Small Build Planning

Hey Everyone.

I'm planning a small 2-3kWh system. With just a regular 240v output to power a single item. Solar, possibly wind to charge. Does not need to be directly connected to my mains but can be.

Been browsing the forum for a bit but cant find any guides or notes that details the calculations needed to plan a system. Can anyone point me in the right direction for this?

Luckily I have many 1000's of cells available to me, 18650's and also various other cells, mostly larger formats so this will be greatly reduce the build cost.

Thanks all.

To do the calculations you need to know what you are going to power with your batteries and how big the load will be.

Will be 1kW computer and only need to power for 12 hours on battery.

A computer with a 1kW power supply or with an actual consumption of 1kW?

1kW 230Vac output from an inverter needs about 1.2kW 24Vdc input. That equals to about 47A. The battery will be 7SxP, x depends on what kind of cells you use. If you use reclaimed 18650s from laptop batteries you should do 90P at least. That means 630 cells in total and about 4.4kWh of energy for an average cell capacity of 1900mAh. That obviously isn't enough for 12 hours though. You need about 15kWh to run a 1kW load for 12 hours or more like 20kWh if you don't want to run your cells all the way down to 3.0V and all the way up to 4.2V all the time.

Thanks DarkRaven. Just what I needed. Fortunately cells are not a problem for me to get hold of as I run a large IT company and my supplier has about 20,000 various cells available of which a good 20% are 18650. The rest are larger Samsung and Sanyo cells but I need to find out more about these and if they are viable in a powerwall build.

ChrisBayne said:

... about 20,000 various cells available of which a good 20% are 18650. The rest are larger Samsung and Sanyo cells but I need to find out more about these and if they are viable in a powerwall build.

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Nah, they're junk.
Send them to me and I'll dispose of them for you