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 919 kWh per year on a south-facing roof. We value self-used electricity at 25.4p 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: £743, Upfront: £10,173, Break-even: 13.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1838 kWh | 735 kWh | 1103 kWh | £187 | £110 | £297 | £4,069 | 13.7 yrs | £1,875 |
| 3 kW | 2756 kWh | 1103 kWh | 1654 kWh | £280 | £165 | £446 | £6,104 | 13.7 yrs | £2,812 |
| 4 kW | 3675 kWh | 1470 kWh | 2205 kWh | £374 | £221 | £594 | £8,138 | 13.7 yrs | £3,749 |
| 5 kW | 4594 kWh | 1838 kWh | 2756 kWh | £467 | £276 | £743 | £10,173 | 13.7 yrs | £4,687 |
| 6 kW | 5513 kWh | 2205 kWh | 3308 kWh | £561 | £331 | £892 | £12,207 | 13.7 yrs | £5,624 |
| 7 kW | 6432 kWh | 2573 kWh | 3859 kWh | £654 | £386 | £1,040 | £14,242 | 13.7 yrs | £6,561 |
| 8 kW | 7351 kWh | 2940 kWh | 4410 kWh | £748 | £441 | £1,189 | £16,276 | 13.7 yrs | £7,499 |
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: £885, Upfront: £12,273, 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 | 1838 kWh | 1103 kWh | 735 kWh | £280 | £74 | £354 | £6,169 | 17.4 yrs | £909 |
| 3 kW | 2756 kWh | 1654 kWh | 1103 kWh | £421 | £110 | £531 | £8,204 | 15.5 yrs | £2,413 |
| 4 kW | 3675 kWh | 2205 kWh | 1470 kWh | £561 | £147 | £708 | £10,238 | 14.5 yrs | £3,918 |
| 5 kW | 4594 kWh | 2756 kWh | 1838 kWh | £701 | £184 | £885 | £12,273 | 13.9 yrs | £5,422 |
| 6 kW | 5513 kWh | 3308 kWh | 2205 kWh | £841 | £221 | £1,062 | £14,307 | 13.5 yrs | £6,927 |
| 7 kW | 6432 kWh | 3859 kWh | 2573 kWh | £981 | £257 | £1,239 | £16,342 | 13.2 yrs | £8,431 |
| 8 kW | 7351 kWh | 4410 kWh | 2940 kWh | £1,122 | £294 | £1,416 | £18,376 | 13.0 yrs | £9,936 |
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: £956, Upfront: £13,673, Break-even: 14.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1838 kWh | 1286 kWh | 551 kWh | £327 | £55 | £382 | £7,569 | 19.8 yrs | £76 |
| 3 kW | 2756 kWh | 1930 kWh | 827 kWh | £491 | £83 | £573 | £9,604 | 16.7 yrs | £1,864 |
| 4 kW | 3675 kWh | 2573 kWh | 1103 kWh | £654 | £110 | £765 | £11,638 | 15.2 yrs | £3,652 |
| 5 kW | 4594 kWh | 3216 kWh | 1378 kWh | £818 | £138 | £956 | £13,673 | 14.3 yrs | £5,440 |
| 6 kW | 5513 kWh | 3859 kWh | 1654 kWh | £981 | £165 | £1,147 | £15,707 | 13.7 yrs | £7,228 |
| 7 kW | 6432 kWh | 4502 kWh | 1930 kWh | £1,145 | £193 | £1,338 | £17,742 | 13.3 yrs | £9,016 |
| 8 kW | 7351 kWh | 5145 kWh | 2205 kWh | £1,308 | £221 | £1,529 | £19,776 | 12.9 yrs | £10,804 |
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: £977, Upfront: £15,423, Break-even: 15.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1838 kWh | 1341 kWh | 496 kWh | £341 | £50 | £391 | £9,319 | 23.8 yrs | £-1,504 |
| 3 kW | 2756 kWh | 2012 kWh | 744 kWh | £512 | £74 | £586 | £11,354 | 19.4 yrs | £369 |
| 4 kW | 3675 kWh | 2683 kWh | 992 kWh | £682 | £99 | £782 | £13,388 | 17.1 yrs | £2,242 |
| 5 kW | 4594 kWh | 3354 kWh | 1240 kWh | £853 | £124 | £977 | £15,423 | 15.8 yrs | £4,115 |
| 6 kW | 5513 kWh | 4024 kWh | 1489 kWh | £1,023 | £149 | £1,172 | £17,457 | 14.9 yrs | £5,988 |
| 7 kW | 6432 kWh | 4695 kWh | 1737 kWh | £1,194 | £174 | £1,368 | £19,492 | 14.3 yrs | £7,862 |
| 8 kW | 7351 kWh | 5366 kWh | 1985 kWh | £1,365 | £198 | £1,563 | £21,526 | 13.8 yrs | £9,735 |
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: £991, Upfront: £17,173, Break-even: 17.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1838 kWh | 1378 kWh | 459 kWh | £350 | £46 | £396 | £11,069 | 27.9 yrs | £-3,140 |
| 3 kW | 2756 kWh | 2067 kWh | 689 kWh | £526 | £69 | £595 | £13,104 | 22.0 yrs | £-1,211 |
| 4 kW | 3675 kWh | 2756 kWh | 919 kWh | £701 | £92 | £793 | £15,138 | 19.1 yrs | £719 |
| 5 kW | 4594 kWh | 3446 kWh | 1149 kWh | £876 | £115 | £991 | £17,173 | 17.3 yrs | £2,649 |
| 6 kW | 5513 kWh | 4135 kWh | 1378 kWh | £1,051 | £138 | £1,189 | £19,207 | 16.2 yrs | £4,579 |
| 7 kW | 6432 kWh | 4824 kWh | 1608 kWh | £1,227 | £161 | £1,388 | £21,242 | 15.3 yrs | £6,508 |
| 8 kW | 7351 kWh | 5513 kWh | 1838 kWh | £1,402 | £184 | £1,586 | £23,276 | 14.7 yrs | £8,438 |
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: £1,005, Upfront: £19,623, Break-even: 19.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1838 kWh | 1415 kWh | 423 kWh | £360 | £42 | £402 | £13,519 | 33.6 yrs | £-5,477 |
| 3 kW | 2756 kWh | 2122 kWh | 634 kWh | £540 | £63 | £603 | £15,554 | 25.8 yrs | £-3,491 |
| 4 kW | 3675 kWh | 2830 kWh | 845 kWh | £720 | £85 | £804 | £17,588 | 21.9 yrs | £-1,504 |
| 5 kW | 4594 kWh | 3537 kWh | 1057 kWh | £900 | £106 | £1,005 | £19,623 | 19.5 yrs | £482 |
| 6 kW | 5513 kWh | 4245 kWh | 1268 kWh | £1,080 | £127 | £1,206 | £21,657 | 18.0 yrs | £2,469 |
| 7 kW | 6432 kWh | 4952 kWh | 1479 kWh | £1,259 | £148 | £1,407 | £23,692 | 16.8 yrs | £4,455 |
| 8 kW | 7351 kWh | 5660 kWh | 1691 kWh | £1,439 | £169 | £1,608 | £25,726 | 16.0 yrs | £6,442 |
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.