| Size | Generation | Savings/yr | Payback | 25yr Savings |
|---|---|---|---|---|
Deciding whether solar is worth it. Solar panel costs have dropped, but it's still a significant investment. This calculator shows you the payback period and total return over 25 years so you can make an informed decision. It factors in UK-specific generation rates, electricity prices, and SEG export income.
Comparing solar with and without a battery. A battery increases self-consumption from around 30% to 60–80%, meaning you buy less from the grid. But batteries aren't cheap. The calculator shows whether the extra savings justify the additional cost, and how it affects your payback period.
Comparing installers' quotes. Got multiple quotes with different system sizes and prices? Plug each one in to see which offers the best return on investment. The cheapest quote isn't always the best value if it uses lower-efficiency panels.
A typical south-facing system in southern England generates about 850–1,000 kWh per kWp per year. A 4 kWp system would produce roughly 3,400–4,000 kWh annually. about the same as an average UK home uses. Further north, generation drops to around 750–850 kWh per kWp.
The SEG is a government scheme requiring energy suppliers to pay you for surplus electricity you export to the grid. Rates vary by supplier. some offer fixed rates around 4–7.5p/kWh, while Octopus offers variable tariffs that can pay 15–30p/kWh at peak times. Use our SEG Earnings Calculator for a detailed comparison.
Yes, but at reduced output. On overcast days, panels typically produce 10–25% of their rated capacity. The UK's annual generation figures already account for cloudy weather. the 850 kWh/kWp figure is an annual average including all weather conditions.
It depends on your usage pattern. If you're out during the day and use most electricity in the evening, a battery significantly increases self-consumption. With time-of-use tariffs like Octopus Agile, a battery can save even more by charging at cheap rates. But at current prices (£3,000–£5,000), the payback on a battery alone is often 8–12 years. Try our Battery Optimiser for a detailed analysis.
For a 4 kWp system costing £5,000–£7,000, with current electricity prices around 28p/kWh, payback is typically 6–9 years. Adding a battery extends this to 10–14 years. After payback, you're effectively earning free electricity for the remaining 15–20 years of the system's life.
Yes. All calculations run in your browser. Your solar and energy data never leave your device.
Solar installers' quotes often show optimistic projections with high electricity price inflation assumptions. This calculator lets you model different scenarios. conservative and optimistic. so you can make a decision based on realistic numbers rather than sales projections.
It's built specifically for the UK, with UK generation figures, SEG rates, and current electricity prices. No tracking, no lead generation, no installer will call you after using it. Works offline too. useful if you're on the roof checking panels.
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