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Hello!
I am a full time boondocker (7 years) with a solar and wind setup. Solar, primarily for my winter stays in the Southwest. Wind, for my stays up in Montana in the summer (where there’s always a 20 mph+ wind). Before full-timing in America, I lived off the grid in the Australian Outback most of my life.
When using alt Energy sources, The first thing to do before buying ANYTHING is to assess your realistic power usage. AC, of course, is OUT. As is electric heat.
Ditto for RV fridges. They’re convenient for their ability to use any heat source, but that convenience comes at the cost of 1/4 the efficiency of compressor-type models. If you don’t want the initial expense of replacing that fridge, just fill up with propane once a month and that will easily last you for fridge alone. I normally got 2 or 3 months out of mine.
Eventually. I sold my RV fridge for $500 (half price of new), and made an Aussie Fridge with the proceeds. It’s a chest freezer with an external thermostat that you can program down to a single degree. The top portion of mine is lined with insulating foil. This allows about a 15 degree temp difference between top & bottom, allowing you to use it as both (soft) freezer and fridge which sits right at 33F. At about 18F, Frozen foods stay good for about 3-5 months, I find. The basics of one are here if interested……………….. http://mtbest.net/chest_fridge.html
Since refrigeration will be your single largest energy user, this allows you to live normally, off the grid, while boondocking. My RV fridge would use 2800 to 4000 watt/hr per day (typical), as measured by my Kill-O-Watt meter. My 120V Aussie chest-fridge, uses only 200-400 watt/hr per day off my 2000Watt Sine-wave inverter! That’s about an hour or two in the sun for my set up. Or a 15 minute drive between the Gym and Sam’s Club, where I often parked.
Once you’ve figured out all your daily energy usage by adding up your various lighting & appliances’ watt rating X hourly draw per day, you have an energy budget. The most economical way to begin is replace every light and heavy used appliance (like TV), with a more energy efficient one. (I run all LED or fluorescent lighting, and LED TV that draws 22W. My netbook is 18W). Remember: CONSERVATION IS ALWAYS CHEAPER THAN PRODUCTION!
As for power calculations, Here’s all you really need to know for now… Watts= Volts X Amps. Volts is the “pressure” of the electric charge and it must be just over your battery pack voltage to charge. Just like water must be at a higher pressure than what it is being pushed into in order to flow. Amps is the actual AMOUNT of electrical charge. Put in Gas Station terms, Volts is the pressure at which the gas is coming out the nozzle. Amps is the volume of gas that’s going into your tank. A pressure washer can shoot out high pressure, but only say, 2 Gallons per minute. (High voltage). A huge pipe may have water just falling out of it at gravity pressure, but when measured, it’s volume is hundreds of gallons per minute (High Amperage). Electricity from/to your batteries is the same way.
Safety Lesson: Dry skin is voltage resistant, and that’s why they chose 12V systems for safety. You may see sparks if you short a wire, but you can grab onto both terminals of the battery and get nothing. You need to get over about 48 volts before you start “feeling” it. If you go with a higher voltage system, you need to watch yourself.
So, a nominal 12 volt system that is putting out 10 amps of juice is putting out 120 watts. A solar panel putting out true 200 watts into a battery (at 12V) would be pumping about 16.6 Amps. That easy. Now it’s time to fit it into your set up.
You’ll begin with batteries. Lead-acid are by far the most cost-efficient still, $$ per Amp Hour. ONLY true deep cycles should be used. You’ll trash anything else within weeks. Don’t skimp on dodgy used ones unless you know their history, just get new. 6V Golf Cart batteries tend to offer the most bang for the buck. I find the GC2 6V at Sams are excellent for the price. Trojans are the marquis brand, but twice or more the price for the same capacity.
The ONLY true measure of these deep cycle batteries are the weight! More Lead= More AH Capacity. Nothing else on the label means squat. Battery groupings (ex. a GC-2 or a Group 27) is just a PHYSICAL size. It says nothing of what’s inside. I’ve had GC-2s that weighed 58lbs and GC-2s that weighed 70. The heavier ALWAYS had more capacity! I always check the spec sheet for actual weight. There’s no way to skimp on battery weight and still get capacity without going to much more expensive chemistry like Li-Ion. I use those in my electric ultralight airplane, but waaaay too pricey for RV use. I keep my GC-2 pack inside, behind the front seats in a special vented box I built. The gassing is negligible. Don’t worry. Under normal usage, you won’t blow up from hydrogen gas generation! If you are working them like a dog, then open a ceiling vent…hydrogen gas is the lightest gas and goes straight up and out!
Next, I find it’s best to have at least 3 days of back-up (no sun or engine running to charge) at your minimum draw. Assuming a 12V setup and inverter, drawing a very conservative 1000 watts per day will mean you’d need about 83 AH/day, or 250AH for 3 days in reserve battery power. That would be just over what 2 GC2’s (220 AH) would supply- IN THEORY.
In reality, your 12V lights will work fine, but your inverter low voltage alarm may start going off. Mine always goes of at 12.18V when the fridge tries to kick on. I usually never let it go that low, but when I do, I have to start the engine to push the voltage up to where the Sine Wave inverter will start the fridge’s compressor. Running, the fridge only draws about 100 watts, or 8 amps. But starting, it can take 8 times that for a few milliseconds. Just enough to trip the low voltage alarm. That’s an example of Real-Life experience Vs. theoretical calculations!
So, in the above example, you would need at least 4 GC2 batteries ($82ea at Sams) to make it through that kind of 3 day spread. I started with 4 (440 AH), but moved to 6 (660AH). I may soon have 8 (880 AH). I’m starting to use alot of power tools in my bigger RV.
NEXT, the solar! Bottom line, the more the better. I started out in my 25ft RV with a single 200 watt panel. Put out about 12 AMPS in full sun. (Today, I have 600 watts for my 35ft RV). I stored it inside, next to my bed, and brought it out each day where I parked on the beach (Great conversation starter!) I Leaned it against the bumper, plugged it into the charge cord hooked to my batteries inside, and re-positioned 3-4 times/day to keep it pointed into the sun. Tracking is vital if you have a small output system like that. If you have alot of roof real-estate you can lay them flat. But you will only get bout half of the daily energy production of a tracking system so you will need at least DOUBLE the panels for the same output. Winter is even worse with the sun so low on the horizon. Even 30 degrees off direct angle, and you can lose 40-50% output. Winter Sun is often 60 degrees off-angle. You also can’t park in the shade.
I split the difference and built a little rack for it on the roof if I was going to be traveling, or in parking lots for awhile. At least I got half output! At the Beach or in the Bush, I could take it down and get full tracking. Obviously, a BIG system is going to have to be roof mounted. They have tracking systems you can install, but they ain’t cheap! There’s some DIY trackers if you’re handy.
You can run a system with 12 volt panel (really about 18 volt Open Circuit Voltage, to account for voltage losses to the battery), but you have to turn them off and on manually via a switch or plug when the charge voltage reaches about 14- 14.5 volts. There are fairly cheap charge controllers that will do it for you automatically, as well. I rarely topped my 200 watt system off with solar alone, so I just unplugged on the few times I hit 14.5 volts.
With my larger system, I use what is called a MPPT controller. The advantage of this more expensive controller is, it allows you to use higher voltage panels (often cheaper) which will still produce output even on hazy/partly cloudy days. If your panels are 60 volt, for example, the MPPT controller uses it’s built in chip to figure all the available Watts comming in, and convert it to the perfect voltage for charging. This means you will get all the available Amps (the TRUE measure of your battery “‘fill”).
So, on a hazy day your 400 watt system is only putting out 100 watts with your voltage cut in half. With 12 volt panels, you probably wouldn’t even generate enough voltage to “push” the amps produced (say 8), into the battery. My 12 volt panel would typically fall to zero output if any normal cloud was overhead. However, with a 60V panel, I still have 30 volts- far above the battery charging threshold. The MPPT takes the 100 watts (30 volts X 3.33 Amps), and converts it to the battery charging voltage I need (say 13.8). NOW, that 100 watts looks like this: (100W= 13.8V X 7.25A)! I get 7.25A charge into my system instead of near zero.
Over time, especially if you are boondocker like me, that extra energy production really adds up. And in the end, THAT’S what you are paying for when you buy these solar panels. May as well get the most out of that investment by spending bot more upfront! Now if you were a casual camper, it would probably be cheaper just to get a nice inverter generator and charge your batteries daily with that. I use both depending on demand. Especially with all the new power tools, satellite TV, satellite radio, etc.
Sorry for the length of the post, but hopefully that details some of the real world experiences from someone who has been off-grid more of his life than he’s been on. I find the minor inconveniences of off-grid living totally worth the absolute freedom I enjoy… Happy Camping!
