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Adding batteries


Tshegofatso

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On 2024/09/20 at 11:08 AM, Tshegofatso said:

How many batteries can I add to my home system

A useful assessment would be to look at the capacity of your solar panels. Size the battery capacity such that the PVs can recharge them completely on a sunny day after deduction of household consumption during the day.

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On 2024/09/22 at 11:55 AM, Beat said:

A useful assessment would be to look at the capacity of your solar panels. Size the battery capacity such that the PVs can recharge them completely on a sunny day after deduction of household consumption during the day.

Actually, I can't agree with that... if you are running off grid, like I am and you may have more than one cloudy day in a row, it is very useful to have more battery capacity than you can charge in a day, just to be able to keep the lights on/fridges running let me give you an example...

have 4k7Wp Solar, this can generate around 30kW app per day at the moment
have 38kW battery capacity
have 5kW inverter... we use around 20-25kW energy per day (24 hour period) just less than half of that, coming from the batteries

now, with some cloudy weather, the batteries may not get to 100% by evening and next day cloudy, again batteries may only get to 70% and down to 40% by morning, but now there's no clouds, the battery will still not get full by evening, since the other consumption also needs to be met, but that does not matter, in my case, since we hardly ever have more than 2 consecutive cloudy days.

The point is, as long as the batteries get enough charge into them, to be able to provide power for overnight without dropping too low, SoC wise, you should not need to have more capacity, just to be able to fill them up 100% during the day, like in my case, they will get there over two or three sunshine days and that is just fine. Also the charge and discharge currents when the battery is more than 7 times the inverter power level is usually hardly ever more than 0.1C, which of course means they are being treated so gingerly that they're likely to live to a *really* ripe old age.

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