Solar system using car batteries

[Triathlete]

I would like to hear from anyone who has had first hand experience using car batteries with their solar system.

[MountainDon]

I do not recommend car batteries for any off grid type power storage.  I also do not recommend the use of batteries sold as RV / Marine batteries for off grid or even RV use.

Why?

They do not have a very satisfactory useful life in that use.  I base this on over 30 years personal experience with RV's.  I never used standard auto batteries. I used the "better for the purpose" battery known as RV / Marine batteries. The first one of those died within a year. But it was used, as was the RV, so I bought two replacements of the same type. Two of them in order to have extra capacity for boondocking. They failed at the beginning of their third year. Upon the advice of an auto electric service center I replaced them with two 6 volt golf cart batteries, in series for 12 volts. That gave virtually the same amp-hour capacity as the two RV / Marine batteries. They were still serviceable 4 years later when we sold that RV. Over the following years I stuck with the golf cart GC-2 size batteries. We received a minimum of 4 years service from them. One set was over 5 years old when the RV was sold. Still working well. .

When we built our off grid cabin I selected GC-2's again. They have now been in service 6 years, 2 months. Barring some unforeseen disaster I fully expect to get another 2 years service; quite possibly more.  IMO, no auto battery can come close to that length of time, even with the same care I have given our GC-2's. 

[Adam Roby]

I am not questioning your experience or expertise, just wondering and playing devil's advocate.
How expensive are the batteries you purchase?  Most of the popup community (other forum I am on) use group 24 or 27 batteries.

Looking at Walmart prices, it seems the GC-2's are anywhere from $250 - $290 each whereas a car battery might cost $100?  If the car batteries are 1/3 the price, then technically for the same money the 3 years usage becomes 9 years usage.  May be more of a hassle, but if on a budget you may actually get more usage per dollar, or am I reading this wrong?

(For the record, I also will eventually be setting something up so want to know in advance what my options are).

[MountainDon]

Good point and I admit I zoned out on the prices. I am so used to the good deals down the road from here.

USA; Sam's Club GC-2, about $85 plus core charge (I imagine the core charge to be about $15 these days)

vs.  RV/Marine 12 volt group 27 at $80 plus core

I have seen the much higher CDN prices and can not explain why    However, when the prices here in NM and other locations in the USA are as shown there is no question as to what battery delivers more bang for the buck. There are GC-2's that do cost more; Trojan and Crown for example. But from what I have seen those are not noticably better than the brands sold at Sam's Club and Costco. (Note: not all of the SC and Costco's sell the golf cart batteries. )



The fact remains that auto and RV/Marine batteries have thinner plates and that translates into a shorter service life when used as an off grid battery. My "evidence" is anecdotal, not scientific, but I do believe it is quite valid. be


OTOH, " more bucks for the bang".... .....    when these GC-2's do reach life's end I will considering LFP (lithium ferrous phosphate) and hoping for a price reduction. There are some advantages that I truly like a lot.

[yobigd20]

pretty massive thread here with many fine grain details about one guy who used two Tesla car battery packs for his off grid solar project.  http://www.teslamotorsclub.com/showthread.php/34531-Plan-Off-grid-solar-with-a-Model-S-battery-pack-at-the-heart

[MountainDon]

Not exactly your std.auto battery though   

[NathanS]

My 2 cents...

My wife and I lived in a trailer for 7 months with 2x 100 watt panels on the roof, and 2x 6v sam's club golf cart batteries.

It was the cheapest thing I could find (by far) that would provide ~100 usable amps @ 12 volts.

I think the problem with battery technology is that chemistry is chemistry. There are no circuit boards to make more efficient. It is what it is.

Also, FYI, car batteries are absolutely not what you want to use. They are designed to provide a strong jolt of energy to get a car running. They are not designed to run a constant load for long periods of time. Golf cart batteries are the way to go in that price range.

I read some time ago that Tesla is opening a battery factory in Texas. I really hope that they come up with something affordable for energy storage. Everyone is always talking about solar, but solar is completely useless without an efficient storage mechanism. That seems like the weak link to me. Tesla must be using lithium, and I seriously wonder what will happen if people actually start adopting lithium batteries on a large scale. There are only a few productive mines in the whole world.

IMO the only good solution to an off grid system involves a flowing water source. This way you don't need to store energy. No matter what, it's expensive...

[MountainDon]

FWIW, the Tesla Gigafactory is to be located in NV.  TX, AZ, CA and NM lost out. It is a joint venture with Panasonic. Panasonic has years and years of experience with Li-ion cylindrical cells such as the type that are used in laptop batteries.

As of Feb 2015 it looked like this...


The batteries that Tesla has been using for its Model S electric car are a lithium-ion battery with a cathode that is a combination of a lithium, nickel, cobalt, aluminum oxide.   Tesla will use a lithium-ion battery with a nickel, manganese, cobalt oxide cathode for its grid battery, while the Powerwall unit intended as a backup battery will use the Model S auto battery chemistry. The daily use battery has lower energy density but a longer projected life.


Also, FWIW the OP has not been back in over a week.

[Triathlete]

Also, FWIW the OP has not been back in over a week.

Ancient Chinese proverb ....

Looked for, can not be seen; listen for, can not be heard; reached for, can not be touched. 

[Triathlete]

It's interesting to research what others are doing with car batteries, particularly in the 3rd world.  I have to find the site which had people using car batteries with their simple solar systems in Afghanistan.

One thing I have learned about the internet is to never accept what has been written at face value, regardless of who it comes from.  Check and confirm with many who have experience.  Often times people regurgitate what others have written or present ideas based on a theory and not fact in order to sound authoritative and credible.  This is why I asked for owners who have used used car batteries and not what has been written by others on the net.

[Adam Roby]

I think with any battery system, the battery's life is only as good as the maintenance done on those batteries.
I have owned motorcycles for many years, and I have friends who say their batteries only last a year or two before needing to be changed, and insisted on only using the dry cell batteries that do not require maintenance.  Still, my batteries tended to last long than theirs.  I did not keep them on a maintainer all winter like many recommend.  Instead, I charge with a very low amperage over 24 hours, let sit for 12 hours, charge again with low amperage for another 12 hours.  I would do this at the beginning of the season, and again at the end of the season.  I would also keep a very close eye on the water levels, and make sure to only use distilled water a few times per season.

I imagine (no evidence of this) that the same maintenance routine would help a solar system in the same way.

[upa]

I have to echo Don's experience with GC batteries being best bang for the buck, especially the costco/sam specials. I have played with all sorts of lead acid batteries with my various solar installation projects over the years including car batteries, rv marine batteries. They all loose capacity fairly quickly to the point of being fairly useless. I'm coming onto my 3rd year of for my sixteen 6v GCs (48V - 2 banks ) batteries, they are are all holding good current and keeping the SGs where they should be.  I fully expect another 2-3 years more out of this bank

[MountainDon]