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 799 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: £672, Upfront: £10,173, Break-even: 15.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1598 kWh | 639 kWh | 959 kWh | £173 | £96 | £269 | £4,069 | 15.1 yrs | £1,308 |
| 3 kW | 2397 kWh | 959 kWh | 1438 kWh | £259 | £144 | £403 | £6,104 | 15.1 yrs | £1,961 |
| 4 kW | 3196 kWh | 1278 kWh | 1917 kWh | £346 | £192 | £538 | £8,138 | 15.1 yrs | £2,615 |
| 5 kW | 3995 kWh | 1598 kWh | 2397 kWh | £432 | £240 | £672 | £10,173 | 15.1 yrs | £3,269 |
| 6 kW | 4794 kWh | 1917 kWh | 2876 kWh | £519 | £288 | £806 | £12,207 | 15.1 yrs | £3,923 |
| 7 kW | 5593 kWh | 2237 kWh | 3356 kWh | £605 | £336 | £941 | £14,242 | 15.1 yrs | £4,577 |
| 8 kW | 6392 kWh | 2557 kWh | 3835 kWh | £692 | £383 | £1,075 | £16,276 | 15.1 yrs | £5,230 |
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: £808, Upfront: £12,273, Break-even: 15.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1598 kWh | 959 kWh | 639 kWh | £259 | £64 | £323 | £6,169 | 19.1 yrs | £298 |
| 3 kW | 2397 kWh | 1438 kWh | 959 kWh | £389 | £96 | £485 | £8,204 | 16.9 yrs | £1,497 |
| 4 kW | 3196 kWh | 1917 kWh | 1278 kWh | £519 | £128 | £647 | £10,238 | 15.8 yrs | £2,696 |
| 5 kW | 3995 kWh | 2397 kWh | 1598 kWh | £649 | £160 | £808 | £12,273 | 15.2 yrs | £3,895 |
| 6 kW | 4794 kWh | 2876 kWh | 1917 kWh | £778 | £192 | £970 | £14,307 | 14.7 yrs | £5,094 |
| 7 kW | 5593 kWh | 3356 kWh | 2237 kWh | £908 | £224 | £1,132 | £16,342 | 14.4 yrs | £6,293 |
| 8 kW | 6392 kWh | 3835 kWh | 2557 kWh | £1,038 | £256 | £1,293 | £18,376 | 14.2 yrs | £7,492 |
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: £877, Upfront: £13,673, 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 | 1598 kWh | 1119 kWh | 479 kWh | £303 | £48 | £351 | £7,569 | 21.6 yrs | £-557 |
| 3 kW | 2397 kWh | 1678 kWh | 719 kWh | £454 | £72 | £526 | £9,604 | 18.3 yrs | £915 |
| 4 kW | 3196 kWh | 2237 kWh | 959 kWh | £605 | £96 | £701 | £11,638 | 16.6 yrs | £2,386 |
| 5 kW | 3995 kWh | 2796 kWh | 1198 kWh | £757 | £120 | £877 | £13,673 | 15.6 yrs | £3,858 |
| 6 kW | 4794 kWh | 3356 kWh | 1438 kWh | £908 | £144 | £1,052 | £15,707 | 14.9 yrs | £5,330 |
| 7 kW | 5593 kWh | 3915 kWh | 1678 kWh | £1,059 | £168 | £1,227 | £17,742 | 14.5 yrs | £6,801 |
| 8 kW | 6392 kWh | 4474 kWh | 1917 kWh | £1,211 | £192 | £1,402 | £19,776 | 14.1 yrs | £8,273 |
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: £897, Upfront: £15,423, Break-even: 17.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1598 kWh | 1166 kWh | 431 kWh | £316 | £43 | £359 | £9,319 | 26.0 yrs | £-2,143 |
| 3 kW | 2397 kWh | 1750 kWh | 647 kWh | £473 | £65 | £538 | £11,354 | 21.1 yrs | £-590 |
| 4 kW | 3196 kWh | 2333 kWh | 863 kWh | £631 | £86 | £718 | £13,388 | 18.7 yrs | £964 |
| 5 kW | 3995 kWh | 2916 kWh | 1079 kWh | £789 | £108 | £897 | £15,423 | 17.2 yrs | £2,517 |
| 6 kW | 4794 kWh | 3499 kWh | 1294 kWh | £947 | £129 | £1,076 | £17,457 | 16.2 yrs | £4,070 |
| 7 kW | 5593 kWh | 4083 kWh | 1510 kWh | £1,105 | £151 | £1,256 | £19,492 | 15.5 yrs | £5,624 |
| 8 kW | 6392 kWh | 4666 kWh | 1726 kWh | £1,263 | £173 | £1,435 | £21,526 | 15.0 yrs | £7,177 |
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: £911, Upfront: £17,173, Break-even: 18.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1598 kWh | 1198 kWh | 399 kWh | £324 | £40 | £364 | £11,069 | 30.4 yrs | £-3,784 |
| 3 kW | 2397 kWh | 1798 kWh | 599 kWh | £486 | £60 | £546 | £13,104 | 24.0 yrs | £-2,176 |
| 4 kW | 3196 kWh | 2397 kWh | 799 kWh | £649 | £80 | £728 | £15,138 | 20.8 yrs | £-568 |
| 5 kW | 3995 kWh | 2996 kWh | 999 kWh | £811 | £100 | £911 | £17,173 | 18.9 yrs | £1,040 |
| 6 kW | 4794 kWh | 3595 kWh | 1198 kWh | £973 | £120 | £1,093 | £19,207 | 17.6 yrs | £2,647 |
| 7 kW | 5593 kWh | 4194 kWh | 1398 kWh | £1,135 | £140 | £1,275 | £21,242 | 16.7 yrs | £4,255 |
| 8 kW | 6392 kWh | 4794 kWh | 1598 kWh | £1,297 | £160 | £1,457 | £23,276 | 16.0 yrs | £5,863 |
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: £924, Upfront: £19,623, Break-even: 21.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1598 kWh | 1230 kWh | 368 kWh | £333 | £37 | £370 | £13,519 | 36.6 yrs | £-6,125 |
| 3 kW | 2397 kWh | 1846 kWh | 551 kWh | £499 | £55 | £555 | £15,554 | 28.0 yrs | £-4,463 |
| 4 kW | 3196 kWh | 2461 kWh | 735 kWh | £666 | £74 | £739 | £17,588 | 23.8 yrs | £-2,800 |
| 5 kW | 3995 kWh | 3076 kWh | 919 kWh | £832 | £92 | £924 | £19,623 | 21.2 yrs | £-1,138 |
| 6 kW | 4794 kWh | 3691 kWh | 1103 kWh | £999 | £110 | £1,109 | £21,657 | 19.5 yrs | £525 |
| 7 kW | 5593 kWh | 4306 kWh | 1286 kWh | £1,165 | £129 | £1,294 | £23,692 | 18.3 yrs | £2,187 |
| 8 kW | 6392 kWh | 4922 kWh | 1470 kWh | £1,332 | £147 | £1,479 | £25,726 | 17.4 yrs | £3,849 |
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.