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 880 kWh per year on a south-facing roof. We value self-used electricity at 27.1p 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: £740, 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 | 1760 kWh | 704 kWh | 1056 kWh | £191 | £106 | £296 | £4,069 | 13.7 yrs | £1,855 |
| 3 kW | 2641 kWh | 1056 kWh | 1584 kWh | £286 | £158 | £444 | £6,104 | 13.7 yrs | £2,782 |
| 4 kW | 3521 kWh | 1408 kWh | 2113 kWh | £381 | £211 | £592 | £8,138 | 13.7 yrs | £3,709 |
| 5 kW | 4401 kWh | 1760 kWh | 2641 kWh | £476 | £264 | £740 | £10,173 | 13.7 yrs | £4,636 |
| 6 kW | 5281 kWh | 2113 kWh | 3169 kWh | £572 | £317 | £889 | £12,207 | 13.7 yrs | £5,564 |
| 7 kW | 6162 kWh | 2465 kWh | 3697 kWh | £667 | £370 | £1,037 | £14,242 | 13.7 yrs | £6,491 |
| 8 kW | 7042 kWh | 2817 kWh | 4225 kWh | £762 | £423 | £1,185 | £16,276 | 13.7 yrs | £7,418 |
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: £891, Upfront: £12,273, Break-even: 13.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1760 kWh | 1056 kWh | 704 kWh | £286 | £70 | £356 | £6,169 | 17.3 yrs | £956 |
| 3 kW | 2641 kWh | 1584 kWh | 1056 kWh | £429 | £106 | £534 | £8,204 | 15.4 yrs | £2,484 |
| 4 kW | 3521 kWh | 2113 kWh | 1408 kWh | £572 | £141 | £712 | £10,238 | 14.4 yrs | £4,012 |
| 5 kW | 4401 kWh | 2641 kWh | 1760 kWh | £715 | £176 | £891 | £12,273 | 13.8 yrs | £5,540 |
| 6 kW | 5281 kWh | 3169 kWh | 2113 kWh | £857 | £211 | £1,069 | £14,307 | 13.4 yrs | £7,067 |
| 7 kW | 6162 kWh | 3697 kWh | 2465 kWh | £1,000 | £246 | £1,247 | £16,342 | 13.1 yrs | £8,595 |
| 8 kW | 7042 kWh | 4225 kWh | 2817 kWh | £1,143 | £282 | £1,425 | £18,376 | 12.9 yrs | £10,123 |
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: £966, Upfront: £13,673, Break-even: 14.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1760 kWh | 1232 kWh | 528 kWh | £333 | £53 | £386 | £7,569 | 19.6 yrs | £156 |
| 3 kW | 2641 kWh | 1848 kWh | 792 kWh | £500 | £79 | £579 | £9,604 | 16.6 yrs | £1,985 |
| 4 kW | 3521 kWh | 2465 kWh | 1056 kWh | £667 | £106 | £773 | £11,638 | 15.1 yrs | £3,813 |
| 5 kW | 4401 kWh | 3081 kWh | 1320 kWh | £834 | £132 | £966 | £13,673 | 14.2 yrs | £5,641 |
| 6 kW | 5281 kWh | 3697 kWh | 1584 kWh | £1,000 | £158 | £1,159 | £15,707 | 13.6 yrs | £7,469 |
| 7 kW | 6162 kWh | 4313 kWh | 1848 kWh | £1,167 | £185 | £1,352 | £17,742 | 13.1 yrs | £9,298 |
| 8 kW | 7042 kWh | 4929 kWh | 2113 kWh | £1,334 | £211 | £1,545 | £19,776 | 12.8 yrs | £11,126 |
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: £988, Upfront: £15,423, Break-even: 15.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1760 kWh | 1285 kWh | 475 kWh | £348 | £48 | £395 | £9,319 | 23.6 yrs | £-1,413 |
| 3 kW | 2641 kWh | 1928 kWh | 713 kWh | £522 | £71 | £593 | £11,354 | 19.1 yrs | £505 |
| 4 kW | 3521 kWh | 2570 kWh | 951 kWh | £696 | £95 | £791 | £13,388 | 16.9 yrs | £2,423 |
| 5 kW | 4401 kWh | 3213 kWh | 1188 kWh | £869 | £119 | £988 | £15,423 | 15.6 yrs | £4,342 |
| 6 kW | 5281 kWh | 3855 kWh | 1426 kWh | £1,043 | £143 | £1,186 | £17,457 | 14.7 yrs | £6,260 |
| 7 kW | 6162 kWh | 4498 kWh | 1664 kWh | £1,217 | £166 | £1,383 | £19,492 | 14.1 yrs | £8,178 |
| 8 kW | 7042 kWh | 5140 kWh | 1901 kWh | £1,391 | £190 | £1,581 | £21,526 | 13.6 yrs | £10,097 |
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: £1,003, Upfront: £17,173, Break-even: 17.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1760 kWh | 1320 kWh | 440 kWh | £357 | £44 | £401 | £11,069 | 27.6 yrs | £-3,043 |
| 3 kW | 2641 kWh | 1980 kWh | 660 kWh | £536 | £66 | £602 | £13,104 | 21.8 yrs | £-1,065 |
| 4 kW | 3521 kWh | 2641 kWh | 880 kWh | £715 | £88 | £803 | £15,138 | 18.9 yrs | £914 |
| 5 kW | 4401 kWh | 3301 kWh | 1100 kWh | £893 | £110 | £1,003 | £17,173 | 17.1 yrs | £2,892 |
| 6 kW | 5281 kWh | 3961 kWh | 1320 kWh | £1,072 | £132 | £1,204 | £19,207 | 16.0 yrs | £4,870 |
| 7 kW | 6162 kWh | 4621 kWh | 1540 kWh | £1,250 | £154 | £1,405 | £21,242 | 15.1 yrs | £6,849 |
| 8 kW | 7042 kWh | 5281 kWh | 1760 kWh | £1,429 | £176 | £1,605 | £23,276 | 14.5 yrs | £8,827 |
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: £1,018, Upfront: £19,623, Break-even: 19.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1760 kWh | 1356 kWh | 405 kWh | £367 | £40 | £407 | £13,519 | 33.2 yrs | £-5,373 |
| 3 kW | 2641 kWh | 2033 kWh | 607 kWh | £550 | £61 | £611 | £15,554 | 25.5 yrs | £-3,335 |
| 4 kW | 3521 kWh | 2711 kWh | 810 kWh | £734 | £81 | £815 | £17,588 | 21.6 yrs | £-1,296 |
| 5 kW | 4401 kWh | 3389 kWh | 1012 kWh | £917 | £101 | £1,018 | £19,623 | 19.3 yrs | £742 |
| 6 kW | 5281 kWh | 4067 kWh | 1215 kWh | £1,100 | £121 | £1,222 | £21,657 | 17.7 yrs | £2,781 |
| 7 kW | 6162 kWh | 4744 kWh | 1417 kWh | £1,284 | £142 | £1,426 | £23,692 | 16.6 yrs | £4,819 |
| 8 kW | 7042 kWh | 5422 kWh | 1620 kWh | £1,467 | £162 | £1,629 | £25,726 | 15.8 yrs | £6,858 |
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.