which batteries for solar storage

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I would like to know which type of batteries are the best for use with solar cell systems. By best I mean the longest life per dollar spent. How is this determined? Thanks! David

-- David Haney (dhgerlb@myokay.net), January 08, 2001

Answers

Being "deep cycle" like marine batteries is important.

-- Jay Blair in N. AL (jayblair678@yahoo.com), January 08, 2001.

Hi David:

You should definitely go with deep-cycle batteries. The best bang for your buck is to use golf cart batteries. We used those in our first system and got about 5 1/2 years hard labor from them. They are designed to tolerate many deep discharges, but cycling them at no more than 50% will greatly increase their lifespan. You can get them for $50.00 to $60.00 each.

The next step up is the L-16 size. It is a 300-350 amp hour battery and will last 8-10 years if properly cared for. We bought eight of them about 2 1/2 years ago. They sell for $120.00 to $150.00.

From that, you can go up to many sizes of batteries that last up to 20 years or more. They usually are in very large, single 2-volt cells.

Many other factors besides price should be considered when purchasing batteries for a solar system: How much power do you need? What voltage will you use to operate the inverter? How much sunlight does your area receive? How much room do you have for batteries? Will you have grid or generator backup?

You can learn more about batteries at the manufacturers websites. www.trojanbattery.com www.usbattery.com www.surrette.com www.nwes.com

-- Jim (catchthesun@yahoo.com), January 08, 2001.


Batteries is one of the biggest hassles and expense of a normal solar system, I'm told (all my actual solar experience involves space and water heating. Oh, yeah, and my solar clothes dryer :)

I read Jim's question about whether you'd have generator or grid backup. To me, if you have grid power available, why have batteries? Why not use the grid as your battery? It's almost 100% efficient, and you can avoid the expense and mess of batteries. Ok, if you have unreliable grid power, go ahead and have a bit of back up battery storage. Or a generator. But I don't see why a person would want to buy all the expensive, messy batteries and eliminate the advantage of using the grid as a "battery". ???

JOJ

-- jumpoffjoe (jumpoff@echoweb.net), January 09, 2001.


Hi Joe:

I assume since you have all those question marks at the end of your post, you wanted a response. I can tell you why we chose to eliminate the advantage of using the grid as a battery. In the Southern Appalachians, where we live, we often get ice as opposed to snow in the winter. Power lines fall. We choose to live wayyyy out in the country, and when the lines go down, our neighbors are sometimes without power for weeks. They get the lines up fast in town for the hospitals and other vital services, but country people are not important to them.

We invested about $12,000 in a modest but well designed solar system. With the rare usage of a backup generator, it provides all our electrical needs with 100% reliability. We operate a business on the internet, and having reliable electrical service is not an option. Oh, I almost forgot, we don't have a power bill. Yeah, it will take some time to recoup that $12,000, but we have neighbors with $250.00 per month power bills right now. It's pay me now, or pay me later.

-- Jim (catchthesun@yahoo.com), January 09, 2001.


We also live in a remote area in the foothills of the Smokies, and chose to use solar/generator instead of having power lines run, even though it would have cost less than $5000. Almost everyone here has total electric for their home, and bills are in the range of $250-$350 per month during winter. Power is out frequently, and I've been told it's not very "clean" voltage, either. Our system is small, but it suits us fine. We use golf cart batteries, and they're fine for our needs right now. We're supposed to be having power lines installed here (free, this time) sometime this winter. I'll be happy to have it for stock tank heaters and an incubator, but don't really think it will change much in how we do things. Except we shouldn't have to run that noisy generator!

-- Teresa in TN (otgonz@bellsouth.net), January 10, 2001.


I don't have solar power or batteries -- yet. But I've been doing some studying. FWIW, I have seen many recommendations from different sources to START with the golf cart type batteries because inexperienced users will inevitably make mistakes, and these batteries are the least expensive to replace.

-- Joy Froelich (dragnfly@chorus.net), January 11, 2001.

Try www.homepower.com They have lots of info on renewable energy and seem happy to answer questions.

-- Mike in wny (jake@2ki.net), January 14, 2001.

When I set up to go off the grid, I looked at the cost of Solar Batteries and decided to find out why ordinary car batteries can't deep cycle so they could be used.

The answer is that a substance called lead sulfate forms on the surface of the battery's plates, which insulates then from the charging current. Ordinary car batteries are designed with a lot of thin plates with a larger surface area so that they can produce a lot of current for a short time. After 20% of the batteries chargable capacity has been used, lead sulfate begins to form at an increasing rate so that if you allow one to be discharged completely (go dead) only 6 to 10 times, it accumulates enough lead sulfate on the plates to keep it from recharging at all.

In the process of learning about batteries, I stumbled across some devices called pulse chargers or desulfators. They claimed to remove the lead sulfate from the batteries plates so the it would once again accept a charge. Since I didn't want to spend several thousand dollars for the size of battery bank I wanted, I decided to try one.

The results, while true, were less than ideal. The device I purchased did indeed remove the lead sulfate by knocking it loose. And this did extend the batteries life, but not enough to allow for the use of ordinary car batteries for solar storage. So I try several other varieties all with the same general results, but with of few exceptions.

Several times, I would connect one of these pulse chargers to a particular battery and it would go wild, pushing pulse of up to 300 amps into the battery and dissolving the lead sulfate without tje loss of any of the lead from the batteries plates.

Finally, in an effort to understand how this could happen, I built my own pulse charger from a microprocessor circuit which allowed me to vary the frequency of the pulses to any desired frequency. Suddenly, the entire mystery was made clear.

By scanning the frequency range, I was able to determine that each battery has a resonant frequency at which the resistence to the pulse drops to a very low point (so the current peaks at very high levels). When the energy of the pulse exceeded the level of 60 amps, the lead sulfate was dissolved instead of being dislodged.

The only remaining problem was that as a battery was charged or as the lead sulfate was dissolved, the batteries resonant frequency changed. To compensate for this effect, I programmed the microprocessor to automatically scan the frequency range to find the resonant frequency every 10 minutes or at any time that the pulse current dropped below 60 amps.

So finally I have a bank of Solar Storage Batteries that I got free, which will deep cycle that have already sustained 200 charging cycles with no loss of charging capacity, no sulfate on the plates and whicvh will probably last at least thirty years.

-- Paul Clint (smithja@sisna.com), April 03, 2001.


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