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Solar Battery Cost Analysis


Gerald_db

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4 minutes ago, plonkster said:

That is awesome news. It changes the picture completely. Thanks for the info!

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:) One Trojan pony possibly converted! 

PS. Not that I think Trojan is a bad quality battery in any sense!

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What numbers are you seeing? It's quite likely that I have the wrong end of the stick, this is just what I remember. I saw the price and cheered up, then I saw the cycle life and lost all that cheer. Let me see if I can find it again.

Here we go... http://www.battery-pmp.co.za/Deltec-Lead-Crystal-Batteries.pdf

Page 5, second chart on the left. Around 1600 cycles to 50%. Same as Trojan T105RE.

http://www.solarsolved.co.za/datasheets/batteries/Deltec/Lead_Crystal_6_CNFJ_200.pdf

Page 2, second chart down on the right. Around 3200 cycles to 50%. That's double.

If there is another spec sheet I should see, please send it to me. The above two are the reason I dismissed the Deltec as a possible option.

Nope not the one with the wrong end of the stick. If you want i can upload it for you

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1 hour ago, CasualCheetah said:

:) One Trojan pony possibly converted! 

PS. Not that I think Trojan is a bad quality battery in any sense!

Have to wait for the Trojans to need replacement ... maybe 8-10 years from now. :)

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I was waiting for someone to mention the temps. :D

Was thinking when I read the specs that some people have their batteries in there garages. 

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Now that I actually have the temperature sensor attached I can see that the batteries rarely exceed 20 to 25 Celsius. Even though they are in the garage.

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Mine will be in the garage however the effect of temperature I would imagine assumes that they stay at that temp for days at a time. Here in Eshowe may get to 40 in summer but then drops to 18 to 20 overnight so average around 22 to 25.

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I have temps recorded going back a bit already for controller and battery. Controller needs it to auto adjust charging based on temps. Nogal cool for a PWM Morningstar ne?

Where my batts are, braai room (polycarbonate sheets), lowest to date has been 12deg.

So your garage, Plonkster, doors facing west-ish(?) with a room on top of garage, is bloody awesome!

But 20-25deg at 4am ... are you sure?

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27 minutes ago, Gerald_db said:

... may get to 40 in summer but then drops to 18 to 20 overnight so average around 22 to 25.

Batteries are optimal at a constant 25deg.

But, having said that, how do people handle it in Alaska / Canada ... ?

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22 minutes ago, The Terrible Triplett said:

Batteries are optimal at a constant 25deg.

But, having said that, how do people handle it in Alaska / Canada ... ?

insulation? It's easy enough to cool down with a fan if the insulation is too much, so coupled with a thermostat, a fan could be activated when necessary. They could probably also heat-up the battery cabinet / chamber with peltier heaters or even "reptile heaters". If the insulation is good enough only a small amount of heat is necessary to keep it warm. 

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16 hours ago, The Terrible Triplett said:

But 20-25deg at 4am ... are you sure?

Yup, door is facing west. But batteries are in the deepest Eastern corner, on the cold floor with a wooden plank below it (because flooded cells have stratification issues... allegedly). Air temperature in there does go up to 35 in summer, but seriously... that's like one or two weeks in February. On average, it's definitely below 30. Under heavy use it will sometimes go up a bit, I've seen a 32 once... but that's it.

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20 minutes ago, The Terrible Triplett said:

And at 4am as I asked? You recon it is lowest 20deg in there at night?

Of course not, it goes right down to 5. Right now it's charging the batteries to 29.1 instead of the configured 28.8 to compensate for that :-) But the point is really that the cycle life goes down when the heat goes up, the useful capacity comes down when it gets cold (but we're sticking with 50% anyway), so the real worry here is the summer heat, not so much the winter cold. Those really extreme cold days is like one week in August too... :-)

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5 minutes ago, plonkster said:

Those really extreme cold days is like one week in August too

Nope ... it has been for a few weeks now in June, July probably worse. I wonder what will happen in August this year.

 

Re. the temps, yes, we all know about too hot and its effect. I think we need to chat about the effect low temps have on the batteries when you discharge them.

Am I correct in saying:
The higher the ambient temp goes above 25deg, the less efficient the batteries are due to the chemical reaction getting to hot, shortening their life.
The lower the ambient temp goes below 25deg, the more efficient the batteries are due to the chemical reaction being more efficient, yet it also shortens their life.

Now at night is when batteries are used, and it is also when it gets the coldest.
Versus charging, which also heats up the batts, should be very carefully monitored in a hot environment.

What is the long term real effect of batteries being quite cold, like under 10deg, when they are discharged?

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47 minutes ago, The Terrible Triplett said:

Nope ... it has been for a few weeks now in June, July probably worse. I wonder what will happen in August this year.

This morning was 6 Celsius. Coldest day so far. I know last winter there was a day we touched zero, but it was one day. We rarely go below 5 in this area, and that is outside. My garage is usually a bit above that, it's actually quite liveable, sometimes warmer than the rest of the house (despite the huge gaping non-sealed gaps between the large wooden door and the wall).

50 minutes ago, The Terrible Triplett said:

The higher the ambient temp goes above 25deg, the less efficient the batteries are due to the chemical reaction getting to hot, shortening their life.

The higher the temp goes, the faster the chemical reactions, so the battery actually becomes MORE efficient, but the faster it works, the faster it dies, so the life is shorter.

51 minutes ago, The Terrible Triplett said:

The lower the ambient temp goes below 25deg, the more efficient the batteries are due to the chemical reaction being more efficient, yet it also shortens their life.

The chemical reactions are slower at lower temperatures, so the batteries are less efficient (it takes more time for the H2SO4 molecule to disassociate, so the maximum rate of discharge will be lower). The battery still has exactly the same capacity, it just cannot work as fast. Capacity is usually rated in terms of discharge rate, usually C20, so your C20 capacity (how much energy you can get out of there in 20 hours) will be lower in winter. This is actually increases the life of the battery.

The things to watch out for though, is stratification, and obviously if you actually freeze the battery it's bye-bye too.

The context here, as I understand it, is that @Gerald_db pointed out my reading of 3200 cycles is optimistic because that's at 20 Celsius, at the higher temperatures we generally experience it's going to be more like 2800 or 2500 cycles.

But even then, around R2.30 to R2.40 per stored kwh, compared to top-end CoCT R2.28 as of this month... it could just be that we have a winner. At 2500 cycles, and if you can get the battery for R6850, then we're there.

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Another interesting variable will be the true hybrid inverter which doesn't cycle the battery at all during the day... (ie bypass direct to load).

Saves cycles during the day when I would hope I use most of my heavy loads.

Throw in a hybrid Wind charge controller/inverter (Infini for wind) that can also bypass to load and things could get very interesting.  Diverse sources of power (pv, wind and hydro...CHRIS)... and hardly any need for a huge battery bank.

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I really want a wind turbine. Just cannot really swallow the 30k price tag. I would be perfectly happy with something much smaller, even under 1kw would be fine for night time loads. On ebay they are quite cheap, but shipping is more than the goods :-)

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1 hour ago, Mike said:

Sure R16k excl & excluding courier for the turbine...... then you find your own controller??

In other words, 20k :-) And then I still have to make my own pole. What has set me thinking is that perhaps, this is a better investment than a big battery bank... and that is what the next windfall (aka December bonus) is tagged for.

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