1. Get the Amp Hour (AH) rating of your battery.
2. Get the Volt (V) rating of your battery
3. Multiply: AH X V = Watts (W) (A joule of energy per second)
4. i.e. A 200AH battery at 48V will provide 4800Watts per hour also written as 4.8kW/h
So what does this mean?
If you have a device that runs at 4800W it will run for 1 hour on your 4800W battery (Assuming you can drain the battery by 100%)
Don't stress, most things in the house use a lot less than that.
- Older fridges may use 500W, newer ones will use 10-80W
- Older light bulbs use 60 - 80W, LED lighs use 1 - 5W.
- A geyser will use 3600W, a heat pump may use 1000W
How much battery capacity you need to keep your house and its things going?
The average house will "idle" at around 500Ws. My house runs at 320W (but thats because I have taken great care to reduce my energy usage which means I can get more out of my batteries).
So, add up all your devices power needs and you will start to understand how many batteries you will need to keep going during loadshedding. The less you use means the less battery capacity you need which equates to a good cost saving.
NOTE: Probably one of my best tools (and most affordable) is a little effergy device which measures current energy usage. I have this living in my kitchen (since we mostly hang out there) and over time it gives us a good indication of what the house is doing energy wise. This is particularly useful as we are limited to a total draw of 4.5kW/h and sometimes someone turns the kettle on while the geyser is on too and it quickly tells us that we are about to trip the house!