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 1041 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: £871, Upfront: £10,173, Break-even: 11.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2082 kWh | 833 kWh | 1249 kWh | £223 | £125 | £348 | £4,069 | 11.7 yrs | £2,898 |
| 3 kW | 3124 kWh | 1249 kWh | 1874 kWh | £335 | £187 | £523 | £6,104 | 11.7 yrs | £4,347 |
| 4 kW | 4165 kWh | 1666 kWh | 2499 kWh | £447 | £250 | £697 | £8,138 | 11.7 yrs | £5,795 |
| 5 kW | 5206 kWh | 2082 kWh | 3124 kWh | £558 | £312 | £871 | £10,173 | 11.7 yrs | £7,244 |
| 6 kW | 6247 kWh | 2499 kWh | 3748 kWh | £670 | £375 | £1,045 | £12,207 | 11.7 yrs | £8,693 |
| 7 kW | 7288 kWh | 2915 kWh | 4373 kWh | £782 | £437 | £1,219 | £14,242 | 11.7 yrs | £10,142 |
| 8 kW | 8329 kWh | 3332 kWh | 4998 kWh | £894 | £500 | £1,393 | £16,276 | 11.7 yrs | £11,591 |
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: £1,046, Upfront: £12,273, Break-even: 11.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2082 kWh | 1249 kWh | 833 kWh | £335 | £83 | £418 | £6,169 | 14.7 yrs | £2,199 |
| 3 kW | 3124 kWh | 1874 kWh | 1249 kWh | £503 | £125 | £628 | £8,204 | 13.1 yrs | £4,348 |
| 4 kW | 4165 kWh | 2499 kWh | 1666 kWh | £670 | £167 | £837 | £10,238 | 12.2 yrs | £6,497 |
| 5 kW | 5206 kWh | 3124 kWh | 2082 kWh | £838 | £208 | £1,046 | £12,273 | 11.7 yrs | £8,647 |
| 6 kW | 6247 kWh | 3748 kWh | 2499 kWh | £1,005 | £250 | £1,255 | £14,307 | 11.4 yrs | £10,796 |
| 7 kW | 7288 kWh | 4373 kWh | 2915 kWh | £1,173 | £292 | £1,464 | £16,342 | 11.2 yrs | £12,946 |
| 8 kW | 8329 kWh | 4998 kWh | 3332 kWh | £1,340 | £333 | £1,674 | £18,376 | 11.0 yrs | £15,095 |
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: £1,134, Upfront: £13,673, Break-even: 12.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2082 kWh | 1458 kWh | 625 kWh | £391 | £62 | £453 | £7,569 | 16.7 yrs | £1,499 |
| 3 kW | 3124 kWh | 2186 kWh | 937 kWh | £586 | £94 | £680 | £9,604 | 14.1 yrs | £3,999 |
| 4 kW | 4165 kWh | 2915 kWh | 1249 kWh | £782 | £125 | £907 | £11,638 | 12.8 yrs | £6,498 |
| 5 kW | 5206 kWh | 3644 kWh | 1562 kWh | £977 | £156 | £1,134 | £13,673 | 12.1 yrs | £8,998 |
| 6 kW | 6247 kWh | 4373 kWh | 1874 kWh | £1,173 | £187 | £1,360 | £15,707 | 11.5 yrs | £11,498 |
| 7 kW | 7288 kWh | 5102 kWh | 2186 kWh | £1,368 | £219 | £1,587 | £17,742 | 11.2 yrs | £13,997 |
| 8 kW | 8329 kWh | 5831 kWh | 2499 kWh | £1,564 | £250 | £1,814 | £19,776 | 10.9 yrs | £16,497 |
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: £1,160, Upfront: £15,423, Break-even: 13.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2082 kWh | 1520 kWh | 562 kWh | £408 | £56 | £464 | £9,319 | 20.1 yrs | £-41 |
| 3 kW | 3124 kWh | 2280 kWh | 843 kWh | £612 | £84 | £696 | £11,354 | 16.3 yrs | £2,564 |
| 4 kW | 4165 kWh | 3040 kWh | 1124 kWh | £815 | £112 | £928 | £13,388 | 14.4 yrs | £5,169 |
| 5 kW | 5206 kWh | 3800 kWh | 1406 kWh | £1,019 | £141 | £1,160 | £15,423 | 13.3 yrs | £7,773 |
| 6 kW | 6247 kWh | 4560 kWh | 1687 kWh | £1,223 | £169 | £1,392 | £17,457 | 12.5 yrs | £10,378 |
| 7 kW | 7288 kWh | 5320 kWh | 1968 kWh | £1,427 | £197 | £1,624 | £19,492 | 12.0 yrs | £12,983 |
| 8 kW | 8329 kWh | 6080 kWh | 2249 kWh | £1,631 | £225 | £1,856 | £21,526 | 11.6 yrs | £15,588 |
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: £1,177, Upfront: £17,173, Break-even: 14.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2082 kWh | 1562 kWh | 521 kWh | £419 | £52 | £471 | £11,069 | 23.5 yrs | £-1,651 |
| 3 kW | 3124 kWh | 2343 kWh | 781 kWh | £628 | £78 | £706 | £13,104 | 18.6 yrs | £1,024 |
| 4 kW | 4165 kWh | 3124 kWh | 1041 kWh | £838 | £104 | £942 | £15,138 | 16.1 yrs | £3,699 |
| 5 kW | 5206 kWh | 3904 kWh | 1301 kWh | £1,047 | £130 | £1,177 | £17,173 | 14.6 yrs | £6,374 |
| 6 kW | 6247 kWh | 4685 kWh | 1562 kWh | £1,257 | £156 | £1,413 | £19,207 | 13.6 yrs | £9,048 |
| 7 kW | 7288 kWh | 5466 kWh | 1822 kWh | £1,466 | £182 | £1,648 | £21,242 | 12.9 yrs | £11,723 |
| 8 kW | 8329 kWh | 6247 kWh | 2082 kWh | £1,675 | £208 | £1,884 | £23,276 | 12.4 yrs | £14,398 |
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: £1,195, Upfront: £19,623, Break-even: 16.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2082 kWh | 1603 kWh | 479 kWh | £430 | £48 | £478 | £13,519 | 28.3 yrs | £-3,960 |
| 3 kW | 3124 kWh | 2405 kWh | 718 kWh | £645 | £72 | £717 | £15,554 | 21.7 yrs | £-1,216 |
| 4 kW | 4165 kWh | 3207 kWh | 958 kWh | £860 | £96 | £956 | £17,588 | 18.4 yrs | £1,529 |
| 5 kW | 5206 kWh | 4009 kWh | 1197 kWh | £1,075 | £120 | £1,195 | £19,623 | 16.4 yrs | £4,274 |
| 6 kW | 6247 kWh | 4810 kWh | 1437 kWh | £1,290 | £144 | £1,434 | £21,657 | 15.1 yrs | £7,019 |
| 7 kW | 7288 kWh | 5612 kWh | 1676 kWh | £1,505 | £168 | £1,673 | £23,692 | 14.2 yrs | £9,764 |
| 8 kW | 8329 kWh | 6414 kWh | 1916 kWh | £1,720 | £192 | £1,912 | £25,726 | 13.5 yrs | £12,508 |
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.