How Much Can a 4kW Solar System Save in the UK?

A 4kW system is a common reference point for UK households, but savings vary widely because your results depend on annual generation, your unit rate, export rate, and (most importantly) how much solar you use at home.

The two sources of value

• Bill savings from self-consumed solar (valued at your unit rate).
• Export income from unused generation exported (valued at your export rate).

The biggest driver: self-consumption

Two households with the same 4kW system can see different outcomes if one is out all day and exports most solar, while another uses appliances during the day or has a battery to store excess generation.

Battery: when it can help a 4kW system

Batteries can increase self-consumption by shifting solar into the evening. Whether it improves payback depends on battery cost versus the uplift in self-consumption. The clean way to test it is to run the calculator with battery on/off and compare payback and 10-year net gain.

Run a quick scenario (recommended)

1. Set system size to 4kW and enter your expected annual generation (kWh).
2. Enter your unit rate and export rate.
3. Choose a realistic self-consumption % based on your household routine.
4. Toggle battery on/off to compare.

Make it more realistic

• Run a conservative scenario by reducing generation (e.g., shading/seasonal effects).
• Test different unit rates (tariffs change over time).
• Test self-consumption changes (daytime usage shifting).

Start: Solar savings calculator · Generation by system size · Battery vs no battery