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 881 kWh per year on a south-facing roof. We value self-used electricity at 25.8p 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: £720, Upfront: £10,173, Break-even: 14.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1763 kWh | 705 kWh | 1058 kWh | £182 | £106 | £288 | £4,069 | 14.1 yrs | £1,690 |
| 3 kW | 2644 kWh | 1058 kWh | 1586 kWh | £273 | £159 | £432 | £6,104 | 14.1 yrs | £2,535 |
| 4 kW | 3526 kWh | 1410 kWh | 2115 kWh | £364 | £212 | £576 | £8,138 | 14.1 yrs | £3,381 |
| 5 kW | 4407 kWh | 1763 kWh | 2644 kWh | £455 | £264 | £720 | £10,173 | 14.1 yrs | £4,226 |
| 6 kW | 5288 kWh | 2115 kWh | 3173 kWh | £547 | £317 | £864 | £12,207 | 14.1 yrs | £5,071 |
| 7 kW | 6170 kWh | 2468 kWh | 3702 kWh | £638 | £370 | £1,008 | £14,242 | 14.1 yrs | £5,916 |
| 8 kW | 7051 kWh | 2820 kWh | 4231 kWh | £729 | £423 | £1,152 | £16,276 | 14.1 yrs | £6,761 |
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: £860, Upfront: £12,273, 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 | 1763 kWh | 1058 kWh | 705 kWh | £273 | £71 | £344 | £6,169 | 17.9 yrs | £707 |
| 3 kW | 2644 kWh | 1586 kWh | 1058 kWh | £410 | £106 | £516 | £8,204 | 15.9 yrs | £2,111 |
| 4 kW | 3526 kWh | 2115 kWh | 1410 kWh | £547 | £141 | £688 | £10,238 | 14.9 yrs | £3,514 |
| 5 kW | 4407 kWh | 2644 kWh | 1763 kWh | £683 | £176 | £860 | £12,273 | 14.3 yrs | £4,918 |
| 6 kW | 5288 kWh | 3173 kWh | 2115 kWh | £820 | £212 | £1,031 | £14,307 | 13.9 yrs | £6,321 |
| 7 kW | 6170 kWh | 3702 kWh | 2468 kWh | £957 | £247 | £1,203 | £16,342 | 13.6 yrs | £7,725 |
| 8 kW | 7051 kWh | 4231 kWh | 2820 kWh | £1,093 | £282 | £1,375 | £18,376 | 13.4 yrs | £9,129 |
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: £929, Upfront: £13,673, Break-even: 14.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1763 kWh | 1234 kWh | 529 kWh | £319 | £53 | £372 | £7,569 | 20.4 yrs | £-134 |
| 3 kW | 2644 kWh | 1851 kWh | 793 kWh | £478 | £79 | £558 | £9,604 | 17.2 yrs | £1,548 |
| 4 kW | 3526 kWh | 2468 kWh | 1058 kWh | £638 | £106 | £743 | £11,638 | 15.7 yrs | £3,231 |
| 5 kW | 4407 kWh | 3085 kWh | 1322 kWh | £797 | £132 | £929 | £13,673 | 14.7 yrs | £4,914 |
| 6 kW | 5288 kWh | 3702 kWh | 1586 kWh | £957 | £159 | £1,115 | £15,707 | 14.1 yrs | £6,597 |
| 7 kW | 6170 kWh | 4319 kWh | 1851 kWh | £1,116 | £185 | £1,301 | £17,742 | 13.6 yrs | £8,280 |
| 8 kW | 7051 kWh | 4936 kWh | 2115 kWh | £1,275 | £212 | £1,487 | £19,776 | 13.3 yrs | £9,962 |
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: £950, Upfront: £15,423, Break-even: 16.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1763 kWh | 1287 kWh | 476 kWh | £333 | £48 | £380 | £9,319 | 24.5 yrs | £-1,717 |
| 3 kW | 2644 kWh | 1930 kWh | 714 kWh | £499 | £71 | £570 | £11,354 | 19.9 yrs | £50 |
| 4 kW | 3526 kWh | 2574 kWh | 952 kWh | £665 | £95 | £760 | £13,388 | 17.6 yrs | £1,816 |
| 5 kW | 4407 kWh | 3217 kWh | 1190 kWh | £831 | £119 | £950 | £15,423 | 16.2 yrs | £3,583 |
| 6 kW | 5288 kWh | 3860 kWh | 1428 kWh | £998 | £143 | £1,140 | £17,457 | 15.3 yrs | £5,349 |
| 7 kW | 6170 kWh | 4504 kWh | 1666 kWh | £1,164 | £167 | £1,330 | £19,492 | 14.7 yrs | £7,116 |
| 8 kW | 7051 kWh | 5147 kWh | 1904 kWh | £1,330 | £190 | £1,520 | £21,526 | 14.2 yrs | £8,883 |
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: £964, Upfront: £17,173, Break-even: 17.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1763 kWh | 1322 kWh | 441 kWh | £342 | £44 | £386 | £11,069 | 28.7 yrs | £-3,355 |
| 3 kW | 2644 kWh | 1983 kWh | 661 kWh | £512 | £66 | £579 | £13,104 | 22.6 yrs | £-1,533 |
| 4 kW | 3526 kWh | 2644 kWh | 881 kWh | £683 | £88 | £771 | £15,138 | 19.6 yrs | £290 |
| 5 kW | 4407 kWh | 3305 kWh | 1102 kWh | £854 | £110 | £964 | £17,173 | 17.8 yrs | £2,112 |
| 6 kW | 5288 kWh | 3966 kWh | 1322 kWh | £1,025 | £132 | £1,157 | £19,207 | 16.6 yrs | £3,934 |
| 7 kW | 6170 kWh | 4627 kWh | 1542 kWh | £1,196 | £154 | £1,350 | £21,242 | 15.7 yrs | £5,757 |
| 8 kW | 7051 kWh | 5288 kWh | 1763 kWh | £1,366 | £176 | £1,543 | £23,276 | 15.1 yrs | £7,579 |
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: £978, Upfront: £19,623, Break-even: 20.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1763 kWh | 1357 kWh | 405 kWh | £351 | £41 | £391 | £13,519 | 34.6 yrs | £-5,693 |
| 3 kW | 2644 kWh | 2036 kWh | 608 kWh | £526 | £61 | £587 | £15,554 | 26.5 yrs | £-3,815 |
| 4 kW | 3526 kWh | 2715 kWh | 811 kWh | £701 | £81 | £783 | £17,588 | 22.5 yrs | £-1,937 |
| 5 kW | 4407 kWh | 3393 kWh | 1014 kWh | £877 | £101 | £978 | £19,623 | 20.1 yrs | £-59 |
| 6 kW | 5288 kWh | 4072 kWh | 1216 kWh | £1,052 | £122 | £1,174 | £21,657 | 18.4 yrs | £1,820 |
| 7 kW | 6170 kWh | 4751 kWh | 1419 kWh | £1,228 | £142 | £1,369 | £23,692 | 17.3 yrs | £3,698 |
| 8 kW | 7051 kWh | 5429 kWh | 1622 kWh | £1,403 | £162 | £1,565 | £25,726 | 16.4 yrs | £5,576 |
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.