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 1086 kWh per year on a south-facing roof. We value self-used electricity at 26.9p 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: £910, Upfront: £10,173, Break-even: 11.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2171 kWh | 868 kWh | 1303 kWh | £234 | £130 | £364 | £4,069 | 11.2 yrs | £3,212 |
| 3 kW | 3257 kWh | 1303 kWh | 1954 kWh | £351 | £195 | £546 | £6,104 | 11.2 yrs | £4,818 |
| 4 kW | 4342 kWh | 1737 kWh | 2605 kWh | £468 | £261 | £728 | £8,138 | 11.2 yrs | £6,424 |
| 5 kW | 5428 kWh | 2171 kWh | 3257 kWh | £584 | £326 | £910 | £10,173 | 11.2 yrs | £8,030 |
| 6 kW | 6513 kWh | 2605 kWh | 3908 kWh | £701 | £391 | £1,092 | £12,207 | 11.2 yrs | £9,636 |
| 7 kW | 7599 kWh | 3039 kWh | 4559 kWh | £818 | £456 | £1,274 | £14,242 | 11.2 yrs | £11,241 |
| 8 kW | 8684 kWh | 3474 kWh | 5211 kWh | £935 | £521 | £1,456 | £16,276 | 11.2 yrs | £12,847 |
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: £1,094, Upfront: £12,273, Break-even: 11.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2171 kWh | 1303 kWh | 868 kWh | £351 | £87 | £438 | £6,169 | 14.1 yrs | £2,581 |
| 3 kW | 3257 kWh | 1954 kWh | 1303 kWh | £526 | £130 | £656 | £8,204 | 12.5 yrs | £4,922 |
| 4 kW | 4342 kWh | 2605 kWh | 1737 kWh | £701 | £174 | £875 | £10,238 | 11.7 yrs | £7,262 |
| 5 kW | 5428 kWh | 3257 kWh | 2171 kWh | £877 | £217 | £1,094 | £12,273 | 11.2 yrs | £9,603 |
| 6 kW | 6513 kWh | 3908 kWh | 2605 kWh | £1,052 | £261 | £1,313 | £14,307 | 10.9 yrs | £11,944 |
| 7 kW | 7599 kWh | 4559 kWh | 3039 kWh | £1,227 | £304 | £1,531 | £16,342 | 10.7 yrs | £14,284 |
| 8 kW | 8684 kWh | 5211 kWh | 3474 kWh | £1,403 | £347 | £1,750 | £18,376 | 10.5 yrs | £16,625 |
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: £1,186, Upfront: £13,673, Break-even: 11.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2171 kWh | 1520 kWh | 651 kWh | £409 | £65 | £474 | £7,569 | 16.0 yrs | £1,916 |
| 3 kW | 3257 kWh | 2280 kWh | 977 kWh | £614 | £98 | £711 | £9,604 | 13.5 yrs | £4,624 |
| 4 kW | 4342 kWh | 3039 kWh | 1303 kWh | £818 | £130 | £948 | £11,638 | 12.3 yrs | £7,332 |
| 5 kW | 5428 kWh | 3799 kWh | 1628 kWh | £1,023 | £163 | £1,186 | £13,673 | 11.5 yrs | £10,040 |
| 6 kW | 6513 kWh | 4559 kWh | 1954 kWh | £1,227 | £195 | £1,423 | £15,707 | 11.0 yrs | £12,748 |
| 7 kW | 7599 kWh | 5319 kWh | 2280 kWh | £1,432 | £228 | £1,660 | £17,742 | 10.7 yrs | £15,456 |
| 8 kW | 8684 kWh | 6079 kWh | 2605 kWh | £1,636 | £261 | £1,897 | £19,776 | 10.4 yrs | £18,164 |
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: £1,213, Upfront: £15,423, Break-even: 12.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2171 kWh | 1585 kWh | 586 kWh | £427 | £59 | £485 | £9,319 | 19.2 yrs | £386 |
| 3 kW | 3257 kWh | 2377 kWh | 879 kWh | £640 | £88 | £728 | £11,354 | 15.6 yrs | £3,204 |
| 4 kW | 4342 kWh | 3170 kWh | 1172 kWh | £853 | £117 | £971 | £13,388 | 13.8 yrs | £6,023 |
| 5 kW | 5428 kWh | 3962 kWh | 1465 kWh | £1,067 | £147 | £1,213 | £15,423 | 12.7 yrs | £8,841 |
| 6 kW | 6513 kWh | 4755 kWh | 1759 kWh | £1,280 | £176 | £1,456 | £17,457 | 12.0 yrs | £11,659 |
| 7 kW | 7599 kWh | 5547 kWh | 2052 kWh | £1,493 | £205 | £1,698 | £19,492 | 11.5 yrs | £14,477 |
| 8 kW | 8684 kWh | 6339 kWh | 2345 kWh | £1,707 | £234 | £1,941 | £21,526 | 11.1 yrs | £17,295 |
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: £1,232, Upfront: £17,173, Break-even: 13.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2171 kWh | 1628 kWh | 543 kWh | £438 | £54 | £493 | £11,069 | 22.5 yrs | £-1,217 |
| 3 kW | 3257 kWh | 2442 kWh | 814 kWh | £658 | £81 | £739 | £13,104 | 17.7 yrs | £1,675 |
| 4 kW | 4342 kWh | 3257 kWh | 1086 kWh | £877 | £109 | £985 | £15,138 | 15.4 yrs | £4,567 |
| 5 kW | 5428 kWh | 4071 kWh | 1357 kWh | £1,096 | £136 | £1,232 | £17,173 | 13.9 yrs | £7,458 |
| 6 kW | 6513 kWh | 4885 kWh | 1628 kWh | £1,315 | £163 | £1,478 | £19,207 | 13.0 yrs | £10,350 |
| 7 kW | 7599 kWh | 5699 kWh | 1900 kWh | £1,534 | £190 | £1,724 | £21,242 | 12.3 yrs | £13,241 |
| 8 kW | 8684 kWh | 6513 kWh | 2171 kWh | £1,753 | £217 | £1,970 | £23,276 | 11.8 yrs | £16,133 |
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: £1,250, Upfront: £19,623, Break-even: 15.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2171 kWh | 1672 kWh | 499 kWh | £450 | £50 | £500 | £13,519 | 27.0 yrs | £-3,520 |
| 3 kW | 3257 kWh | 2508 kWh | 749 kWh | £675 | £75 | £750 | £15,554 | 20.7 yrs | £-555 |
| 4 kW | 4342 kWh | 3343 kWh | 999 kWh | £900 | £100 | £1,000 | £17,588 | 17.6 yrs | £2,410 |
| 5 kW | 5428 kWh | 4179 kWh | 1248 kWh | £1,125 | £125 | £1,250 | £19,623 | 15.7 yrs | £5,375 |
| 6 kW | 6513 kWh | 5015 kWh | 1498 kWh | £1,350 | £150 | £1,500 | £21,657 | 14.4 yrs | £8,341 |
| 7 kW | 7599 kWh | 5851 kWh | 1748 kWh | £1,575 | £175 | £1,750 | £23,692 | 13.5 yrs | £11,306 |
| 8 kW | 8684 kWh | 6687 kWh | 1997 kWh | £1,800 | £200 | £2,000 | £25,726 | 12.9 yrs | £14,271 |
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.