Solar Panels for battery charging

Thanks for all the responses and advice. Good info for me and the OP, now to find that money tree.

Hi Tony,

Thanks for the link.

Poly seem to outperform in less than ideal conditions from what I've read on rvnet. They appear to be more cloud tolerant.

I was hoping for a scholarly article--not just an opinion.

This is not "rocket science" here folks. The amount of Solar and reserve battery power is based on three things:

1. How much energy do you use?
2. How much usable daylight do you have?
3. How long do you plan on parking in one location?

The "simple test" (only need DVM) is to go camping, arrive and setup camp (I usually keep the truck running while I do this) and then after you shut off your truck (and before you start switching DC loads on) with a DVM measure your battery voltage to ensure you have a good full charge. (there are voltage "state of charge" charts available on the web)

Finish setting up camp and "camp normally" by using whatever fans, lights, furnace, whatever that you normally use and goto bed. The next morning (after the sun comes up) before you start turning DC loads back on take your DVM and measure your battery. Compare the voltage reading to the "state of charge" chart we looked at earlier.

If you've used much less than 50% of your battery capacity at this point you can stay parked where you are, "camp normally" using whatever DC loads that you normally would and all you have to do is keep an eye on the TIME as you'll want to take another voltage reading 24hrs after arrival to see how much energy you use in a 24hr period.

To make things simple, there are three different readings you can have: 1) you used MORE than 50% of your battery capacity, 2) you used 50% of your battery capacity and 3) you used less than 50% of your battery capacity.

If your 24hr usage was >=50% capacity you need more battery capacity. In a "perfect world" cycling your leadacid battery to 50% charge ought to be rare.

Next, whatever AH you used out of the battery you'll want to replace with Solar. Granted, you may not have the roof space for this so here's where we factor in "how long are you going to stay?" into sizing the Solar.

If your only staying overnight or 2 nights over a weekend you don't have to replenish all the energy you used out of the battery - just try to keep the state of charge above 50%. So if you use 25% in a 24hr period without Solar your going to be at 50% charge in 48hrs.

Worse case in Oregon we get sun 8am-4PM - a whole whooping 8hrs of usable daylight. (your location might be worse)

Where I live officially "check in time" is 4PM and check out time is 1PM. If I arrive and setup right at 4PM Friday and stay until ~noon Sunday I won't have ANY charging light Friday, a full 8hrs Saturday and 4hrs on Sunday. A whole whooping 12hrs of charge time which if I can coax +2A of charge current I'll make up 25AH of battery charge by the time I start my truck Sunday.

Personally I think a 40-50W solar panel would be plenty in the above situation.

If I was staying all week then that is a different story, I'd want to replace ALL the 25AH capacity I used and would have to do it in a mere 8hrs or less. (Saturday) Here I think a 80-100W solar panel would be plenty in the above situation.

If I was using more than 25AH a day, I'd need more battery and more solar.

YMMV, the above works for me.

http://www.ehow.com/list_5783187_solar-panels-low-light_.html

Sources are plentiful, here's one. Monocrystalline panels are also smaller for the same watts and weigh less. I do see that poly's are improving due to better techniques.

Hi tony,

I've heard that poly do better in low light than mono. Do you have a source?

tonymull wrote:
By having more solar than you need you will be better off on cloudy days or when in shade. Monocrystalline panels are much more productive in low light, are smaller, but cost a little more.

By having more solar than you need you will be better off on cloudy days or when in shade. Monocrystalline panels are much more productive in low light, are smaller, but cost a little more.

Hi CAJW,

Once the battery bank reaches 85% of fully charged, acceptance rate per 100 amp-hours is approximately 12.5 amps, or about 144 watts. It would not matter if you had 1440 watts--the battery simply won't accept a higher rate of charging. When the bank is at 95% even fewer amps will flow in.

So, in your case, about 220 watts is all that is prudent, for battery charging.

If you are wanting automatic equalization the number of watts drops to about 60 per 100 amp-hours. If you have a large battery bank that becomes the number to use. So if your bank were 600 amp hours instead of 146 the ideal number would be about 360 watts.

However, IF you want to run other loads then a case can be made for more wattage.

Now that I full time, I'd populate the entire roof with panels, because I'm a "hungry" power user with a big inverter.

CAJW wrote:

pianotuna wrote:
Hi,

Start with a big battery. Add 150 watts of solar for every 100 amp-hours of battery bank, with a good controller. Cost is currently under $2 per watt for materials.

If I'm understanding the above correctly, since I have two HD24-DP Interstates that have approx. 73 Amp hours each, I'd need 219 watts of solar capacity to recharge them? I've seen others put up 300-500 watts of solar capacity so is this overkill or have I misconstrued your information? Maybe he's already done so, but seems to me the OP would want the same information on the Costco system before committing.

CAJW - There is no set rule on how many watts of solar is required for a given battery size. The general rule of thumb is 150 watts of solar for every 100 amp-hours of battery.

You could setup a TC with adequate solar while in Arizona, and you probably would be very disappointed in northern states simply due to the suns position or bad weather.

You could have a setup that is great during the summer months, but inadequate during the winter. Typically, you AH use would be much greater during the winter months due running the furnace and longer use of lights. You also have less sun to charge your batteries.

Many people are of the belief you can simply just add more solar or add bore batteries. This is not necessarily true. If you just add batteries, without enough solar, it just takes longer to drain the batteries. If you only add more solar, no batteries added, you probably charge faster and maybe gain a little in usable AHs. The key is energy audit, which measures what you have, using, output of the solar, and condition of the battery/ies.

So, if you build a system using the 150 watts of solar for every 100 amp-hours of battery guide, You will have a very good base. You may or may not need additional battery or solar. The down side is if you need to add more battery, you will be mixing old with new, which could (note could) be a bad thing.

You have just under 150 AH of battery, and probably camp mostly in California. I think all you need is about 120 to 150 watts of solar. Again, it is greatly determined by what AH's you use. I suggest a controller capable of 25 amps or more, so you could add more solar later if needed. With a three stage charger, in the worse weather conditions, you could run your generator for 30 minutes to an hour and recharge your batteries up to 70 to 80 percent. How many times a year would you need to do that?

Wayne

I think I installed/updated my 12-volt system in mid 2006. My TC was not manufactured with a battery. I am on my second AGM. I think I killed my first (100 AH Lifeline AGM) one through testing.

I purchased my Trimetric, UB121000 (Universal) 100 AH Deep Cycle AGM, and 55 amp Iota DLS Converter/Charger with IQ4 from Bestconverter

I purchased my two Kyocera 65-watt, 17.4 volts @ 3.75 amps. 29.6" x 25.7" x 2.1" (with J-box), Blue Sky Solar Boost 2000E MPPT Charge Controller. 25 Amp, 12 Volt, Battery temperature sensor, and MC Cable 10awg (50 ft) from Northern Arizona Wind and Sum

I purchased my L.E.D.s from various sources. I use the flat board type with regulators (9 to 30 volts)

I have absolutely nothing but praise for each of the companies. Exceptionally easy to talk to, very knowledgeable and helpful.

Since 2006, I have had zero maintenance with any part of my 12-volt system. I think I did destroy my first AGM through testing. I opted to install the two panels to maximize my roof space and if one panel becomes damaged or shaded I have lost only 1/2 of my solar. I still have room for about an additional 200 to 300 watts of solar. Only two or three times have ever needed more than the one 100 AH battery and 130 watts of solar.

Wayne

pianotuna wrote:
Hi,

Start with a big battery. Add 150 watts of solar for every 100 amp-hours of battery bank, with a good controller. Cost is currently under $2 per watt for materials.

If I'm understanding the above correctly, since I have two HD24-DP Interstates that have approx. 73 Amp hours each, I'd need 219 watts of solar capacity to recharge them? I've seen others put up 300-500 watts of solar capacity so is this overkill or have I misconstrued your information? Maybe he's already done so, but seems to me the OP would want the same information on the Costco system before committing.