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 935 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: £758, Upfront: £10,173, Break-even: 13.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1869 kWh | 748 kWh | 1122 kWh | £191 | £112 | £303 | £4,069 | 13.4 yrs | £1,995 |
| 3 kW | 2804 kWh | 1122 kWh | 1682 kWh | £287 | £168 | £455 | £6,104 | 13.4 yrs | £2,992 |
| 4 kW | 3738 kWh | 1495 kWh | 2243 kWh | £382 | £224 | £606 | £8,138 | 13.4 yrs | £3,989 |
| 5 kW | 4673 kWh | 1869 kWh | 2804 kWh | £478 | £280 | £758 | £10,173 | 13.4 yrs | £4,987 |
| 6 kW | 5608 kWh | 2243 kWh | 3365 kWh | £573 | £336 | £910 | £12,207 | 13.4 yrs | £5,984 |
| 7 kW | 6542 kWh | 2617 kWh | 3925 kWh | £669 | £393 | £1,061 | £14,242 | 13.4 yrs | £6,982 |
| 8 kW | 7477 kWh | 2991 kWh | 4486 kWh | £764 | £449 | £1,213 | £16,276 | 13.4 yrs | £7,979 |
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: £903, Upfront: £12,273, 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 | 1869 kWh | 1122 kWh | 748 kWh | £287 | £75 | £361 | £6,169 | 17.1 yrs | £1,057 |
| 3 kW | 2804 kWh | 1682 kWh | 1122 kWh | £430 | £112 | £542 | £8,204 | 15.1 yrs | £2,636 |
| 4 kW | 3738 kWh | 2243 kWh | 1495 kWh | £573 | £150 | £723 | £10,238 | 14.2 yrs | £4,215 |
| 5 kW | 4673 kWh | 2804 kWh | 1869 kWh | £716 | £187 | £903 | £12,273 | 13.6 yrs | £5,793 |
| 6 kW | 5608 kWh | 3365 kWh | 2243 kWh | £860 | £224 | £1,084 | £14,307 | 13.2 yrs | £7,372 |
| 7 kW | 6542 kWh | 3925 kWh | 2617 kWh | £1,003 | £262 | £1,265 | £16,342 | 12.9 yrs | £8,951 |
| 8 kW | 7477 kWh | 4486 kWh | 2991 kWh | £1,146 | £299 | £1,445 | £18,376 | 12.7 yrs | £10,530 |
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: £976, Upfront: £13,673, Break-even: 14.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1869 kWh | 1308 kWh | 561 kWh | £334 | £56 | £390 | £7,569 | 19.4 yrs | £239 |
| 3 kW | 2804 kWh | 1963 kWh | 841 kWh | £501 | £84 | £586 | £9,604 | 16.4 yrs | £2,108 |
| 4 kW | 3738 kWh | 2617 kWh | 1122 kWh | £669 | £112 | £781 | £11,638 | 14.9 yrs | £3,977 |
| 5 kW | 4673 kWh | 3271 kWh | 1402 kWh | £836 | £140 | £976 | £13,673 | 14.0 yrs | £5,847 |
| 6 kW | 5608 kWh | 3925 kWh | 1682 kWh | £1,003 | £168 | £1,171 | £15,707 | 13.4 yrs | £7,716 |
| 7 kW | 6542 kWh | 4580 kWh | 1963 kWh | £1,170 | £196 | £1,366 | £17,742 | 13.0 yrs | £9,585 |
| 8 kW | 7477 kWh | 5234 kWh | 2243 kWh | £1,337 | £224 | £1,562 | £19,776 | 12.7 yrs | £11,455 |
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: £998, Upfront: £15,423, Break-even: 15.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1869 kWh | 1365 kWh | 505 kWh | £349 | £50 | £399 | £9,319 | 23.3 yrs | £-1,337 |
| 3 kW | 2804 kWh | 2047 kWh | 757 kWh | £523 | £76 | £599 | £11,354 | 19.0 yrs | £620 |
| 4 kW | 3738 kWh | 2729 kWh | 1009 kWh | £697 | £101 | £798 | £13,388 | 16.8 yrs | £2,576 |
| 5 kW | 4673 kWh | 3411 kWh | 1262 kWh | £872 | £126 | £998 | £15,423 | 15.5 yrs | £4,533 |
| 6 kW | 5608 kWh | 4094 kWh | 1514 kWh | £1,046 | £151 | £1,197 | £17,457 | 14.6 yrs | £6,489 |
| 7 kW | 6542 kWh | 4776 kWh | 1766 kWh | £1,220 | £177 | £1,397 | £19,492 | 14.0 yrs | £8,446 |
| 8 kW | 7477 kWh | 5458 kWh | 2019 kWh | £1,395 | £202 | £1,596 | £21,526 | 13.5 yrs | £10,402 |
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: £1,012, Upfront: £17,173, Break-even: 17.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1869 kWh | 1402 kWh | 467 kWh | £358 | £47 | £405 | £11,069 | 27.3 yrs | £-2,971 |
| 3 kW | 2804 kWh | 2103 kWh | 701 kWh | £537 | £70 | £607 | £13,104 | 21.6 yrs | £-956 |
| 4 kW | 3738 kWh | 2804 kWh | 935 kWh | £716 | £93 | £810 | £15,138 | 18.7 yrs | £1,059 |
| 5 kW | 4673 kWh | 3505 kWh | 1168 kWh | £895 | £117 | £1,012 | £17,173 | 17.0 yrs | £3,073 |
| 6 kW | 5608 kWh | 4206 kWh | 1402 kWh | £1,075 | £140 | £1,215 | £19,207 | 15.8 yrs | £5,088 |
| 7 kW | 6542 kWh | 4907 kWh | 1636 kWh | £1,254 | £164 | £1,417 | £21,242 | 15.0 yrs | £7,103 |
| 8 kW | 7477 kWh | 5608 kWh | 1869 kWh | £1,433 | £187 | £1,620 | £23,276 | 14.4 yrs | £9,118 |
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: £1,027, Upfront: £19,623, Break-even: 19.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1869 kWh | 1439 kWh | 430 kWh | £368 | £43 | £411 | £13,519 | 32.9 yrs | £-5,304 |
| 3 kW | 2804 kWh | 2159 kWh | 645 kWh | £552 | £64 | £616 | £15,554 | 25.2 yrs | £-3,232 |
| 4 kW | 3738 kWh | 2879 kWh | 860 kWh | £735 | £86 | £821 | £17,588 | 21.4 yrs | £-1,159 |
| 5 kW | 4673 kWh | 3598 kWh | 1075 kWh | £919 | £107 | £1,027 | £19,623 | 19.1 yrs | £914 |
| 6 kW | 5608 kWh | 4318 kWh | 1290 kWh | £1,103 | £129 | £1,232 | £21,657 | 17.6 yrs | £2,987 |
| 7 kW | 6542 kWh | 5038 kWh | 1505 kWh | £1,287 | £150 | £1,438 | £23,692 | 16.5 yrs | £5,060 |
| 8 kW | 7477 kWh | 5757 kWh | 1720 kWh | £1,471 | £172 | £1,643 | £25,726 | 15.7 yrs | £7,133 |
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.