A typical roof here lands around 4.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 990 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: £822, Upfront: £10,173, Break-even: 12.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1979 kWh | 792 kWh | 1188 kWh | £210 | £119 | £329 | £4,069 | 12.4 yrs | £2,507 |
| 3 kW | 2969 kWh | 1188 kWh | 1781 kWh | £315 | £178 | £493 | £6,104 | 12.4 yrs | £3,761 |
| 4 kW | 3959 kWh | 1584 kWh | 2375 kWh | £420 | £238 | £658 | £8,138 | 12.4 yrs | £5,015 |
| 5 kW | 4948 kWh | 1979 kWh | 2969 kWh | £525 | £297 | £822 | £10,173 | 12.4 yrs | £6,268 |
| 6 kW | 5938 kWh | 2375 kWh | 3563 kWh | £630 | £356 | £986 | £12,207 | 12.4 yrs | £7,522 |
| 7 kW | 6928 kWh | 2771 kWh | 4157 kWh | £735 | £416 | £1,151 | £14,242 | 12.4 yrs | £8,775 |
| 8 kW | 7918 kWh | 3167 kWh | 4751 kWh | £840 | £475 | £1,315 | £16,276 | 12.4 yrs | £10,029 |
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: £986, Upfront: £12,273, Break-even: 12.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1979 kWh | 1188 kWh | 792 kWh | £315 | £79 | £394 | £6,169 | 15.6 yrs | £1,716 |
| 3 kW | 2969 kWh | 1781 kWh | 1188 kWh | £473 | £119 | £591 | £8,204 | 13.9 yrs | £3,624 |
| 4 kW | 3959 kWh | 2375 kWh | 1584 kWh | £630 | £158 | £789 | £10,238 | 13.0 yrs | £5,532 |
| 5 kW | 4948 kWh | 2969 kWh | 1979 kWh | £788 | £198 | £986 | £12,273 | 12.5 yrs | £7,440 |
| 6 kW | 5938 kWh | 3563 kWh | 2375 kWh | £945 | £238 | £1,183 | £14,307 | 12.1 yrs | £9,348 |
| 7 kW | 6928 kWh | 4157 kWh | 2771 kWh | £1,103 | £277 | £1,380 | £16,342 | 11.8 yrs | £11,256 |
| 8 kW | 7918 kWh | 4751 kWh | 3167 kWh | £1,260 | £317 | £1,577 | £18,376 | 11.7 yrs | £13,164 |
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: £1,067, Upfront: £13,673, Break-even: 12.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1979 kWh | 1386 kWh | 594 kWh | £368 | £59 | £427 | £7,569 | 17.7 yrs | £970 |
| 3 kW | 2969 kWh | 2078 kWh | 891 kWh | £551 | £89 | £640 | £9,604 | 15.0 yrs | £3,206 |
| 4 kW | 3959 kWh | 2771 kWh | 1188 kWh | £735 | £119 | £854 | £11,638 | 13.6 yrs | £5,441 |
| 5 kW | 4948 kWh | 3464 kWh | 1485 kWh | £919 | £148 | £1,067 | £13,673 | 12.8 yrs | £7,676 |
| 6 kW | 5938 kWh | 4157 kWh | 1781 kWh | £1,103 | £178 | £1,281 | £15,707 | 12.3 yrs | £9,911 |
| 7 kW | 6928 kWh | 4849 kWh | 2078 kWh | £1,287 | £208 | £1,494 | £17,742 | 11.9 yrs | £12,146 |
| 8 kW | 7918 kWh | 5542 kWh | 2375 kWh | £1,470 | £238 | £1,708 | £19,776 | 11.6 yrs | £14,382 |
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: £1,092, Upfront: £15,423, 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 | 1979 kWh | 1445 kWh | 534 kWh | £383 | £53 | £437 | £9,319 | 21.3 yrs | £-583 |
| 3 kW | 2969 kWh | 2167 kWh | 802 kWh | £575 | £80 | £655 | £11,354 | 17.3 yrs | £1,750 |
| 4 kW | 3959 kWh | 2890 kWh | 1069 kWh | £767 | £107 | £874 | £13,388 | 15.3 yrs | £4,083 |
| 5 kW | 4948 kWh | 3612 kWh | 1336 kWh | £958 | £134 | £1,092 | £15,423 | 14.1 yrs | £6,417 |
| 6 kW | 5938 kWh | 4335 kWh | 1603 kWh | £1,150 | £160 | £1,310 | £17,457 | 13.3 yrs | £8,750 |
| 7 kW | 6928 kWh | 5057 kWh | 1871 kWh | £1,342 | £187 | £1,529 | £19,492 | 12.7 yrs | £11,084 |
| 8 kW | 7918 kWh | 5780 kWh | 2138 kWh | £1,533 | £214 | £1,747 | £21,526 | 12.3 yrs | £13,417 |
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: £1,108, Upfront: £17,173, Break-even: 15.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1979 kWh | 1485 kWh | 495 kWh | £394 | £49 | £443 | £11,069 | 25.0 yrs | £-2,202 |
| 3 kW | 2969 kWh | 2227 kWh | 742 kWh | £591 | £74 | £665 | £13,104 | 19.7 yrs | £196 |
| 4 kW | 3959 kWh | 2969 kWh | 990 kWh | £788 | £99 | £887 | £15,138 | 17.1 yrs | £2,595 |
| 5 kW | 4948 kWh | 3711 kWh | 1237 kWh | £985 | £124 | £1,108 | £17,173 | 15.5 yrs | £4,994 |
| 6 kW | 5938 kWh | 4454 kWh | 1485 kWh | £1,182 | £148 | £1,330 | £19,207 | 14.4 yrs | £7,393 |
| 7 kW | 6928 kWh | 5196 kWh | 1732 kWh | £1,378 | £173 | £1,552 | £21,242 | 13.7 yrs | £9,792 |
| 8 kW | 7918 kWh | 5938 kWh | 1979 kWh | £1,575 | £198 | £1,773 | £23,276 | 13.1 yrs | £12,190 |
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: £1,125, Upfront: £19,623, Break-even: 17.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1979 kWh | 1524 kWh | 455 kWh | £404 | £46 | £450 | £13,519 | 30.1 yrs | £-4,522 |
| 3 kW | 2969 kWh | 2286 kWh | 683 kWh | £607 | £68 | £675 | £15,554 | 23.0 yrs | £-2,057 |
| 4 kW | 3959 kWh | 3048 kWh | 911 kWh | £809 | £91 | £900 | £17,588 | 19.5 yrs | £407 |
| 5 kW | 4948 kWh | 3810 kWh | 1138 kWh | £1,011 | £114 | £1,125 | £19,623 | 17.4 yrs | £2,871 |
| 6 kW | 5938 kWh | 4572 kWh | 1366 kWh | £1,213 | £137 | £1,350 | £21,657 | 16.0 yrs | £5,335 |
| 7 kW | 6928 kWh | 5334 kWh | 1593 kWh | £1,415 | £159 | £1,575 | £23,692 | 15.0 yrs | £7,800 |
| 8 kW | 7918 kWh | 6096 kWh | 1821 kWh | £1,617 | £182 | £1,800 | £25,726 | 14.3 yrs | £10,264 |
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.