Why you can only use half of the calculated battery storage.
Batteries have a limited cycle life, cycle life is determined by various factors but the most important being state of charge and discharge, the more charge you remove from a battery the more the battery suffers. If you completely discharge a battery the cycle life could be as little as 2 or 3 cycles – think of your car battery, if you run it flat once – it needs to be replaced. Unfortunately it is just not feasible to keep batteries at a 95% charge rate, you’d need far too many batteries to get to a decent usable storage capacity so the best compromise is a 50% state of discharge, and this strikes the best balance between cost and longevity.
Why do we differentiate between calculated storage and usable storage?
It is most companies practice to only give you the calculated storage capacity of the batteries, this makes the system look more attractive. (storage is calculated as follows, Ah of the batteries multiplied by the Volts multiplied by the number of batteries give you watt/hour storage – 200ah X 12V X 8Batteries = 19200w/h or 19,2KW). We give you the usable storage so that you know exactly what you are buying and can compare apples with apples
Do the other suppliers run batteries completely flat?
Probably not, most inverters and charge controllers only allow a 50% state of discharge, we just tell you about it upfront so that you don’t think you’re buying 20 hours of storage and only getting 10 in reality.
KVA vs KW – why do we use KW
There are a few ways to measure electricity usage, most generators and solar kits are quoted in KVA, we prefer to use KW to make it easier for you to calculate your needs, as that is what you are charged by energy suppliers and almost all appliances have a KW or watt rating rather than a KVA rating. To convert from one to the other use this simple calculation, KW is approximately 80% of KVA, so 1KVA is 800W, 2 KVA is 1,6kw etc.