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 940 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: £760, 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 | 1880 kWh | 752 kWh | 1128 kWh | £191 | £113 | £304 | £4,069 | 13.4 yrs | £2,011 |
| 3 kW | 2820 kWh | 1128 kWh | 1692 kWh | £287 | £169 | £456 | £6,104 | 13.4 yrs | £3,017 |
| 4 kW | 3760 kWh | 1504 kWh | 2256 kWh | £382 | £226 | £608 | £8,138 | 13.4 yrs | £4,023 |
| 5 kW | 4700 kWh | 1880 kWh | 2820 kWh | £478 | £282 | £760 | £10,173 | 13.4 yrs | £5,029 |
| 6 kW | 5640 kWh | 2256 kWh | 3384 kWh | £574 | £338 | £912 | £12,207 | 13.4 yrs | £6,034 |
| 7 kW | 6580 kWh | 2632 kWh | 3948 kWh | £669 | £395 | £1,064 | £14,242 | 13.4 yrs | £7,040 |
| 8 kW | 7520 kWh | 3008 kWh | 4512 kWh | £765 | £451 | £1,216 | £16,276 | 13.4 yrs | £8,046 |
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: £905, 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 | 1880 kWh | 1128 kWh | 752 kWh | £287 | £75 | £362 | £6,169 | 17.0 yrs | £1,072 |
| 3 kW | 2820 kWh | 1692 kWh | 1128 kWh | £430 | £113 | £543 | £8,204 | 15.1 yrs | £2,658 |
| 4 kW | 3760 kWh | 2256 kWh | 1504 kWh | £574 | £150 | £724 | £10,238 | 14.1 yrs | £4,244 |
| 5 kW | 4700 kWh | 2820 kWh | 1880 kWh | £717 | £188 | £905 | £12,273 | 13.6 yrs | £5,829 |
| 6 kW | 5640 kWh | 3384 kWh | 2256 kWh | £861 | £226 | £1,086 | £14,307 | 13.2 yrs | £7,415 |
| 7 kW | 6580 kWh | 3948 kWh | 2632 kWh | £1,004 | £263 | £1,267 | £16,342 | 12.9 yrs | £9,001 |
| 8 kW | 7520 kWh | 4512 kWh | 3008 kWh | £1,147 | £301 | £1,448 | £18,376 | 12.7 yrs | £10,587 |
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: £978, 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 | 1880 kWh | 1316 kWh | 564 kWh | £335 | £56 | £391 | £7,569 | 19.4 yrs | £252 |
| 3 kW | 2820 kWh | 1974 kWh | 846 kWh | £502 | £85 | £587 | £9,604 | 16.4 yrs | £2,128 |
| 4 kW | 3760 kWh | 2632 kWh | 1128 kWh | £669 | £113 | £782 | £11,638 | 14.9 yrs | £4,004 |
| 5 kW | 4700 kWh | 3290 kWh | 1410 kWh | £837 | £141 | £978 | £13,673 | 14.0 yrs | £5,880 |
| 6 kW | 5640 kWh | 3948 kWh | 1692 kWh | £1,004 | £169 | £1,173 | £15,707 | 13.4 yrs | £7,756 |
| 7 kW | 6580 kWh | 4606 kWh | 1974 kWh | £1,171 | £197 | £1,369 | £17,742 | 13.0 yrs | £9,632 |
| 8 kW | 7520 kWh | 5264 kWh | 2256 kWh | £1,339 | £226 | £1,564 | £19,776 | 12.6 yrs | £11,508 |
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: £999, Upfront: £15,423, Break-even: 15.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1880 kWh | 1372 kWh | 508 kWh | £349 | £51 | £400 | £9,319 | 23.3 yrs | £-1,324 |
| 3 kW | 2820 kWh | 2059 kWh | 761 kWh | £523 | £76 | £600 | £11,354 | 18.9 yrs | £639 |
| 4 kW | 3760 kWh | 2745 kWh | 1015 kWh | £698 | £102 | £799 | £13,388 | 16.7 yrs | £2,602 |
| 5 kW | 4700 kWh | 3431 kWh | 1269 kWh | £872 | £127 | £999 | £15,423 | 15.4 yrs | £4,565 |
| 6 kW | 5640 kWh | 4117 kWh | 1523 kWh | £1,047 | £152 | £1,199 | £17,457 | 14.6 yrs | £6,528 |
| 7 kW | 6580 kWh | 4803 kWh | 1777 kWh | £1,221 | £178 | £1,399 | £19,492 | 13.9 yrs | £8,491 |
| 8 kW | 7520 kWh | 5489 kWh | 2030 kWh | £1,396 | £203 | £1,599 | £21,526 | 13.5 yrs | £10,454 |
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: £1,014, Upfront: £17,173, Break-even: 16.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1880 kWh | 1410 kWh | 470 kWh | £359 | £47 | £406 | £11,069 | 27.3 yrs | £-2,958 |
| 3 kW | 2820 kWh | 2115 kWh | 705 kWh | £538 | £70 | £608 | £13,104 | 21.5 yrs | £-937 |
| 4 kW | 3760 kWh | 2820 kWh | 940 kWh | £717 | £94 | £811 | £15,138 | 18.7 yrs | £1,084 |
| 5 kW | 4700 kWh | 3525 kWh | 1175 kWh | £896 | £117 | £1,014 | £17,173 | 16.9 yrs | £3,105 |
| 6 kW | 5640 kWh | 4230 kWh | 1410 kWh | £1,076 | £141 | £1,217 | £19,207 | 15.8 yrs | £5,126 |
| 7 kW | 6580 kWh | 4935 kWh | 1645 kWh | £1,255 | £164 | £1,419 | £21,242 | 15.0 yrs | £7,147 |
| 8 kW | 7520 kWh | 5640 kWh | 1880 kWh | £1,434 | £188 | £1,622 | £23,276 | 14.3 yrs | £9,168 |
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: £1,028, 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 | 1880 kWh | 1448 kWh | 432 kWh | £368 | £43 | £411 | £13,519 | 32.9 yrs | £-5,292 |
| 3 kW | 2820 kWh | 2171 kWh | 649 kWh | £552 | £65 | £617 | £15,554 | 25.2 yrs | £-3,213 |
| 4 kW | 3760 kWh | 2895 kWh | 865 kWh | £736 | £86 | £823 | £17,588 | 21.4 yrs | £-1,134 |
| 5 kW | 4700 kWh | 3619 kWh | 1081 kWh | £920 | £108 | £1,028 | £19,623 | 19.1 yrs | £945 |
| 6 kW | 5640 kWh | 4343 kWh | 1297 kWh | £1,104 | £130 | £1,234 | £21,657 | 17.5 yrs | £3,024 |
| 7 kW | 6580 kWh | 5066 kWh | 1513 kWh | £1,288 | £151 | £1,440 | £23,692 | 16.5 yrs | £5,103 |
| 8 kW | 7520 kWh | 5790 kWh | 1730 kWh | £1,472 | £173 | £1,645 | £25,726 | 15.6 yrs | £7,182 |
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.