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 981 kWh per year on a south-facing roof. We value self-used electricity at 25.6p 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: £797, Upfront: £10,173, 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 | 1962 kWh | 785 kWh | 1177 kWh | £201 | £118 | £319 | £4,069 | 12.8 yrs | £2,308 |
| 3 kW | 2942 kWh | 1177 kWh | 1765 kWh | £302 | £177 | £478 | £6,104 | 12.8 yrs | £3,463 |
| 4 kW | 3923 kWh | 1569 kWh | 2354 kWh | £402 | £235 | £638 | £8,138 | 12.8 yrs | £4,617 |
| 5 kW | 4904 kWh | 1962 kWh | 2942 kWh | £503 | £294 | £797 | £10,173 | 12.8 yrs | £5,771 |
| 6 kW | 5885 kWh | 2354 kWh | 3531 kWh | £604 | £353 | £957 | £12,207 | 12.8 yrs | £6,925 |
| 7 kW | 6865 kWh | 2746 kWh | 4119 kWh | £704 | £412 | £1,116 | £14,242 | 12.8 yrs | £8,079 |
| 8 kW | 7846 kWh | 3138 kWh | 4708 kWh | £805 | £471 | £1,275 | £16,276 | 12.8 yrs | £9,233 |
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: £951, Upfront: £12,273, Break-even: 12.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1962 kWh | 1177 kWh | 785 kWh | £302 | £78 | £380 | £6,169 | 16.2 yrs | £1,435 |
| 3 kW | 2942 kWh | 1765 kWh | 1177 kWh | £453 | £118 | £570 | £8,204 | 14.4 yrs | £3,203 |
| 4 kW | 3923 kWh | 2354 kWh | 1569 kWh | £604 | £157 | £760 | £10,238 | 13.5 yrs | £4,971 |
| 5 kW | 4904 kWh | 2942 kWh | 1962 kWh | £754 | £196 | £951 | £12,273 | 12.9 yrs | £6,739 |
| 6 kW | 5885 kWh | 3531 kWh | 2354 kWh | £905 | £235 | £1,141 | £14,307 | 12.5 yrs | £8,506 |
| 7 kW | 6865 kWh | 4119 kWh | 2746 kWh | £1,056 | £275 | £1,331 | £16,342 | 12.3 yrs | £10,274 |
| 8 kW | 7846 kWh | 4708 kWh | 3138 kWh | £1,207 | £314 | £1,521 | £18,376 | 12.1 yrs | £12,042 |
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: £1,027, Upfront: £13,673, 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 | 1962 kWh | 1373 kWh | 588 kWh | £352 | £59 | £411 | £7,569 | 18.4 yrs | £649 |
| 3 kW | 2942 kWh | 2060 kWh | 883 kWh | £528 | £88 | £616 | £9,604 | 15.6 yrs | £2,724 |
| 4 kW | 3923 kWh | 2746 kWh | 1177 kWh | £704 | £118 | £822 | £11,638 | 14.2 yrs | £4,798 |
| 5 kW | 4904 kWh | 3433 kWh | 1471 kWh | £880 | £147 | £1,027 | £13,673 | 13.3 yrs | £6,873 |
| 6 kW | 5885 kWh | 4119 kWh | 1765 kWh | £1,056 | £177 | £1,233 | £15,707 | 12.7 yrs | £8,947 |
| 7 kW | 6865 kWh | 4806 kWh | 2060 kWh | £1,232 | £206 | £1,438 | £17,742 | 12.3 yrs | £11,022 |
| 8 kW | 7846 kWh | 5492 kWh | 2354 kWh | £1,408 | £235 | £1,644 | £19,776 | 12.0 yrs | £13,096 |
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: £1,050, Upfront: £15,423, Break-even: 14.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1962 kWh | 1432 kWh | 530 kWh | £367 | £53 | £420 | £9,319 | 22.2 yrs | £-917 |
| 3 kW | 2942 kWh | 2148 kWh | 794 kWh | £551 | £79 | £630 | £11,354 | 18.0 yrs | £1,250 |
| 4 kW | 3923 kWh | 2864 kWh | 1059 kWh | £734 | £106 | £840 | £13,388 | 15.9 yrs | £3,416 |
| 5 kW | 4904 kWh | 3580 kWh | 1324 kWh | £918 | £132 | £1,050 | £15,423 | 14.7 yrs | £5,583 |
| 6 kW | 5885 kWh | 4296 kWh | 1589 kWh | £1,101 | £159 | £1,260 | £17,457 | 13.9 yrs | £7,749 |
| 7 kW | 6865 kWh | 5012 kWh | 1854 kWh | £1,285 | £185 | £1,470 | £19,492 | 13.3 yrs | £9,916 |
| 8 kW | 7846 kWh | 5728 kWh | 2118 kWh | £1,469 | £212 | £1,680 | £21,526 | 12.8 yrs | £12,082 |
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: £1,066, Upfront: £17,173, Break-even: 16.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1962 kWh | 1471 kWh | 490 kWh | £377 | £49 | £426 | £11,069 | 26.0 yrs | £-2,544 |
| 3 kW | 2942 kWh | 2207 kWh | 736 kWh | £566 | £74 | £639 | £13,104 | 20.5 yrs | £-316 |
| 4 kW | 3923 kWh | 2942 kWh | 981 kWh | £754 | £98 | £852 | £15,138 | 17.8 yrs | £1,912 |
| 5 kW | 4904 kWh | 3678 kWh | 1226 kWh | £943 | £123 | £1,066 | £17,173 | 16.1 yrs | £4,140 |
| 6 kW | 5885 kWh | 4413 kWh | 1471 kWh | £1,132 | £147 | £1,279 | £19,207 | 15.0 yrs | £6,367 |
| 7 kW | 6865 kWh | 5149 kWh | 1716 kWh | £1,320 | £172 | £1,492 | £21,242 | 14.2 yrs | £8,595 |
| 8 kW | 7846 kWh | 5885 kWh | 1962 kWh | £1,509 | £196 | £1,705 | £23,276 | 13.7 yrs | £10,823 |
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: £1,081, Upfront: £19,623, Break-even: 18.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1962 kWh | 1510 kWh | 451 kWh | £387 | £45 | £432 | £13,519 | 31.3 yrs | £-4,871 |
| 3 kW | 2942 kWh | 2266 kWh | 677 kWh | £581 | £68 | £649 | £15,554 | 24.0 yrs | £-2,582 |
| 4 kW | 3923 kWh | 3021 kWh | 902 kWh | £775 | £90 | £865 | £17,588 | 20.3 yrs | £-293 |
| 5 kW | 4904 kWh | 3776 kWh | 1128 kWh | £968 | £113 | £1,081 | £19,623 | 18.2 yrs | £1,996 |
| 6 kW | 5885 kWh | 4531 kWh | 1353 kWh | £1,162 | £135 | £1,297 | £21,657 | 16.7 yrs | £4,286 |
| 7 kW | 6865 kWh | 5286 kWh | 1579 kWh | £1,355 | £158 | £1,513 | £23,692 | 15.7 yrs | £6,575 |
| 8 kW | 7846 kWh | 6042 kWh | 1805 kWh | £1,549 | £180 | £1,730 | £25,726 | 14.9 yrs | £8,864 |
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.