How to easily calculate battery capacity for a project

#1

Hi All,

I am reading on how to calculate the minimum required battery bank to support my intended project. Going by the usual 5hrs peak solar period, I concluded on a 200KW solar solution for the client. They consume approximately 30,000kWh monthly.

When I run a profile on their usage, it came out they had an average load of a little less than 28kW. I suggested they used the on grid solution but because of the unstable power supply in our region, they insist on going with the hybrid solution that would not shut down whenever the grid goes down.

Could you please help me with the formula for calculating the kWh battery size for a 15-hour stand-by period especially for the night? They actually want to be independent of grid.

Secondly, how helpful are these power walls on the market? I tried contacting Tesla to sell me a powerwall but they would not go out of America and some parts of the globe. I found OptalmaxNano and Polinovel who are ready to sell. Do you have any information on these products?

Thanks.

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#2

Hi @Alloy, thanks for posting again. It’s interesting to hear the projects you have happening in Ghana.

Let me preface this answer by saying I am not particularly knowledgeable on battery sizing. My opinion though:

To be completely independent of the grid in this situation would require a very large and expensive battery setup. There are clear equations to work out what you need to be fully independent, but that would assume there is no grid, and would need to account for long periods without sun. In this instance, you are accounting for periods without the grid, but how long do they last usually? You may want to look at the equation in another way i.e. how many hours or storage you want.

If they use 1000kWh / day, depending on the batteries you need to account for different depth of discharge (dod), let’s assume lead acid batteries at 50% dod - then you’ll need 2000kWh of battery for 24h of independence. That’s not accounting for the solar, but you can’t really rely on it in any given 24 hr period.

That’s a lot of battery. So, the first thing you would want to do is a load profile, working out what are the essential loads that you require when the grid goes down. Then you can size up more effectively. I’m not sure how to weigh up whether a generator, or batteries, or combination would be preferable.

Hope that helps.

Marty

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#3

You may find these calculators useful.
http://www.micropowergrids.com.au/Calculators/Battery_Bank_Storage_Calculators.html

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#4

Hi Alloy

Just remenber 1 important thigs
If your battery is not sufficiently charged you may ruined the battery in a long term
That can proved to be an expensive affair
You may contact GSES to do the designs if that can help

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#5

That’s a good idea. If you can’t find someone in Ghana to design the system, you can use an Australian company.

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#6

Alright. I’ll talk to GSES. Any contact number please?

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#7

This seems to be the website:

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