Figuring out the right system size
Choosing the right solar system size starts with understanding your household energy use and the solar potential of your site. System size is commonly measured in kilowatts (kW) of DC capacity and is selected to meet a percentage of your annual electricity consumption.
Key steps to determine size:
- Review past electricity bills to find average monthly and annual kWh usage.
- Consider future changes like electric vehicle charging or increased appliance use.
- Get an on-site assessment or use solar mapping tools to estimate sunlight and shading.
Typical guidance
- Small energy users: 2–4 kW systems can offset partial usage for apartments or very efficient homes.
- Average U.S. home: 5–7 kW systems often cover 70–100% of annual usage depending on location and consumption.
- Large homes or EV owners: 8–12 kW systems may be needed to cover higher loads.
Other considerations
- Roof size and orientation: South-facing roofs perform best in the northern hemisphere, but east and west roofs can also work.
- Shading: Trees, tall buildings or chimneys reduce output and may require adjusted system size or panel placement.
- Net metering and billing: If your utility credits excess generation, you might design a system to maximize net metering benefits. If not, you may size closer to your annual use to avoid excess production without value.
Work with a solar installer to get a production estimate specific to your location and roof. They will use your historical kWh and site data to recommend a system size that balances budget and energy goals. A professional proposal typically shows expected annual kWh generation, system size in kW, and estimated bill savings to help you decide.