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 1037 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: £860, 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 | 2074 kWh | 830 kWh | 1244 kWh | £220 | £124 | £344 | £4,069 | 11.8 yrs | £2,813 |
| 3 kW | 3111 kWh | 1244 kWh | 1866 kWh | £329 | £187 | £516 | £6,104 | 11.8 yrs | £4,219 |
| 4 kW | 4148 kWh | 1659 kWh | 2489 kWh | £439 | £249 | £688 | £8,138 | 11.8 yrs | £5,626 |
| 5 kW | 5185 kWh | 2074 kWh | 3111 kWh | £549 | £311 | £860 | £10,173 | 11.8 yrs | £7,032 |
| 6 kW | 6222 kWh | 2489 kWh | 3733 kWh | £659 | £373 | £1,032 | £12,207 | 11.8 yrs | £8,438 |
| 7 kW | 7258 kWh | 2903 kWh | 4355 kWh | £769 | £436 | £1,204 | £14,242 | 11.8 yrs | £9,845 |
| 8 kW | 8295 kWh | 3318 kWh | 4977 kWh | £879 | £498 | £1,376 | £16,276 | 11.8 yrs | £11,251 |
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: £1,031, 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 | 2074 kWh | 1244 kWh | 830 kWh | £329 | £83 | £412 | £6,169 | 15.0 yrs | £2,080 |
| 3 kW | 3111 kWh | 1866 kWh | 1244 kWh | £494 | £124 | £619 | £8,204 | 13.3 yrs | £4,170 |
| 4 kW | 4148 kWh | 2489 kWh | 1659 kWh | £659 | £166 | £825 | £10,238 | 12.4 yrs | £6,260 |
| 5 kW | 5185 kWh | 3111 kWh | 2074 kWh | £824 | £207 | £1,031 | £12,273 | 11.9 yrs | £8,350 |
| 6 kW | 6222 kWh | 3733 kWh | 2489 kWh | £988 | £249 | £1,237 | £14,307 | 11.6 yrs | £10,440 |
| 7 kW | 7258 kWh | 4355 kWh | 2903 kWh | £1,153 | £290 | £1,444 | £16,342 | 11.3 yrs | £12,530 |
| 8 kW | 8295 kWh | 4977 kWh | 3318 kWh | £1,318 | £332 | £1,650 | £18,376 | 11.1 yrs | £14,620 |
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: £1,117, 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 | 2074 kWh | 1452 kWh | 622 kWh | £384 | £62 | £447 | £7,569 | 16.9 yrs | £1,363 |
| 3 kW | 3111 kWh | 2178 kWh | 933 kWh | £577 | £93 | £670 | £9,604 | 14.3 yrs | £3,795 |
| 4 kW | 4148 kWh | 2903 kWh | 1244 kWh | £769 | £124 | £893 | £11,638 | 13.0 yrs | £6,227 |
| 5 kW | 5185 kWh | 3629 kWh | 1555 kWh | £961 | £156 | £1,117 | £13,673 | 12.2 yrs | £8,659 |
| 6 kW | 6222 kWh | 4355 kWh | 1866 kWh | £1,153 | £187 | £1,340 | £15,707 | 11.7 yrs | £11,090 |
| 7 kW | 7258 kWh | 5081 kWh | 2178 kWh | £1,345 | £218 | £1,563 | £17,742 | 11.3 yrs | £13,522 |
| 8 kW | 8295 kWh | 5807 kWh | 2489 kWh | £1,538 | £249 | £1,786 | £19,776 | 11.1 yrs | £15,954 |
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: £1,142, 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 | 2074 kWh | 1514 kWh | 560 kWh | £401 | £56 | £457 | £9,319 | 20.4 yrs | £-182 |
| 3 kW | 3111 kWh | 2271 kWh | 840 kWh | £601 | £84 | £685 | £11,354 | 16.6 yrs | £2,353 |
| 4 kW | 4148 kWh | 3028 kWh | 1120 kWh | £802 | £112 | £914 | £13,388 | 14.7 yrs | £4,887 |
| 5 kW | 5185 kWh | 3785 kWh | 1400 kWh | £1,002 | £140 | £1,142 | £15,423 | 13.5 yrs | £7,421 |
| 6 kW | 6222 kWh | 4542 kWh | 1680 kWh | £1,203 | £168 | £1,371 | £17,457 | 12.7 yrs | £9,955 |
| 7 kW | 7258 kWh | 5299 kWh | 1960 kWh | £1,403 | £196 | £1,599 | £19,492 | 12.2 yrs | £12,490 |
| 8 kW | 8295 kWh | 6056 kWh | 2240 kWh | £1,604 | £224 | £1,828 | £21,526 | 11.8 yrs | £15,024 |
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: £1,159, 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 | 2074 kWh | 1555 kWh | 518 kWh | £412 | £52 | £464 | £11,069 | 23.9 yrs | £-1,795 |
| 3 kW | 3111 kWh | 2333 kWh | 778 kWh | £618 | £78 | £696 | £13,104 | 18.8 yrs | £808 |
| 4 kW | 4148 kWh | 3111 kWh | 1037 kWh | £824 | £104 | £927 | £15,138 | 16.3 yrs | £3,410 |
| 5 kW | 5185 kWh | 3888 kWh | 1296 kWh | £1,030 | £130 | £1,159 | £17,173 | 14.8 yrs | £6,013 |
| 6 kW | 6222 kWh | 4666 kWh | 1555 kWh | £1,236 | £156 | £1,391 | £19,207 | 13.8 yrs | £8,616 |
| 7 kW | 7258 kWh | 5444 kWh | 1815 kWh | £1,442 | £181 | £1,623 | £21,242 | 13.1 yrs | £11,218 |
| 8 kW | 8295 kWh | 6222 kWh | 2074 kWh | £1,647 | £207 | £1,855 | £23,276 | 12.5 yrs | £13,821 |
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: £1,176, Upfront: £19,623, Break-even: 16.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2074 kWh | 1597 kWh | 477 kWh | £423 | £48 | £471 | £13,519 | 28.7 yrs | £-4,108 |
| 3 kW | 3111 kWh | 2395 kWh | 715 kWh | £634 | £72 | £706 | £15,554 | 22.0 yrs | £-1,437 |
| 4 kW | 4148 kWh | 3194 kWh | 954 kWh | £846 | £95 | £941 | £17,588 | 18.7 yrs | £1,234 |
| 5 kW | 5185 kWh | 3992 kWh | 1192 kWh | £1,057 | £119 | £1,176 | £19,623 | 16.7 yrs | £3,905 |
| 6 kW | 6222 kWh | 4791 kWh | 1431 kWh | £1,269 | £143 | £1,412 | £21,657 | 15.3 yrs | £6,576 |
| 7 kW | 7258 kWh | 5589 kWh | 1669 kWh | £1,480 | £167 | £1,647 | £23,692 | 14.4 yrs | £9,247 |
| 8 kW | 8295 kWh | 6387 kWh | 1908 kWh | £1,691 | £191 | £1,882 | £25,726 | 13.7 yrs | £11,918 |
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.