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 898 kWh per year on a south-facing roof. We value self-used electricity at 27.1p 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: £756, Upfront: £10,173, 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 | 1797 kWh | 719 kWh | 1078 kWh | £194 | £108 | £302 | £4,069 | 13.5 yrs | £1,976 |
| 3 kW | 2695 kWh | 1078 kWh | 1617 kWh | £292 | £162 | £453 | £6,104 | 13.5 yrs | £2,964 |
| 4 kW | 3593 kWh | 1437 kWh | 2156 kWh | £389 | £216 | £605 | £8,138 | 13.5 yrs | £3,952 |
| 5 kW | 4491 kWh | 1797 kWh | 2695 kWh | £486 | £269 | £756 | £10,173 | 13.5 yrs | £4,940 |
| 6 kW | 5390 kWh | 2156 kWh | 3234 kWh | £583 | £323 | £907 | £12,207 | 13.5 yrs | £5,928 |
| 7 kW | 6288 kWh | 2515 kWh | 3773 kWh | £681 | £377 | £1,058 | £14,242 | 13.5 yrs | £6,916 |
| 8 kW | 7186 kWh | 2874 kWh | 4312 kWh | £778 | £431 | £1,209 | £16,276 | 13.5 yrs | £7,904 |
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: £909, Upfront: £12,273, 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 | 1797 kWh | 1078 kWh | 719 kWh | £292 | £72 | £364 | £6,169 | 17.0 yrs | £1,102 |
| 3 kW | 2695 kWh | 1617 kWh | 1078 kWh | £438 | £108 | £545 | £8,204 | 15.0 yrs | £2,703 |
| 4 kW | 3593 kWh | 2156 kWh | 1437 kWh | £583 | £144 | £727 | £10,238 | 14.1 yrs | £4,304 |
| 5 kW | 4491 kWh | 2695 kWh | 1797 kWh | £729 | £180 | £909 | £12,273 | 13.5 yrs | £5,905 |
| 6 kW | 5390 kWh | 3234 kWh | 2156 kWh | £875 | £216 | £1,091 | £14,307 | 13.1 yrs | £7,506 |
| 7 kW | 6288 kWh | 3773 kWh | 2515 kWh | £1,021 | £252 | £1,272 | £16,342 | 12.8 yrs | £9,107 |
| 8 kW | 7186 kWh | 4312 kWh | 2874 kWh | £1,167 | £287 | £1,454 | £18,376 | 12.6 yrs | £10,708 |
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: £986, Upfront: £13,673, Break-even: 13.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1797 kWh | 1258 kWh | 539 kWh | £340 | £54 | £394 | £7,569 | 19.2 yrs | £315 |
| 3 kW | 2695 kWh | 1886 kWh | 808 kWh | £510 | £81 | £591 | £9,604 | 16.2 yrs | £2,223 |
| 4 kW | 3593 kWh | 2515 kWh | 1078 kWh | £681 | £108 | £788 | £11,638 | 14.8 yrs | £4,130 |
| 5 kW | 4491 kWh | 3144 kWh | 1347 kWh | £851 | £135 | £986 | £13,673 | 13.9 yrs | £6,038 |
| 6 kW | 5390 kWh | 3773 kWh | 1617 kWh | £1,021 | £162 | £1,183 | £15,707 | 13.3 yrs | £7,945 |
| 7 kW | 6288 kWh | 4402 kWh | 1886 kWh | £1,191 | £189 | £1,380 | £17,742 | 12.9 yrs | £9,853 |
| 8 kW | 7186 kWh | 5030 kWh | 2156 kWh | £1,361 | £216 | £1,577 | £19,776 | 12.5 yrs | £11,760 |
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: £1,008, Upfront: £15,423, Break-even: 15.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1797 kWh | 1311 kWh | 485 kWh | £355 | £49 | £403 | £9,319 | 23.1 yrs | £-1,251 |
| 3 kW | 2695 kWh | 1967 kWh | 728 kWh | £532 | £73 | £605 | £11,354 | 18.8 yrs | £748 |
| 4 kW | 3593 kWh | 2623 kWh | 970 kWh | £710 | £97 | £807 | £13,388 | 16.6 yrs | £2,748 |
| 5 kW | 4491 kWh | 3279 kWh | 1213 kWh | £887 | £121 | £1,008 | £15,423 | 15.3 yrs | £4,747 |
| 6 kW | 5390 kWh | 3934 kWh | 1455 kWh | £1,065 | £146 | £1,210 | £17,457 | 14.4 yrs | £6,747 |
| 7 kW | 6288 kWh | 4590 kWh | 1698 kWh | £1,242 | £170 | £1,412 | £19,492 | 13.8 yrs | £8,746 |
| 8 kW | 7186 kWh | 5246 kWh | 1940 kWh | £1,420 | £194 | £1,614 | £21,526 | 13.3 yrs | £10,746 |
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: £1,024, Upfront: £17,173, Break-even: 16.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1797 kWh | 1347 kWh | 449 kWh | £365 | £45 | £410 | £11,069 | 27.0 yrs | £-2,879 |
| 3 kW | 2695 kWh | 2021 kWh | 674 kWh | £547 | £67 | £614 | £13,104 | 21.3 yrs | £-818 |
| 4 kW | 3593 kWh | 2695 kWh | 898 kWh | £729 | £90 | £819 | £15,138 | 18.5 yrs | £1,243 |
| 5 kW | 4491 kWh | 3369 kWh | 1123 kWh | £912 | £112 | £1,024 | £17,173 | 16.8 yrs | £3,304 |
| 6 kW | 5390 kWh | 4042 kWh | 1347 kWh | £1,094 | £135 | £1,229 | £19,207 | 15.6 yrs | £5,364 |
| 7 kW | 6288 kWh | 4716 kWh | 1572 kWh | £1,276 | £157 | £1,433 | £21,242 | 14.8 yrs | £7,425 |
| 8 kW | 7186 kWh | 5390 kWh | 1797 kWh | £1,458 | £180 | £1,638 | £23,276 | 14.2 yrs | £9,486 |
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: £1,039, Upfront: £19,623, Break-even: 18.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1797 kWh | 1383 kWh | 413 kWh | £374 | £41 | £416 | £13,519 | 32.5 yrs | £-5,206 |
| 3 kW | 2695 kWh | 2075 kWh | 620 kWh | £562 | £62 | £623 | £15,554 | 24.9 yrs | £-3,084 |
| 4 kW | 3593 kWh | 2767 kWh | 826 kWh | £749 | £83 | £831 | £17,588 | 21.2 yrs | £-962 |
| 5 kW | 4491 kWh | 3458 kWh | 1033 kWh | £936 | £103 | £1,039 | £19,623 | 18.9 yrs | £1,160 |
| 6 kW | 5390 kWh | 4150 kWh | 1240 kWh | £1,123 | £124 | £1,247 | £21,657 | 17.4 yrs | £3,282 |
| 7 kW | 6288 kWh | 4842 kWh | 1446 kWh | £1,310 | £145 | £1,455 | £23,692 | 16.3 yrs | £5,404 |
| 8 kW | 7186 kWh | 5533 kWh | 1653 kWh | £1,497 | £165 | £1,663 | £25,726 | 15.5 yrs | £7,526 |
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.