The article explains the “20 percent rule” for solar panels: sizing a system to produce about 20% more electricity than a household typically uses. This buffer can help households meet demand during cloudy weather, darker winter days and periods of heavier use, while potentially reducing bills through exported surplus electricity.

For example, a home using 40kWh daily would aim for 48kWh of solar generation. Extra capacity may also accommodate future changes such as working from home, installing air conditioning or buying an electric vehicle, but savings depend on installation costs and local grid buyback rates; in the US, these can vary considerably by state.