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 1031 kWh per year on a south-facing roof. We value self-used electricity at 26.5p 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: £855, Upfront: £10,173, Break-even: 11.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2061 kWh | 825 kWh | 1237 kWh | £218 | £124 | £342 | £4,069 | 11.9 yrs | £2,771 |
| 3 kW | 3092 kWh | 1237 kWh | 1855 kWh | £328 | £186 | £513 | £6,104 | 11.9 yrs | £4,157 |
| 4 kW | 4123 kWh | 1649 kWh | 2474 kWh | £437 | £247 | £684 | £8,138 | 11.9 yrs | £5,543 |
| 5 kW | 5153 kWh | 2061 kWh | 3092 kWh | £546 | £309 | £855 | £10,173 | 11.9 yrs | £6,929 |
| 6 kW | 6184 kWh | 2474 kWh | 3710 kWh | £655 | £371 | £1,026 | £12,207 | 11.9 yrs | £8,314 |
| 7 kW | 7215 kWh | 2886 kWh | 4329 kWh | £764 | £433 | £1,197 | £14,242 | 11.9 yrs | £9,700 |
| 8 kW | 8246 kWh | 3298 kWh | 4947 kWh | £873 | £495 | £1,368 | £16,276 | 11.9 yrs | £11,086 |
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: £1,025, Upfront: £12,273, Break-even: 12.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2061 kWh | 1237 kWh | 825 kWh | £328 | £82 | £410 | £6,169 | 15.0 yrs | £2,030 |
| 3 kW | 3092 kWh | 1855 kWh | 1237 kWh | £491 | £124 | £615 | £8,204 | 13.3 yrs | £4,095 |
| 4 kW | 4123 kWh | 2474 kWh | 1649 kWh | £655 | £165 | £820 | £10,238 | 12.5 yrs | £6,161 |
| 5 kW | 5153 kWh | 3092 kWh | 2061 kWh | £819 | £206 | £1,025 | £12,273 | 12.0 yrs | £8,226 |
| 6 kW | 6184 kWh | 3710 kWh | 2474 kWh | £983 | £247 | £1,230 | £14,307 | 11.6 yrs | £10,291 |
| 7 kW | 7215 kWh | 4329 kWh | 2886 kWh | £1,146 | £289 | £1,435 | £16,342 | 11.4 yrs | £12,356 |
| 8 kW | 8246 kWh | 4947 kWh | 3298 kWh | £1,310 | £330 | £1,640 | £18,376 | 11.2 yrs | £14,421 |
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: £1,110, Upfront: £13,673, Break-even: 12.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2061 kWh | 1443 kWh | 618 kWh | £382 | £62 | £444 | £7,569 | 17.0 yrs | £1,310 |
| 3 kW | 3092 kWh | 2164 kWh | 928 kWh | £573 | £93 | £666 | £9,604 | 14.4 yrs | £3,715 |
| 4 kW | 4123 kWh | 2886 kWh | 1237 kWh | £764 | £124 | £888 | £11,638 | 13.1 yrs | £6,120 |
| 5 kW | 5153 kWh | 3607 kWh | 1546 kWh | £955 | £155 | £1,110 | £13,673 | 12.3 yrs | £8,524 |
| 6 kW | 6184 kWh | 4329 kWh | 1855 kWh | £1,146 | £186 | £1,332 | £15,707 | 11.8 yrs | £10,929 |
| 7 kW | 7215 kWh | 5050 kWh | 2164 kWh | £1,337 | £216 | £1,554 | £17,742 | 11.4 yrs | £13,334 |
| 8 kW | 8246 kWh | 5772 kWh | 2474 kWh | £1,528 | £247 | £1,776 | £19,776 | 11.1 yrs | £15,739 |
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: £1,135, Upfront: £15,423, 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 | 2061 kWh | 1505 kWh | 557 kWh | £398 | £56 | £454 | £9,319 | 20.5 yrs | £-236 |
| 3 kW | 3092 kWh | 2257 kWh | 835 kWh | £598 | £83 | £681 | £11,354 | 16.7 yrs | £2,270 |
| 4 kW | 4123 kWh | 3010 kWh | 1113 kWh | £797 | £111 | £908 | £13,388 | 14.7 yrs | £4,777 |
| 5 kW | 5153 kWh | 3762 kWh | 1391 kWh | £996 | £139 | £1,135 | £15,423 | 13.6 yrs | £7,284 |
| 6 kW | 6184 kWh | 4514 kWh | 1670 kWh | £1,195 | £167 | £1,362 | £17,457 | 12.8 yrs | £9,791 |
| 7 kW | 7215 kWh | 5267 kWh | 1948 kWh | £1,395 | £195 | £1,589 | £19,492 | 12.3 yrs | £12,298 |
| 8 kW | 8246 kWh | 6019 kWh | 2226 kWh | £1,594 | £223 | £1,817 | £21,526 | 11.9 yrs | £14,804 |
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: £1,152, Upfront: £17,173, Break-even: 14.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2061 kWh | 1546 kWh | 515 kWh | £409 | £52 | £461 | £11,069 | 24.0 yrs | £-1,851 |
| 3 kW | 3092 kWh | 2319 kWh | 773 kWh | £614 | £77 | £691 | £13,104 | 19.0 yrs | £724 |
| 4 kW | 4123 kWh | 3092 kWh | 1031 kWh | £819 | £103 | £922 | £15,138 | 16.4 yrs | £3,299 |
| 5 kW | 5153 kWh | 3865 kWh | 1288 kWh | £1,023 | £129 | £1,152 | £17,173 | 14.9 yrs | £5,874 |
| 6 kW | 6184 kWh | 4638 kWh | 1546 kWh | £1,228 | £155 | £1,383 | £19,207 | 13.9 yrs | £8,448 |
| 7 kW | 7215 kWh | 5411 kWh | 1804 kWh | £1,433 | £180 | £1,613 | £21,242 | 13.2 yrs | £11,023 |
| 8 kW | 8246 kWh | 6184 kWh | 2061 kWh | £1,638 | £206 | £1,844 | £23,276 | 12.6 yrs | £13,598 |
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: £1,169, Upfront: £19,623, Break-even: 16.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2061 kWh | 1587 kWh | 474 kWh | £420 | £47 | £468 | £13,519 | 28.9 yrs | £-4,165 |
| 3 kW | 3092 kWh | 2381 kWh | 711 kWh | £630 | £71 | £702 | £15,554 | 22.2 yrs | £-1,522 |
| 4 kW | 4123 kWh | 3175 kWh | 948 kWh | £841 | £95 | £935 | £17,588 | 18.8 yrs | £1,121 |
| 5 kW | 5153 kWh | 3968 kWh | 1185 kWh | £1,051 | £119 | £1,169 | £19,623 | 16.8 yrs | £3,763 |
| 6 kW | 6184 kWh | 4762 kWh | 1422 kWh | £1,261 | £142 | £1,403 | £21,657 | 15.4 yrs | £6,406 |
| 7 kW | 7215 kWh | 5555 kWh | 1659 kWh | £1,471 | £166 | £1,637 | £23,692 | 14.5 yrs | £9,049 |
| 8 kW | 8246 kWh | 6349 kWh | 1896 kWh | £1,681 | £190 | £1,871 | £25,726 | 13.8 yrs | £11,691 |
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.