticipated sun, too.

Within reason, and ignoring some minor issues, the bigger the battery reserve you have, the smaller the actual solar generating system you need, because the batteries are smoothing out the peaks and the troughs as between your energy production and your energy consumption.

Batteries for Bad Days

So, we know that the solar power you’ll generate will vary from day-to-day, and some days will have less power generated than you want, and perhaps even less than you need.

There are three ways to respond to this.  The first is to upgrade your solar generating capacity still further, so that you still get the energy you need, even with much less sunlight.  The second is to have some alternate backup sources of power generation.  The third is to have more battery capacity, so you can smooth out the peaks and the flows of daily power generation with stored battery power.

In this third case, you are using batteries for two purposes.  The first is to take power generated during the day and use it the immediately following night, with the expectation that come shortly after sunrise the next day, you’ll have used up your battery power (at least to the discharge level you set yourself) but that at the same time this happens, energy will be flowing back into your retreat from the solar panels.

The second purpose is to allow for cases when, after discharging your overnight batteries, the sun does not come up and shine as brightly as hoped for the next morning and you need to continue relying on your batteries for some/much of your energy.  (A similar situation is where you generate enough energy during the day for your day’s needs, but not enough for the next night’s needs too.)

The chances are that you’ll have the same batteries doing both tasks – this is not like, for example, a motor home which might have both a starter battery for starting the engine and a separate ‘house’ battery for running appliances from.  At your retreat, you simply increase the size of your battery installation and use them for both overnight and top-up during the day purposes as needed.

This is a good thing for another reason too, because it means on a typical day, you’ll be discharging your total battery system less than you would with a lower capacity system, meaning you’ll have more charge/discharge cycles in total before the batteries eventually die.

How Much Extra Battery Capacity to Add?

To use a similar scenario to that in previous articles, if you need 20 kWh of energy a day, and if you have a system that can generate 25 kW per hour of full sunlight, let’s also assume that on average you expect to get 2 – 2.5 hours of full sunlight a day, and you have configured things on the expectation of it all working right even with only 1.125 hours of full sunlight.

Maybe you could say ‘Well, we know that, no matter what, the sun will always rise, every morning, so even on the worst of all days, there will still be perhaps 15% of the full energy available for harvesting through the system.  That would mean a really bad day would give you 0.34 hours of full sunlight equivalent, and you could get 6.75 kWh of energy from that weak amount of sunlight.

You need 20 kWh of energy a day, so you have a 13.25 kWh shortfall.  You already have a battery resource designed to give you at least 5 kWh of energy for nighttime, so it seems you need to increase your battery resource by another 8.25 kWh of net capacity to give you the ability to work through a really bad day.

Now, what say you have two bad days in a row?  Do you need to add still more battery capacity?  Maybe, you do.  But perhaps not quite as much as you might think.  We’ll assume that, on the second day with very little sunlight, you’ll stop using any electrically powered things that aren’t essential.  You’ll stop using your hair dryer, your dishwasher, and so on.  And on the third day, you’ll cut back even further, so that your 20 kWh consumption figure drops way down to start with, approaching closer to the perhaps 6.75 kWh of energy created.

Don’t get us wrong.  More batteries and more panels are always good, but there comes a point where you truly do have enough, and should think of better ways to spend your prepping budget.

There’s another thought that you need to keep in mind, too.  Your system has been sort of designed to have enough capacity for a day’s normal use, and to recharge your 5 kWh of overnight battery capacity, but if you need it to also be able to recharge another 8.25 kWh of battery capacity, do you need to increase your array size, too?

Maybe yes, but maybe also no.  Here’s the surprising thing.  Sooner or later, the pendulum will swing and instead of having bad days with less than average sunlight, you’ll have a normal day with normal sunlight, and even sometimes a good day with more than normal sunlight.  Remember that, on average, you will get 2 – 2.5 hrs of sunlight equivalent, and you’ve designed your system to work with only 1.125 hrs of sunlight per day, and to withstand any two-day period with only 1.465 hrs of sunlight over the two days.

Maybe the third day will see you back to normal, with between 2 – 2.5 hours of sunlight.  Your 25 kW system will be gushing out so much energy you’ll have your batteries topped up in double-quick time, and you’ll be able to use all your appliances without any care or concern at all.  And the next day, maybe you’ll get 3 or 4 hours of sunlight – you could potentially generate 100 kWh of energy in a case where you only need 20 kWh for your daily needs.

On the other hand, if you now have a much larger battery reserve, they will be consuming a measurable amount of energy each day to keep ‘trickle charged’, and conditioned.  We’d recommend you allow at least 1% of the total battery capacity for daily losses, and depending on the type of system you have, maybe this could rise to 2% or more.  2% of a 13.25 kWh system is 0.27 kWh for battery maintenance every day.

So, where do you draw the line?  For many people, roof size is one practical consideration.  You’ll likely max out your roof space with these types of configurations.  And the other is budget based.  For those of us with finite budgets (and that is most of us) we always need to be juggling our funds between all the different ways we need to spend them, and ensuring that, just like a chain is only as strong as its weakest link, our retreat has no weak links as a consequence of also having some ridiculously strong ones.


There’s another thing to consider in working up the specifications for your solar power system.  You need to have redundancy built-in to the system, so that everything still works as you need it to if any one thing fails.

So, for example, maybe you end up with a net battery power requirement of 5 kWh, as per the example we’ve been working through, and you find a single Solar-One battery which itself has a net 6 kWh of power.  Don’t just buy it and consider your battery needs fully solved, because you have also created a part of your system with no backup/redundancy.

Instead, you should buy two of these batteries.  Or perhaps you find a different brand of battery that has a net capacity, per battery, of 3 kWh.  Don’t just buy two.  Buy three, so you can have one fail and still sufficient battery capacity remaining.

Always buy (at least) one more than you need for anything and everything.  And if it is an item which you have/need many of, consider buying more than one additional.  For example, maybe you end up with 50 solar panels.  Even though the panels are very reliable and low maintenance, we’d be tempted to buy not just one but two or three spares for ‘just in case’ scenarios in the future.

So, buy the system you need, then buy an extra at least one of every item in the system.  Sometimes, it might make sense to immediately deploy the extra items so as to make your system bigger and better right from day one, other times (maybe power controllers, extra cables and connectors, etc), there is no need to do this and you can keep them in reserve, so that they’re not wearing out or getting ‘used up’ or whatever other issues might apply.

In the case of batteries, we’d probably immediately connect up all the batteries we had.  The slight downside is a greater energy consumption every day to keep them charged, but the upside is that you are using a smaller amount of each battery’s charge each night, and so they will last more cycles in total.

Should You Buy More Batteries, or More Solar Panels?

So at what point does it make sense to spend money on more batteries rather than on more solar panels (or vice versa)?  How much of each should you have?

There are several ways to answer that question, and several issues to consider.  Two important considerations are the relative cost of solar panels compared to batteries, and the confidence you have in how predictable each day’s energy production will be.  Another issue may be any constraints you might have in terms of how large a solar array you can deploy – although in theory there is no limit, because assuming you have a reasonable sized property, you can simply add more rows of panels just above the ground if you’ve run out of roof.  In practice, the higher up your panels, the better protected they are from accidental damage of all kinds, and once you’ve filled all your roof area,

Prices for batteries (and the associated control and conversion equipment to charge them, monitor them, and subsequently then change their power to 110V AC for use around your retreat) and for solar panels (and all the various similar associated equipment for them) varies to a certain degree, and it is hard for us to be too definitive about that part of the equation in an article that we hope will remain useful for an extended time.  But to give a quick example of some pricing at present, you could plan to spend about $5000 for a battery and related equipment that stores 12 kWh of energy (for example, these batteries), and/or you could spend about $1/watt of solar panel generating power plus, say, $1500 or so for an inverter, meaning the same $5000 would buy you about 3500 watts of power generating capacity.  Note that you would only want to discharge the 12 kWh of battery to perhaps 75%, so it actually gives you 9 kWh of usable energy.

If we say that on a worst case day, you’ll have under one hour of full sunlight energy equivalent, then your $5000 would buy you either 9 kWh of stored and usable energy in additional batteries, or less than 3.5 kWh of additional energy generated.  All other things being equal, it would seem, with these respective prices, you would be better to spend the money on batteries.

But – and here’s the thing.  All things are not always equal.  If you increase the size/capacity of your bank of storage batteries, you also need to have sufficient generating power to be able to charge them up – and, don’t also forget, that once you’ve charged them up, you then need to give them ongoing trickle charging to keep them charged and in good condition.

Perhaps a better equivalent would be to say that if you buy the 9 kWh of extra usable battery for $5000, you also spend another $5000 to get the 3.5kW of extra solar cells so as to have additional capacity to charge the additional batteries, making a total cost to service the 9 kWh more like $10,000.

So, to compare how you’d spend $10,000, one way you’d get 12 kWh (with 9 kWh usable) of batteries and maybe 3.5kW of solar cells, the other way, you’d get maybe 7 kW of solar cells and no extra battery.  But, remember, you’re planning for a worst case scenario with less than one effective sunlight hour, so the 7 kWh of extra solar cells might only bring you a net 5 kWh of energy, much less than you’ll hopefully have stored and usable in your 12 kWh of extra battery.  It still makes sense, after adding this extra detail, to buy batteries (and some additional supporting solar panels) than just to buy panels by themselves.

Note that these numbers will vary depending on what you already have and what else extra you are looking at getting, and you should do your own sums your own way, but at least this worked example, as of late April 2014, clearly shows that for energy storage strategies, you should go big on batteries.

And now, for an opposite thought.  Rather than looking only at the implications of adding extra batteries and panels, think also of what you already have.  In our example, with 5 kWh of battery storage, and then you add an extra 8.25 kWh for bad days, and then you add a further 12 kWh for really bad days, you also already have 25 kW of panels and a daily/daytime need for only 15 kWh of energy (plus 5 kWh at night).

As soon as you transition from bad weather to average weather, you then have (in this example) 2 hours of full sunlight energy, and the panels will then give you 50 kWh of energy to use and store.  That’s enough for your 15 kWh of daytime use, and to charge your full bank of batteries too, plus more besides.  Maybe you don’t need additional panels – in this situation – to support your extra batteries.

Wow.  So – more batteries?  More panels?  Truly, it totally depends on your present situation and the types of assumptions you are comfortable living with.  Is this the point where we also mention our consulting services and how we can help you ‘tune’ the correct balance of power generating and energy storing capacities?  Rates are reasonable and start at $250.  Let us know if we can help.


How much reserve power generating and energy storage capacity should you have at your retreat?  Well, that depends on how much you have of both to start with, and then from there it depends on how pessimistic you want to be in terms of semi-random/worst-case scenarios for a shortfall between average days of sunlight and really bad days of sunlight.

We suggest that your ‘normal’ system specification should already embody some conservative projections about how much power you’ll get on bad days in winter, and then from that point, add some extra battery and perhaps some extra panels.  We often see solar panels sold with the assumption they’ll generate 5 hours worth of full-on energy a day.  We tend to base our projections not on these best case summer scenarios, but rather on worst-case winter scenarios, where (particularly in the northern states) you’ll sometimes struggle to get even one hour of full-on energy from your panels each day.

The good news is that even on the darkest dimmest gloomiest day, there will still be a very little bit of energy generated, so even if you exhaust all your batteries, you should still get a tiny trickle of electricity – enough to at least keep some lights going and maybe one or two essential appliances too.

Oh – the big mistake present in the picture of the battery array at the top of the article?  The problem is the batteries are outdoors.  In winter time, the battery temperatures will massively drop, and the colder the battery, the less capacity it can store and return back to you.  You want to keep your batteries as warm as you are – temperatures in the 70s are ideal.

Apr 252014
A lot of energy is wasted when hot water goes down your shower drain.

A lot of energy is wasted when hot water goes down your shower drain.

There are lots of devices out there at present to make one’s life more energy-efficient.  The problem that most of them face is that few of them are cost-effective when we’re paying so little for reliable ever-present energy.

But if – when – energy prices skyrocket, and/or if/when energy becomes scarce and unreliable, all these devices will come into their own and become valuable and essential.  Needless to say, as we prepare for ‘discontinuities’ in society, one of the biggest discontinuities we have to consider is an interruption to our energy supplies, and so it behooves us to consider all such energy-saving devices, not so much for their present benefit today, as for their future benefit, subsequent to TEOTWAWKI.

Here’s an interesting article that profiles three similar but different approaches to recycling some of the heat from your shower’s waste water.  The concepts are immediately and intuitively sensible, and the savings apparently quite substantial – reducing the energy cost of the hot water used in the shower by up to 60%.  Depending on how often you shower and how many gallons of water you use each time, this can reduce your daily energy consumption by 4 – 6 kWh a day.  That might not sound like a lot, but when you consider that the average household uses 30 kWh each day, and your retreat will definitely use much less, this becomes a significant reduction in your total daily needs.

While water heating may not be a fully mission-critical part of your retreat’s energy planning (we are assuming you’ll fit a solar water heater to supplement any other water heating strategies you have) there’s no harm and potentially some benefit in recycling every possible watt-hour of energy you possibly can, and these three approaches all seem reasonably low-tech and low-maintenance and sensible.

Whether you buy the equipment from one of the three companies, or simply create your own similar system, it is definitely something to consider.

In case the linked article should disappear, here are direct links to the three companies and their products :

Heatback :  http://www.heatback.co.nz/home

CINTEP :  http://www.recyclingshower.com.au/

Recoh-vert :  http://www.recohvert.com.au/

All three companies come from NZ or Australia, probably because the magazine is published in Australia.

Apr 222014
Chances are you'll end up choosing to cover most, if not all your roof with solar panels.

Chances are you’ll end up choosing to cover most, if not all your roof with solar panels.

This is a further part of our series on solar energy.  Please also visit our sections on energy in general and solar energy in particular for more related articles.

We’ve already written an article pointing out something you hopefully already know – solar power is a wonderful energy source for preppers.  If you don’t already have some solar power on tap at your retreat, you should urgently add some.

But – how much solar power do you need?  That’s clearly an essential question to ask and answer.  But answering it is not as easy as asking it (hence this article!).

There are two drawbacks (or, if you prefer, ‘complications’) when it comes to assessing how solar power can meet your energy needs.  The first is that every night, when the sun goes down, your solar power generation drops down to zero, and doesn’t start again until the next morning’s dawn.  You’ll have to create enough energy during the hours of strong sunlight to have sufficient to store (ie in batteries) to see you through the nighttime, too.  This is actually the less serious of the two drawbacks, because this is something you can readily understand and plan for.

The possibly more important drawback is that the power you get from your solar panels depends on how much sun there is, each day.  A bright sunny day without a cloud in the sky means you’ll get lots of power from your panels.  A light haze and some high-up cirrus clouds, while hardly detracting from your overall perception of a bright sunny day, might cut the power you generate by 20%, possibly even 30%.  As for when there are clouds covering the sun, well, your power generated might drop down to barely one-third of what it could in optimum conditions.  It is still clear ‘bright’ daylight and you can see perfectly well, but the clouds have blocked much/most of the sun’s energy from reaching you.

This means when you plan for a solar sourced power supply, you need to have an array that is many times more powerful than you might think you need (so as to provide sufficient power on cloudy as well as bright days), and you need to support the array with a large reservoir of power storage (ie almost certainly batteries – see our article on using batteries to store electricity and the other articles in that four part series).

As an aside, while this seems to be an unfortunate situation, with the total energy ‘harvested’ from the sun varying widely and not very predictably from day-to-day, at least on the very gloomiest of days, you are still getting a small trickle of energy – it is only at night-time that the energy flow stops completely, so you always have some tiny emergency supply.  This is not the case with wind power, where on some days (too windy, or not windy enough) you will get no energy at all.

The good news is that solar panel systems are reasonably affordable, and the further good news is that there is very helpful data to help you understand just how much energy you can realistically get from your panels, if not hour by hour, at least on an averaged basis, daily/weekly (note – this helpful information is usually not the materials provided by the seller of the panels!).

What a Panel’s Rated Power Output Means

The most important part of the specifications of solar panels, for this purpose, is to see how many watts of power it is rated to generate.  Sure, there’ll be other data ranging from size and weight to how it should be mounted, and you’ll also see information on voltages and current ratings, but focus primarily, when planning your array, on the watt rating.

Almost certainly, this watt rating will assume that the panel is directly facing the sun and that the sun is operating at ‘full rated power’ – ie, 1 kW of radiated energy landing on every square meter of panel surface.  As of the current time, it is normal to expect to see panels that are about 15% efficient – ie, they will create about 150 W of electrical power for every square meter of panel surface, in these ideal conditions.

But, as you well know, life is seldom ideal, and the sun doesn’t always shine.  Even when the sun is shining and there are no clouds blocking it, the panel isn’t always directly aimed at the sun (because the sun moves around the sky each day), and the more ‘off target’ the panel is, the less efficiently it converts sunlight to electricity.

Furthermore, it is common for panels to slightly under-perform their rated power output, albeit only by a few percent, and as they age, their power output slowly drops further (by about 0.5% – 1% a year).  And then, from the power output at the panel connector, you start losing power through things such as wire resistance as the power travels from the panel to your appliances, and conversion losses as you convert the panel’s low voltage DC into high voltage AC for your appliances.

If you are storing the panel’s power into batteries, you are again losing power in the process of converting the electricity from the panel voltage to the appropriate battery charging voltage, and then from that into chemical potential energy in the battery (and then back to electrical energy when you start running things from the stored power in the battery).

There are other output modifiers to consider as well.  For example, a partial shadow falling on less than 10% of a panel doesn’t reduce the panel’s power output by 10%, but rather maybe by 50%.

So be very wary of using the rated panel power outputs without understanding exactly what this means and making the appropriate adjustments – ie, probably massively reducing down the number!

One more word of caution.  A panel should only be rated in terms of watts (or maybe kW) of power output.  Sometimes you’ll see this rating then converted into (kilo)watt hours of energy generated per day/week/month/year.  This is a terribly fictitious number, which you should ignore totally, because it is almost certainly based on a ‘best case’ number of hours of bright sunlight per day/week/month/whatever, and as preppers, we never want to build our future on ‘best case’ assumptions, do we!  (By the way, if you’re a bit confused as to the difference between power and energy, please visit our page that explains this – understanding the difference between power and energy).

You must – you absolutely must – create your own calculation for how many kWh of energy you’ll get from your panels, using worst case rather than best case scenarios, in winter rather than summer, and based on the sunlight values applicable to your specific location.  This article and others in the series helps you do so.

Step One – Your Retreat’s Energy Needs

The first thing you need to do is create – well, for want of a better term, an energy budget for your retreat.  How much energy are you going to allow yourself every day or month, and how much of that energy will be in the form of electricity?  The chances are you’ll have a multi-energy strategy for your retreat – you will most likely have some type of wood burning energy source; and for finite term level two situations, you might have propane to power your cooking appliances, you might use solar/thermal energy to heat your water, and so on.

You might also have multiple electricity sources – a generator (suitable for level 1/2 situations, but less so for level 3 because you’ll run out of fuel) as well as solar power.  Perhaps there’s even some wind power, and in very rare situations, you might have a micro-hydro generator too.

For the purpose of this article, our primary focus is on electrical energy needs, and we’re also assuming that this electricity will be sourced solely from solar panels.  Feel free to adjust the process if you’re incorporating other electricity sources too.

So, how much electrical energy (from solar panels) does your retreat need; and perhaps also, how much more than the bare minimum would be nice to also have?

We suggest you work through this question for three scenarios – summer, fall/spring, and winter.  There will be changes in your heating, cooling, and lighting needs for these different times of year.

We also suggest you might wish to assign each item a priority – ‘Must Have’ for the absolute essential items you can’t live without, ‘Should Have’ for some extra items that make life more pleasant, and ‘Would Like but Don’t Need’ for the luxuries that you’d like to be able to treat yourself to but probably can’t.

Go through your retreat, room by room, and inventory every electrical thing in every room, and work out the energy each item requires on a daily basis.  At the same time, as part of an ‘energy audit’ make sure that every electricity consuming item is optimized – for example, do you have LED lighting everywhere, and is it sufficiently but not extravagantly bright?  Do you really need a waste disposal unit in your sink, in a grid-down scenario?  (Answer – almost certainly not, food scraps can be used in a compost heap.)

Sometimes you might have an essential item that you record a certain amount of usage for in the must have category, and additional usage in the less essential categories, too – maybe you plan for an hour a day of radio monitoring as a must have item, but then add another few hours of radio listening in the ‘Should Have’ category, and a few more hours in the ‘Would like but don’t need’ category.

Add it all up, redo for the different seasons, and you’ll end up with your total energy requirements.  If you did this thoroughly, you’ll have nine different numbers (three seasons multiplied by three scenarios).  These numbers are all interesting, but the most important number – the one you’ll start from – is the highest of the three ‘Must Have’ numbers.  This is your absolute bare minimum energy requirement; depending on your budget and other constraints, you’ll of course try to build your system bigger than this.

Here’s a helpful list showing some of the wattages of various home appliances.

Step Two – Your Retreat’s Power Needs

The second thing you need to know is how much power your retreat needs to get the energy you’ve calculated in the preceding section.  You’ll understand this distinction from our article explaining the difference between power and energy.

What is the maximum amount of power your retreat will require at any given moment?  Add together the power requirements of everything that might be on simultaneously, and include an allowance for startup power peaks.

You need to do this only once, for a scenario where you have whatever you want simultaneously operating.  Due to the difference between power and energy, there is no need to redo this for each of the nine scenarios you were studying above.

Either/Or Circuits to Manage Peak Power Needs

As you’ve probably now calculated, although your house/retreat might have modest total energy consumption, it still might have occasional massive peaks in maximum power requirements.  You want to keep your peak power requirement as low as possible, as well as your total energy consumption – this will allow for smaller more economical systems for your property.

One easy way to do this is to have ‘either/or’ circuits in your house.  For example, maybe you have things set up so either your washing machine is on or your dryer is on, but never both.  The easiest way of doing this would be to have the two units sharing the one power outlet, so that only one can be plugged in at a time.

Maybe you also have an either/or setup for your kitchen – either your dishwasher is on, or your oven and stove top are on, but never both.  Perhaps this is controlled from an electrical distribution panel, where you have a switch that can be set to either enable one circuit or the other, but not both simultaneously.

Maybe you also have a switch that powers on either your laundry or your kitchen, so you now have two levels of either/or – ‘Either I have something in the kitchen on or something in the laundry on, and if it is something in the laundry, it is either my washer or my dryer’.  Another example would be either your hot water heater or your furnace – because they both cycle on and off, you’ll not notice the difference at all if you have it set up so they alternate drawing power (as long as their duty cycles are less than 50% each, which they should normally be).  Either the lights in the living areas or in the bedrooms and bathrooms.  And so on, any which way that makes sense for your lifestyle and living situation.

Another and more ‘automatic’ solution would be, if you have, for example, a separate fridge and freezer, would be to put them on timers.  Maybe you have the fridge on a timer that runs for the first and third quarters of each hour, and the freezer to run on the second and fourth quarters.  Better would be to have the fridge running for 13 minutes, then a two minute gap in case the timers get out of synch, then the freezer for 13 minutes, and so on.  Or get a timer that has multiple outlets so it is always in synch with itself, alternately switching on and off different circuits and appliances.

Some other examples of ‘either/or’ scheduling might just require some personal discipline, or a different way of controlling things – for example, don’t do the vacuuming at the same time you do the ironing (both require over 1kW of power).  Maybe you keep the iron and the vacuum cleaner in the same place with a big placard saying ‘Do not use both of these items simultaneously’.

Indeed, it doesn’t have to be limited to a simple either/or choice between two things.  Maybe it is a ‘choose any one of three’ things – in addition to the iron and the vacuum cleaner, perhaps you also have the hair dryer in the same place and the big placard now says ‘Only use one of these three things at any time’.

You can adjust your instantaneous power requirement down by adopting some of these strategies.

Step Three – Timing Your Energy Needs

Remember that solar power only flows from your panels when the sun is shining.  It will flow at the greatest rate around the middle of the day, when your panels will be most perpendicular to the sun, and at lesser rates before and after that time.

So, for anything that you can conveniently time-shift into the middle of the day, you should do that.  Other things, wherever possible, still try to schedule for daylight hours rather than nighttime so as to take power direct from the solar panels rather than from the batteries.  For example, instead of having a shower, washing your hair and then drying it at night, do that in the morning when the sun is shining and your panels are giving you power for the hair dryer.

It is always better to use energy direct from your panels than to require the energy to detour through a battery system – this keeps things simpler and cheaper, and your batteries will probably fail long before your panels do.

In winter time, cook hot meals before the sun sets.  Do all your ‘chores’ that require appliances during the day, not at night.

Work out the power profile and total energy you need during the daylight hours and do a similar calculation for the night-time hours.  We suggest you consider daylight to start from perhaps 30 minutes after sunrise and to finish perhaps 30 minutes before sunset.  Sure, there’ll be some sunlight and energy flow in the time you’ve omitted, but keep that as ’emergency/bonus’ power.  It won’t be all that much, anyway.

So now you should end up with information for the peak power consumption and total energy needed, day and night, for the three seasons – spring/fall, summer and winter, with splits showing essential power, desirable power, and not necessary power.

Well done.  Let’s now look at what you do with these numbers.

Step Four – Sunlight Hours

Use the resources on this page to see how many sunlight hours a day you can expect at your location for winter, spring/fall, and summer.  Use the monthly PV Solar Radiation (10 km) static maps.

Now you are going to need to start massaging the numbers and making some assumptions.  What you see on these maps are the average daily sun hours.  But we know some days will have more than this, and other days will have less than this.  Do you want to plan your energy supply based on the hope that you never have a bad day (in terms of sunlight)?  That would be foolishly optimistic, wouldn’t it!  You need to be willing to spend some more for additional capacity so as to allow for some days giving you less energy than average.

Depending on the point at where your comfort level starts and stops, we suggest you might choose to reduce the daily hours of sunlight by 50%, to get a moderately pessimistic prediction of how much energy you can get on a cloudy day.  If you wanted to be truly pessimistic, you could reduce by 70%.  (Note there is a balancing factor – how much battery storage you have – in general terms, the greater their energy storage, the less the power capacity you need.)

Anyway, let’s say you reduced the sunlight rating by 50%, and let’s say that your retreat was in an area with 2 – 2.5 hours of sunlight a day in winter.  So you are now looking at 1 – 1.25 hours of sunlight a day; perhaps you’ll round that down and call it 1 hour, or perhaps you’ll take the midpoint and call it 1.125 hours.  Your call.

You also look up sunrise and sunset tables for your location, and see that on the shortest day, you have almost 9 hours between sunrise and sunset, and after taking off 30 minutes from the sunrise and sunset time, that leaves you with 8 hours during which there will be useful power flowing from your solar array.

You’ve also done your figuring, and let’s say you’ve ended up needing 20 kWh of energy for the 24 hr period, of which you can use up 15 kWh during daylight hours and need the other 5 kWh for night-time.  (Note – this is probably a high number, so don’t panic at the figures that follow below.  Most people are likely to come up with a number half this or even less, so all other numbers would halve, too.)

The first thing you now know is that you’ve got 1.125 full sunlight hours to generate 20 kWh of energy.  You need your panels to be rated to give you 17.8 kW of power in full sunlight, plus some extra to allow for inefficiencies and losses in the system – at least 10% extra, and better to go up 25% extra.  We’d suggest a 25 kW system would be the minimum to handle this.

There’s an interesting extra thing you now know, too.  With 1.125 sunlight hours, spread over 8 hours with the sun in the sky, your system will typically be generating power at about 1.125/8 of its full rated power, ie, at about 14% of its 25 kW full power rating – about 3.5 kW.  Sometimes it might go way higher than this, and other times, it will drop down below that.

But what you know, from this, is that you’re not likely to be able to run much more than about 3 kW worth of appliances simultaneously during the eight hours of the day.  If you need more instantaneous power than this, you’ll probably need to increase your system’s capacity beyond 25 kW.  On the other hand, you will have a flood of ‘bonus’ power – instead of it trickling in to your retreat at 3.5 kW, it will be flooding in at 25 kW.  It would be nice to have some ways of using/banking/storing this extra power when it does come in (maybe heating your hot water hotter than normal at such times, maybe using appliances more, maybe slightly overheating or overcooling your retreat, and so on).

You can – if you wish – do the sunlight calculation for the three different seasons and match that against the power requirements for each of the three seasons, but probably you’ll find the critical calculation will be the sunlight available in winter matched against your winter energy needs.

Step Five – Batteries for Overnight

Now to consider the implications of your energy storage needs.

Continuing the example from the previous step, you know that you need to store 5 kWh of energy for night-time, while the sun is down and the solar system isn’t generating any power.  So clearly you need a battery capacity sufficient for this, and with some extra to allow for the power losses between converting from the energy stored in your battery bank to the electricity for your retreat.

Calculating the amount of battery capacity you’ll need is a complicated process, and we discuss it in this article – Using Batteries to Store Electricity.

You need to allow for the fact that not all the energy stored in the battery can be converted back to electricity, and you need to also adjust for the fact that you’ll probably only want to discharge your batteries down to somewhere between 50% and 75% of their rated capacity (depending on the battery type you have) each night, and adjust further for the rate of discharge being, for much of the time, probably faster than the discharge rate used to calculate their capacity (the faster you discharge a battery, the less charge you’ll get from it).

Oh yes, the battery capacity is probably also based on the possibly unrealistic expectation that it is stored at a temperature in the high 70s – and as it gets colder than that, it loses capacity (at 50°, you’ve probably lost 10% of its capacity due to the colder temperature, and at 30° you’d have lost 20%).

So, put all that together, and what do you get?  Some sort of a guess figure – in this case, if I had batteries I was comfortable discharging to 75% of capacity, I’d first say ‘5 kWh is 75% of 6.7 kWh’ and then I’d adjust for the discharge rate used to make the 6.7 kWh capacity, which might require another 20% increase in capacity (up to 8.3 kWh) and then maybe I need to add another 10% for converter and distribution losses (taking us up to 9.3 kWh), and then another 10% for the batteries being stored at less than 77°.

That takes us up to 10.3 kWh, and so I’d probably round that up to 11 kWh.

Note that this means that your earlier 20 kWh of energy figure, based on 5 kWh of battery power, needs to be increased for these losses.  You sort of did that already when you went from 20 kWh to 25 kWh, but if your battery power needs are much larger than in this worked example, you might need to adjust up even further.

Putting it All Together

So, you’ve worked out how much energy you need, and when you need it.  You’ve also worked out the maximum power supply you’ll need, and you’ve done the calculations three times, variously for spring/fall, summer and winter.  Maybe you’ve done them even more times, to adjust for the bare essential minimum of power, some more power that would be desirable, and still more power that would be ‘luxurious’.

You’ve also worked out the hours of effective sunlight you’ll get at the worst points of these three seasons, and adjusted down from there for a ‘worst case’ scenario, and used that to work out the specifications for the solar panels you need and their power generating ability, and how much battery storage you need to see you through each night.

Is that all?

Actually, no.  You probably should now add some extra margin into your figures to allow for truly worst case scenarios – for two or three or four days with much less sun than you were figuring on happening in a row (and, when you think about it, really bad storms can last for several days, can’t they).

You also should include some system redundancy for failures and other unexpected events.

How much more do you need to add to your system?  Please read the next article in this series – ‘How much emergency/reserve capacity does your solar power system need‘ for a detailed discussion on that point.

For now, you’ve worked out that for your retreat, needing 15 kWh of energy during the day and 5 kWh of energy at night, and with winter sunlight averaging 2 – 2.5 hours a day, you should choose a solar system rated at 25kW and a battery bank with 11 kWh of storage.

Please keep reading to see how much further this will need to grow.

Can We Help?

If this is all a bit too much for you, we are happy to consult with you and do most of this all on your behalf, and to walk you through the personal preference/lifestyle choices that we can’t make for you.  Rates are reasonable and start at $250.  Let us know if we can assist.

Mar 212014
A split system heat pump for heating and cooling your retreat might be surprisingly practical to consider.

A split system heat pump for heating and cooling your retreat might be surprisingly practical to consider.

One of the basic principles of planning a retreat is to minimize your energy needs, and a key part of that is the design of the retreat so as to make it as well insulated as possible.  This will cut down on your heating energy requirements in the colder months, and should also cut down on your cooling energy requirements in the warmer months.

Well, that’s the theory of it, anyway.  The reality is a bit different.

The thing is that while a well insulated house will slow down the rate at which outside heat comes in to your house, it also traps the heat inside and, well, keeps it there, which can mean that inside temperatures will rise to match the outside temperatures, no matter how extreme it may be outside, and you’ll be forced to ‘give in’ and open up all the doors and windows in the summer months, just to get some air flow, even if of hot ambient air.

You’ll also try to also flush out the hot air in the coolest hours of the night, so you start off each day with as low an indoor temperature as possible, and for the first part of the day, as it inexorably rises, you’ll be moderately comfortable, then when inside and outside temperatures approach the same point, you switch from an all shut up to an all open strategy for the rest of the day.

A related issue may be humidity control, depending on if you’re blessed with a relatively dry climate or cursed with a humid one.

This heating effect is of course more pronounced in summer than winter.  In winter, it is a good thing, but in summer, not so good.  Our bodies are radiating heat all the time (100W – 150W for a typical moderately active adult, less while we sleep, more when doing strenuous physical activity), and all the energy we use indoors eventually ends up as heat, too.  So, depending on your energy consumption each day, you probably have the equivalent of a one bar heater on all day every day, which is why, all year round, your indoors temperature is warmer than outdoors, even before you start adding specific additional heating.

We, ourselves, hate being hot, and productivity studies have shown people become materially less productive whenever temperatures start to climb above 70°.  We also hate trying to sleep in a hot stuffy room, and can confirm from personal experience the additional studies that correlate good or bad sleeping with the ambient room temperature.  We love air conditioning.

On the other hand, air conditioning can consume large amounts of energy.  A typical 110V a/c window unit will run at about 1 watt for every 10 BTU of cooling – a 10,000 BTU unit would draw 1000 watts, although note that its duty cycle – that is, the amount of time it will be on – will be maybe 25% – 50%, so you’re getting an hour of cooling for maybe only 250 – 500 watt hours of energy.  Larger a/c systems, and using higher voltages and/or three-phase power, can be more efficient than this and give you more cooling per Watt hour.

As an interesting additional comment, did you know that because a/c units simply shift heat rather than create cold, they move more heat than the energy they consume.  This has implications for both winter and summer – if you have a heat pump, it will create probably two to three times as much heat per kWh of energy as would a normal resistance heater, depending on the temperature of the outside air.  Cooling units typically ‘suck out’ three or four times as much energy as they consume.

Energy Efficiency Issues

Needless to say, if you are installing a/c at your retreat, you want it to be as energy-efficient as possible.

In the US, a/c systems are given a SEER rating or sometimes an EER rating.  Both are a measure of their energy efficiency – the higher the number, the better.  SEER numbers are higher than EER numbers for the same unit by about 15% (ie something with a 14 EER rating would be the closely similar to something else with a 17 SEER rating.

Normally, when a person buys an a/c unit, they give some passing thought to the SEER rating, but pay more attention to other issues like the cost, the noise level, and so on.  However, for a grid-down situation, where energy is never plentiful and always ‘expensive’ in some form or another, you’ll want to make the SEER rating one of your primary focuses.

Generally, split systems, with a unit outside and a separate unit inside are more efficient than all-in-one units such as are typically installed in window frames.  Split systems can give you SEER ratings into the mid to high 20s; all-in-one units struggle to reach 15.

Heating Too?

As we hinted at obliquely above, if you’ll be needing to use electrical heating in the winter, do consider a heat pump rather than just basic simple resistance heaters, because you’ll get two or three times as much heat from each unit of electrical energy with a heat pump than a regular resistance heater.

The efficiency of a heat pump, for heating purposes, depends on its design and the outside temperatures you’ll likely encounter.  The colder it is outside, the less efficient the heat pump becomes.

There are heat pumps specifically designed to work better in very low outside temperatures, and beyond that, you can also switch from an air-exchange heat pump to one with underground piping, transferring the heat from the warmer ground rather than from the cooler air.  Underground piped systems can become quite a lot more complicated and expensive, so we’d consider those with caution, unless you really need an electrically powered heating solution for your retreat.

In general, we’d hesitate to recommend relying primarily on a solar based electrical heating system, unless you’re so overflowing with solar power that you have plenty spare, even on the coldest and least sunny winter days.  If, for whatever reason, you have no other sources of energy from which to create heat (such as firewood), then maybe you have to use solar, and in such a case, it might be a better and more direct approach to simply install a solar heating system, directly transferring what heat there might be from the sun from outside to inside.

Whereas with cooling, the more sun there is, the more you need cooling, and the more solar power you have available to meet that need, with heating, the equation is the opposite.  The less there is sun, the more you need heating, but the less solar energy you have available, in any form, to use for heat.

But, having said that, we’d probably look at the cost difference between getting a cooling-only a/c system and a dual heat/cool system.  If there’s not a lot of difference in cost, we’d get the dual purpose system, because on the days when we do have surplus solar power, why not save our firewood or other energy sources and use the solar power for our heating needs.

Your A/C Needs are Matched by Your Solar Power Outputs

So, as mentioned in the preceding paragraph, there’s a wonderful thing about solar power that makes it sensible to consider about using your solar power to drive an a/c unit.  The stronger the sun, the higher the temperatures, and, at the same time, the greater the power output from your solar panels.  Okay, so that’s a bit of a simplification – in some areas, it can be hot, humid and horrible, even if there’s little or no sun at all, but in other areas, if the sun is obscured, the temperatures drop.

Our point is simply this.  You’ve probably tailored your solar power system to provide you all the power you need in the winter months with little sunlight.  So, now you’re in the summer months, with more and stronger sun each day, you’ll be getting a lot more energy from your solar setup – maybe even more than you need.  Because of the close relationship between your solar panels generating more ‘bonus’ energy for your use, and the times when you’d most benefit from a/c, it becomes possible to plan to use your a/c only when you have surplus spare power, because those times are also the times you most want your a/c running.

So, if the climate warrants it, go ahead and treat yourself, and fit some a/c to your retreat.

Dec 202013
A roof that uses solar energy three ways - solar power panels, solar hot water heating, and a skylight.

A roof that uses solar energy three ways – solar power panels, solar hot water heating, and a skylight.

This is the first part of a series on solar energy.  Please visit our sections on energy in general and solar energy in particular for more related articles.

Every part of our world is defined – and/or constrained – by energy.  Our modern civilization – something you might think of as being all about computers and the internet, or perhaps all about big cities and high-rise buildings, or perhaps jet planes and satellites – has one universal thing at the root of every part of it – energy.

Try and think of any part of your normal life in which energy is not an important part.  Energy makes your home warm in the winter and cool in the summer.  Energy allows you to commute to work.  Energy enables you to work on the 10th or even 100th floor of a building.  Energy is converted into food, is used to transport food to your local supermarket, to store it there, and more energy is used by you to cook the food.  Energy also brings you the water you need, and takes away the sewage you don’t need.

Energy powers your cell phone and computer, and also the internet they connect to.

Energy comes in many forms, of course.  In earliest times, energy was primarily either in the form of our own personal labors, or in the form of fire.  In time, we harnessed additional energy sources – we used animals to magnify our own personal energy outputs, and of course, we started to develop new ways to channel the energy of a fire – the external combustion engine (or, if you prefer, the steam engine) was the breakthrough that allowed for the Industrial Revolution, and subsequently for the settling of the United States, and we know all about the internal combustion engine’s subsequent impacts.

Okay, we will skip the rest of the history of energy development, and simply say, for our purposes, the biggest challenge we have to face in a Level 2 or 3 situation will be the loss of our usual energy sources and the critical energy shortage that will result.  There’ll no longer be gas at the gas station, or electricity in our sockets at home, or other sources of energy in other places, either.  Our lives will fall apart due to the lack of energy to maintain, manage and improve our lives.

So one of the most important preparations we have to make is to identify suitable sources of energy to carry us through any future Level 1, 2 or 3 situation.  A level one situation is relatively trivial, and we won’t dwell on that here, but when we start to think about extended level two and three scenarios, we realize that a supply of spare batteries, some stored petrol, a generator, and an outdoor barbecue with a couple of spare propane tanks isn’t going to take us very far.

Sure, we could grow our fuel dump and instead of 5 or 50 gallons of petrol, look instead at 500 or 5,000 or more gallons, and probably of diesel.  Instead of a couple of standard 5 gallon propane tanks, we could install a below-ground series of 1,000 gallon tanks, even 10,000 gallon tanks.

We’re not saying you shouldn’t do all these things, but these are non-trivial preparations, costing probably tens of thousands of dollars and requiring large storage spaces and possibly needing special permits to store large quantities of fuel.  And, even if none of these challenges are problems to you, there’s still the ultimate problem that you’re merely delaying – no matter how much fuel you store, sooner or later, you will run out, and then what do you do?

So, we preppers are always keen to find renewable energy sources.  The three most common are hydro, wind and solar.

Hydro has very limited applicability for most of us, and wind power is not often a practical consideration either.  Even if you are fortunate to be able to add a wind powered turbine to your retreat, you will need to plan for ongoing repairs and maintenance and the replacement of stressed moving parts from time to time.

Which leaves us with the other common source of renewable energy – solar cells (or, if you prefer, PVs – photo voltaic cells).

If you live in an apartment with no roof and only a small amount of northern facing windows, then you probably can not get much value from solar power.  But if you have a reasonable amount of sky-facing space, and ideally giving you an unobstructed view of the horizon for 150+ degrees from east, rotating down through south and over to west, then solar might be a good choice.

Solar cells continue to drift down in price and to drift up in functionality and efficiency – that is, a given size of solar panel seems able to generate more and more power with each new generation of solar cell technology, while costing less and less.  That’s not to say they are a cost affordable alternative to normal utility provided electricity and natural gas in normal times, but in a Level 2/3 situation, they become an affordable and essential energy source.

Of course, they only work when the sun is shining (well, they’ll still generate power at a diminished rate on cloudy days, but not at all when it is night), so they need to be considered in conjunction with some type of energy storage system (ie, for most of us, batteries).

Perhaps the most appealing part of a solar array is that the solar cell panels have a long lifetime.  They are typically warranted for periods of about 25 years (although the warranties usually allow for some diminution in power output over time, but typically warranted to still generate 80% or more of their initially rated power after 25 years).  With no moving parts, there’s almost nothing to maintain (you need to keep them clean, and their associated battery bank and charging electronics may need maintenance) and almost nothing to go wrong.  Indeed, some solar cells are still working perfectly after 50 years, so even the 25 year warranty might be conservative.

That’s not to say that the panels are (literally) bullet proof, and indeed, a very remote possible source of damage might be hail.  But the slope on your panels will help deflect hail rather than directly absorb its impact, and assuming your hail never gets powerful enough to start smashing roofs and car windshields, your solar cells should be just fine (see this story about one exception to this, but it involved hail the size of tennis balls).

How Much Power Can You Expect?

Clearly, the more sunlight, the more power.  But let’s start off with an assumption – bright sunlight – and then understand how much power we can get from normal bright sunlight.

PV cells these days seem to typically be about 14% – 15% efficient.  Planners work on the basis of the sun providing about 1000 watts of power per square meter on a bright sunny day – an interestingly round figure, but one that is good enough for many planning purposes.  A square meter is about 10.8 square feet, so if you prefer, you can also say the sun provides about 93 watts per square foot.

This means that a PV cell with 15% efficiency will convert that 1000 watts of solar power (per sq m) into 150 watts of electrical power (or about 14 watts psf).

This 15% efficiency is massively better than nothing at all, and the sunlight is free to start with.  New types of solar cell are promised in the future, with higher efficiency ratings (up into the mid twenties and possibly even over 30%), and some are even available now, but they are very much more expensive, and may be more fragile and less long-lived, so for now, you are best advised to stick with traditional technologies.

Now that you understand the typical maximum power output to expect, the next issue becomes how much you’ll actually get in real life.  Nowhere in the US has bright sunlight all day every day, and even those places with high levels of bright sunlight still have a mix of day and night each 24 hour period.

There are some very useful maps created by the National Renewable Energy Laboratory which show you, for your specific part of the country, how many equivalent hours of bright sunlight a day you can expect, both month by month and a summary for the entire year.  Use the PV Solar Radiation (10km) monthly map series for the most accurate and detailed information.

You’ll see that most of the US seems to average, over the course of an entire year, at least 5 kWhrs of sunlight per sq m per day.  Another way of putting that is to simply say ‘at least five hours of bright sun in total, even if spread over more than five hours of daylight’.

Remember to now allow for the 15% or so efficiency in converting this sunlight energy into electrical energy, and be sure to look at winter month figures as well as summer, and you can start to get a feeling for how much you’ll actually get from your solar panels.  If you’re up in American Redoubt territory, you’ll see you’ll be struggling to get much more than 2.5 hours of bright sunlight equivalent each day in winter.  You’ll need a lot of panels to get any appreciable energy in winter in such locations.

In other words, if you have a solar panel setup that is rated for, say, 10 kW, and you’re in a part of the country with 5 hours of sunlight a day, you can expect your 10 kW panel to give you almost 50 kWhrs of power per day.

Needless to say, it is best, when considering how much power to get from your setup, to always be conservative and plan for worst case rather than best case scenarios.  Make sure you understand the methodology being used to quote power outputs and total energy generated from systems, because these are more likely to be best-case scenarios.

Please see our article ‘How Much Solar Power Do You Need’ for a more detailed look not just at power outputs from solar panels, but at the power requirements you are likely to have in your retreat and how they can best be handled via solar power, and, if helpful, our article explaining the difference between power and energy, between watts and watt hours.

Partial Shade Problems

Here’s something we learned ourselves, when trying to install a solar panel system in an area that had trees that would cast partial shade patterns on some of the panels.

You need to have even sunlight on each entire panel, and ideally on the complete multi-panel structure.  If you don’t, you’ll find that a small amount of shade, on a small part of one panel, might be enough to cause the entire panel to lose half its power output, and possible to reduce its power output completely down to zero.  Indeed, and here’s the really surprising thing – a panel that is evenly shaded will probably generate more power than a panel that is half in the shade and the other half in full sunlight.

This is not something you’d guess at (which is why we mention it).  The reason for the disproportionate impact of partial shade is the way the panels are made up of the separate cells within them.  While you probably think of your total solar installation as being a collection of panels, you also need to appreciate that each panel is a collection of individual solar cells.  These solar cells are joined together in an electrical series (and sometimes might have several of these series strings of cells all connected together in parallel), so as to take the voltage generated per cell (usually about 0.5V per cell) and have this combined to create a more useful voltage (the higher the voltage, the less power loss in the wiring and the less thick the wiring needs to be) to actually work with.

If one of the cells in the series of cells all joined together gets less sunlight than the others, then instead of generating some power, it can end up in effect ‘sucking’ power from the other cells, and that may cause safety circuits in the panel to then drop the voltage across all the cells in the string to prevent this from happening.  You can sort of think of it as the difference between a band playing a tune all in time with each other, and the disproportionate chaos that results if even one person in a large band starts playing wrong notes.

This is why you want to have even sunlight on the entire panel, so all the cells within it are working together equally.  Be sure to locate your panels appropriately.

The same problem usually affects multiple panel setups, too.  Normally the panels are also connected in series, and if any one panel (or part of one panel) gets less sun, then all the panels suffer.

Note that new micro-inverter circuitry can reduce some of these impacts, and in general give a better ‘yield’ of usable electricity from a given amount of sunlight on the panels.

Three Types of Solar Power

Now for an interesting extension of the concept of solar ‘power’.  Up to this point, we’ve been considering solar power in terms of photo voltaic cells that turn sunlight into electricity.  But there is at least one scenario where there is a better way of harnessing the sun’s energy.

That is when you want to simply heat something up.  Providing hot water, or heating your home in general, requires a great deal of energy to start with (heating up 10 gallons of water from 45 degrees to 95 degrees to give yourself a five-minute shower with warm/hot water, for example, requires 1.22 kWh of electricity.  Or, to put it another way, a full half charge cycle of a 400 Amp hour 6 Volt battery, just for one five-minute shower.

It is more efficient to heat the water directly through a solar water heater than it is to first generate electricity, then store it in a battery, then subsequently route it to the water heater and convert it to heat.

Solar water heaters typically cost slightly more than half the cost of solar power generators, for a similar power output, and whereas you have additional costs for batteries, etc, with the electric power system, you don’t have these at all for the solar water heating (the hot water becomes your ‘store’ of energy).

Amazingly, solar water heaters can still create hot water for you, even if the outside temperature is very cold.  On a bright clear winter’s day, you might have below freezing temperatures, but still be getting hot water from your solar water heater.

So it is sensible to have both solar (electric) power panels and a solar water heater at your retreat.  That will save you substantially, particularly in terms of batteries, and also gives you the added benefit of two separate power generating systems, albeit both dependent on the sun.

There are also several different styles of solar heating that can be used to heat the air inside a retreat.  The simplest of these is, of course, a glass window.

Requirements for A Simple Installation

Ideally, you’ll design and build a system that gives you full energy independence, and allows you to enjoy an energy intensive lifestyle, even in an extended ‘grid down’ Level 2 or 3 event.

But if you want to start off simply and do a ‘proof of concept’ installation, there’s no reason not to do this.  Anything is better than nothing.  You can buy complete systems that include the panels, some type of mounting system, wiring, distribution panel and an inverter (to convert the power from the DC that comes from the panels to regular 110V 60 Hz AC that your appliances use).  This type of simple system (a ‘grid-tied’ system) works when the sun shines, and doesn’t work when the sun doesn’t shine.

The next step up from that is to add a charge controller and a bank of batteries.  Now your panels can either be directly powering your appliances, or, if there is spare power, can be using the power that is coming in to charge up some batteries.  When the sun goes down, your system automatically switches over and now draws power from the batteries to continue supplying your home with 110V AC power, and automatically switches off when your batteries have used up the optimum amount of their charge.

More sophisticated systems can interface with your regular electric power supply (assuming it is available), so that you first use your own solar power and only after that use the utility company’s power.  Many states allow you to now ‘run your meter backwards’ and sell any surplus solar power to the utility company.  Even more amazingly, some states will require the utility company to pay you more for electricity they buy from you than the cost they charge you for the electricity you buy from them.

But we’re talking simple installations to start.  A simple ‘grid-tied’ system that is capable of generating about 1 kW of power in bright sunlight will probably run you just over $3,000; more if you have someone do the installation for you, and if you add a battery bank to this for off-grid operation, then your cost will probably double.  These costs may qualify for a 30% federal tax credit, and maybe there are state and local programs to further reduce your net cost.  There are lots of specialty stores that sell solar power systems, and of course, you can also browse through Amazon (here is just some of the gear they sell) too.

There is little economy of scale with solar systems.  You may get a lower rate per panel when buying ten or twenty or more panels at a time, and if you are using a single inverter rather than micro inverters for each panel, then there might be some savings there, but in general, if you get a system four times as large as a different system, then the cost will be close to four times as much too.

Our point here is simple.  You can get a fairly basic system for under $5000 and a good system for under $20,000.

Installing a Solar Power System

Ideally you want your panels facing south, on an incline the same number of degrees as your latitude north of the equator.  An easy way to align the bank of panels is to place a stick on them, sticking up perpendicular from the panel surface.  Then at exactly midday (or 1pm during daylight saving hours) align the panel so the stick casts no shadow.

If you can’t get it exactly right, don’t worry.  A 15° misalignment only reduces the power generated by perhaps 3.5%.

Panels are typically mounted on the roof of a structure, but there’s no reason why this must be so other than the good sense of using a mounting structure that is more or less already in place.  If you are mounting panels on a roof, it pays to make sure the roof itself, underneath the panels, has a goodly life remaining in it.  If not, perhaps you should first replace the roof before adding the panels above it.

If you are placing panels on the ground, consider if you need some stand-off height so that winter snow won’t reach up and obscure the bottom of any of the panels.

Wherever you choose to mount your panels, try to keep the cable runs as short as possible from the panels to your retreat’s main electrical supply area.  Longer cable runs mean wasted energy through resistance in the cables.

You’ll want to be able to regularly access the panels for cleaning purposes, so consider that.  If you have a very large array of panels, maybe you want to have some walkways in them to make it easy to reach over and clean dust, dirt, excrement, leaves, moss, etc off the panel surfaces.

The vast majority of solar panels are fixed, but it is possible to get panels that move to maintain an angle more closely perpendicular to the sun.  The sun travels through an arc each day, both horizontally and vertically, meaning that for most of every day, the energy collection from the solar cells is not as efficient as it theoretically could be.  A system that aligns itself to point more closely at the sun can generate more than 20% extra energy per day.

But the added complexity and cost of systems that track the sun, either in a horizontal or vertical axis, or even in both axes, generally seems to argue against their implementation, and they are harder to mount on a rooftop.  It is usually cheaper and easier to take the money that a tracker type system would require, and to spend that money on simply increasing the total array size and number of panels, while at the same time avoiding the added maintenance issues and complications that the tracker units would otherwise require.

So, Why is Solar so Good for Preppers?

Solar is an excellent source of energy for several reasons that appeal to preppers.  It is cost-effective (compared to other renewable energy sources) and can be deployed widely across the country.  It is long-lived and reliable and low maintenance, and once it is installed, requires no special skills to keep operational.  It is also ‘low profile’ – there are no sounds or smells or sights or smoke associated with solar power generation, unlike wind turbines, generators, or fires.

It is easy to add to a retreat, and easy to grow and expand over time.  While it is dependent on sunlight, you can adjust your array size to reflect the best and worst case scenarios for the availability of sunlight at your location.  The less sunlight, the larger your array and the greater your battery reservoir.

When designing a retreat, it is helpful to have an east-west roofline so you can fill the south-facing roof side with solar panels for electricity, and solar heating units for your hot water too.

If you don’t yet have any solar power generating resource, you should definitely get some.

Nov 202013
This 'power meter' actually measures energy, while visually displaying the rate of power being provided.  Confused?  Please read the article and hopefully all will be explained.

This ‘power meter’ actually measures energy, while visually displaying the rate of power being provided. Confused? Please read the article and hopefully all will be explained.

One of the most important parts of planning and managing your retreat is to optimize its power and energy requirements.

The two terms – power and energy – are often used, in normal casual conversation, as meaning the same thing (for example, sometimes you’ll see references to electric power and sometimes to electric energy, although both terms probably are referring to the same thing), and we’ll wager that if we carefully read through the half million words of content already published on this site, we’d find some cases where we too have used one term while meaning the other, so we will try to be scrupulously correct in this article.

Most of the time, there is little harm and no misunderstanding caused when a person is talking, generally, about things to do with power/energy, and when they use the word power or energy in the wrong context.  But, when it comes to ‘doing the sums’ and understanding exactly what your power and energy needs are, you do need to exactly understand the difference between the two concepts, and make sure you are using the correct units (and also making sure that the specifications for the equipment you’re considering are also correct, and/or being able to work through their assumptions to understand exactly what it is you are being sold).

To make things more complicated, both power and energy can be measured in several different types of units.  You are probably already familiar with some of the measurement systems and their names, and some other terms you know of you perhaps didn’t even realize were measuring power or energy.  These would be terms such as horsepower, btu, therm, watt, kilowatthour, joule, erg, calorie, foot pounds, newton meters, and various other terms too.

Power – The Watt

For the purpose of this explanation, we’ll talk about two simple units of measurement – the watt, as a measure of power, and the watt hour as a measure of energy.  First, let’s understand the terms, then we’ll explain what they mean, their differences, and how to convert between them.

In the US system of measurements, the watt is a common measure of power.  You are probably familiar with its use to measure electrical power, and other systems can be used to measure power too – for example, in Europe, the power of a vehicle is usually measured in watts rather than in horsepower.

The abbreviation for the watt is the letter W (an upper case W) – yes, this can be confusing.  If you are using the word, you typically use lower case when writing it, but if using the abbreviation, you should use upper case.

It can also come in smaller units – milliwatts, microwatts, and potentially even smaller numbers.  You will occasionally see things such as small portable appliances have their power requirement described in milliwatts (mW).  A milliwatt is one thousandth of a watt, and is abbreviated with a small letter m and a capital W.  It is very important you do this, because if you write it MW, that means megawatt, which is a totally different number entirely!  You are unlikely to come across measurements in microwatts or smaller, these are quantities that normally only appear in scientific calculations and not in domestic appliances.

Going the other way, to larger quantities than a few watts, you will commonly find kilowatts (kW), megawatts (MW), and sometimes larger quantities such as gigawatts (GW) and even terawatts (TW).  If this sounds sort of familiar, it might be because you see similar suffixes for measuring computer storage, and so you probably already know that kilo means one thousand, mega means one million, giga means a billion, and tera means a trillion.

Note that kilowatts are written as kW, whereas megawatts (and other larger quantities) are written MW, etc. Watts can of course be converted to other units of power.  For example, 1000 watts (ie 1 kW) equals 1.34 horsepower, so your car with 300 hp can also be described as having 224 kW of power.

We’ll stick with watts for this discussion rather than muddy the waters unnecessarily with other terms.  But if you do need to do conversions, you’ll find websites such as this to be helpful.


So, what is a watt?  It is a measure of power, and we’ll give you some examples of what we mean by power.

The first example is to think of a simple electrical heater.  Maybe it is an old-fashioned one with two or three ‘bars’ in it, and you can choose to have one, two or all three of the bars turned on.  Perhaps with one bar turned on, the heater is rated at 500 W, with two it is a 1000 W (or 1 kW) heater, and with three, it is giving you 1.5 kW of power.

Think also of light bulbs.  The more watts the light bulb consumes, the brighter the light, right?  If you think back to the now old-fashioned incandescent bulbs, you would probably be using 60 W or 75 W or maybe even 100 W and sometimes more powerful bulbs to light your rooms.  More watts means more power means more light (with a light bulb) or more heat (with a heater).

Now let’s think of an analogy, which we’ll use to explain the difference between power and energy. Think of a garden hose.  Turn it on a bit, and water will trickle out of the hose, and you can’t squirt it very far.  You would describe that as not very powerful, right?  Turn it on full, and more water will come out, and you can squirt it further.  The flow of water is now more powerful. You can think of electricity and power in general in similar terms to water flow, and whereas we measure water flow in things like gallons per minute, we measure electricity flow and power in general in watts.

Okay, so hopefully now you understand what power is.  Next, we will explain energy.


Let’s keep thinking about the flow of water through the hose.  The faster it goes, the more power it gives us, right?  And, also, the faster it goes, the more gallons of water it uses.  This is sort of totally obvious.  We can short of think of the total gallons of water used as a measure of the total energy consumed, and the flow as being the rate at which the energy is consumed.

If we had, for example, 100 gallons of water, that could flow through a hose in 10 minutes at a rate of 10 gallons per minute, or it could take 50 minutes at a rate of 2 gallons per minute.

And, there in a nutshell, is the relationship between power and energy.  Energy is like the total store of water, and power is the rate at which the energy is being consumed.

Let’s go back to thinking about our light bulbs and heater, and see how much energy they consume.  We know that the power used by, eg, a light bulb is maybe 100 W which means that is the rate at which electricity is going through the bulb.  If the bulb is on for an hour, then it will have used 100 watt hours of energy.  If it is on for 30 minutes (ie half an hour) it will have used 50 watt hours of energy (or, if you prefer, 3000 watt minutes or 3 kilowatt minutes).

And so on for any other scenario – you are simply multiplying the rate of power usage (as measured in watts) by the time the power is being used.

Watt Hours – Energy

We normally measure energy in watt hours, or kilowatt hours, and so on.  Sure, you could also measure in watt minutes, in watt seconds, or in watt days, but normally you’ll see this expressed in terms of hours.  The abbreviation for a watt hour is Wh or W h (with a space), and of course the abbreviation for other quantities would be, for example, kWh for kilowatt hour and so on.  We generally prefer to omit the space, just to more obviously tie in the h to the W.

If you are starting to get the hang of this, you will realize that a gallon of petrol contains energy (and could be measured in Wh), and the speed at which it is consumed is described as the power of the thing consuming the petrol (and could be measured in watts).  A more powerful thing (eg a car driving faster) will use the energy (the gallon of gas) more quickly than a less powerful thing (a car driving more slowly, perhaps).

Other types of energy measures also exist, of course.  For example, if you consume natural gas, you might see that your gas consumption is measured in Therms or BTUs rather than in watt hours (1 Therm = 29.31 kWh; 1 Btu = 0.293 Wh, and therefore, 1 Therm = 100,000 Btus).

Power is the rate at which we consume energy.  For example, it might take a certain amount of energy to heat your house from 50° to 60° – let’s say it will require 20 kWh of energy to do this.  That means (ignoring heat losses, etc) you could turn on a 1 kW heater and wait 20 hours for it to heat up your house, or you could turn on five 1 kW heaters and wait four hours, or you could turn on your furnace that, for this example, we’ll say uses 10 kW of power, and wait only two hours.

In all cases, you use the same amount of energy and get the same outcome, but you use it at different rates/speeds.

We Pay for Energy, Not Power

Now for the next thing, which hopefully logically flows from the house heating example above.  In most cases with most utilities, we are charged for the energy we use, not for the rate at which we use the energy (there are exceptions to this, particularly for commercial users that sometimes have high power draws, where they get charged for both the energy they use and also the amount of power available to them to draw from).

In the previous example, we will pay for the 20kWh to heat our house, no matter if we use it quickly or slowly.  In case you wondered, you can see on your utility bill the rate you pay for your electricity, and the chances are you’re probably paying 10c – 15c per kWh, so you’d be paying maybe $2 – $3 for the 20kWh.

Both Energy and Power Calculations are Necessary for a Retreat

When you are planning your retreat, you want to of course minimize its total energy requirement.  But you also want to consider its maximum and typical power requirements, too.

The typical US house (if there is such a thing!) consumes an average of 30 kWh of energy a day.  Hopefully, a well designed retreat can get by with much less than that.  Here’s an interesting table showing how energy is typically consumed in an average home.

The good news part of this table is that your greatest energy requirements – for home heating, cooling, and water heating (which between them comprise 60% of your total energy needs) can be greatly reduced by good insulation and home design, and may also be provided, at least in part, through alternate energy sources such as fires for heating and solar for water heating.  You don’t need electrical energy for all your retreat’s energy requirements.

It is important to understand your home/retreat’s total energy needs (and where/how you will source the energy for these requirements).  But you also need to think about the power requirement.  In the most simple sense, think of buying a generator to power your home.  If you consume 30 kWh of energy per day, that sort of seems like you are using 30/24 = 1.25kW of power, and so if you get a 1250 watt generator, you should be in good shape.  Right?

Wrong.  Sure, your house might use in total 30 kWh of energy for a typical 24 hour period, but it does not use this in a steady even flow.  At some times, for example 4am, maybe it is using no power at all.  But at 4pm, maybe it is using energy at a rate that sometimes peaks upwards of 15 kW, because you have some lights on, the stove top on, the vacuum cleaner running, the fridge compressor cycled on, and so on.  Your 1250 watt portable generator isn’t going to be any use to you at all, because any time you turn your stove on, you are needing way more than 1250 watts of power.

You need to understand both the total energy requirements for your retreat, and also the peak power requirements at which the energy will be needed.

Actually, the calculation needs to be fine-tuned even more.  Your retreat will most likely use more energy in the winter months than in the summer months (more heating, more lighting), and so you need to consider not only the typical average daily energy needs, but also the ‘worst case’ peak daily energy needs, and then translate those into the associated power rates needed.

Appliance Power Ratings and Energy Consumption

Most home appliances have a power rating in watts or kilowatts.  Some may also make some sort of vague claim about how much energy they consume a year – perhaps in the form of an Energy Star rating that compares it to other similar products.

The energy an appliance consumes each year depends on its ‘duty cycle’ – how much time each year it is actually turned on and working.  Think, for example, of a fridge or freezer.  Although it is plugged in and switched on 24/7, it actually is only working for perhaps one-third, maybe less, of the time.  Its compressor will turn on, cool the unit down to a certain temperature, then will switch off and wait until the temperature slowly drifts up from the ‘cold enough to stop cooling’ setting to the ‘hot enough to start cooling again’ setting, at which point in will then repeat the cycle.  It is the same for your furnace or your water heater or your oven or stove top element – these things cycle on and off, all the time, probably with you not even noticing.

So it is difficult to translate from a power rating to a total energy consumption, unless you know how many hours a day/week/month/year the device will be operating.  Energy Star ratings can give you some guesstimates, but these numbers, which are typically self-assessed by the manufacturers, are sometimes massively understated, so consider them as indicative best case scenarios rather than as the gospel truth.

The power ratings are useful when working out what your peak power requirements will be.  Simply add together the wattages of everything that you think might be on at the same time.

There’s one more issue to consider, when considering your peak power requirement.  Many appliances draw more power when they first switch on than they then consume while running.  This can be thought of as the extra power to spin their motor up to speed, as compared to the lesser power required to keep it turning once it is at normal speed.  For a couple of seconds, some appliances will draw two or even three times their rated power.

So, potentially, you need to not only plan for a ‘worst case’ scenario with all appliances running simultaneously (or, alternatively, plan your system so this is not possible) but you also need to plan for a scenario where all the appliances start at the same time, too.

We discuss ways to minimize these issues in other parts of this series.


Watts measure the rate at which something consumes (or creates) power.  There are other ways of measuring power, too, with different names and units, and there are simple conversion tables to convert any unit of power to any other unit of power.

Anything that provides or consumes power can have its power input/output measured in watts – even open fires.

Watt hours measure the total amount of energy something has consumed (or created) over a certain period of time.  There are, again, other measurements of energy in addition to watt hours, and they can of course be converted between the different measuring systems if needed.

It is convenient for us to consider everything in the same units, and we suggest we stick to watts and watt hours.

The most important thing for us as preppers is to understand the total amount of energy we need per day or week or month, and then to understand the rate at which we need the energy provided (the amount of maximum power we need).

Explaining the Power Meter Picture

Finally, in case it remains still unclear to you, an explanation of the ‘power’ meter we showed at the top of this article.  The rotating disk shows the rate of power flow – the faster it turns, the more power is flowing into your house.  The dials are counting up the total energy supplied, and it is the dial reading each month or two which establishes the total energy you have consumed.

Aug 032013
This 4WD $11,500 Polaris UTV can carry 1,000lbs and tow another 1,250lbs.

This 4WD $11,500 Polaris electric UTV can carry 1,000lbs and tow another 1,250lbs at speeds of up to 25 mph, and some tens of miles in distance.

We wrote before about the benefits of considering electric vehicles for your future retreat transport needs – see our article ‘Is a Tesla the Best Car for a Prepper‘.

We concluded that some sort of electric vehicle would be excellent in a Level 3 situation, because electricity might be easier to generate/create than other fuel/energy types.  But of course a Tesla is a very expensive vehicle, and not well suited for ‘working’ purposes on a farm.

There is also a much less expensive possibility that would be suitable for many preppers.  Getting an electric ‘golf cart’ type vehicle, sometimes also referred to as a ‘golf car’.  You might initially think of true golf carts and reject the thought of such things having any use at all in a grid down retreat situation, and while it is true that the type of vehicle you’d see on a golf course or in use by a ‘Mall Cop’ would not be a good general purpose vehicle at your retreat, that’s not the type of vehicle we have in mind.

Instead, and as well as the traditional/commonly seen type slow sedate golf cart type vehicles, there are many more types of electric vehicle that might be better suited for off-grid use.

Different Types of Electric Vehicles

We are talking about a probably open vehicle that has seating for two or four people, and some load carrying capacity (up to maybe 1000 lbs) to carry general stuff about the farm and even from your retreat to a local town and back.  It might also be able to tow another 1000 lbs or more, and could even be 4WD.

Some are more like mini-tractors, and can be fitted with various accessories to help you in your farming (and with a snow plow blade too for winter driveway clearing).  Some are fairly slow, others are surprising sporty, with maximum speeds in excess of 25 mph.  These types of vehicles are sometimes termed a ‘utility task vehicle’ or UTV, or perhaps a ‘Side by Side’ vehicle, or a Recreational Off highway Vehicle (ROV).

So the first thing you need to do is define the ‘mission’ of the electric vehicle.  Is it to primarily be used to transport you and trade or shopping goods to/from the local town, or will it be used as a mini-tractor type farm vehicle?  If the former, depending on the type of roads you expect to encounter, especially after a few years of zero maintenance and with no snow removal in winter, you’ll know the sort of traction system you need and the range the vehicle should have.  Maybe a regular golf cart will be fine, maybe you’ll need an off-road type vehicle.  Maybe the range of the vehicle with standard batteries is fine, or maybe you need heavy-duty batteries.

If you want to have a mini-tractor type vehicle, you’ll be needing a very different set of capabilities and design considerations.  If you want a vehicle to carry back deer and other game when you go hunting, then obviously other issues apply, including having a cargo tray.


These electric utility vehicles vary widely in price, the same as cars.  But as a round figure, plan to spend more than $10,000 on a new vehicle, depending on the features you want.

Of course, there are much less expensive second-hand ones out there, but if you are buying second-hand, you should probably factor in the cost of a new set of batteries too.  The chances are whoever is selling a used vehicle will claim the batteries are almost brand new, and maybe they even have a recent manufacture date on them, but because lead-acid batteries are very susceptible to mistreatment (particularly being discharged down too far) even a new set of batteries might have a very short remaining life.

Ebay Motors has a UTV section in it with a number of listings at any time for electric type UTVs, and a separate section (under Other Vehicles and Trailers) for Golf Cars.  We’ve sometimes seen them listed on Craigslist, and most medium/larger cities have dealers who specialize in such vehicles.

When buying any sort of electric vehicle, you also need to understand if the charger is included with the vehicle or if that is an additional extra item.


Range is – or should be – measured differently for a UTV than for an electric car, because they use different types of batteries.  A regular car probably uses Li-ion batteries, and they can be discharged pretty much all the way down to zero charge without harming the batteries, so if the car’s range is quoted as ‘how far you can go on a complete charge’ that is a valid measurement to consider.

But a UTV is probably powered by Lead-acid type batteries, and they behave very differently.  The more you discharge a Lead-acid battery, the fewer the number of times that you can recharge it, and the greater the harm you do to the battery.  So when you are being quoted a range for a UTV, you need to understand what percentage of charge depletion is being used to assess the vehicle’s range.  Is it the range to use up half the battery charge, 80% of the charge, or the theoretical maximum 100% charge range which you should never use?

Best practice for Lead-acid batteries is to discharge them only 50% before recharging; some, but not all, of the better ‘deep cycle’ batteries can allow up to an 80% discharge.  We discuss matters to do with caring for and best using Lead-acid batteries here.

There are two more things to consider when assessing range capabilities.  The first is that the range assumes new batteries in best condition, and the second is that the range assumes moderate speeds and good surfaces.  As the batteries age, they will hold less charge each cycle, and your range will therefore drop every time you recharge the batteries.  If you ‘need’ to be able to travel 20 miles on one charge, you ideally should get a vehicle with a 30 or 40 mile range, so that you can continue to get at least 20 miles of travel from the UTV for a long time before needing to replace its batteries.

It is common to see UTVs claiming ranges from about 20 miles up to about 50 miles ‘per charge’ but you’ll need to carefully understand what ‘per charge’ means’.

Batteries and ‘Fuel Economy’

There is no standard battery configuration for UTVs, and so simply understanding the different range capabilities doesn’t directly equate to how much electricity each vehicle requires to travel one mile.  That’s a bit like saying ‘this car gets 200 miles per tank of gas, and that car gets 300 miles’ – unless you know how many gallons of gas in the tank, the range figure doesn’t directly equate to fuel economy.

So you should understand the battery configuration for the UTV.  Generally, UTVs have some number of either 6V, 8V or 12V batteries, and probably all connected in series.

Many vehicles operate on 48V or 72V, but whether this is the result of a series chain of 6V, 8V or 12V batteries varies from brand to brand.

To understand the ‘fuel economy’ of the vehicle, you need to know how many kWhrs of electricity are used to drive how many miles.  Divide the miles traveled by the kWhrs used, and you’ll get miles per kWhr.  Probably this will range from 2 to 5, and noting how electricity will become scarce and expensive in the future, you should pay attention to this number and be willing to pay an up-front premium to get a more efficient/economical vehicle.

We are starting to see some UTVs with range/economy boosting features such as higher efficiency motors (rather than old-fashioned series wound motors) and regenerative breaking (ie, when you press the brake pedal, the motor becomes a generator and starts charging the battery again).  Search out the most efficient UTV you can find, as long as it also provides the other functionality you need as well.


Many UTVs will recharge from a regular 110V AC power outlet, and many will also accept direct DC charging too.  Ideally, you’d like a vehicle that will work both ways so as to give you more flexibility for the type of charging equipment you use.

If you live in a sunny area, you might even decide to mount solar cells on the vehicle’s roof (and some models come with a solar roof already installed).  We’re a long way short of being able to have the solar cells power the vehicle real-time, but if you have maybe 200W of solar cells on the roof, then when the sun was shining directly on them, that would give you the equivalent of about a 1 mph speed from solar power alone.  That’s not exactly brilliant, but if you are driving into a town and back again, and if you get five hours of sun, that could give you as much as another kilowatt-hour of power which might give you as much as 5 more miles range on your day’s use of the vehicle.

If you do get an electric UTV, you should of course remember to increase the number of solar panels (or whatever else you’ll use to generate electricity) you have to reflect your increased electricity need and consumption.

Safety Considerations

If you are buying some type of UTV, and plan to take it anywhere other than on perfect road surfaces, you probably should be sure to get a vehicle with a roll cage on it to protect you in case it tips over.  These protective cages also require you to have seat belts fastened, so you want good seat belts in the vehicle too.

A vehicle with four-wheel braking would be slightly preferable to one with two-wheel braking.


It is true that an electric UTV doesn’t need some things to be maintained that would otherwise be required in a gas-powered UTV.  Clearly it has no internal combustion engine and all the related things to do with that, but equally clearly, it still has plenty of moving parts plus it has a battery system too.

Whatever vehicle you get will have a detailed owner’s manual with maintenance schedules included.  Our point here is merely to point out that electric vehicles are not maintenance free.  They still need work on their brakes, steering and suspension, for example, and they need regular attention to their batteries, water levels in them if applicable, checks for any corrosion around the batteries, and so on.

Plus, every some years, depending on your usage, you’ll need to replace the batteries themselves.

As an interesting aside, in a normal modern-day living environment, the total costs of ownership as between a gas or electric UTV are similar – some people claim one is better than the other, others claim the opposite.  Certainly, a gas-powered unit that might have 200 miles of range before needing refueling is much more convenient than an electric one which might need some hours of recharging every 30 miles.  But in our case, we’re buying not so much for present convenience as we are for future utility.


Ideally you want to be able to continue using some forms of powered vehicles in a Level 3 situation.  In a Level 1 or 2 situation, this is easily achieved by simply using the fuel you have stored.  But in an extended Level 3 situation, you need to be able to make your own fuel.  There are a number of different ways of making gasoline or ethanol type fuels, LPG or methane type gas fuels, and diesel, and in addition to that, you’ll of course have some methods of generating electricity too.

The best prepper will have several vehicles, each powered from different fuel sources.  At least one should be electric.

Jul 292013
Some people deride coal as being dirty, ugly, and old fashioned.  They are foolish to do so.

Some people deride coal as being dirty, ugly, and old-fashioned. They are short-sighted to do so.

It is only slightly an exaggeration to say that coal has fueled and been a significant enabler of much of the modern world’s development.

But these days, ‘conventional wisdom’ denigrates coal as being dirty, environmentally unfriendly, and generally nasty.  The popular perception (which is completely wrong) is that the US (and possibly world-wide) coal industry is in terminal decline, because it is an obsolete and no longer effective/useful energy source.

Is there actually any continued role for coal in the future – either in our ‘normal’ future or WTSHTF?  Due to the prominence of coal for much of our past, that is a question we need to research and resolve.  So, please keep reading.

Historically, coal has been a long time and low-tech energy source, being reasonably easy to mine, to transport, to store, and to use.  Any low-tech energy source becomes very relevant to us when we consider a future where our high-tech infrastructure may have failed.

Coal has been used for hundreds if not thousands of years in homes, then subsequently as a fuel for stationary boilers in factories, then as a fuel for steam ships and steam locomotives, and as a feedstock for gasworks making city gas supplies, and as an energy source for power stations, and even as a raw source for hydrocarbon products of all sorts.  As recently as the mid 2000s, more than half of our nation’s energy came from coal-fired power stations.

In times of oil scarcity, coal has been used to make ‘artificial’ petrol and other liquid fuels.

Coal is also used in the production of steel, cement, even paper, and many other things.  The US is the world’s second largest coal producer and has the world’s largest reserves – more than 240 years of supply.  So coal would definitely seem to be something all preppers should consider.

As preppers, our major focus on coal would be as an energy source.  The good news is that coal is a very good value source of energy, less than half the cost of most other major energy sources.

There are very many different ways to measure the costs of energy, but the disparity between the cost of coal and other energy sources is so huge as to make it unnecessary to quibble over the last few percents.  If you look at the table on page 3 of this document, you’ll see the following costs per million BTUs of energy for a range of different energy sources (2010 data averaged across the US).

Energy Source Cost ($ per million BTU)
Coal $2.42
Natural Gas $7.41
(note – prices in 2013 are about half this)
Distillate Fuel Oil $20.62
Jet Fuel $16.28
LPG $19.61
Motor Gasoline $21.98
Residual Fuel Oil $11.70
Other $17.97
Average for all Petroleum $20.32
Nuclear $0.62
Wood and waste biomass $3.45
Electric Power Industrial $2.62
Electric Power Retail $28.92
National Average $18.73


As you can very clearly see, and based on these wholesale/industrial rates, nuclear power is massively better value than any other power source, but coal comes second, followed closely by wood.  Natural gas is three times the cost of coal, LPG and gasoline are about eight times the cost.

So, in terms of theoretical cost per theoretical unit of energy, coal is massively better than all other energy sources open to us, both now and in the future.

Another interesting point is that one ton of coal can create two barrels of oil.  At the time of writing, this regularly updated coal price report shows coal varies in price from as low as $10.30/ton to as high as $68.25/ton.  To put this number into clear perspective, even after allowing for carbon capture and other ‘best practice’ environmental considerations, it costs less than half as much to convert coal to oil than it does to buy a barrel of oil directly (here’s an interesting report on that topic).

We point this out not to suggest we all create Fischer-Tropsch plants to convert coal into oil in our back yards, but merely to open your eyes to the enormous potential of coal for many different energy applications, both at present and in the future.  It is very wrong to think of coal as ‘old fashioned’ (and as ‘bad’).

If the preceding is even half-true, why don’t we all build massive coal bunkers and store tons of coal?  Sure, it is true that coal is not a very ‘clean burning’ energy source, but who would worry about that after TEOTWAWKI, when all sources of industrial pollution with have been close to zeroed out?  Let’s learn some more about coal.

Different Types of Coal

As you might have noticed from the coal price report linked in the preceding section, the amount of energy you can get from a ton of coal can vary widely, as do other factors such as its sulphur content.  Here’s an interesting chart that sets out the varying amounts of sulphur and energy from coal in different parts of the US.

The wide range of different properties of coal have been categorized into four broad categories (and there are sub-categories within each of these four main categories).  The ‘best’ coal for most purposes is generally anthracite, followed by bituminous, sub-bituminous, and finally lignite type coal.

Anthracite has the highest calorific (energy) value, the highest carbon content, and is the oldest coal.  Each of the three subsequent grades have less energy, less carbon, and are more recent (albeit in geological terms of hundreds of millions of years).

The subbituminous category is of interest, even though it would seem to be the third of the four grades, because it has a low sulphur content.

Using Coal

Coal burns hotter than wood and can create more soot.  If you are going to burn coal in your house, you’ll need to make sure that your fireplace and chimney system can handle the greater heat of coal.

Coal also needs a different type of air flow than does wood.  You need to have coal on a grate with air able to come in from under the great and go through the coal bed for its combustion.  This is fairly critical – a solid bed of coal (as may happen after some hours of burning and a layer of ash being created) will prevent air flow and proper combustion; whereas too porous a bed will also fail to allow for optimum burning.

A well tuned coal fire should generate little smoke, although that depends a bit on the type of coal being burned.  Typically anthracite is preferred for home use and it is a ‘clean’ burning coal.

Coal comes available in different size ranges.  Here’s a list from small to large, and with sizes (which seem to vary from place to place somewhat)

  • #5 (typical size 3/64″ x 100 mesh)
  • #4 (typical size 3/32″ x 3/64″)
  • Barley (Buckwheat #3) (typical size 3/16″ x 3/32″)
  • Rice (Buckwheat #2) (typical size 3-5/16″ x 3/16″)
  • Buckwheat (typical size 9/16″ x 3-5/16″)
  • Pea (typical size 13/16″ x 9/16″)
  • Nut (typical size 1 5/8″ x 13/16″)
  • Stove (typical size 2 7/16″ x 1 5/8″)
  • Egg (typical size 3 1/4″ x 2 7/16″)
  • Broken or lump (typical size 6-8″ x 4″)

We’ve seen people express opinions favoring one size over the other, and others favoring quite the opposite (for example here), and the best size probably depends on the type of stove/furnace and grate you are using.  If you are using an auto-stoker device, then size becomes even more relevant.  Suggestion – experiment to start with, using different sizes until you find the size that works best for you.

As with any type of combustion indoors, we’d recommend you have a couple of CO detectors to keep an eye on CO levels, just in case unusual conditions interfere with the normal safe operation of your fireplace/stove.  You should also have a fire extinguisher or two, and perhaps a bucket of sand (or baking soda) as an excellent way of damping down a coal fire if it starts to get out of hand.

We’d also suggest you regularly inspect your flue/chimney setup for any ash accumulation and sweep it clear as needed.  After a while you’ll get a feeling for the needed frequency of maintaining this – failure to do so might interfere with the venting of the fire and cause dangerous gas buildups inside your house, and/or might encourage chimney fires.

Of course, if you change your coal type, you’ll need to ‘recalibrate’ your expectation of how regularly you need to clean your flues.

Real World Costs and Benefits

We were earlier quoting the wholesale costs of different energy sources.  As you can doubtless guess, there’s a world of difference between the ex-mine cost per pound of buying 1,000 tons of coal, and the cost of having one single 50 lb bag of coal delivered to your doorstep.

Here’s a very useful fuel comparison calculator you can use to compare the respective costs of different energy sources for home heating.  It comes with some default numbers that aren’t enormously out of line, but adjust them for the actual costs you’d pay in your area, and you’ll get a clearer view of the actual costs and benefits of different heating sources.

Coal’s benefit reduces somewhat when you’re buying coal in small quantities, but it typically still shows some advantage over most other heating options.

Read More in the Second Part

This was the first part of a two-part article on coal.  Please now click on to read the second part of the article – Practical Issues to Do With Using Coal.


Jul 292013

We love coal fires and their distinctive appearance and smell.  The fact they are a very efficient and low cost way of heating is a further reason to consider coal as a fuel source.

We love coal fires and their distinctive appearance and smell. The fact they are also a very efficient and low cost way of heating is a further reason to consider coal as a fuel source.

If the concept of coal as a fuel source appeals, you need to shift from the theory to the practicalities of what it will cost to buy the coal, how you will store it, and other related issues and considerations.  Our earlier article, ‘Coal – A Prepper’s Friend of Foe‘ looked at the overall issues to do with coal, this article looks at some further specific things to consider when evaluating coal.

Where the Coal Is and Buying It

Clearly the closer you are to a coal mine, the lower your cost of coal will be, although another factor will be the ease of shipping coal to your location.  Here’s a somewhat dated but still accurate map showing the spread of coal fields across the country, and here’s a link to the latest US Energy Information Annual Report on coal which has details of mines and their production levels and much more.

If you are wanting to buy significant amounts of coal, then you could consider buying full rail wagon or truck loads.  A full truck load is about 24 tons.  But if you are wanting more moderate amounts (especially to start with when you might be experimenting with different sizes and grades of coal to see what works best with your setup), you should find the closest possible coal merchant.  If you can’t find any nearby coal merchants, you could contact the closest coal mines and ask them for referrals.  Of course there are online services such as this and this too (but we’ve yet to see Amazon start selling it complete with free second day delivery included!).

However, please wait a few minutes before rushing to buy some hundreds of tons of coal.  You should read on to the next section.

The Downsides of Coal

There are two major problems (as well as some minor problems) with coal that argue against our broad adoption of a coal strategy for our future energy sources.

The first is that burning coal is harder on our furnaces than burning wood.  The sulphur that is present in coal creates compounds that attack the metal of our stoves, fireplaces, chimneys, and other structures.  This is nothing that can’t be reasonably compensated for when designing and building such structures, but it does accelerate the wear on all such things, compared to burning wood or natural gas or fuel oil.

The second major problem is storing coal.  Now, you might think that a natural unrefined substance such as coal, which has been slowly forming for 300 million years, and which you may also know is fairly hard to set on fire and to keep burning, would last another few million years without any problems after taking it out of the ground, but if you thought that, you’d be surprisingly wrong.

Coal can be a potentially troublesome product to store.  It reacts with air and with water, and the result of the reaction causes a release of heat.

The release of heat does two things.  First, it speeds up the reaction (making for a positive-feedback loop), and secondly, if it builds up sufficiently, it ignites the coal.  So you can have a pile of coal, even in a cool and/or damp environment, that sets itself on fire.  Amazingly, and completely counter-intuitively, spraying a pile of coal with water can increase the chances of it self-combusting.

Coal not only burns spontaneously after it has been mined, it can also do so while still in the ground; indeed, according to this article, thousands of coal fires are burning all around the world, all the time.  Coal fires in China burn through 120 million tons of coal every year, and contribute 2% – 3% of the total annual worldwide CO2 emissions from fossil fuels.

Coal fires in stored coal piles are far from uncommon, and take very little time to start (75% of such fires start within three months of a coal pile being formed, and many of those fires within the first two weeks).  A little known fact about the Titanic is that when it put to sea on its maiden voyage, it had a fire burning in its number six coal bunker.

If you have large-sized piles of coal, you need a way to monitor their core temperatures.  If the core temperatures reach 140°F, then you need to consider preventative measures, and by the time it gets to 150° it is time to break the pile and allow the coal to cool before repiling it.  Coal generally will start to smoke at about 180°, and at that point, it is a bit too late because it is starting to combust.

Note that coal will often steam as water dries off, this is different to smoking.

Large lumps of coal are more resistant to spontaneous combustion than smaller lumps, and anthracite is the least susceptible, while lignite is the most susceptible.

If there is a lot of air flow through the pile, that will keep the coal cool.  If there is no air flow through the pile, that will keep oxygen away from the coal and limit the reaction.  But somewhere in the middle, between ‘no air’ and ‘lots of air’ is a danger zone with enough air to encourage spontaneous combustion.  It can only take a small amount of air flow for this to occur.

So, if you are storing coal, you need to keep the piles small and monitor their core temperatures.

A related issue is that coal deteriorates over time.  It again seems strange that something which is formed so slowly over 200 – 300 million years is so apparently ‘unstable’, but you will definitely start to notice reductions in heat output from coal that has been stored for extended periods of time.

These heat output reductions are probably not profoundly significant, and you can still store coal for many years, even tens of years, and still get valuable energy from it, and when you compare this to storing wood (which might rot) and liquid fuels (which need stabilizer and even then have a maximum storage life of perhaps ten years) it is clear that coal is as suitable for storing long-term as other energy sources.  But it isn’t perfect.

Legal Restrictions on Burning Coal

Another problem might be any clean air regulations in your state/county/city that restrict your ability to burn coal.  The problem is that such laws almost certainly don’t say ‘except in an emergency when you can burn anything you like at any time for any purpose’.  If the law says it is illegal to burn coal today, it will still be illegal to burn coal WTSHTF, and while enforcement might be thin, sooner or later some enterprising person will realize you are burning coal and will use the law as an excuse to legally ‘fine’ you, with the fine perhaps being the forfeiture of your remaining coal or food or anything else they wish it to be.

On the other hand, if your region just has occasional, weather/air quality dependent burning bans, then perhaps, after TSHTF, the authority that rules on such things will no longer function, and/or, the lower level of general industrial activity will reduce the number of times during the year when coal is banned.

Clearly if you plan to rely on coal as a year-round fuel source (eg firing a boiler that then provides heating, hot water, and possibly even electricity generation or a mechanical power source) you need to be sure you can legally use it year round.

How Much Space Does a Ton of Coal Take Up?

So, if you do decide to set aside space to store coal in bulk, how much space will you need?

Our first comment is to remind you of the problems outlined in the preceding section to do with coal’s propensity to spontaneously self-combust.  It is better to have a number of smaller piles/bunkers/whatevers of coal than one large one.  If nothing else, we’d want to be sure that nowhere in our fuel pile was more than four feet from the outside.  That might sound like a restrictively small size, but you could get as much as 6 tons of coal in such a pile.

This is a very conservative suggestion, but better safe than sorry.  Back in the 1920s, the Railroad Administration suggested piling coal for railroad storage not over twelve to fifteen feet in height when the track is placed on top of the coal pile, and not over twenty feet when a locomotive crane is used.  The Home Insurance Company advised against piling in excess of twelve feet, or more than 1500 tons in any pile, and suggested trimming the piles so that no point in the interior was more than ten feet from an air-cooled surface.

Coal is dense, but due to its irregular size and shape, it doesn’t pack efficiently.  In general, you can expect to get from about 43lbs to 59 lbs of coal per cubic foot.  Because coal is heavier than water, wet coal takes up more space for a given amount of weight than does dry coal.  Older coal (ie bituminous or anthracite) will have a greater weight of coal per unit of volume than does newer coal.

So, back to our suggestion you keep a coal supply in piles measuring 8′ x 8′ on their base and 4′ high – a total of 256 cu ft.  If you work on say an average of 50 lbs of coal per cu ft, that would be about 12,800 lbs of coal, or 6.4 short tons per pile.  You are using 10 sq ft of floor space to store a ton of coal.


This was the second part of a two-part article about coal.  If you’ve not already done so, you might choose to now read our first part, ‘Coal – A Prepper’s Friend or Foe‘.

Coal is usually the second cheapest energy source in the US today.

The two cheapest sources of energy in this country are strangely the two which ‘greenies’ hate the most – coal and nuclear.  On the other hand, arguably the ‘cleanest’ source of energy is also the most expensive (electricity) and being as how almost half of all electricity comes from coal fueled power stations (and most of the rest from stations burning either natural gas or oil) the ‘cleanness’ of electricity relates only to what you see coming out of the wall rather than the total process of generating the power in the first place!  But it isn’t our place, here, to get into a discussion on the illogic that surrounds too much environmentalism….

Suffice it simply to say that while it is of course entirely impractical to consider building your own personal nuclear power plant; depending on where you are, where you could source coal from (and at what cost) and any local restrictions on burning coal, you might find coal to be a surprisingly cost-effective and good solution for much of your future energy requirements.

If you do choose a coal based approach to some of your energy needs, you are well advised to choose specific stoves/furnaces that are designed and optimized for the different burning characteristics of coal (compared to wood).

We’d recommend you research the issues to do with using coal at your retreat.  You might be surprised at how positive a coal based energy approach could be.

Here’s an interesting reader forum type website that could be a good resource for preppers wanting to find out more about buying, storing, and using coal.