What payback means
Payback is the point where cumulative bill savings and export income recover the upfront cost of the system. It is useful because it is easy to understand, but it should be read alongside lifetime return, system warranty length and downside cases.
A shorter payback usually comes from a good roof, a sensible installation price and high self-consumption. A longer payback can still be acceptable if the system has strong long-term profit or if the household values resilience and lower exposure to energy prices.
How the calculator treats battery storage
Battery storage can increase self-consumption, but it also increases upfront cost. The calculator compares solar-only against solar plus battery so the battery is not treated as an automatic upgrade.
- Homes using more electricity in the evening may gain more from storage.
- Homes exporting a large share of generation may benefit if export rates are weak.
- Homes on strong export tariffs may prefer a smaller battery or solar-only setup.
Example payback calculation
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.
If that system costs about GBP 7,000 and produces GBP 850 of annual benefit, simple payback is roughly 8.2 years. If export rates or self-consumption are lower, payback stretches; if installation cost falls or import rates rise, it shortens.