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 958 kWh per year on a south-facing roof. We value self-used electricity at 25.6p 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: £779, Upfront: £10,173, Break-even: 13.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1917 kWh | 767 kWh | 1150 kWh | £197 | £115 | £312 | £4,069 | 13.1 yrs | £2,163 |
| 3 kW | 2875 kWh | 1150 kWh | 1725 kWh | £295 | £173 | £467 | £6,104 | 13.1 yrs | £3,245 |
| 4 kW | 3834 kWh | 1534 kWh | 2300 kWh | £393 | £230 | £623 | £8,138 | 13.1 yrs | £4,327 |
| 5 kW | 4792 kWh | 1917 kWh | 2875 kWh | £491 | £288 | £779 | £10,173 | 13.1 yrs | £5,408 |
| 6 kW | 5751 kWh | 2300 kWh | 3450 kWh | £590 | £345 | £935 | £12,207 | 13.1 yrs | £6,490 |
| 7 kW | 6709 kWh | 2684 kWh | 4026 kWh | £688 | £403 | £1,091 | £14,242 | 13.1 yrs | £7,571 |
| 8 kW | 7668 kWh | 3067 kWh | 4601 kWh | £786 | £460 | £1,246 | £16,276 | 13.1 yrs | £8,653 |
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: £929, Upfront: £12,273, Break-even: 13.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1917 kWh | 1150 kWh | 767 kWh | £295 | £77 | £372 | £6,169 | 16.6 yrs | £1,262 |
| 3 kW | 2875 kWh | 1725 kWh | 1150 kWh | £442 | £115 | £557 | £8,204 | 14.7 yrs | £2,944 |
| 4 kW | 3834 kWh | 2300 kWh | 1534 kWh | £590 | £153 | £743 | £10,238 | 13.8 yrs | £4,625 |
| 5 kW | 4792 kWh | 2875 kWh | 1917 kWh | £737 | £192 | £929 | £12,273 | 13.2 yrs | £6,306 |
| 6 kW | 5751 kWh | 3450 kWh | 2300 kWh | £885 | £230 | £1,115 | £14,307 | 12.8 yrs | £7,987 |
| 7 kW | 6709 kWh | 4026 kWh | 2684 kWh | £1,032 | £268 | £1,301 | £16,342 | 12.6 yrs | £9,669 |
| 8 kW | 7668 kWh | 4601 kWh | 3067 kWh | £1,180 | £307 | £1,486 | £18,376 | 12.4 yrs | £11,350 |
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: £1,004, Upfront: £13,673, Break-even: 13.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1917 kWh | 1342 kWh | 575 kWh | £344 | £58 | £402 | £7,569 | 18.8 yrs | £462 |
| 3 kW | 2875 kWh | 2013 kWh | 863 kWh | £516 | £86 | £602 | £9,604 | 15.9 yrs | £2,443 |
| 4 kW | 3834 kWh | 2684 kWh | 1150 kWh | £688 | £115 | £803 | £11,638 | 14.5 yrs | £4,424 |
| 5 kW | 4792 kWh | 3355 kWh | 1438 kWh | £860 | £144 | £1,004 | £13,673 | 13.6 yrs | £6,405 |
| 6 kW | 5751 kWh | 4026 kWh | 1725 kWh | £1,032 | £173 | £1,205 | £15,707 | 13.0 yrs | £8,386 |
| 7 kW | 6709 kWh | 4696 kWh | 2013 kWh | £1,204 | £201 | £1,405 | £17,742 | 12.6 yrs | £10,367 |
| 8 kW | 7668 kWh | 5367 kWh | 2300 kWh | £1,376 | £230 | £1,606 | £19,776 | 12.3 yrs | £12,348 |
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: £1,026, Upfront: £15,423, Break-even: 15.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1917 kWh | 1399 kWh | 518 kWh | £359 | £52 | £411 | £9,319 | 22.7 yrs | £-1,108 |
| 3 kW | 2875 kWh | 2099 kWh | 776 kWh | £538 | £78 | £616 | £11,354 | 18.4 yrs | £963 |
| 4 kW | 3834 kWh | 2799 kWh | 1035 kWh | £718 | £104 | £821 | £13,388 | 16.3 yrs | £3,034 |
| 5 kW | 4792 kWh | 3498 kWh | 1294 kWh | £897 | £129 | £1,026 | £15,423 | 15.0 yrs | £5,105 |
| 6 kW | 5751 kWh | 4198 kWh | 1553 kWh | £1,076 | £155 | £1,232 | £17,457 | 14.2 yrs | £7,176 |
| 7 kW | 6709 kWh | 4898 kWh | 1811 kWh | £1,256 | £181 | £1,437 | £19,492 | 13.6 yrs | £9,247 |
| 8 kW | 7668 kWh | 5597 kWh | 2070 kWh | £1,435 | £207 | £1,642 | £21,526 | 13.1 yrs | £11,318 |
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: £1,041, Upfront: £17,173, Break-even: 16.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1917 kWh | 1438 kWh | 479 kWh | £369 | £48 | £417 | £11,069 | 26.6 yrs | £-2,738 |
| 3 kW | 2875 kWh | 2157 kWh | 719 kWh | £553 | £72 | £625 | £13,104 | 21.0 yrs | £-607 |
| 4 kW | 3834 kWh | 2875 kWh | 958 kWh | £737 | £96 | £833 | £15,138 | 18.2 yrs | £1,524 |
| 5 kW | 4792 kWh | 3594 kWh | 1198 kWh | £922 | £120 | £1,041 | £17,173 | 16.5 yrs | £3,655 |
| 6 kW | 5751 kWh | 4313 kWh | 1438 kWh | £1,106 | £144 | £1,250 | £19,207 | 15.4 yrs | £5,786 |
| 7 kW | 6709 kWh | 5032 kWh | 1677 kWh | £1,290 | £168 | £1,458 | £21,242 | 14.6 yrs | £7,917 |
| 8 kW | 7668 kWh | 5751 kWh | 1917 kWh | £1,474 | £192 | £1,666 | £23,276 | 14.0 yrs | £10,048 |
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: £1,056, Upfront: £19,623, Break-even: 18.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1917 kWh | 1476 kWh | 441 kWh | £378 | £44 | £423 | £13,519 | 32.0 yrs | £-5,068 |
| 3 kW | 2875 kWh | 2214 kWh | 661 kWh | £568 | £66 | £634 | £15,554 | 24.5 yrs | £-2,877 |
| 4 kW | 3834 kWh | 2952 kWh | 882 kWh | £757 | £88 | £845 | £17,588 | 20.8 yrs | £-686 |
| 5 kW | 4792 kWh | 3690 kWh | 1102 kWh | £946 | £110 | £1,056 | £19,623 | 18.6 yrs | £1,505 |
| 6 kW | 5751 kWh | 4428 kWh | 1323 kWh | £1,135 | £132 | £1,268 | £21,657 | 17.1 yrs | £3,696 |
| 7 kW | 6709 kWh | 5166 kWh | 1543 kWh | £1,325 | £154 | £1,479 | £23,692 | 16.0 yrs | £5,886 |
| 8 kW | 7668 kWh | 5904 kWh | 1764 kWh | £1,514 | £176 | £1,690 | £25,726 | 15.2 yrs | £8,077 |
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.