Solar generation, export, and battery storage

Solar adds a second energy stream on top of grid imports. For battery sizing, the useful idea is not “how big is the array?” alone, but how much energy the home self-consumes during the day versus how much it exports.

Generation vs export

Daily generation is roughly how many kWh the panels produce on a typical day. Monitor apps, inverter portals, and many bills show this. It varies with season, cloud cover, and system health — use a representative ordinary day, not a record sunny weekend.

Grid export is the surplus sent back to the network. The difference generation − export is energy used at home while the system is producing (self-consumption), assuming simple metering.

Why bills look “net of solar”

When the sun is up and loads are on, solar can meet demand without that energy appearing as grid import. So bill daily usage already embeds solar offset. If you size a battery only from import numbers, you may understate total household energy and mis-size cover hours.

Solar hours and cover hours

You enter approximate start and stop hours for useful production (for example 9:00–17:00). Those hours define a solar window; the remainder of the day is the default period we ask the battery to support. Evening peaks, cloudy consecutive days, and overnight baseload are exactly the periods storage is for.

For the step-by-step capacity method, read how battery size is estimated or run the calculator.