Living With Photovoltaic Power, by D.P.

So, you’ve been wondering if you should be buying some photovoltaic (PV) panels to avoid the darkest of ages? And you have some specific questions:
– how many panels do I need?
– which type of panel do I need?
– what’s it going to cost?
– what about an inverter?
– what can I actually get done with my energy?

In this post I will try to answer these questions, having gone through the process myself in the last few years. My hope is that by relating my journey, it will help some of you make the right decisions for your situation. My main goal is to be able to collect and store enough energy that my life can continue without being totally thrown back into the 19th century. ‘Little House on the Prairie‘ may be nice to watch but I am not sure I would enjoy every aspect of that lifestyle. Example: I do have a woodstove with built-in oven but would really rather use my breadmaker to bake a loaf of bread. On the other hand: our house has electrical heat and the kWh it consumes on a winter day can only be delivered by a fully operational power grid (even rolling blackouts could be a disaster), so drastic measures are required.

I decided to go with solar energy because PV panels make no noise, need no gas and are maintenance free. Three plusses over a generator when you find yourself in the dark age. They have downsides as well in the comparison: up-front cost per kWh for panels is much higher and you will need more batteries. What tipped the balance for me is that I do not know how long the grid will be down, so I do not know how much gas I have to store, or if I can get gas at any price if I run out for that matter. As J.E.B. pointed out in his letter to SurvivalBlog (published July 17, 2012): a worst case scenario will be measured in years, not days. A second consideration for me is that if everything works out I may go off-grid voluntarily. In that case the system would pay for it self rather quickly.

Having said that, creating a system for collecting/storing/using solar energy does not come cheap. If you cannot set aside $1000-$2000 without seriously compromising your prepping budget, my approach may not be the correct one for you. Let me first explain this figure a bit more because
it may strike many of you as too much or too little.

First of all: you do not have to plan on spending much more. If you can that is great, but installing $10,000 worth of panels on the roof of your retreat is asking for trouble IMHO. It may give you a lifestyle similar to what you have today, but in a situation where law and order breaks down,
this display simply says: Hey guys, I have got the goods here, come and get me first. Personally I am not a gunslinger trying to attract targets, so keeping a (very) low profile is my first line of defense.

Secondly, if you can’t afford that much money, you will need to adjust your expectations and priorities because very inexpensive components are expensive to run in that they are usually less efficient and therefore leave you with much less useable energy. I will give you some ideas of what you can do for $100-$250 at the end of this post.

As a side note on budgeting: if you are in the lucky circumstance of being able to set aside some money and save (or have saved) it in the form of dollars, please stop doing so, take that money and start buying the goods that you will need soon enough. The US dollar is being pushed out of its position of global reserve currency day by day. When that process reaches its inevitable tipping point, the dollar’s purchasing power will evaporate and the only official notification you will get is a message from your friendly neighborhood ATM that it is currently out of order. This comes from someone who, up until a few years ago, spent decades saving for a rainy day. Which has now arrived … and so I feel I have no choice but to convert a good chunk of my savings to goods that I expect to be able to put to good use.

While on the topic of budgeting:
If you don’t have or plan to purchase an over-the-top system, you will need to get used to an energy budget. You know: supply and demand. Like an old farmer, you will have to make hay when the sun shines [modern farmers can’t afford to wait for the sun so they make haylage instead]. Supply can be increased by buying additional panels; demand can be lowered by energy conservation measures; you can do both until you find your happy or affordable middle ground.

Starting with demand, how can we keep it low? What are the things you really want electricity for? Here is my list:
– lighting (LED type uses the least energy and is long lasting)
– walk-in cooler to store food, seeds, etc. (our house has no basement)
– monitoring systems
– water pumps
– communications (radio, 2-way radios)
– small kitchen appliances (mixer, blender, breadmaker, etc.)
– security (keeping wildlife out of the garden and the chicken coop)
– laptop, e-reader, battery powered flashlights
– handheld power tools (drill, saw, angle grinder, rotary tool)

No washer? Nope, grandma got the job done with a few hand tools and so can I.
No dryer? Hot air from the woodstove will do just fine.
No dishwasher? Never had one.
No plasma television? What are you going to watch when the grid is down?
No entertainment center? I can watch DVDs on my laptop.
No microwave? I would use it if possible, but I am not budgeting for it.
No air conditioner? I do have a small (500W – 1 room – fits in a window)
air conditioner but don’t plan on using it unless I really have to. I prefer to sit under a tree beside a brook when compared to the air conditioner’s noise. As for heating rooms and/or water with a solar panel: don’t even think about it; that is a job for wood or coal. Yes you can use a solar heat exchanger for that, but what if it breaks down and you can’t get the repairman to come over? And the wind chills are around -40?

When determining the feasibility of solar power to run a tool or appliance, you need to keep in mind it’s power rating and the time it’s actually on. For instance if you need to cut a 2×4 your saw may be rated at 1200W but if your cut only takes 10 seconds, the energy used is 10 * 1200 / 3600 = 3.3Wh / 12V = .28Ah. Not worth talking about if your batteries are full. A 50W solar panel will generate 3.3Wh in about 4 minutes on a sunny summer day.

On the other end of the scale: let’s say you want to bake loaf of bread using an automatic breadmaker. The appliance is rated at 600W and the process takes 3 hours. About half an hour is used kneading dough and 1 hour to actually bake the bread. Its energy usage amounts to:
.5 * 100 = 50Wh for kneading
1 * 600 * .67 = 402Wh for baking at 2/3 duty cycle
Total = 452Wh over a 3 hour period, which equates to a 150W demand.

The numbers above are pretty close to what I have observed personally: I can use my hand-held power tools all day and only need a 30W – 60W panel to maintain battery charge. My breadmaker tests showed that on a sunny summer day I need 180W worth of rated panel capacity to maintain battery charge over the entire baking cycle.

Another item that can take up a lot of power is pumping water. This year I have put in a small aquaponic garden with 4 grow beds just to see what it takes to grow veggies that way. It’s an ebb and flow system that uses a 1000 gallon/hr bilge pump with a 1″ outlet. Though the pump is rated for 5 Amps, it draws only 3.5 Amps and runs 20 seconds every half hour. As a result a 15W rated panel keeps up with it with capacity to spare. But if I want to warm up the water quickly after a cool night by using an small aquarium pump to push water through a heat exchanger, I need to go to a 60W panel because that second pump draws 1.3 Amps continually. Lesson for water pumps: try to use big lines and low working pressure and lift.

Because I don’t want to be tied down too much by carrying around a ton of documents, I keep most everything in electronic format (mht or pdf) on hard drives and DVDs. That means I need something to read them with. Laptops tend to take 50-60W (or more depending on CPU/graphics card in it). So running it for 8 hours a day to play solitaire, …err study documents, will set me back 8 * 60 = 480Wh. Sigh! Just ain’t gonna happen on a cold winter day… A small tablet or e-reader would work much better under the circumstances.

For those of you wondering about getting enough juice for your tablets and smart phones to continue life in the cloud (Facebook, Twitter, on-line gaming and data storage): don’t worry, by the time you really NEED your solar panels, in a grid down situation, cell towers will cease to function within 24 hours as their batteries run out and (access to) the cloud will simply disappear like a morning fog.

Phantom Loads
You will waste precious amp hours to run your systems. There is no way around that because no appliance or battery is 100% efficient, but with some advance planning we can keep the leakage to a minimum. Biggest single issue is your inverter. Don’t buy one unless its idle power draw is less than 250 mA. You do not want to waste 1 or 2 amps on heating your inverter while its idling. This is not much of an issue for a 100W inverter that you use only to run your electric shaver because you can turn it off when you’re done. However for large inverters that you leave on all day to run your power tools on-demand you do not want their idle draw to exceed 250 mA and the lower that number the better. I learned this the hard way a few years ago when I left a 300W inverter on thinking only its LED was drawing power. After two days the new 120Ah battery was run down to the point where the inverter’s low voltage alarm went off … at 3AM …

Second inverter issue: do not leave appliances that use standby power plugged into the inverter because that draw will keep the inverter revved up continuously costing a few amps in the process. This may not sound like much but look at it this way: if the inverter uses 2 amps for 12 hours, that is 24 AmpHours. A 60W panel will generate about 3 Amps (averaged over an entire sunny day), so it needs to run 24 / 3 = 8 hours to make up for that loss. At current prices that 60W panel will cost you around $135 (+ S/H & taxes).

As an example: I once kept a yard light plugged in overnight with only its infrared sensor active and it took about 10% of my battery bank’s capacity in the process. My inverter was luke warm that morning whereas it stays cold even if I use it all day with my power tools. Another lesson learned and BTW I am running most of these tests on purpose right now, so I will know what to expect when it counts.

Third big cause of energy leakage: bad cells in your battery bank. I have dealt with this extensively in another post called ‘battery life extension’ and won’t repeat that now. Sufficeth to say that if your bank discharges itself from 12.6V to 12.35V overnight, you have a huge power drain on your hands.

Now, let’s assume you have dealt with all three biggies above; what is there left to do? Actually quite a bit, though exactly how much and what is a bit dependent on your handyman IQ. I am now referring to a couple of specific items on my list: lighting and monitoring systems. By their very nature they have to run many hours, some of them 24/7. The nice thing is that you can get a 12V (or lower voltage) version of pretty much any item you need.

Let me give you some examples:
– The 110V yard light I talked about earlier can be replaced with a 12V infrared sensor connected to a 12V LED flood light. Yes, if you get the right parts it can be as simple as connecting 4 wires.
– The walk-in cooler I mentioned needs to have its temperature monitored and regulated 24/7. Thermistors (temperature sensors) are a dollar a dozen and 12V computer case fans @ $5 each move enough air to get the job done.
– My primary heat source is a woodstove in a rather small work space. To avoid problems the space is outfitted with a dual fire/smoke alarm and carbon monoxide and carbon dioxide alarms. You can get these in 110V AC or 5V, 9V or 12V DC versions.
5V versions tend to come with a “wallwart” power cube, 9V versions run on a battery and 12V versions intended for RV use. If you can’t get them locally, try to find a supplier on-line. [JWR Adds: I have found that Camping World is a great source for 12 VDC appliances and gadgets.]

LED Lighting:
Despite candlemakers waxing nostalgic about the power grid being down, LED type should be used to cover your basic lighting needs due to its simplicity and longevity. In essence: put it in and forget about it; I have wrecked some LEDs by putting too much current through them but never seen one fail due to old age. There are many 12V LED lights available these days, though some are still pricey. I took a different (= less expensive) route by getting a bag full of UFO lights (the type you can put in tents) from China and using those. There are 2 types commonly available as of this writing: one with 60 LEDS and the other with 20-24 LEDs. I have used them both and there is not a lot of difference in the total amount of light they produce for the same current.

These units are designed to run on 4 AA batteries (= 5-6V), so you will need to solder 2 pieces of wire into the battery compartment. If you only need 2 or 3 units, you can connect them in series and then directly to your battery. [2 units may need a small series resistor if LEDs get hot.] I put 4 or more per room (very even lighting throughout the room) by connecting all units in parallel and then putting a ‘circuit breaker’ in the wire that connects them to the negative pole of a 12V battery. The ‘circuit breaker’ is a 555 timer chip that switches a MJE3055T transistor on/off @ 120Hz and about 15% duty cycle. This runs the lights flicker free @ 2.8V which leaves the LEDs cold to the touch but produces ample light. You can adjust the lights’ output by changing the duty cycle of the ‘circuit breaker’.

DC-DC converters:
These do what their name implies and convert one DC voltage into another. Use them to run devices and/or monitoring devices directly from a 12V supply. You want to avoid running an inverter to run a wallwart to run a monitoring device that draws 150mA at all cost. Some DC-DC converter examples:
– a laptop power supply that runs off your car battery (produces 18V-22V; should have no problem charging cordless tools)
– a AA, AAA, 9V battery charger that runs off your car battery.
– a 12V desktop computer power supply (this replaces your standard PSU)
– generic DC-DC step up/step down converters in all shapes and sizes on eBay
– for those with a soldering iron: 78xx voltage regulators are hard to beat and can generally be run without heat sink for loads of less than 250mA.

Try to take advantage of your environment:
This example applies mostly to northeners, mountain and desert dwellers. I built the walk-in cooler that I mentioned earlier because at my location we mostly have cool nights [think morning temperature lower than 60 degrees Fahrenheit] (>340/year). The idea is to use a differential thermostat to start the fans whenever the outside air is colder than the air in the cooler and simply flush out the hot air that accumulates during the day. This approach does a decent job of tracking nighttime lows if you can inhibit air flow throughout the day. The cooler itself is a 7’x5′ room that is also 7′ high. It is completely lined with 2 layers of 1″ thick styrofoam (this allows me to overlap joints to achieve lower air leakage). There should be no wooden or metal breaks in the lining as this will seriously lower the cooler’s overall insulation value. The door is currently sealed by weather stripping, but I may replace that with a magnetic seal like the ones used in a fridge. Your best location is against a north wall on a lower floor. If you can’t avoid a sun baked wall, try to incorporate a layer of aluminum foil on the outside of the styrofoam. That construction needs a small airspace between the wall and the the foil (shiny side out) but is worth its weight in gold. I should point out that in the winter I have to blow hot air from the woodstove into the cooler every now and then to prevent its contents from freezing solid and you may need to provide for that as well.

Inside my cooler there is a separate box that is double insulated. Even on hot summer days it’s temperature rarely exceeds 60 degrees F. The outer part of the cooler may get up to 70 degrees at the end of a hot summer day, cooling down to 55 degrees by morning on most days. I can expect to see these temperatures from the middle of June through the middle of August. Before and after that nights are colder and so is my cooler. So in the summer it emulates a good basement and the rest of the year its more like a fridge. This is plenty good enough to provide additional storage life to whatever you put in there for a small energy footprint.

And so I don’t have to budget for a fridge, but what about a freezer? I would like to have a freezer but haven’t run any tests yet to see how much power it really takes. The good thing about using a freezer is that it requires the most power just when it is most readily available. The problem I see is that I will need to make a custom 12V control circuit to determine when to turn power to the freezer on and off because I do not want the freezer to keep my inverter active 24/7. Apart from that I do not consider a freezer critical because there is always the art of canning to preserve food.

To summarize:
It may sound strange but based on what I discussed above I have decided that if I have enough solar panels to be able to bake one loaf of bread each day year round, I will have enough capacity to run everything I need to run. The catch is in ‘year round’ (I don’t live in the Arizona desert) so let’s look at the supply side of my budget.

The calculations above reflect the situation in mid summer, say, from the middle of May till early August. By the end of August the sun is so much lower in the sky that the solar panels’ output is noticeably dropping and of course the days are shorter. This trend accelerates as you go into fall and by late September I need to use 2 60W panels where I need only 1 in June. The darkest part of the year is in November before we get snow on the ground and on a cloudy fall day I have to use 3 60W panels to produce roughly the same AmpHours a single 60W panel produces in the summer.

A solid cloud cover tends to cut power production 50%-70% compared to a sunny day. Light cumulus cloud cover (a few fair weather clouds) isn’t much of an issue. Cirrus clouds (high feathery clouds made of ice crystals) on the other hand can drop the panel’s output 30% even though it still looks ‘sunny’ on the ground. If you are in a situation where there is frequent fog or smog around a city, you will probably need to make an allowance for that too, but I have no experience with it.

Above all, avoid the situation where your panels are shaded part of the day. This may sound strange but my setup doesn’t have any fixed rooftop panels as most commercial installations do. Such a setup would make it hard to do all the tests that I have run but I also consider it inefficient. Even if the rooftop panels’ alignment is properly adjusted for your location you will have only 2 times a year where they are perfectly aligned with the sun’s rays hitting them at a 90 degree angle. But what is worse is that every morning and every evening the sun’s rays hit them at very low angles or not at all (assuming they are facing due south).

A mono-crystalline 60W panel measures approximately 2′ x 2.5′ and weighs around 12 lbs. So its easy to handle and move. Its also a lot sturdier than I thought (I can assure you that those ‘tests’ were unintentional) Some of my panels are hung vertically on the inside of doors. If the door is closed the panel is safely stored inside. If the door is open it faces the sun, which can be tracked from southeast to west. In the summer time when the weather is quiet, I usually tilt those panels upward as well. In winter time they stay in a vertical position to take advantage of light reflected off the snow on the ground, but can still follow the sun from southeast to southwest.

Other panels are completely detached and follow the batteries where-ever they are needed. Those panels get repositioned a few times during the day to track the sun. Lots of work? Not really: I only adjust the panels’ positions when I happen to be around anyway. Besides when the grid is down, your kids will be home and can’t play video games …

But is it really good enough?
Yes, I started out skeptical too; not really wanting to put down $x000 on something that might not meet my needs. So I started small with a 30W panel and a few not so great batteries and built the system from there. Nevertheless right from the start of the work on my ‘retreat’ I have run all power tools off that little system. Granted if I needed to rip a bunch of 2x4s lengthwise, I had to do it on a sunny afternoon or the inverter would kick out due to low battery voltage. But for those of us that grew up and/or live in the countryside, to go with the weather is just a normal way of doing things. The system has been up for more than a year now and it has never left me without enough power to do the things I wanted to do.

At present I have 270W of rated generating capacity and my batteries are in good condition. Last month we had a stretch of 5 cloudy days where we didn’t see the sun at all. None of the batteries fell below 50% capacity even though I didn’t hold back on any planned activities. That is how I am building the confidence that I am on the right track.

Now the math:
150W (for the breadmaker) * 3 (for year round use) = 450W. Based upon what I have seen so far I am confident that this is enough generating capacity for my setup. Making a loaf of bread takes only three hours, so even if my minimum usable day length would be no more than 6 hours there are still 3 hours (~400Wh assuming panels produce at 30% of rated output) left to run all other devices, lights, etc. And if the batteries run low after a stretch of dreary weather I just won’t be able to use my laptop or power tools for a while. Keep in mind that running low means the batteries are approaching the 50% charge level, there is plenty of power left for lighting, emergency repairs, etc. During most of the year 450W generating capacity is too much for my immediate needs but this is partly absorbed by running more water pumps, power tools, freezer, etc. than in the winter. And I can always store unused panels till I need them again.

450W worth of panels @ $2.50/W (includes shipping/taxes) will set me back around $1100. A good inverter $250 and another $250 for batteries add up to $1600. And I was lucky because I was able to purchase good used deep cycle batteries for 10% of their retail value. New they will set you back around $250 apiece. I purchased my solar panels and inverter via the Internet. I can get them locally but for 2-3x as much money. Depending on your situation, you may want to get them on-line too, but only order from a supplier in the country you live in. Getting these items straight from China will probably get you B-grade and that is not what you want on high priced goods. And.. your warranty would be a nightmare at best.

As of the time of this writing (July 2012) the prices that I have quoted are available on eBay from North-American suppliers.

Types of panels:
I am getting the best performance from mono-crystalline panels that are rated at 16.5-17.5% efficiency. Poly-crystalline comes in just under that at around 16% efficiency and is sometimes a bit less expensive per watt. Amorphous type panels are still less expensive per watt but have only 8-9% efficiency and therefore have almost twice the surface area for the same wattage. They also seem to deliver power at a lower voltage.

Inverter size:
My inverter is rated for 2500W with 5000W surge capacity. This sounds like a lot but you should take the ratings with a grain of salt. I tried to run a 2 h.p. industrial motor off it but that didn’t work because the inverter shut itself down after a few seconds on each attempt. On the other hand I have no problems running a 1200W circular saw, a 1500W vacuum cleaner and a 15A stick welder. So my inverter probably delivers close to 2000W in real life. Its a big box which means it runs cool and that is a good thing. Its fans only come on when I am baking bread on a hot day or when I put it in the full sun because its outer shell is used as heat sink. Given my experience I doubt you will be happy for long if you try to use an inverter rated for less than 2000W as your main inverter. Since you probably want a backup unit as well, its worth considering to get a stackable inverter. Those units allow you to connect them in parallel in a single system effectively doubling your capacity.

System building note:
If you buy an inverter you will most likely see in the instructions that it should be grounded. I suggest you ignore that instruction because it will seriously compromise your system without adding safety for people that use it. Here is why: Your system’s common ground is the minus side of your battery bank. Assuming your batteries’ casing is intact it is isolated from the earth you walk on, so its impossible for you to be the switch that closes the loop (i.e. get electrocuted if you touch a hot wire; and yes, I personally tried it and am still writing…). The downside of tying your system to earth was pointed out by J.E.B. in his letter: your system could get fried just when you need it most. He is entirely correct in his assertion. The earth is a large capacitor and when excited by externally induced currents, it rings like a bell. As with any capacitor the rise and fall times of the currents are very small compared to the current’s size leading to near vertical ‘walls of energy’ that are fully capable of destroying a system through its ground connection alone. Exactly what size of external event is required to take down a given system depends on many factors but why take a chance? For that reason my solar powered system is not grounded to earth.

How about the $100-$250 setup?
If you have been reading the entire article you may be able to guess where this is going:
– Forget about using 110 VAC tools and devices. This will save you the expense of an inverter. Definitely skip a charge controller in this setup.
– Buy a 40W or 50W mono- or poly-crystalline solar panel (=$100 to $125). If you live south of 40 degrees latitude, you can probably get by with a
30W-40W panel. I do not recommend using panel sizes below 30W for use with deep cycle and marine batteries. 15W is the minimum for car batteries and 5W for garden tractor and motorcycle batteries. The reason is that small panels cannot generate the power required to charge a large battery to
100% capacity. It may charge to 75% or 80% of capacity but that leaves a lot to be desired capacity wise and will at some point lead to quicker deterioration of the cells inside your battery. Rule of thumb: if your battery never reaches 13.6V in full sun around noon time, your panel is too small (or you have a bad cell in your battery).
– Try to get 1 or 2 used batteries that measure 12.3V or higher at rest. If that doesn’t work, buy 1 with 100Ah (or more) capacity. Deep cycle is great, but marine type is okay too and less expensive and easier to get. Car batteries will work fine but they cannot be discharged as deeply and won’t last as long (but still at least a few years) due to their different grid construction.
– If you can no longer use your car (for any reason you can think of) its quite alright to take out its battery and use that as free additional storage capacity, but you shouldn’t mix new and used batteries in a single battery bank. Perhaps you can even round up some additional batteries in the neighborhood, though I strongly suggest you ask the owners’ permission first.
– Connect panel to batteries and point panel at the sun. Depending on your panel’s connectors, you may need to get or make an adapter for this.
– You now have a system that can provide you with light, a radio and the ability to charge flashlights, 2-way radios, small rechargeable batteries, some gadgets and, likely, your cordless tools year round.
– Since you operate on a shoestring and want your investment to last:
* buy a (inexpensive) small voltmeter and make sure your batteries never drop below 12V (12.2V for car batteries).
* buy a gallon of de-ionized water (it is still inexpensive and easy to get) and keep all cells in your batteries topped up.
* cover the battery terminals and connections with a layer of petroleum jelly (a.k.a. vaseline) to avoid corrosion.
– Best of all: your system is portable. If you have to leave you can take it with you, maybe not on a bicycle but definitely in a car. And so you will be in much better shape than if you had nothing at all.