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 995 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: £827, Upfront: £10,173, 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 | 1990 kWh | 796 kWh | 1194 kWh | £211 | £119 | £331 | £4,069 | 12.3 yrs | £2,544 |
| 3 kW | 2986 kWh | 1194 kWh | 1791 kWh | £317 | £179 | £496 | £6,104 | 12.3 yrs | £3,816 |
| 4 kW | 3981 kWh | 1592 kWh | 2389 kWh | £422 | £239 | £661 | £8,138 | 12.3 yrs | £5,088 |
| 5 kW | 4976 kWh | 1990 kWh | 2986 kWh | £528 | £299 | £827 | £10,173 | 12.3 yrs | £6,360 |
| 6 kW | 5971 kWh | 2389 kWh | 3583 kWh | £634 | £358 | £992 | £12,207 | 12.3 yrs | £7,632 |
| 7 kW | 6967 kWh | 2787 kWh | 4180 kWh | £739 | £418 | £1,157 | £14,242 | 12.3 yrs | £8,904 |
| 8 kW | 7962 kWh | 3185 kWh | 4777 kWh | £845 | £478 | £1,323 | £16,276 | 12.3 yrs | £10,176 |
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: £991, Upfront: £12,273, 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 | 1990 kWh | 1194 kWh | 796 kWh | £317 | £80 | £396 | £6,169 | 15.6 yrs | £1,760 |
| 3 kW | 2986 kWh | 1791 kWh | 1194 kWh | £475 | £119 | £595 | £8,204 | 13.8 yrs | £3,690 |
| 4 kW | 3981 kWh | 2389 kWh | 1592 kWh | £634 | £159 | £793 | £10,238 | 12.9 yrs | £5,620 |
| 5 kW | 4976 kWh | 2986 kWh | 1990 kWh | £792 | £199 | £991 | £12,273 | 12.4 yrs | £7,550 |
| 6 kW | 5971 kWh | 3583 kWh | 2389 kWh | £951 | £239 | £1,189 | £14,307 | 12.0 yrs | £9,481 |
| 7 kW | 6967 kWh | 4180 kWh | 2787 kWh | £1,109 | £279 | £1,388 | £16,342 | 11.8 yrs | £11,411 |
| 8 kW | 7962 kWh | 4777 kWh | 3185 kWh | £1,267 | £318 | £1,586 | £18,376 | 11.6 yrs | £13,341 |
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: £1,073, Upfront: £13,673, Break-even: 12.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1990 kWh | 1393 kWh | 597 kWh | £370 | £60 | £429 | £7,569 | 17.6 yrs | £1,018 |
| 3 kW | 2986 kWh | 2090 kWh | 896 kWh | £554 | £90 | £644 | £9,604 | 14.9 yrs | £3,277 |
| 4 kW | 3981 kWh | 2787 kWh | 1194 kWh | £739 | £119 | £859 | £11,638 | 13.6 yrs | £5,536 |
| 5 kW | 4976 kWh | 3483 kWh | 1493 kWh | £924 | £149 | £1,073 | £13,673 | 12.7 yrs | £7,796 |
| 6 kW | 5971 kWh | 4180 kWh | 1791 kWh | £1,109 | £179 | £1,288 | £15,707 | 12.2 yrs | £10,055 |
| 7 kW | 6967 kWh | 4877 kWh | 2090 kWh | £1,294 | £209 | £1,503 | £17,742 | 11.8 yrs | £12,314 |
| 8 kW | 7962 kWh | 5573 kWh | 2389 kWh | £1,479 | £239 | £1,717 | £19,776 | 11.5 yrs | £14,573 |
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: £1,098, Upfront: £15,423, Break-even: 14.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1990 kWh | 1453 kWh | 537 kWh | £385 | £54 | £439 | £9,319 | 21.2 yrs | £-534 |
| 3 kW | 2986 kWh | 2180 kWh | 806 kWh | £578 | £81 | £659 | £11,354 | 17.2 yrs | £1,823 |
| 4 kW | 3981 kWh | 2906 kWh | 1075 kWh | £771 | £107 | £878 | £13,388 | 15.2 yrs | £4,181 |
| 5 kW | 4976 kWh | 3633 kWh | 1344 kWh | £964 | £134 | £1,098 | £15,423 | 14.0 yrs | £6,539 |
| 6 kW | 5971 kWh | 4359 kWh | 1612 kWh | £1,156 | £161 | £1,318 | £17,457 | 13.2 yrs | £8,897 |
| 7 kW | 6967 kWh | 5086 kWh | 1881 kWh | £1,349 | £188 | £1,537 | £19,492 | 12.7 yrs | £11,255 |
| 8 kW | 7962 kWh | 5812 kWh | 2150 kWh | £1,542 | £215 | £1,757 | £21,526 | 12.3 yrs | £13,613 |
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: £1,115, Upfront: £17,173, Break-even: 15.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1990 kWh | 1493 kWh | 498 kWh | £396 | £50 | £446 | £11,069 | 24.8 yrs | £-2,153 |
| 3 kW | 2986 kWh | 2239 kWh | 746 kWh | £594 | £75 | £669 | £13,104 | 19.6 yrs | £271 |
| 4 kW | 3981 kWh | 2986 kWh | 995 kWh | £792 | £100 | £892 | £15,138 | 17.0 yrs | £2,694 |
| 5 kW | 4976 kWh | 3732 kWh | 1244 kWh | £990 | £124 | £1,115 | £17,173 | 15.4 yrs | £5,118 |
| 6 kW | 5971 kWh | 4479 kWh | 1493 kWh | £1,188 | £149 | £1,337 | £19,207 | 14.4 yrs | £7,542 |
| 7 kW | 6967 kWh | 5225 kWh | 1742 kWh | £1,386 | £174 | £1,560 | £21,242 | 13.6 yrs | £9,965 |
| 8 kW | 7962 kWh | 5971 kWh | 1990 kWh | £1,584 | £199 | £1,783 | £23,276 | 13.1 yrs | £12,389 |
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: £1,131, Upfront: £19,623, Break-even: 17.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1990 kWh | 1533 kWh | 458 kWh | £407 | £46 | £452 | £13,519 | 29.9 yrs | £-4,471 |
| 3 kW | 2986 kWh | 2299 kWh | 687 kWh | £610 | £69 | £679 | £15,554 | 22.9 yrs | £-1,982 |
| 4 kW | 3981 kWh | 3065 kWh | 916 kWh | £813 | £92 | £905 | £17,588 | 19.4 yrs | £508 |
| 5 kW | 4976 kWh | 3832 kWh | 1145 kWh | £1,017 | £114 | £1,131 | £19,623 | 17.3 yrs | £2,997 |
| 6 kW | 5971 kWh | 4598 kWh | 1373 kWh | £1,220 | £137 | £1,357 | £21,657 | 16.0 yrs | £5,487 |
| 7 kW | 6967 kWh | 5364 kWh | 1602 kWh | £1,423 | £160 | £1,583 | £23,692 | 15.0 yrs | £7,976 |
| 8 kW | 7962 kWh | 6131 kWh | 1831 kWh | £1,626 | £183 | £1,810 | £25,726 | 14.2 yrs | £10,465 |
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.