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Forum Index : Windmills : Lead acid batteries and temp performance

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davef
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Joined: 14/05/2006
Location: New Zealand
Posts: 499

Posted: 10:39am 11 Jan 2009

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Perhaps a bit off-topic, but I thought there would be quite a bit of battery experience here.

My system is currently an 85Watt solar panel fed into a Morning Star SHS-10 controller and then to 6*2.2Volt 550Amp/hour ex-Telecom batteries.

I am aware that the float voltage varies with temperature, according to one source the float voltage at 15 degrees C is about 13.6Volts and at 30 degrees C is about 13.2Volts.

But, what I have noticed is that recently even at 5-6 Amps the battery terminal voltage does not get much above 13.6V, when months ago the voltage would easily get up to the the cut-off of the SHS-10, ie 14.3Volts.

I think the difference could be caused by battery temperature, months ago we were around 15 degrees and lately we had some 30-35 degree days. It seems that lead-acid batteries become quite inefficient when over-charged at higher temperatures.

Couldn't find any info on this specific issue, could someone enlighten me?

Thank you,
davef

Gill

Senior Member

Joined: 11/11/2006
Location: Australia
Posts: 669

Posted: 11:23am 11 Jan 2009

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G'day davef,
I think your biggest problem is you just don't have enough panels for that size battery bank. Even with moderate cycling I think a minimum of six times your existing panel input is needed.

I'm sure someone will have some figures to quote, though I think they will need the depth of cycling (usage) to give the best advice.

Solar panels have always cost too much per watt but with big multinationals having the stranglehold of the industry I don't expect things to ever change.

was working fine... til the smoke got out.
Cheers Gill _Cairns, FNQ

GWatPE

Senior Member

Joined: 01/09/2006
Location: Australia
Posts: 2127

Posted: 01:13pm 11 Jan 2009

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Hi Davef,

I have a battery that was originally 1000Ah @ 24V. Unfortunately I was given these way past their U/S date. They are about 200Ah now.

The single solar panel can recharge approx a maximum 5A or about. The battery capacity is probably well below the original 550Ahr. On a good day, you will probably get 30-40Ahr from the solqar panel. If the battery was discharged 50% say, then this will take 4-5days to recharge, even when there was no usage.

There is a certain amount of self discharge, but lead/acid is not as bad as NiCd.

There are many formulae used to calculate the generating capacity for a system, based on usage and battery capacity.

I would increase the generating capacity by a similar amount to Gills recommendations. I opt for equivalent generation from at least 2 sources, be it solar/wind/or hydro or veg/diesel etc.

The generating capacity should be able to recharge the battery in approx 2 days, and still provide some usage. This normally results in an excess generating capacity, hence a regulator will be needed.

Gordon.

become more energy aware

davef
Guru

Joined: 14/05/2006
Location: New Zealand
Posts: 499

Posted: 10:07am 14 Jan 2009

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Thanks for the comments, guys. I rarely discharge the batteries below 12.5Volts, which according to one graph I have seen is about 85%. On a good day, I will be back up to full charge by lunch time (6Amps for 4 hours).

Now 24AmpHours to get them up to full charge does suggest that they have lost quite a bit of capacity over 20 years as Telecom float batteries! Thanks Gordon.

I take both of your points about generating capacity. Within a year or two I plan to have at least 2 panels tracking, 150Watts/H from a micro hydro setup and a wind gennie as well.

Maybe old lead-acid batteries also become more inefficient when over-charging at high temperatures.

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