Enter your annual electricity usage (check your bills or smart meter), your current electricity rate, and how much you expect energy prices to rise each year. Then configure a solar system — choose your panel size and whether to include a battery. Select your comparison period (10-25 years) and hit calculate. The tool shows the total cost of each option, when solar breaks even, and how much you’ll save or lose over time.
This shows which option costs less over your chosen period and by how much. Green means solar wins; purple means staying on grid is cheaper. The margin can be significant — often £10,000-30,000 over 25 years depending on your inputs.
The two cards show the full cost breakdown for each option. For grid-only, you’ll see how your annual bill grows with inflation — this is often surprising when you see year 25’s projected bill. For solar, the breakdown shows your upfront investment, remaining grid costs (you’ll still buy some electricity), export income from the Smart Export Guarantee, and maintenance costs.
This visual comparison shows how costs build up over time. Solar starts higher (your upfront investment) but the line flattens while grid costs keep climbing. Where the lines cross is your break-even point — after this, every year of solar is essentially free electricity.
This tells you how many years until your solar investment pays for itself. Typical UK systems break even in 7-12 years depending on system size, electricity rates, and price inflation. After break-even, you’re generating free electricity for the remaining 15+ years of panel life.
The ROI percentage shows your total return compared to your initial investment. The “equivalent interest rate” converts this to an annual percentage, making it easy to compare against savings accounts or other investments. Solar often delivers 8-15% annual equivalent returns — better than most savings accounts.
This is the biggest variable and the hardest to predict. UK electricity prices have risen roughly 5-6% annually over the past decade, but recent years have seen dramatic spikes. Higher inflation makes solar look much better; lower inflation favours staying on grid. Try different scenarios to see how sensitive your results are.
Adding a battery increases your upfront cost but dramatically improves self-consumption — from around 40% without a battery to 70% with one. This means more free solar electricity and less bought from the grid. However, batteries have shorter lifespans than panels (10-15 years vs 25+), so the calculator factors in a replacement around year 12.
Larger systems generate more electricity but cost more upfront. The sweet spot depends on your usage and roof space. Oversizing beyond your annual usage means more reliance on export income (lower value than self-consumption), while undersizing means buying more from the grid.
In most scenarios, yes — significantly so over 20-25 years. The key factor is energy price inflation. Even at modest 4% annual increases, grid electricity costs compound dramatically. Solar locks in your generation cost at today’s prices, providing a hedge against future price rises. The higher electricity prices go, the more valuable your solar investment becomes.
Try the “Low (2%/year)” inflation setting to see a conservative scenario. Even with minimal price rises, solar typically still wins over 25 years, though the margin is smaller. The break-even point simply moves later. That said, UK electricity prices have never stayed flat for long — the long-term trend has consistently been upward.
It depends on your usage pattern. If you’re home during the day and use electricity as it’s generated, a battery adds cost without much benefit. If you’re out during the day and use most electricity in evenings, a battery captures otherwise-wasted solar and significantly improves your economics. Try both scenarios to see the difference.
The calculator shows an “equivalent interest rate” to help you compare. Solar often delivers 8-15% annual equivalent returns, tax-free. Current savings accounts offer 4-5% (taxable). Of course, solar isn’t liquid — you can’t withdraw your panels. But if you’re planning to stay in your home long-term, solar is often a better use of capital than savings.
Solar panels add value to your property — studies suggest around £5,000-10,000 depending on system size and location. You may not recover 100% of your investment if you sell early, but you won’t lose it all either. The calculator assumes you stay put for the full comparison period. If you’re likely to move within 5-7 years, factor in potential resale value.
This calculator provides a comprehensive long-term comparison between solar and grid electricity. While the upfront cost of solar is significant, the compound effect of rising energy prices typically makes solar far cheaper over 20-25 years. Use different inflation scenarios to stress-test your decision, and remember that solar also provides energy independence, environmental benefits, and protection against volatile energy markets.