A typical roof here lands around 6.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 889 kWh per year on a south-facing roof. We value self-used electricity at 25.4p and exported surplus at a baseline 10p via SEG. Use the calculator above for your exact tariff.
Browse the scenarios below. Each battery size has its own expand — open the one that matches your plan (or just explore). For each system size (2–8 kW) we show annual output, how much you use directly, what gets exported, annual benefit, upfront cost, break-even, and a 20-year net. Negative numbers are possible — that’s the honest trade-off when adding more battery than your usage profile justifies.
No battery 5 kW example → Annual benefit: £719, Upfront: £10,173, Break-even: 14.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1778 kWh | 711 kWh | 1067 kWh | £181 | £107 | £288 | £4,069 | 14.1 yrs | £1,683 |
| 3 kW | 2667 kWh | 1067 kWh | 1600 kWh | £271 | £160 | £431 | £6,104 | 14.1 yrs | £2,524 |
| 4 kW | 3557 kWh | 1423 kWh | 2134 kWh | £362 | £213 | £575 | £8,138 | 14.1 yrs | £3,365 |
| 5 kW | 4446 kWh | 1778 kWh | 2667 kWh | £452 | £267 | £719 | £10,173 | 14.1 yrs | £4,207 |
| 6 kW | 5335 kWh | 2134 kWh | 3201 kWh | £543 | £320 | £863 | £12,207 | 14.1 yrs | £5,048 |
| 7 kW | 6224 kWh | 2490 kWh | 3734 kWh | £633 | £373 | £1,007 | £14,242 | 14.1 yrs | £5,889 |
| 8 kW | 7113 kWh | 2845 kWh | 4268 kWh | £724 | £427 | £1,150 | £16,276 | 14.1 yrs | £6,731 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
3 kWh battery 5 kW example → Annual benefit: £856, Upfront: £12,273, Break-even: 14.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1778 kWh | 1067 kWh | 711 kWh | £271 | £71 | £342 | £6,169 | 18.0 yrs | £680 |
| 3 kW | 2667 kWh | 1600 kWh | 1067 kWh | £407 | £107 | £514 | £8,204 | 16.0 yrs | £2,070 |
| 4 kW | 3557 kWh | 2134 kWh | 1423 kWh | £543 | £142 | £685 | £10,238 | 14.9 yrs | £3,460 |
| 5 kW | 4446 kWh | 2667 kWh | 1778 kWh | £678 | £178 | £856 | £12,273 | 14.3 yrs | £4,851 |
| 6 kW | 5335 kWh | 3201 kWh | 2134 kWh | £814 | £213 | £1,027 | £14,307 | 13.9 yrs | £6,241 |
| 7 kW | 6224 kWh | 3734 kWh | 2490 kWh | £950 | £249 | £1,199 | £16,342 | 13.6 yrs | £7,631 |
| 8 kW | 7113 kWh | 4268 kWh | 2845 kWh | £1,085 | £285 | £1,370 | £18,376 | 13.4 yrs | £9,021 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
5 kWh battery 5 kW example → Annual benefit: £925, Upfront: £13,673, Break-even: 14.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1778 kWh | 1245 kWh | 533 kWh | £317 | £53 | £370 | £7,569 | 20.5 yrs | £-171 |
| 3 kW | 2667 kWh | 1867 kWh | 800 kWh | £475 | £80 | £555 | £9,604 | 17.3 yrs | £1,493 |
| 4 kW | 3557 kWh | 2490 kWh | 1067 kWh | £633 | £107 | £740 | £11,638 | 15.7 yrs | £3,158 |
| 5 kW | 4446 kWh | 3112 kWh | 1334 kWh | £791 | £133 | £925 | £13,673 | 14.8 yrs | £4,822 |
| 6 kW | 5335 kWh | 3734 kWh | 1600 kWh | £950 | £160 | £1,110 | £15,707 | 14.2 yrs | £6,487 |
| 7 kW | 6224 kWh | 4357 kWh | 1867 kWh | £1,108 | £187 | £1,295 | £17,742 | 13.7 yrs | £8,151 |
| 8 kW | 7113 kWh | 4979 kWh | 2134 kWh | £1,266 | £213 | £1,480 | £19,776 | 13.4 yrs | £9,816 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
7.5 kWh battery 5 kW example → Annual benefit: £945, Upfront: £15,423, Break-even: 16.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1778 kWh | 1298 kWh | 480 kWh | £330 | £48 | £378 | £9,319 | 24.6 yrs | £-1,756 |
| 3 kW | 2667 kWh | 1947 kWh | 720 kWh | £495 | £72 | £567 | £11,354 | 20.0 yrs | £-10 |
| 4 kW | 3557 kWh | 2596 kWh | 960 kWh | £660 | £96 | £756 | £13,388 | 17.7 yrs | £1,737 |
| 5 kW | 4446 kWh | 3245 kWh | 1200 kWh | £825 | £120 | £945 | £15,423 | 16.3 yrs | £3,484 |
| 6 kW | 5335 kWh | 3894 kWh | 1440 kWh | £990 | £144 | £1,134 | £17,457 | 15.4 yrs | £5,231 |
| 7 kW | 6224 kWh | 4544 kWh | 1680 kWh | £1,155 | £168 | £1,323 | £19,492 | 14.7 yrs | £6,978 |
| 8 kW | 7113 kWh | 5193 kWh | 1921 kWh | £1,320 | £192 | £1,513 | £21,526 | 14.2 yrs | £8,724 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
10 kWh battery 5 kW example → Annual benefit: £959, Upfront: £17,173, Break-even: 17.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1778 kWh | 1334 kWh | 445 kWh | £339 | £44 | £384 | £11,069 | 28.9 yrs | £-3,397 |
| 3 kW | 2667 kWh | 2001 kWh | 667 kWh | £509 | £67 | £575 | £13,104 | 22.8 yrs | £-1,595 |
| 4 kW | 3557 kWh | 2667 kWh | 889 kWh | £678 | £89 | £767 | £15,138 | 19.7 yrs | £207 |
| 5 kW | 4446 kWh | 3334 kWh | 1111 kWh | £848 | £111 | £959 | £17,173 | 17.9 yrs | £2,008 |
| 6 kW | 5335 kWh | 4001 kWh | 1334 kWh | £1,017 | £133 | £1,151 | £19,207 | 16.7 yrs | £3,810 |
| 7 kW | 6224 kWh | 4668 kWh | 1556 kWh | £1,187 | £156 | £1,343 | £21,242 | 15.8 yrs | £5,612 |
| 8 kW | 7113 kWh | 5335 kWh | 1778 kWh | £1,357 | £178 | £1,534 | £23,276 | 15.2 yrs | £7,413 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
13.5 kWh battery 5 kW example → Annual benefit: £973, Upfront: £19,623, Break-even: 20.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1778 kWh | 1369 kWh | 409 kWh | £348 | £41 | £389 | £13,519 | 34.7 yrs | £-5,737 |
| 3 kW | 2667 kWh | 2054 kWh | 614 kWh | £522 | £61 | £584 | £15,554 | 26.6 yrs | £-3,880 |
| 4 kW | 3557 kWh | 2739 kWh | 818 kWh | £696 | £82 | £778 | £17,588 | 22.6 yrs | £-2,024 |
| 5 kW | 4446 kWh | 3423 kWh | 1023 kWh | £871 | £102 | £973 | £19,623 | 20.2 yrs | £-167 |
| 6 kW | 5335 kWh | 4108 kWh | 1227 kWh | £1,045 | £123 | £1,167 | £21,657 | 18.6 yrs | £1,689 |
| 7 kW | 6224 kWh | 4792 kWh | 1432 kWh | £1,219 | £143 | £1,362 | £23,692 | 17.4 yrs | £3,546 |
| 8 kW | 7113 kWh | 5477 kWh | 1636 kWh | £1,393 | £164 | £1,556 | £25,726 | 16.5 yrs | £5,402 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
Figures are illustrative and use the same method as the calculator above. For exact results, adjust your roof direction, tariff, and usage in the calculator.