What this solar ROI calculator estimates

The calculator models three investment paths: solar panels only, home battery only, and solar panels plus battery storage. Each result includes upfront cost, annual bill benefit, export income, payback period, long-term net profit and a confidence range.

  • Estimated annual solar generation by UK region and roof orientation.
  • Self-consumption versus exported electricity.
  • Import tariff savings, export tariff income and battery shifting savings.
  • Sensitivity ranges for a 20-year ownership period.

How solar ROI is calculated

Solar ROI compares total lifetime benefit against the upfront system cost. Annual benefit combines avoided grid imports, export payments and tariff-shifting savings where battery storage is included. Lifetime benefit compounds the annual energy value using the calculator's energy-price assumption.

Worked example: a 4 kW south-west-facing system on a typical 3-bed semi-detached home using about 3,800 kWh a year may generate roughly 3,600 to 4,000 kWh annually before shading losses. If the home uses 40% to 50% of that generation directly and exports the rest, avoided import cost is usually worth more than export income, which is why usage pattern matters as much as headline system size.

What affects your payback period?

  • System cost, including scaffolding, inverter and battery hardware.
  • Electricity use, especially daytime demand that can absorb solar generation.
  • Import and export tariffs, including time-of-use spreads.
  • Roof orientation, shading and regional solar yield.
  • Battery capacity, round-trip efficiency and how often it cycles.