How to Calculate the Right Solar Battery Size for Your Home

A battery that’s too small leaves you buying grid power at night, while an oversized one wastes money. If you already have solar power panels for home use, sizing your storage correctly helps you get the most from every sunny day.

Step 1: Check Your Daily Usage

Find your average daily consumption in kilowatt-hours (kWh) on your electricity bill. A typical household uses 15 to 25 kWh per day. Focus on evening and overnight usage, since that is when the battery does its work, usually 40 to 60 percent of the total.

Step 2: Define Your Backup Goals

Decide whether you simply want lower bills or also want essentials like the fridge, lights and internet running during outages. Backup power often calls for extra capacity.

Step 3: Match Your Solar Output

Your battery is charged by surplus solar energy. If your system exports only 8 kWh a day, a much larger battery will never fill completely.

Step 4: Consider Usable Capacity

Check the depth of discharge and efficiency. A 10 kWh battery with 90 percent usable capacity delivers about 9 kWh. A GoodWe solar battery, for example, lists its usable capacity clearly, which makes comparing options easier.

Step 5: Get a Professional Assessment

Local experts can size a system to your roof, tariff and lifestyle. South Australian homeowners can search for solar battery installers in Adelaide, while Queensland households can compare options for solar battery installation in Brisbane.

Quick formula: Battery size (kWh) = evening and overnight usage ÷ usable capacity. Example: 12 kWh ÷ 0.9 = about 13.3 kWh.