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 832 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: £679, Upfront: £10,173, Break-even: 15.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1663 kWh | 665 kWh | 998 kWh | £172 | £100 | £272 | £4,069 | 15.0 yrs | £1,366 |
| 3 kW | 2495 kWh | 998 kWh | 1497 kWh | £258 | £150 | £408 | £6,104 | 15.0 yrs | £2,048 |
| 4 kW | 3327 kWh | 1331 kWh | 1996 kWh | £344 | £200 | £543 | £8,138 | 15.0 yrs | £2,731 |
| 5 kW | 4158 kWh | 1663 kWh | 2495 kWh | £430 | £250 | £679 | £10,173 | 15.0 yrs | £3,414 |
| 6 kW | 4990 kWh | 1996 kWh | 2994 kWh | £516 | £299 | £815 | £12,207 | 15.0 yrs | £4,097 |
| 7 kW | 5822 kWh | 2329 kWh | 3493 kWh | £602 | £349 | £951 | £14,242 | 15.0 yrs | £4,780 |
| 8 kW | 6654 kWh | 2661 kWh | 3992 kWh | £688 | £399 | £1,087 | £16,276 | 15.0 yrs | £5,463 |
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: £811, Upfront: £12,273, 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 | 1663 kWh | 998 kWh | 665 kWh | £258 | £67 | £324 | £6,169 | 19.0 yrs | £320 |
| 3 kW | 2495 kWh | 1497 kWh | 998 kWh | £387 | £100 | £487 | £8,204 | 16.9 yrs | £1,529 |
| 4 kW | 3327 kWh | 1996 kWh | 1331 kWh | £516 | £133 | £649 | £10,238 | 15.8 yrs | £2,739 |
| 5 kW | 4158 kWh | 2495 kWh | 1663 kWh | £645 | £166 | £811 | £12,273 | 15.1 yrs | £3,949 |
| 6 kW | 4990 kWh | 2994 kWh | 1996 kWh | £774 | £200 | £973 | £14,307 | 14.7 yrs | £5,159 |
| 7 kW | 5822 kWh | 3493 kWh | 2329 kWh | £903 | £233 | £1,136 | £16,342 | 14.4 yrs | £6,368 |
| 8 kW | 6654 kWh | 3992 kWh | 2661 kWh | £1,032 | £266 | £1,298 | £18,376 | 14.2 yrs | £7,578 |
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 | 1663 kWh | 1164 kWh | 499 kWh | £301 | £50 | £351 | £7,569 | 21.6 yrs | £-553 |
| 3 kW | 2495 kWh | 1747 kWh | 749 kWh | £451 | £75 | £526 | £9,604 | 18.3 yrs | £920 |
| 4 kW | 3327 kWh | 2329 kWh | 998 kWh | £602 | £100 | £702 | £11,638 | 16.6 yrs | £2,393 |
| 5 kW | 4158 kWh | 2911 kWh | 1248 kWh | £752 | £125 | £877 | £13,673 | 15.6 yrs | £3,866 |
| 6 kW | 4990 kWh | 3493 kWh | 1497 kWh | £903 | £150 | £1,052 | £15,707 | 14.9 yrs | £5,340 |
| 7 kW | 5822 kWh | 4075 kWh | 1747 kWh | £1,053 | £175 | £1,228 | £17,742 | 14.5 yrs | £6,813 |
| 8 kW | 6654 kWh | 4658 kWh | 1996 kWh | £1,204 | £200 | £1,403 | £19,776 | 14.1 yrs | £8,286 |
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 | 1663 kWh | 1214 kWh | 449 kWh | £314 | £45 | £359 | £9,319 | 26.0 yrs | £-2,145 |
| 3 kW | 2495 kWh | 1821 kWh | 674 kWh | £471 | £67 | £538 | £11,354 | 21.1 yrs | £-593 |
| 4 kW | 3327 kWh | 2429 kWh | 898 kWh | £628 | £90 | £717 | £13,388 | 18.7 yrs | £959 |
| 5 kW | 4158 kWh | 3036 kWh | 1123 kWh | £784 | £112 | £897 | £15,423 | 17.2 yrs | £2,512 |
| 6 kW | 4990 kWh | 3643 kWh | 1347 kWh | £941 | £135 | £1,076 | £17,457 | 16.2 yrs | £4,064 |
| 7 kW | 5822 kWh | 4250 kWh | 1572 kWh | £1,098 | £157 | £1,255 | £19,492 | 15.5 yrs | £5,616 |
| 8 kW | 6654 kWh | 4857 kWh | 1796 kWh | £1,255 | £180 | £1,435 | £21,526 | 15.0 yrs | £7,169 |
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: £910, 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 | 1663 kWh | 1248 kWh | 416 kWh | £322 | £42 | £364 | £11,069 | 30.4 yrs | £-3,790 |
| 3 kW | 2495 kWh | 1871 kWh | 624 kWh | £484 | £62 | £546 | £13,104 | 24.0 yrs | £-2,185 |
| 4 kW | 3327 kWh | 2495 kWh | 832 kWh | £645 | £83 | £728 | £15,138 | 20.8 yrs | £-580 |
| 5 kW | 4158 kWh | 3119 kWh | 1040 kWh | £806 | £104 | £910 | £17,173 | 18.9 yrs | £1,025 |
| 6 kW | 4990 kWh | 3743 kWh | 1248 kWh | £967 | £125 | £1,092 | £19,207 | 17.6 yrs | £2,630 |
| 7 kW | 5822 kWh | 4366 kWh | 1455 kWh | £1,128 | £146 | £1,274 | £21,242 | 16.7 yrs | £4,235 |
| 8 kW | 6654 kWh | 4990 kWh | 1663 kWh | £1,289 | £166 | £1,456 | £23,276 | 16.0 yrs | £5,840 |
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: £923, Upfront: £19,623, Break-even: 21.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1663 kWh | 1281 kWh | 383 kWh | £331 | £38 | £369 | £13,519 | 36.6 yrs | £-6,135 |
| 3 kW | 2495 kWh | 1921 kWh | 574 kWh | £496 | £57 | £554 | £15,554 | 28.1 yrs | £-4,477 |
| 4 kW | 3327 kWh | 2562 kWh | 765 kWh | £662 | £77 | £738 | £17,588 | 23.8 yrs | £-2,819 |
| 5 kW | 4158 kWh | 3202 kWh | 956 kWh | £827 | £96 | £923 | £19,623 | 21.3 yrs | £-1,161 |
| 6 kW | 4990 kWh | 3842 kWh | 1148 kWh | £993 | £115 | £1,108 | £21,657 | 19.6 yrs | £496 |
| 7 kW | 5822 kWh | 4483 kWh | 1339 kWh | £1,158 | £134 | £1,292 | £23,692 | 18.3 yrs | £2,154 |
| 8 kW | 6654 kWh | 5123 kWh | 1530 kWh | £1,324 | £153 | £1,477 | £25,726 | 17.4 yrs | £3,812 |
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.