A typical roof here lands around 3.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 876 kWh per year on a south-facing roof. We value self-used electricity at 25.8p 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: £715, Upfront: £10,173, Break-even: 14.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1751 kWh | 700 kWh | 1051 kWh | £181 | £105 | £286 | £4,069 | 14.2 yrs | £1,652 |
| 3 kW | 2627 kWh | 1051 kWh | 1576 kWh | £271 | £158 | £429 | £6,104 | 14.2 yrs | £2,479 |
| 4 kW | 3502 kWh | 1401 kWh | 2101 kWh | £362 | £210 | £572 | £8,138 | 14.2 yrs | £3,305 |
| 5 kW | 4378 kWh | 1751 kWh | 2627 kWh | £452 | £263 | £715 | £10,173 | 14.2 yrs | £4,131 |
| 6 kW | 5253 kWh | 2101 kWh | 3152 kWh | £543 | £315 | £858 | £12,207 | 14.2 yrs | £4,957 |
| 7 kW | 6129 kWh | 2452 kWh | 3677 kWh | £633 | £368 | £1,001 | £14,242 | 14.2 yrs | £5,783 |
| 8 kW | 7005 kWh | 2802 kWh | 4203 kWh | £724 | £420 | £1,144 | £16,276 | 14.2 yrs | £6,609 |
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: £854, Upfront: £12,273, Break-even: 14.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1751 kWh | 1051 kWh | 700 kWh | £271 | £70 | £342 | £6,169 | 18.1 yrs | £662 |
| 3 kW | 2627 kWh | 1576 kWh | 1051 kWh | £407 | £105 | £512 | £8,204 | 16.0 yrs | £2,043 |
| 4 kW | 3502 kWh | 2101 kWh | 1401 kWh | £543 | £140 | £683 | £10,238 | 15.0 yrs | £3,424 |
| 5 kW | 4378 kWh | 2627 kWh | 1751 kWh | £679 | £175 | £854 | £12,273 | 14.4 yrs | £4,805 |
| 6 kW | 5253 kWh | 3152 kWh | 2101 kWh | £814 | £210 | £1,025 | £14,307 | 14.0 yrs | £6,186 |
| 7 kW | 6129 kWh | 3677 kWh | 2452 kWh | £950 | £245 | £1,195 | £16,342 | 13.7 yrs | £7,567 |
| 8 kW | 7005 kWh | 4203 kWh | 2802 kWh | £1,086 | £280 | £1,366 | £18,376 | 13.5 yrs | £8,948 |
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: £923, 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 | 1751 kWh | 1226 kWh | 525 kWh | £317 | £53 | £369 | £7,569 | 20.5 yrs | £-183 |
| 3 kW | 2627 kWh | 1839 kWh | 788 kWh | £475 | £79 | £554 | £9,604 | 17.3 yrs | £1,475 |
| 4 kW | 3502 kWh | 2452 kWh | 1051 kWh | £633 | £105 | £739 | £11,638 | 15.8 yrs | £3,133 |
| 5 kW | 4378 kWh | 3065 kWh | 1313 kWh | £792 | £131 | £923 | £13,673 | 14.8 yrs | £4,792 |
| 6 kW | 5253 kWh | 3677 kWh | 1576 kWh | £950 | £158 | £1,108 | £15,707 | 14.2 yrs | £6,450 |
| 7 kW | 6129 kWh | 4290 kWh | 1839 kWh | £1,109 | £184 | £1,292 | £17,742 | 13.7 yrs | £8,108 |
| 8 kW | 7005 kWh | 4903 kWh | 2101 kWh | £1,267 | £210 | £1,477 | £19,776 | 13.4 yrs | £9,767 |
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: £944, 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 | 1751 kWh | 1278 kWh | 473 kWh | £330 | £47 | £378 | £9,319 | 24.7 yrs | £-1,767 |
| 3 kW | 2627 kWh | 1918 kWh | 709 kWh | £495 | £71 | £566 | £11,354 | 20.0 yrs | £-25 |
| 4 kW | 3502 kWh | 2557 kWh | 946 kWh | £661 | £95 | £755 | £13,388 | 17.7 yrs | £1,716 |
| 5 kW | 4378 kWh | 3196 kWh | 1182 kWh | £826 | £118 | £944 | £15,423 | 16.3 yrs | £3,458 |
| 6 kW | 5253 kWh | 3835 kWh | 1418 kWh | £991 | £142 | £1,133 | £17,457 | 15.4 yrs | £5,199 |
| 7 kW | 6129 kWh | 4474 kWh | 1655 kWh | £1,156 | £165 | £1,322 | £19,492 | 14.7 yrs | £6,941 |
| 8 kW | 7005 kWh | 5113 kWh | 1891 kWh | £1,321 | £189 | £1,510 | £21,526 | 14.3 yrs | £8,682 |
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: £958, 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 | 1751 kWh | 1313 kWh | 438 kWh | £339 | £44 | £383 | £11,069 | 28.9 yrs | £-3,406 |
| 3 kW | 2627 kWh | 1970 kWh | 657 kWh | £509 | £66 | £575 | £13,104 | 22.8 yrs | £-1,609 |
| 4 kW | 3502 kWh | 2627 kWh | 876 kWh | £679 | £88 | £766 | £15,138 | 19.8 yrs | £188 |
| 5 kW | 4378 kWh | 3283 kWh | 1094 kWh | £848 | £109 | £958 | £17,173 | 17.9 yrs | £1,985 |
| 6 kW | 5253 kWh | 3940 kWh | 1313 kWh | £1,018 | £131 | £1,149 | £19,207 | 16.7 yrs | £3,782 |
| 7 kW | 6129 kWh | 4597 kWh | 1532 kWh | £1,188 | £153 | £1,341 | £21,242 | 15.8 yrs | £5,579 |
| 8 kW | 7005 kWh | 5253 kWh | 1751 kWh | £1,357 | £175 | £1,533 | £23,276 | 15.2 yrs | £7,376 |
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: £972, 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 | 1751 kWh | 1348 kWh | 403 kWh | £348 | £40 | £389 | £13,519 | 34.8 yrs | £-5,745 |
| 3 kW | 2627 kWh | 2023 kWh | 604 kWh | £523 | £60 | £583 | £15,554 | 26.7 yrs | £-3,892 |
| 4 kW | 3502 kWh | 2697 kWh | 806 kWh | £697 | £81 | £777 | £17,588 | 22.6 yrs | £-2,040 |
| 5 kW | 4378 kWh | 3371 kWh | 1007 kWh | £871 | £101 | £972 | £19,623 | 20.2 yrs | £-187 |
| 6 kW | 5253 kWh | 4045 kWh | 1208 kWh | £1,045 | £121 | £1,166 | £21,657 | 18.6 yrs | £1,665 |
| 7 kW | 6129 kWh | 4719 kWh | 1410 kWh | £1,219 | £141 | £1,360 | £23,692 | 17.4 yrs | £3,518 |
| 8 kW | 7005 kWh | 5394 kWh | 1611 kWh | £1,394 | £161 | £1,555 | £25,726 | 16.5 yrs | £5,370 |
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.