Solar power batteries

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Re: Solar power batteries

Unread post by flysouth » Tue Feb 26, 2019 12:50 pm

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Re: Solar power batteries

Unread post by MadMacs » Tue Feb 26, 2019 7:54 pm

flysouth wrote:
Tue Feb 26, 2019 12:50 pm
Thanks, I needed a good laugh and yes I've done a few of those over the years. :lol:
The closest I get to flying these days is when I put my cellphone in 'flight mode'.
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Re: Solar power batteries

Unread post by heisan » Thu Mar 21, 2019 1:56 pm

With all the load shedding, I started looking at on-line shopping sites for available batteries, and summarising their price/specifications.

Here is a short summary, ranked by cost/kWh over the rated life of the battery:
Screenshot_2019-03-21_13-37-06.png
I find it quite remarkable that only the first 5 are cheaper than municipal electricity (and this is ONLY the battery, nothing else considered). It might just be possible to actually come out ahead with a solar system based on the latest Lithium batteries.

And none of the maintenance free lead acids made it into the top 5 - only one flooded cell, and at only 20% DoD...

(This is based on my home use, where there is virtually no day-time consumption, so no direct solar power - all stored.)
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Re: Solar power batteries

Unread post by vanjast » Thu Mar 21, 2019 9:57 pm

Ideally you'd be looking for this... (A simplified diagram - no protections shown.. etc)
Lot's of chargers, or one that can handle many batteries separately.

Image
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Re: Solar power batteries

Unread post by heisan » Thu Mar 21, 2019 10:01 pm

vanjast wrote:
Thu Mar 21, 2019 9:57 pm
Ideally you'd be looking for this... (A simplified diagram - no protections shown.. etc)
Lot's of chargers, or one that can handle many batteries separately.

Image
Unless the charger can compensate for the diode voltage drop, you will end up with significantly under charged batteries. If the batteries have the same chemistry, it is better to just connect them in parallel and use one big charger.
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Re: Solar power batteries

Unread post by vanjast » Thu Mar 21, 2019 11:27 pm

As mentioned ..not a complete circuit, just a drawing to convey the idea.

- Each charger would normally have it's internal diode to prevent high discharge, so they would charge normally.

- The output diode would ensure that the batteries are discharged at equivalent rates, prevent them from discharging into each other when one 'blinks'.

- A separate charger for each battery (as compared to a single charger) will add redundancy, quick determination of a faulty battery and allow for hot swopping repair work.
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Re: Solar power batteries

Unread post by heisan » Fri Mar 22, 2019 11:10 am

vanjast wrote:
Thu Mar 21, 2019 11:27 pm
As mentioned ..not a complete circuit, just a drawing to convey the idea.

- Each charger would normally have it's internal diode to prevent high discharge, so they would charge normally.

- The output diode would ensure that the batteries are discharged at equivalent rates, prevent them from discharging into each other when one 'blinks'.

- A separate charger for each battery (as compared to a single charger) will add redundancy, quick determination of a faulty battery and allow for hot swopping repair work.
Still making assumptions about the internals of the charger... If you absolutely have to have the redundancy of dual chargers, then just get chargers that are designed to run in parallel, and connect them as per their instructions.
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Re: Solar power batteries

Unread post by vanjast » Fri Mar 22, 2019 10:25 pm

Still making assumptions about the internals of the charger...
Having done a few engineering (electronic) designs, so yes, you can only do certain things wrt to efficiency. :!:
If you absolutely have to have the redundancy of dual chargers, then just get chargers that are designed to run in parallel
I have mentioned this :wink:

I have 'over-simplified' things as it's not worth going into detail until the OP decides which route he/she takes.
Even with that, I'm not paid to do this..so.. just a guideline is good enough.
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Re: Solar power batteries

Unread post by rainier » Sat Mar 23, 2019 11:33 am

Flooded tubular cells still provide the best solution to a solar system for typical usage provided the following is in place:
a) You understand how these batteries work and you can baby them.
b) You dimension your solar system correctly which includes installed battery capacity.

Practical real World example that has been operating flawless for 4 years:

1) Three phase 15KW inverter capacity (one 5KW inverter per phase), synchonized.
2) 43KWh of installed battery capacity flooded tubular lead acid cells, 24 cells, 48V/900AH @C100
3) 6 KWp of poly crystaline PV

The system is designed to not exceed 20% DOD unless there is a grid failure. Batteries are used at night, charged during the day. Grid power is only used if 80% discharge level reached or power demand exceeds inverter capacity.
The batteries are taken care of and regularly and correctly equalized, all charge parameters set correctly and changed for time of year and temperature - they last decades if used like this. You do have to top up distilled water and they use quite a bit over time (I have a destiller so I make my own). These batteries are sold as solar batteries but are actually types used for mine locomotives - designed to be abused.

The key to a successful solar system is correct design for the purpose you need it for - everything has to be in balance for it to be efficient - this equation INCLUDES THE OWNER.

Battery care and feeding is not for the faint of heart - if you don't like doing this - Lithium batteries of various descriptions have come down in price a lot. While they are still much more expensive if you take capacity into consideration they do have higher cycle life at higher DOD so that partly compensates in the sense you can buy a lower capacity battery for the same price as the tubular lead acid types and get about the same usage from it without the maintenance hassles.

I have seen too many solar installations at other houses that are simply unsuitable and do not operate well. A good example is a system very similar to mine with the same type of batteries - the batteries after three years are completely destroyed (a cool R100K+ loss). The installer put everything together selected the correct battery type on the charge controllers but left all settings at defaults which were unsuitable for these batteries. They were never fully charged or equalized so it did not take long for them to sulfate and left in this state for years leaving them in an unrecoverable mess.
Who said the sky is the limit ? I think not.
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Re: Solar power batteries

Unread post by heisan » Sat Mar 23, 2019 11:58 am

...Lithium batteries of various descriptions have come down in price a lot. While they are still much more expensive if you take capacity into consideration they do have higher cycle life at higher DOD so that partly compensates in the sense you can buy a lower capacity battery for the same price as the tubular lead acid types and get about the same usage from it without the maintenance hassles.[/quote]

NOTE: The information below is based on manufacturer claims (generally backed by guarantees, but the manufacturers have not been around long enough for those guarantees to mean anything).

If you look at the chart I posted above (compiled from on-line prices, and manufacturer data sheets), Lithium batteries are about half the price of flooded cells for the same cycle capacity, and around 30% cheaper in life cycle costs.

The major difference is that you only have an extra 30% capacity to dig into for emergency reserves compared to 60% for the flooded cells. But then you can double the installed lithium capacity for the same price as flooded, and have pretty much equivalent emergency capacity.

Of course, 4 years ago when you built your system, this would not have been the case - lithium batteries have come down a lot in price since then.

Does your personal experience with the flooded cells differ from what the manufacturer data sheets say? Can you let me know the brand and model, so I can add it to my spreadsheet?
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Re: Solar power batteries

Unread post by Ugly Duckling » Sat Mar 23, 2019 12:44 pm

Lithium needs a very good active BMS, Battery Management Sysytem, to be effective.
The 2 industrial batteries of 24 Volts 600 Amp hours I was involved with had a good over current / over discharge system fitted BUT the equailising /over charge / cell balancing was ineffective. It would terminate the charge if a cell got out of line, apply a 1 Amp, YES 1 Amp on 600 Ah, discharge load to the naughty cell and then continue the charge. Not good enough.
The capacity/mass/volume is great but beware if it gets out of step. A swimming pool is the only way to get rid of the imense energy released when they go-walk-about.
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Re: Solar power batteries

Unread post by heisan » Sat Mar 23, 2019 1:58 pm

Some do not explicitly state battery chemistry, but I believe all on my list are Lithium Iron Phosphate batteries, so they do not have the thermal runaway problems of the older lithium ion batteries.

All have active BMS, and most have spare cells, so bad cells are isolated but the battery still makes its rated capacity. if enough cells fail to impact capacity, you still have the 10 year warranty to fall back on...
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