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 1038 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: £863, Upfront: £10,173, Break-even: 11.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2077 kWh | 831 kWh | 1246 kWh | £220 | £125 | £345 | £4,069 | 11.8 yrs | £2,831 |
| 3 kW | 3115 kWh | 1246 kWh | 1869 kWh | £331 | £187 | £518 | £6,104 | 11.8 yrs | £4,247 |
| 4 kW | 4154 kWh | 1661 kWh | 2492 kWh | £441 | £249 | £690 | £8,138 | 11.8 yrs | £5,662 |
| 5 kW | 5192 kWh | 2077 kWh | 3115 kWh | £551 | £312 | £863 | £10,173 | 11.8 yrs | £7,078 |
| 6 kW | 6230 kWh | 2492 kWh | 3738 kWh | £661 | £374 | £1,035 | £12,207 | 11.8 yrs | £8,493 |
| 7 kW | 7269 kWh | 2908 kWh | 4361 kWh | £771 | £436 | £1,208 | £14,242 | 11.8 yrs | £9,909 |
| 8 kW | 8307 kWh | 3323 kWh | 4984 kWh | £882 | £498 | £1,380 | £16,276 | 11.8 yrs | £11,324 |
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: £1,034, Upfront: £12,273, 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 | 2077 kWh | 1246 kWh | 831 kWh | £331 | £83 | £414 | £6,169 | 14.9 yrs | £2,104 |
| 3 kW | 3115 kWh | 1869 kWh | 1246 kWh | £496 | £125 | £620 | £8,204 | 13.2 yrs | £4,206 |
| 4 kW | 4154 kWh | 2492 kWh | 1661 kWh | £661 | £166 | £827 | £10,238 | 12.4 yrs | £6,308 |
| 5 kW | 5192 kWh | 3115 kWh | 2077 kWh | £826 | £208 | £1,034 | £12,273 | 11.9 yrs | £8,411 |
| 6 kW | 6230 kWh | 3738 kWh | 2492 kWh | £992 | £249 | £1,241 | £14,307 | 11.5 yrs | £10,513 |
| 7 kW | 7269 kWh | 4361 kWh | 2908 kWh | £1,157 | £291 | £1,448 | £16,342 | 11.3 yrs | £12,615 |
| 8 kW | 8307 kWh | 4984 kWh | 3323 kWh | £1,322 | £332 | £1,655 | £18,376 | 11.1 yrs | £14,717 |
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: £1,120, Upfront: £13,673, Break-even: 12.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2077 kWh | 1454 kWh | 623 kWh | £386 | £62 | £448 | £7,569 | 16.9 yrs | £1,391 |
| 3 kW | 3115 kWh | 2181 kWh | 935 kWh | £579 | £93 | £672 | £9,604 | 14.3 yrs | £3,836 |
| 4 kW | 4154 kWh | 2908 kWh | 1246 kWh | £771 | £125 | £896 | £11,638 | 13.0 yrs | £6,282 |
| 5 kW | 5192 kWh | 3634 kWh | 1558 kWh | £964 | £156 | £1,120 | £13,673 | 12.2 yrs | £8,727 |
| 6 kW | 6230 kWh | 4361 kWh | 1869 kWh | £1,157 | £187 | £1,344 | £15,707 | 11.7 yrs | £11,172 |
| 7 kW | 7269 kWh | 5088 kWh | 2181 kWh | £1,350 | £218 | £1,568 | £17,742 | 11.3 yrs | £13,618 |
| 8 kW | 8307 kWh | 5815 kWh | 2492 kWh | £1,543 | £249 | £1,792 | £19,776 | 11.0 yrs | £16,063 |
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: £1,146, Upfront: £15,423, Break-even: 13.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2077 kWh | 1516 kWh | 561 kWh | £402 | £56 | £458 | £9,319 | 20.3 yrs | £-153 |
| 3 kW | 3115 kWh | 2274 kWh | 841 kWh | £603 | £84 | £687 | £11,354 | 16.5 yrs | £2,395 |
| 4 kW | 4154 kWh | 3032 kWh | 1121 kWh | £804 | £112 | £917 | £13,388 | 14.6 yrs | £4,944 |
| 5 kW | 5192 kWh | 3790 kWh | 1402 kWh | £1,006 | £140 | £1,146 | £15,423 | 13.5 yrs | £7,492 |
| 6 kW | 6230 kWh | 4548 kWh | 1682 kWh | £1,207 | £168 | £1,375 | £17,457 | 12.7 yrs | £10,040 |
| 7 kW | 7269 kWh | 5306 kWh | 1963 kWh | £1,408 | £196 | £1,604 | £19,492 | 12.2 yrs | £12,589 |
| 8 kW | 8307 kWh | 6064 kWh | 2243 kWh | £1,609 | £224 | £1,833 | £21,526 | 11.7 yrs | £15,137 |
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: £1,163, Upfront: £17,173, Break-even: 14.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2077 kWh | 1558 kWh | 519 kWh | £413 | £52 | £465 | £11,069 | 23.8 yrs | £-1,766 |
| 3 kW | 3115 kWh | 2336 kWh | 779 kWh | £620 | £78 | £698 | £13,104 | 18.8 yrs | £851 |
| 4 kW | 4154 kWh | 3115 kWh | 1038 kWh | £826 | £104 | £930 | £15,138 | 16.3 yrs | £3,468 |
| 5 kW | 5192 kWh | 3894 kWh | 1298 kWh | £1,033 | £130 | £1,163 | £17,173 | 14.8 yrs | £6,085 |
| 6 kW | 6230 kWh | 4673 kWh | 1558 kWh | £1,240 | £156 | £1,395 | £19,207 | 13.8 yrs | £8,702 |
| 7 kW | 7269 kWh | 5452 kWh | 1817 kWh | £1,446 | £182 | £1,628 | £21,242 | 13.0 yrs | £11,319 |
| 8 kW | 8307 kWh | 6230 kWh | 2077 kWh | £1,653 | £208 | £1,861 | £23,276 | 12.5 yrs | £13,936 |
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: £1,180, Upfront: £19,623, Break-even: 16.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2077 kWh | 1599 kWh | 478 kWh | £424 | £48 | £472 | £13,519 | 28.6 yrs | £-4,079 |
| 3 kW | 3115 kWh | 2399 kWh | 717 kWh | £636 | £72 | £708 | £15,554 | 22.0 yrs | £-1,393 |
| 4 kW | 4154 kWh | 3198 kWh | 955 kWh | £849 | £96 | £944 | £17,588 | 18.6 yrs | £1,293 |
| 5 kW | 5192 kWh | 3998 kWh | 1194 kWh | £1,061 | £119 | £1,180 | £19,623 | 16.6 yrs | £3,979 |
| 6 kW | 6230 kWh | 4797 kWh | 1433 kWh | £1,273 | £143 | £1,416 | £21,657 | 15.3 yrs | £6,664 |
| 7 kW | 7269 kWh | 5597 kWh | 1672 kWh | £1,485 | £167 | £1,652 | £23,692 | 14.3 yrs | £9,350 |
| 8 kW | 8307 kWh | 6397 kWh | 1911 kWh | £1,697 | £191 | £1,888 | £25,726 | 13.6 yrs | £12,036 |
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.