Cost of solar batteries?

chuckr30February 7, 2006

A solar PV system typically uses the sun to charge a bank of batteries. Your house then uses the power from these batteries for various purposes.

My question is, how long do these batteries last?

What weekly maintenance do you have to do on the batteries?

What is the replacement cost of these batteries? I.e. if I have to replace one per year how much does that cost me?

This is my major concern for hybrid type vehicles. I asked a dealer for an estimate on replacing the battery used in a Honda Civic hybrid several years ago, in 2004. They didn't want to give it to me, but I was firm and they relented. Their estimate was $6000 and the batteries last about 5 years.

$6000 every 5 years is expensive! That's $1200 per year, or $100 per month just for the use of the battery. I will never save $100 a month in gas to pay for the battery in a hybrid.

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Only off grid homes are set up like you describe.

I use Surrett batteries, made in Nova Scotia they are probably the best deep cycle manufacture in the world(they market under a different name in the US). I have a 48 volt system(8 6v batteries wired in sequence) of what Surrett call their "big red" solar batteries, they weigh about 250lb each.

They last for about 15 years.

The acid level should be checked at least once a month. I do daily checks on the specific gravity reading.

The batteries cost about $900 CND. You don't replace one battery a year, you replace them all together. A battery bank is only as good as its weakest battery.

Hybrid cars do not use the same batteries and they have a very different charge and discharge rate and type.

    Bookmark   February 7, 2006 at 2:01PM
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I'm grid-tied AND decided to have battery back-up . . my own choice to deal with the inevitable outages.

I've got a bank of ( 8 )Rolls ( American counterpart of Surrette ) S-460's in a 48v configuration; about 120 lbs each. $2000 to $2500 for the set. Cost is based upon capacity; you need to know that to properly size the battery bank. Just as car batteries are "specialized" for their particular function, golf carts too, RV batteries etc . . so too are these types of batteries specialized. They all use the same basic chemistry; but vary in what they are optimized for.

You must treat them properly to get good life out of them; mine are warranted for 7 years ( pro-rated ) and are expected to give a service life of 8 - 10 years. Overuse, or abuse will reduce that. I check the specific gravity in them about once a month. That's the ONLY way to truly know a battery's health . . voltage varies with temp, if it's being charged or discharged, at what rate . . etc. GOOD chargers are quite sophisticated; and when you've got some spondolas tied up in batteries this is NO place to scrimp. I also use Hydrocaps; they are used in place of the typical battery cap and reduce (normal) water loss to virtually nothing. I consume roughly 1 kWh / day . . just in floating them ( "idle" state ) . . and you must maintain them that way . . or when you need them they may not be ready. You also must occasionally equalize them; that is a special controlled overcharge. This keeps batteries in a string all in the same health. They like to be about 70 deg F all the time if possible . . for best performance / capacity.

Car batteries, and hybrid batteries are two different beasts . . believe the Prius batteries are warranted for 7 years. You don't get something for nothing . . . does replacement cost get paid for by less gas used ? ? ? Dunno . . run the numbers . . .


    Bookmark   February 7, 2006 at 6:35PM
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I have a modest stand-alone PV system in my remote home in the woods. The batteries I use are deep-cycle lead acid golf car batteries. My first set of four lasted 10 years. Then one cell went bad and I replaced the entire set.

Shopping around I found new ones for $55 each (exchange) so my total battery bank cost around $220. If I get ten years out of these I'll be very happy. They will be three years old in May. I should have a birthday party for them.

    Bookmark   February 10, 2006 at 10:43AM
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Are gel batteries better than lead-acid in terms of performance and maintenance but just too expensive to justify the higher cost?

Or do they underperform in terms of lifetime?

Are there any considerations one should be aware of re: local ordinances and having batteries in the house? For example, would lead-acid batteries (which I gather do outgas) be likely to require a ventilated space? I realize that local code varies per, er, locale, but just wondering if there are general statements that could be made as to whether lead-acid is harder to get approval from a town in they're in the house versus garage or other non-living space?

Thanks, just trying to learn! --Steve

    Bookmark   February 19, 2006 at 3:31PM
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I would NOT recommend gel-cells for these types of applications . . . they have their place; PV / back-up systems are NOT it. By the way, gel cells are just another form of lead acid . . the chemistry is the same; the construction is what makes them behave somewhat differently. You CANNOT equalize a gel cell . . well, without ruining it. You CAN do so with flooded cell types ( the "traditional" car / golf cart etc type battery ) . . and equalizing is very important in a string of cells to keep them all happy. Equalizing is a controlled overcharge which keeps them healthy and equal to each other . . . otherwise; the bank of cells is only as strong as the weakest one in the string.

They do outgas when charging / equalizing, and in fact when they are just "floating" as well. I highly suggest Hydro-Caps or such; they go in place of the existing battery caps . . and via a catalyst inside them; recombine the hydrogen and oxygen normally vented; back into water which then drips back into the cells. Basically; they are "self-watering" . . normally NO water addition is needed when using them.

In my installation inside my basement; I have a separate box for the batteries. Firstly, temperature was a concern as it's unheated. By building a closed, insulated box; I've got them contained, and the heat from floating them along with the insulation keeps them at a good temperature. Remember; just like car batteries; their output drops dramatically with lower temperatures. There is also a separate fan to ventilate the box; run by the charger. It also has a backdraft preventer so that air could not be drawn IN through the vent and into the basement when other devices try to draw outside air. I was also required to keep the bank 4' from any gas-burning appliance. Codes may vary place to place.

I'll also say that golf cart batteries are probably the best choice of conventional types, for such systems . . but if you're really serious you should get types MEANT for such systems. Car, RV, golf cart, and Alternative Energy ( AE ) uses; all have their own peculiarities . . getting the proper type for the application will give LONGEST life. I've used golf cart types for 12 years now for a small PV system in a screenhouse; and while it gives acceptable lifetime; it is not optimal . . . it is also not critical. If it was; I'd use solar-intended types there too.

Hope that answers your questions . . .


    Bookmark   February 20, 2006 at 6:26AM
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Thanks, Bob. A requirement to vent them to the outside might encourage me to place them elsewhere, as our basement has ICF walls and no windows, so it'd mean drilling to bring air in. OTOH, it stays ~ 60 degrees down there year 'round, so it'd probaby be perfect for battery life?

Thanks for the explanation about gel cells. I did go google and read a bit after posting (should've done it thr other way around!), and realized my misunderstanding.

I'm nowhere near trying to install anything, just trying to gather information.


    Bookmark   February 20, 2006 at 7:44AM
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My friend who had a system that was off-grid managed to get hold of some large cells that had been used in a telephone system.

Can someone tell me whether setting such cells on a cencrete floor will cause them to lose charge, as I've heard happens with car, farm eqpt., etc., batteries stored on concrete floor in house basement over winter?

He had his bank of cells in a small room attached to his garage - but I don't recall whether they were sitting on a wood frame, etc. or directly on the floor - I think possibly on a wooden platform.

For several years he and wife lived in a 12' X 60' trailer, with add-a-room and after his death a couple of years ago his wife built the new home that they'd planned on. I've only visited once, briefly, and don't know whether she hooked up to the grid or is still entirely off-grid (I think perhaps the latter).

Their son's an electrician.

The dad was the guy who said, after he'd sold two kinds of corn-fired heating stoves, about 17 years ago, that he could build a better one - and did. Has several patents, and a number of his innovative ideas have been compied by competitors.

His other son, who's now operating that business, told me on a visit at Christmas that he was 20 weeks behind in building them.

Good wishes to all for efficient and frugal use of precious energy.

ole joyful

    Bookmark   February 21, 2006 at 4:19PM
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Leaving batteries on a concrete floor . . . discharging them . . . . I finally read an explanation of it.

Any battery not being charged, will slowly discharge on it's own. Does putting them on a ( cold ) floor make it worse / faster ? ? . . Yes. Here's why:

While the cold floor itself does not draw out any charge per se; what happens in a liquid electrolyte cell ( such as car battery etc ) is that since cold liquid is denser; it tends to settle to the bottom. It tends to remain there as long as it's cold. You've got stratification in the cell. Since batteries are a pretty simple chemical reaction, different levels of the cell perform differently . . both discharge AND charge. Recharging a cell on a cold floor does NOT equalize the temperature of the eletrolyte . . therefore different levels in the cell are being recharged differently . . . effectively reducing the effective capacity of the cell. Parts of it are fully charged, parts are not . . .

Keeping the WHOLE battery at a lower but equal temperature will result in lower capacity, but will allow the entire cell to be at the same temp . . . and therefore the cell is discharged / charged equally. While it's capacity is lower, that will return when brought back to a more normal temperature.

Bottom line: Don't put such batteries on a concrete ( or similar large mass ) floor. Cold is OK if necessary; but do so in such a way that the ENTIRE battery is subject to the same temperature on all sides . . . . . .


    Bookmark   February 21, 2006 at 6:40PM
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