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The size of a battery in kWh is a measure of the amount of energy that it can store.

The best battery size for you will depend upon how much spare solar you generate during the day, and how much you pay for the electricity you use at night. The bigger the battery size is in kWh, the more solar you can save and use at night or when the sun is not shining.

For example, a fully charged 10kWh battery is able to provide ~2kW of power for up to 5 hours, or 1.5kW of power for around 6-7 hours.

If you’re still not sure what size is right for your property, you can test out a few different sizes and compare your new estimates.

Batteries are expensive and adding one to a system will significantly increase the payback time. If the payback time is near to the warranty period (around 10 years), it is not an economic investment.

However, you may want to install a battery for environmental reasons or for back-up power if you have frequent grid outages, which could outweigh the high upfront costs.

You can also check with your state or local governments for any rebates or programs that might help finance a battery.

This is the proportion of your electricity usage that is met by your solar generation. A battery allows you to use more of your solar power at night, increasing your self-sufficiency.

There a lots of different ways that a battery can be operated, but at the moment SunSPOT uses a simple load-following battery operation. This means that when you add a battery, it will store as much excess solar as possible during the day then use as much of that stored energy on-site as possible at night.

The battery pricing data is updated quarterly and reflects usable kWh (not nameplate capacity). The federal rebate is included in these prices, calculated at $344 per usable kWh (equivalent to $37 per STC).

State-based incentives are not included in this pricing.