Reply To: Is there a recommended way to calculate what battery storage requirements would give me power 98% of the time?

Home Forums Battery and Storage Is there a recommended way to calculate what battery storage requirements would give me power 98% of the time? Reply To: Is there a recommended way to calculate what battery storage requirements would give me power 98% of the time?

#60132

Hi Giles/Craig,

Solar Choice has been working on an energy storage system size estimator tool which will soon be available to the public. Plugging in the numbers that you have there, our tool says that you would be 100% self-reliant with regard to electricity on the average day of the year if you had roughly 5-7kWh of capacity (thanks mainly to your very low electricity consumption level!) Because of your higher consumption level in winter and the lower solar irradiation levels, you wouldn’t quite make it then.

This wouldn’t necessarily translate into being energy self-sufficient 98% of the time for the non-winter months, however – if you had a few cloudy days in a row, you’d quickly run the batteries down. Even if you decided to get a larger energy storage system, your small solar system would not be able to fill it up. Whether you’d want to charge up your batteries using the grid overnight would be another question, but I’m assuming that you’d prefer to rely on your solar panels.

Obviously there are a quite a few assumptions here (in particular about how you use electricity throughout the day, and also that you live in Sydney), but the point is it is not at all unrealistic for someone with your low level of electricity usage to find a way to become virtually energy independent by installing an energy storage system.

Graph of usage on the average day, assuming 5kWh daily usage and 7kWh battery bank:

Same assumptions, but for summer:

And then plugging in 7kWh daily consumption in winter:

Also note that I’m assuming that your battery starts the day with whatever charge would be left over following a sunny yesterday. If the previous day wasn’t sunny, you’d start the day with zero charge.

If you have any follow-up questions or want to know more about how I arrived at these conclusions, give me a shout at james@solarchoice.net.au.