best solar/battery setup?

[anchors]

Hi, all,
I’d like to ask your input concerning the optimum house-battery/solar combo for potential FT 75% boondockers who either don’t have or prefer to not use a propane or gas generator:

If you were going to be somewhere with decent amounts of sunshine most of the time, and wanted to be off-grid for 7 -10 days at a time, using power mostly for fridge, attic fans, water pumps, consumer junk (radios, computers, gizmos) and very little AC, what battery setup would give you plenty of capacity?

I’ve read articles, and I “think” the following is true (or close to it):
It appears regular lead/flooded batteries are probably a better buy if you don’t mind topping them off with h2o.
It also appears that two 6V (GC2) provide as much and even better deep cycle capabilities than a single 12V.
Two 6V GC are probably cheaper and more durable than two 12V. But I assume that 2 6V weigh more (2X more?) than a single 12 V, so more weight to haul.
I’ll make a guess that having four 6V batteries would more or less double the characteristics (power, weight, etc) of having just two 6V batteries.

So, is having, for instance, 300 W of solar on the roof, and four 6V batteries in the basement a good setup? (Assuming heavier cables, good components, and a good pure-sine inverter are being used). Would having more solar wattage (400W?) and only two 6V batteries be almost as good at maintaining charge? (and saving the weight/space of two more 6V batteries). That idea seems to be the easiest to implement.

Lastly, if the factory offers two 12 V batteries (assuming deep cycle), is that a decent setup that can be used for solar boondocking?

I am planning on staying a good amount of time in the SW and hope to take advantage of solar-boondocking without too much generator fuel use.
Thank you all!
Frank

• This topic was modified 9 years, 5 months ago by Pippi.
• This topic was modified 9 years, 1 month ago by Pippi.

[Wayne Mills]

<It appears regular lead/flooded batteries are probably a better buy if you don’t mind topping them off with h2o.>

Correct

</Two 6V GC are probably cheaper and more durable than two 12V. But I assume that 2 6V weigh more (2X more?) than a single 12 V, so more weight to haul.>

Cheaper, not sure. More durable, absolutely. Heaver, yes, they have thicker plates, but not double the weight. Maybe 20lbs more per battery.

<I’ll make a guess that having four 6V batteries would more or less double the characteristics (power, weight, etc) of having just two 6V batteries.>

Correct.

</So, is having, for instance, 300 W of solar on the roof, and four 6V batteries in the basement a good setup?>

That very much depends on that refrigerator. There are some special small refrigerators that are designed to run on as little as 35 watts, but most RV refrigerators are not nearly that efficient. Most refrigerators consume hundreds of watts and can drain batteries in a hurry. Look at the energy consumption plate on your refrigerator to see how much power it draws. This will allow you to calculate how much battery and PV system you need.

</Would having more solar wattage (400W?) and only two 6V batteries be almost as good at maintaining charge?>

Not at all. You need those batteries. You may need more than that.

</Lastly, if the factory offers two 12 V batteries (assuming deep cycle), is that a decent setup that can be used for solar boondocking?>

Afraid not. The batteries may say deep cycle on the side, but they are not. A 12v battery at best can only be a hybrid between engine batteries and deep cycle batteries. You will kill a 12v battery in about 18 months. You need to go with 6v batteries paired in series to obtain 12v. This will give you a true deep cycle battery.

[anchors]

Wayne,
Thank you for the excellent reply. Everything you said makes good sense, and I appreciate the heads up on the refrigerator load. I’ve got to gather some more specifics on how much power stuff will use.

I definitely agree about four batteries or more being a good idea. The added weight is a small price to pay to be able to have a lot of storage ability. I saw a vid recently where the owner had six batteries hooked up. So a very solar existence can be done with a bit of planning and hard work.
Thanks again. Happy Trails…
Frank

[Umbilical]

Hello all,

I’m not an RV’er yet but am researching (and there’s a lot to learn). I came across a blog written by a guy named Bob who was renamed HandyBob by some of the people he helped with their under-performing solar systems. He is an opinionated cuss but has his reasons and there’s a lot to read on his site but well worth the hours needed to read it all as it may save you many $ and headaches. He has learned over the years that most batteries in RVs are not being charged properly. He has become very cynical about the installation industry in the RV solar world and makes a good case (maybe he’s just realistic). He does not have Pippi’s sunny disposition but both she and HandyBob have hands-on advice to give (in other words real world hard knocks kind of knowledge). I’m no expert here but what he writes makes sense to me in a been there, done that kind of way and anyone considering doing anything with solar would be well repaid for their time reading his words.

Cheers,
Mike

[Jesse Knight]

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!

[Jorn]

I’ve put together several systems. Flat on the roof, one looses deficiency so the rule that applies to installation for a home does not apply. I’d go with 400 watts, and 2 6v deep cycle batteries from Cost Co. These are made by Johnson Control and have a 700 cycle rating, yet cost a much less than a Trojan T-105RE that are rated at 750 cycles. The AMG batteries are very expensive, however if one can afford them, go for it. They do have certain advantages and they do not have to be equalized. Go to Renology.com and get their 100 watt panels for 150 bucks each including shipping, and their el cheapo charge controller with the LCD read out, or best yet , get a charge controller from Morning Star that can equalize the batteries and has a remote temperature sensor. They also offer kits.

200 watts in a sunny area will run most of watt RV’ers need, yet 400 watts will take much better care of you all year long and any place you might wander. I just spent a winter in Montana with only 270 watts and had to run a Honda everyday. Also, 400 watts has a better chance of charging up a small battery bank completely and that translates into longer battery life. I do not let my batteries go below 60 percent, and typically 70 percent,(12.4 volts) of a full charge even during the winter. I may get 3 or more years out of them. It is cheaper to save power than make power. Convert your lighting to LED and save tons of power. A netbook uses about half the power of a laptop. During the winter when using the Honda to make all the power, no more than .6 gallons of fuel is used….. I run a wood stove in the winter to heat and cook and do During party cloudy days the generator gets run perhaps an hour or two at most, and uses less than .2 tenths of a gallon to bulk charge the batts up to 14.1 volts. Then the panels are allowed to do the rest. Good Luck, Jørn

[Jorn]

Also, avoid inverters as these are power hogs. Convert to 12vdc. With 2 golf cart deep cycle batteries you will only have 2 days of power if your consumption rate is conservative. Do not let batteries go below 12.1 volts if you can help it. Check batt voltage in the morning before sun rise to get an accurate reading.

jornjacobsen@gmailcom

[Jorn]

The minimum would be a 200 watt system with 2 golf cart batteries from costco and a el cheapo 30 amp charge controller from Renology.com. Cost is around 600 bucks

Jørn

Hilsen til Pipi fra Montana. Loved your Mouse video. That is what brought me here.

[balr333]

correction on the website – it is http://www.renogy.com Thanks for all the useful information on this page.

• This reply was modified 8 years, 8 months ago by balr333.

[Comp Fxr]

Nice Read…I enjoyed all helpful information!

[OldJohnT]

For much dry camping at all, I would consider the very MINIMUM would be:

200 Watts of Solar and Two 6 volt True Deep Cycle Golf Cart batteries in series (around 225 Amp Hours). I just purchased a 235 Watt 24/30 volt panel for 90 cents per watt which measures 39″ x 54″.

The next step up system which I have is TWO of those 235 watt panels (470 total watts) and Four Trojan T-105’s wired in Series/Parallel for 450 Amp hours.

HOWEVER these are flat rooftop mounted panels. Its my experience if you use a 100 Watt portable suitcase set out panel AND KEEP IT AIMED DIRECT AT THE SUN ALL DAY you might harvest almost as much energy as 200 watts permanently flat mounted on the roof. THAT BEING SAID I guess you could revise my very MINIMUM system recommendations to be a 100 Watt portable suitcase panel and two 6 volt true deep cycle golf cart batteries.

Of course, a couple series connected true deep cycle 6 volt golf cart batteries is far superior to the cheaper semi deep cycle so called “RV/Marine” batteries sold at Walmart for extended dry camping.

To greatly extend battery life I suggest use of a so called “Smart” 3 or 4 stage (Bulk, Absorption, Float, 4th Equalize Cycle) charger and likewise a “Smart 3/4 Stage Solar Charge Controller when dry camping.

John T
Retired Electrical Engineer in Indiana

[Author]

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