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 978 kWh per year on a south-facing roof. We value self-used electricity at 26.8p 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: £818, 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 | 1955 kWh | 782 kWh | 1173 kWh | £210 | £117 | £327 | £4,069 | 12.4 yrs | £2,473 |
| 3 kW | 2933 kWh | 1173 kWh | 1760 kWh | £315 | £176 | £491 | £6,104 | 12.4 yrs | £3,710 |
| 4 kW | 3911 kWh | 1564 kWh | 2347 kWh | £420 | £235 | £654 | £8,138 | 12.4 yrs | £4,946 |
| 5 kW | 4889 kWh | 1955 kWh | 2933 kWh | £524 | £293 | £818 | £10,173 | 12.4 yrs | £6,183 |
| 6 kW | 5866 kWh | 2347 kWh | 3520 kWh | £629 | £352 | £981 | £12,207 | 12.4 yrs | £7,419 |
| 7 kW | 6844 kWh | 2738 kWh | 4106 kWh | £734 | £411 | £1,145 | £14,242 | 12.4 yrs | £8,656 |
| 8 kW | 7822 kWh | 3129 kWh | 4693 kWh | £839 | £469 | £1,308 | £16,276 | 12.4 yrs | £9,892 |
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: £982, 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 | 1955 kWh | 1173 kWh | 782 kWh | £315 | £78 | £393 | £6,169 | 15.7 yrs | £1,689 |
| 3 kW | 2933 kWh | 1760 kWh | 1173 kWh | £472 | £117 | £589 | £8,204 | 13.9 yrs | £3,583 |
| 4 kW | 3911 kWh | 2347 kWh | 1564 kWh | £629 | £156 | £786 | £10,238 | 13.0 yrs | £5,477 |
| 5 kW | 4889 kWh | 2933 kWh | 1955 kWh | £787 | £196 | £982 | £12,273 | 12.5 yrs | £7,372 |
| 6 kW | 5866 kWh | 3520 kWh | 2347 kWh | £944 | £235 | £1,179 | £14,307 | 12.1 yrs | £9,266 |
| 7 kW | 6844 kWh | 4106 kWh | 2738 kWh | £1,101 | £274 | £1,375 | £16,342 | 11.9 yrs | £11,161 |
| 8 kW | 7822 kWh | 4693 kWh | 3129 kWh | £1,259 | £313 | £1,572 | £18,376 | 11.7 yrs | £13,055 |
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: £1,064, 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 | 1955 kWh | 1369 kWh | 587 kWh | £367 | £59 | £426 | £7,569 | 17.8 yrs | £947 |
| 3 kW | 2933 kWh | 2053 kWh | 880 kWh | £551 | £88 | £639 | £9,604 | 15.0 yrs | £3,170 |
| 4 kW | 3911 kWh | 2738 kWh | 1173 kWh | £734 | £117 | £852 | £11,638 | 13.7 yrs | £5,393 |
| 5 kW | 4889 kWh | 3422 kWh | 1467 kWh | £918 | £147 | £1,064 | £13,673 | 12.8 yrs | £7,616 |
| 6 kW | 5866 kWh | 4106 kWh | 1760 kWh | £1,101 | £176 | £1,277 | £15,707 | 12.3 yrs | £9,840 |
| 7 kW | 6844 kWh | 4791 kWh | 2053 kWh | £1,285 | £205 | £1,490 | £17,742 | 11.9 yrs | £12,063 |
| 8 kW | 7822 kWh | 5475 kWh | 2347 kWh | £1,468 | £235 | £1,703 | £19,776 | 11.6 yrs | £14,286 |
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: £1,089, Upfront: £15,423, Break-even: 14.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1955 kWh | 1427 kWh | 528 kWh | £383 | £53 | £436 | £9,319 | 21.4 yrs | £-606 |
| 3 kW | 2933 kWh | 2141 kWh | 792 kWh | £574 | £79 | £653 | £11,354 | 17.4 yrs | £1,716 |
| 4 kW | 3911 kWh | 2855 kWh | 1056 kWh | £766 | £106 | £871 | £13,388 | 15.4 yrs | £4,038 |
| 5 kW | 4889 kWh | 3569 kWh | 1320 kWh | £957 | £132 | £1,089 | £15,423 | 14.2 yrs | £6,360 |
| 6 kW | 5866 kWh | 4282 kWh | 1584 kWh | £1,149 | £158 | £1,307 | £17,457 | 13.4 yrs | £8,682 |
| 7 kW | 6844 kWh | 4996 kWh | 1848 kWh | £1,340 | £185 | £1,525 | £19,492 | 12.8 yrs | £11,004 |
| 8 kW | 7822 kWh | 5710 kWh | 2112 kWh | £1,531 | £211 | £1,743 | £21,526 | 12.4 yrs | £13,325 |
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: £1,106, 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 | 1955 kWh | 1467 kWh | 489 kWh | £393 | £49 | £442 | £11,069 | 25.0 yrs | £-2,225 |
| 3 kW | 2933 kWh | 2200 kWh | 733 kWh | £590 | £73 | £663 | £13,104 | 19.8 yrs | £163 |
| 4 kW | 3911 kWh | 2933 kWh | 978 kWh | £787 | £98 | £884 | £15,138 | 17.1 yrs | £2,551 |
| 5 kW | 4889 kWh | 3666 kWh | 1222 kWh | £983 | £122 | £1,106 | £17,173 | 15.5 yrs | £4,939 |
| 6 kW | 5866 kWh | 4400 kWh | 1467 kWh | £1,180 | £147 | £1,327 | £19,207 | 14.5 yrs | £7,326 |
| 7 kW | 6844 kWh | 5133 kWh | 1711 kWh | £1,377 | £171 | £1,548 | £21,242 | 13.7 yrs | £9,714 |
| 8 kW | 7822 kWh | 5866 kWh | 1955 kWh | £1,573 | £196 | £1,769 | £23,276 | 13.2 yrs | £12,102 |
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: £1,122, Upfront: £19,623, Break-even: 17.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1955 kWh | 1506 kWh | 450 kWh | £404 | £45 | £449 | £13,519 | 30.1 yrs | £-4,543 |
| 3 kW | 2933 kWh | 2259 kWh | 675 kWh | £606 | £67 | £673 | £15,554 | 23.1 yrs | £-2,090 |
| 4 kW | 3911 kWh | 3011 kWh | 900 kWh | £808 | £90 | £898 | £17,588 | 19.6 yrs | £364 |
| 5 kW | 4889 kWh | 3764 kWh | 1124 kWh | £1,010 | £112 | £1,122 | £19,623 | 17.5 yrs | £2,817 |
| 6 kW | 5866 kWh | 4517 kWh | 1349 kWh | £1,211 | £135 | £1,346 | £21,657 | 16.1 yrs | £5,271 |
| 7 kW | 6844 kWh | 5270 kWh | 1574 kWh | £1,413 | £157 | £1,571 | £23,692 | 15.1 yrs | £7,724 |
| 8 kW | 7822 kWh | 6023 kWh | 1799 kWh | £1,615 | £180 | £1,795 | £25,726 | 14.3 yrs | £10,178 |
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.