Versatile Photovoltaic Power – Part 1, by Tractorguy

Solar power from photovoltaic (PV) cells is an inexpensive, plentiful source of versatile energy for off-grid locations. This piece is not intended to be a comprehensive treatise on solar power design – there are many excellent books on the subject. Rather, this is a discussion specializing on considerations for solar power in a bug out location (BOL) or homestead, especially with some thoughts toward going forward after a grid-down event. It also describes some tips on what I have found works the best at my BOL.

System Voltage – 12, 24, 36, or 48V?

The higher voltage used, the more potential power you have for a given battery capacity and wire size. However, in a BOL, an important consideration is how versatile the system is when you consider what you are going to run. While 12 Volt DC requires the biggest gauge wiring and has the potential for the most energy loss in the wiring, I feel that it is more than made up for by the variety of things you can run on it. Nearly every cordless tool you get now can be had with a vehicular charger, and so can also be charged off a 12V solar system. 12V LED bulbs are ubiquitous, both in automotive applications and in standard Edison screw base bulbs for house lighting – 12V Edison base LED bulbs are even stocked at many home improvement stores now, albeit at a much higher price than you can get them for on-line.

DC well pumps, on the other hand, require higher voltages due to the amount of power required, and the length of wire necessary to go down the well to the pump. If you are considering a DC well pump, you will probably have to go with a system voltage higher than 12V. I have a gravity-fed rainwater system that I described in an earlier article for my water needs, so my well pump is strictly for backup.

And while we’re on the system voltage discussion, the next thing to consider is controller type and panel voltage.

Charge Controllers

Solar power system design, up until recently, typically had solar panel voltage closely matched to battery voltage. Now, the latest and greatest technique is to use a Maximum Power Point Tracking (MPPT) controller, which efficiently reduces the panel voltage to your system voltage, and use solar panel voltages much higher than your battery and system distribution voltage, with consequently less current for the same amount of power. This has the advantage of minimizing the incoming wire diameter required and the energy loss in the wiring between your solar panels and the controller.

However, the Achilles’ heel in this is the possibility of the controller failing, either on its own or from an EMP event. With the old-style system, matching panel voltage more closely to system voltage, you can bypass the controller and directly charge the batteries from the panels, with the batteries themselves acting to regulate the system voltage. You have to watch things closely, to make sure the batteries are not overcharged in bright sunlight – but it will work, thus giving you a plan B in case of controller failure. Keeping with the prepper mantra of ‘two is one and one is none’, with the knowledge that I may have to keep this system running for many years without replacement parts, I went with the conventional non-MPPT design.

Most controllers also can act as a load controller, and have an output that is shut off when the system voltage drops below a predetermined threshold, usually around 11.0V. I would suggest using that to power loads that are less critical (I have my refrigerator powered by that output), and have at least some of your lights powered directly from the battery, so even if the battery bank gets severely run down, you can still see to arrange some backup power, or to make emergency arrangements. My system has two fuse blocks for load distribution, one direct from the battery for critical lighting loads, and one that is switched through the load controller for less critical loads like refrigerator, battery charging for my radio desk, trickle charging the generator battery, etc.

Panel Orientation

My solar system is four 120 watt panels, and two older, smaller ones of 100W and 80W, for a total of 660 watts total capacity – but as you can see in the picture, not all of them are oriented to simultaneously output the maximum. Four panels are set facing South and produce the bulk of the system output, one is faced East to catch early morning sun, and one is faced West to catch the last sun in the evening. Since solar panels only output during daylight, maximizing the number of hours you can get output from them, and minimizing the hours that you are going to have to rely on your batteries alone, is very important. This becomes even more critical when you are running refrigeration twenty-four hours a day with your system, and have a significant load on it overnight.

The change in the angle of the Sun’s rays reaching the earth over the course of a year is very significant. Solar panels need to be inclined much more in the winter than in the summer, when the sun is lower in the sky, to make the most output. One useful web site will show you your optimum inclination angle for your particular location. Scroll partway down the page and you will find the “Solar Angle Calculator” where you will input your country, state, and city to find the optimum inclination angle for each month.

Practically, I have found that you really don’t need to change them monthly. In my system, I have a winter (24 degrees, nearly vertical), spring/fall (48 degrees), and summer (72 degrees, nearly horizontal) setting. I set my panels to the winter setting for November, December, and January (centered around the winter solstice at December 21), spring/fall setting for February, March, April, August, September, and October (centered around the spring/fall dates of March 21 and September 21), and summer setting for May, June, and July (centered around the summer solstice at June 21).

For the East and Western-facing panels, they will need to be oriented straight East and West during the summer months, and more Southeast and Southwest during the fall and winter months. These can be set at a much higher angle than the South facing panels, as the angle of the sun will be lower in the sky when these panels come into play. The best option here is to go out there at sunrise and sunset times and observe what azimuth they need to face, and what angle, so that the sun falls as perpendicularly on them as possible for highest output. If there are any trees or other obstructions in the area where your panels are, also observe to see any shadows thrown by those obstructions, and place your panels to avoid the shade created by those objects as much as possible. This will of course change during the year as the angle of the sun changes.

Sophisticated systems are available that move the panels to follow the sun during the course of a day. These systems are complex and expensive for the results that they give. For that reason, and the likelihood of failure, both mechanically (from the motors and actuators wearing out) and electrically (an EMP taking out the controller), I decided to go with a simple brute-force system that fixed the orientation of the panels to the South sky (and one each to the East and West), and manually adjust the inclination four times a year, as described.

Panel cleanliness is often ignored. A slight film of dust or dirt on the panels will result in a significant loss of output. A combination sponge and squeegee, like is used for cleaning windshields at a filling station, makes cleaning the panels a lot easier. Likewise, in the winter, a standard windshield ice scraper and brush makes a convenient tool to clean ice and snow off of them.


Golf cart batteries are designed for deep cycle service and are ideal for solar power systems. There is some concern about battery life, but I have one set that I have been using for over ten years that still tests fine. Maintenance is important. Most of the charge controllers I have seen charge the batteries to a much higher voltage than is required (14.4V versus 13.5V), with a lot of water evaporated away from the cells as a result. Check the water levels in the cells at least once a month, particularly in the summertime when it is hot. Add distilled or clean rainwater as necessary to bring the level up to the split ring.

My 12-Volt system has groups of two six-volt golf cart batteries in series for twelve volts. In addition, I have one twelve volt marine deep cycle battery that I have tied to the system with an Anderson power pole connector so I can easily disconnect it for portable use. I have a twelve-volt Minibrute chain saw that I power it from, and it also gives me a portable high-current source to jump-start vehicles, etc. A conventional ‘jump pack’ would be a good alternative here, with its portability, but make sure it has a deep-cycle rated battery in it to withstand deep discharges.

If your system has more than one set of batteries, it is a good idea to have a high-current switch in series with each set so you can isolate them for maintenance and testing. Simple high-current switches that mount on the battery posts, designed for use in vehicles as a main switch to disable the vehicle when they are opened, are commonly and inexpensively available at auto parts stores.

(To be concluded tomorrow, in Part 2.)


  1. I’m looking at installing a PV system and motor to run a Simple Pump. There are many persons with these pumps that could retrofit them with a motor that is powered by a dedicated PV system. However if lots of water is not needed, or additional capacity in the form of batteries or panels can be added, one gets both a well pump that is powered electrically and a small PV system. The cost for the components appears to be around $2,000 for this particular job. With the cost of panels so low these days, I’m inclined use additional panels instead of batteries that have limited life spans. Typical lead acid deep cycle batteries if used to 50 percent of capacity regularly, usually loose significant amount storage capacity for the system in about 3 years. By adding enough panels to run a pump in full sun the battery life will be extended several years if the the depth of discharge can be limited to only 20 percent when the sun is shining, verses 50 percent otherwise. The same approach can be used when design a PV system for the home.

    BTW, battery voltage is only a rough indication, or estimate of battery capacity that is only useful during the first few years of battery life that looses accuracy as the batteries ages. For example, I have an old set of batteries that tests 12.7 volts, yet their actual storage capacity is perhaps only one fourth of that when they were new.
    These batteries are still useful, but not in a system that requires more amp hours than these old batteries can provide. However, they are still useful in a system were the demand is about one fourth of their rated capacity. Old batteries, like old people can still be useful.

    1. Hey Tunnel Rabbit: Have you had any experience restoring older 12 volt batteries — whether they be SLA, AGM, or deep cycle?  I know there are a bunch of YouTube videos on this subject using a variety of techniques (such as replacing the old acid, cycling the charging voltage with high current, and using high frequency charging signals). However, I’ve also heard that most of these ideas don’t really work too well.

      I’m just wondering if you (or any other SB readers) have discovered a technique that really works — or at least works best in partially restoring battery storage capacity.  Thanks for any help you can offer.

  2. Hey Tractorguy, nice write up. I’m trying to get totally off grid by this time next year so there’s lots to read up on. Your personal story is helpful. Looking forward to part 2.

    For anyone who clicked on the link, the same guy has a book called Solar Electricity Handbook. I highly recommend it. It’s very short, concise and easy to understand. I used it for installing my solar panels and was very pleased with the book.

    For those who can remember that the earth is tilted 23½ degrees on its axis, there’s a very easy way to figure out your seasonal optimum inclination angles for your particular location without having to consult charts. The ideal angle if your panels don’t tilt is the same as your latitude. If they’re adjustable, then you add 23½ degrees to your latitude to get your best wintertime angle, and subtract 23½ degrees to get your best summer angle.

  3. Tractorguy, I don’t understand the point of setting up the two panels oriented differently to capture early morning and afternoon sunlight. Logically, there is only so much sunlight out there and it doesn’t matter when you grab it. Am I missing something?

    The Quiet One

    1. I know I’m not Tractorguy, but I’ll try to answer your question.

      If you have fixed panels they only get peak power output for a part of the day. If you were to put a voltage meter to measure the voltage output periodically throughout the day, and record the results, you would see a hump, Voltage output would start out low, climb to it’s peak at mid day and then taper off by the end of the day. The reason for the side panels is to pick up the sunlight earlier, literally flatten the curve, so you have closer to peak output for a longer period of time. This is especially important in the winter, as the daylight hours are so much shorter.

      There are web sites out there that give the average sunhours/day. This is based on fixed panels facing south. As an example, in the Michigan’s Upper Peninsula, parts of it only average 2.9 hours per day based on a 365 day year, Arizona has an average of about 7 hours. With Tractorguy’s system I would suspect, not knowing where he lives, that he may increase his average sunhours/day by at least an hour, maybe more.

      With electrical/mechanical tracking, the increase can be as much as 35%, maybe more, likely less, depending on the tracking system used. Tractorguy is correct, tracking systems are expensive and you better have spare parts handy.

      Hope this helps.

    2. Charles, the reason for the East and West panels is to capture the first sunlight of the day at sunrise and the last sunlight of the day at sunset, in order to minimize the number of hours you need to rely solely on your battery bank. You don’t get a lot of energy from them, but you do get some, before the sun gets high enough in the sky to get a significant amount of energy from your South facing panels.


    1. It is cheap and effective on a very small scale. It gets subsidies because it can’t cope with the amount of energy a city uses. Most people who wan the cities to “go green” are trying to get a square peg through a round hole.

      1. It is sometimes necessary on a small scale and therefore the user is willing to pay the premium to solve a problem. It get’s subsidies because it is in fact very expensive. It is about 16 times more expensive than coal or NG fired electrical generation and about 20 times more expensive than hydro generation. It simply is not sustainable.

        1. You have to factor in freedom from knuckleheads. The political environment that put PG&E where it is at is an example.

          Also, the security of being able to provide for your family until the linemen can get to the system that provides power to your house.

          Would give anything for a similar alternative for internet access….

    2. I’ve had an off grid home for 22 years and finally solved the short life problem of lead acid batteries. Two years ago I installed a bank of Iron Edison batteries. They use potassium hydroxide as the electrolyte instead of sulphuric acid. The manufacturer says they are good for 30 years. I hope to live long enough to wear them out!! they are on the internet. Doc

  4. Great post,

    We’ve seen the decline of Western civiliation in recent years, with institutions and infastruction failing or becoming less reliable. Many countries are having a hard time maintaining their power grids.

    For years, we’ve been made aware of varous threats to the electrical power grid: cyber attack, coordinated direct action by enemies foreign and domestic, electromagnetic pulse, coronal mass ejection, weather, etc…

    The most I have ever been without power is about ten days, and was nearing the end of the gas generator stored fuel supply with limited resupply. Historically, the power grid has been very reliable.

    It would be wise to prepare for future long term grid down events by installing renewable energy generators.

    Solar energy seems to have fewer, if any, moving parts compared with wind, hydro, geothermal, & bioenergy.

    Solar can be done at most locations with direct sunlight.

    A small system like the one described in this post can power life sustaining devices, lights, comms, computers, small AC devices, [maybe a chest freezer] for a long time without resupply.

    It is probably not going to run the washer/dryer, H/VAC, stove, water heater, or water well pump.

    If practicable, I would encourage all readers to install and learn to maintain a small solar system like this one, and to encourage their families, friends, and co-workers to as well.

    Can you imagine how the country would have done in the past six months without the power grid?

  5. Beware EMP. While it is possible to harden solar power systems for EMP (Sol-Ark for example offers this), most solar power systems will be ravaged and rendered inoperable by a serious EMP event unless the system is hardened against it.

    1. Well I guess it depends on your point of view. I did some back-of-the-envelope calculations using a 120W solar panel providing power for six hours per day, at an average utility electric rate of $.10 per kilowatt-hour. My figures say that you will pay for it in about five years, and from then on the electricity is free. With a projected life of twenty years, that would be fifteen years of free power. In the ten years I have been playing around with solar power, the prices of the panels have come down considerably. It’s anyone’s guess whether or not they will continue to fall significantly.

  6. Also keep in mind that the only LED bulbs and Lithium Ion batteries that will survive a serious EMP event are the ones in Faraday cages. The DC only (no onboard AC to DC conversion) LED bulbs should fair better than the ones that rectify AC to DC for use with AC power systems. Lithium Ion batteries all have onboard electronics that the E3 pulse from HEMP will likely damage. The good old lead acid batteries should be fine.

  7. tried to revive old batteries. Not much luck. If they can’t be brought back by a long slow charge (just sulphated) then they are not worth doing much else with other than using them as trade ins on new ones. Most modern batteries are not meant to be rebuilt. Usually they are too far gone (internal shorts, too much plate material gone, too badly sulphated, too many cycles, run dry, run down and left dead too long etc.)

  8. I’ve been totally off grid now for two years. My main system is six 300 watt panels for a total of 1800 watts with sixteen 24 volt sealed gel batteries and an automatic propane generator when needed. It’s been a great system so far and no complaints, but it wasn’t cheap by any means. I think you could go cheaper for sure, but you need to weigh your needs such as dependability and amount of generated and stored power you’re going to require and then make your choices. I felt my power system was one of the main things I did not want to compromise on.

  9. About 2010, we mounted six 305-Watt panels atop our ExpeditionVehicle.
    That 1,830-Watts feeds six 105-ah AGM batteries.

    To get to this particular system, we established our 12vdc needs.
    Part of our needs is inverting some 12vdc-to-120vac through our 750-Watt inverters.
    We use several inverters for redundancy.

    Our fridge is a 12vdc/120vac top-door dual-zone SnoMaster 61LP 61-liter low-profile.
    We can set it as dual fridge, dual freezer, or half-half.
    We chose this maker and model after reading hundreds of positive reviews from expedition folks using them on rough remote tracks in the middle of nowhere (‘now here’).

    All our power tools are 20-volt battery operated.
    The batteries are consumable, so we acquired dozens.
    Our tools include the usual:
    * chain-saws
    * drills
    * impact wrenches
    * orbital sanders (not ‘Sanders…’; the name ‘Bernie’ is reserved for the neighborhood buzzard, as in “Oh, look. Bernie is circling for a snack!”)
    * and fuel pumps.

    To transfer fuel, we get a good return from the 12vdc Fill-Rite brand.
    Our older heavier versions are rated to ‘pull a head’ of twenty-four feet… plenty to extract fuel from underground tanks in abandoned stations during a disaster.
    Operating that battery-draw in a farm-truck requires running the engine at a high idle.

    And ‘no’, this phase of this Economic Lock-Down hardly qualifies as a disaster.

    For us, photovoltaic panels make much more sense than a genset.

    Epstein was not a suicide.
    George Floyd, on the other hand, is.

  10. FWIW when we installing autonomous radar systems in the Canadian NW Territories, they all had battery UPS that used calcium/iron(?) batteries with an output of 2.4v(?)
    and massive current. The batteries were about 12″X12″X12″.
    There were somewhat over 360+ batteries that had an output of 600+ volts. which was inverted to 480v to run the system for ~30 minutes – worst case – while one of the two 100Kw gens came back on line and brought up one of two identical systems. There was a 3rd gen that did nothing except keep the battery pack charged.
    ‘Course these systems were replacing the manned DEW and BMEWS line systems so there was a bit of over-engineering involved.
    But I always thought that those batteries might have interesting possibilities for an off grid system, ’cause those radars were about as far off grid as they could and still be on the planet, heh, heh.

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