A typical roof here lands around 5.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 647 kWh per year on a south-facing roof. We value self-used electricity at 27.1p 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: £544, Upfront: £10,173, Break-even: 18.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1294 kWh | 518 kWh | 776 kWh | £140 | £78 | £218 | £4,069 | 18.7 yrs | £285 |
| 3 kW | 1941 kWh | 776 kWh | 1165 kWh | £210 | £116 | £327 | £6,104 | 18.7 yrs | £427 |
| 4 kW | 2588 kWh | 1035 kWh | 1553 kWh | £280 | £155 | £435 | £8,138 | 18.7 yrs | £570 |
| 5 kW | 3235 kWh | 1294 kWh | 1941 kWh | £350 | £194 | £544 | £10,173 | 18.7 yrs | £712 |
| 6 kW | 3882 kWh | 1553 kWh | 2329 kWh | £420 | £233 | £653 | £12,207 | 18.7 yrs | £854 |
| 7 kW | 4529 kWh | 1811 kWh | 2717 kWh | £490 | £272 | £762 | £14,242 | 18.7 yrs | £997 |
| 8 kW | 5176 kWh | 2070 kWh | 3105 kWh | £560 | £311 | £871 | £16,276 | 18.7 yrs | £1,139 |
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: £655, Upfront: £12,273, Break-even: 18.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1294 kWh | 776 kWh | 518 kWh | £210 | £52 | £262 | £6,169 | 23.6 yrs | £-932 |
| 3 kW | 1941 kWh | 1165 kWh | 776 kWh | £315 | £78 | £393 | £8,204 | 20.9 yrs | £-348 |
| 4 kW | 2588 kWh | 1553 kWh | 1035 kWh | £420 | £104 | £524 | £10,238 | 19.6 yrs | £235 |
| 5 kW | 3235 kWh | 1941 kWh | 1294 kWh | £525 | £129 | £655 | £12,273 | 18.7 yrs | £819 |
| 6 kW | 3882 kWh | 2329 kWh | 1553 kWh | £630 | £155 | £786 | £14,307 | 18.2 yrs | £1,403 |
| 7 kW | 4529 kWh | 2717 kWh | 1811 kWh | £735 | £181 | £916 | £16,342 | 17.8 yrs | £1,987 |
| 8 kW | 5176 kWh | 3105 kWh | 2070 kWh | £840 | £207 | £1,047 | £18,376 | 17.5 yrs | £2,571 |
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: £710, Upfront: £13,673, Break-even: 19.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1294 kWh | 906 kWh | 388 kWh | £245 | £39 | £284 | £7,569 | 26.7 yrs | £-1,891 |
| 3 kW | 1941 kWh | 1359 kWh | 582 kWh | £368 | £58 | £426 | £9,604 | 22.6 yrs | £-1,086 |
| 4 kW | 2588 kWh | 1811 kWh | 776 kWh | £490 | £78 | £568 | £11,638 | 20.5 yrs | £-282 |
| 5 kW | 3235 kWh | 2264 kWh | 970 kWh | £613 | £97 | £710 | £13,673 | 19.3 yrs | £523 |
| 6 kW | 3882 kWh | 2717 kWh | 1165 kWh | £735 | £116 | £852 | £15,707 | 18.4 yrs | £1,328 |
| 7 kW | 4529 kWh | 3170 kWh | 1359 kWh | £858 | £136 | £994 | £17,742 | 17.9 yrs | £2,132 |
| 8 kW | 5176 kWh | 3623 kWh | 1553 kWh | £980 | £155 | £1,136 | £19,776 | 17.4 yrs | £2,937 |
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: £726, Upfront: £15,423, Break-even: 21.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1294 kWh | 945 kWh | 349 kWh | £256 | £35 | £291 | £9,319 | 32.1 yrs | £-3,508 |
| 3 kW | 1941 kWh | 1417 kWh | 524 kWh | £383 | £52 | £436 | £11,354 | 26.1 yrs | £-2,638 |
| 4 kW | 2588 kWh | 1889 kWh | 699 kWh | £511 | £70 | £581 | £13,388 | 23.0 yrs | £-1,767 |
| 5 kW | 3235 kWh | 2361 kWh | 873 kWh | £639 | £87 | £726 | £15,423 | 21.2 yrs | £-896 |
| 6 kW | 3882 kWh | 2834 kWh | 1048 kWh | £767 | £105 | £872 | £17,457 | 20.0 yrs | £-25 |
| 7 kW | 4529 kWh | 3306 kWh | 1223 kWh | £895 | £122 | £1,017 | £19,492 | 19.2 yrs | £846 |
| 8 kW | 5176 kWh | 3778 kWh | 1397 kWh | £1,022 | £140 | £1,162 | £21,526 | 18.5 yrs | £1,717 |
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: £737, Upfront: £17,173, Break-even: 23.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1294 kWh | 970 kWh | 323 kWh | £263 | £32 | £295 | £11,069 | 37.5 yrs | £-5,170 |
| 3 kW | 1941 kWh | 1456 kWh | 485 kWh | £394 | £49 | £442 | £13,104 | 29.6 yrs | £-4,255 |
| 4 kW | 2588 kWh | 1941 kWh | 647 kWh | £525 | £65 | £590 | £15,138 | 25.7 yrs | £-3,340 |
| 5 kW | 3235 kWh | 2426 kWh | 809 kWh | £657 | £81 | £737 | £17,173 | 23.3 yrs | £-2,425 |
| 6 kW | 3882 kWh | 2911 kWh | 970 kWh | £788 | £97 | £885 | £19,207 | 21.7 yrs | £-1,510 |
| 7 kW | 4529 kWh | 3397 kWh | 1132 kWh | £919 | £113 | £1,032 | £21,242 | 20.6 yrs | £-595 |
| 8 kW | 5176 kWh | 3882 kWh | 1294 kWh | £1,050 | £129 | £1,180 | £23,276 | 19.7 yrs | £320 |
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: £748, Upfront: £19,623, Break-even: 26.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1294 kWh | 996 kWh | 298 kWh | £270 | £30 | £299 | £13,519 | 45.2 yrs | £-7,532 |
| 3 kW | 1941 kWh | 1494 kWh | 446 kWh | £404 | £45 | £449 | £15,554 | 34.6 yrs | £-6,573 |
| 4 kW | 2588 kWh | 1993 kWh | 595 kWh | £539 | £60 | £599 | £17,588 | 29.4 yrs | £-5,613 |
| 5 kW | 3235 kWh | 2491 kWh | 744 kWh | £674 | £74 | £748 | £19,623 | 26.2 yrs | £-4,654 |
| 6 kW | 3882 kWh | 2989 kWh | 893 kWh | £809 | £89 | £898 | £21,657 | 24.1 yrs | £-3,695 |
| 7 kW | 4529 kWh | 3487 kWh | 1042 kWh | £944 | £104 | £1,048 | £23,692 | 22.6 yrs | £-2,736 |
| 8 kW | 5176 kWh | 3985 kWh | 1190 kWh | £1,078 | £119 | £1,197 | £25,726 | 21.5 yrs | £-1,777 |
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.