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 689 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: £579, Upfront: £10,173, Break-even: 17.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1377 kWh | 551 kWh | 826 kWh | £149 | £83 | £232 | £4,069 | 17.6 yrs | £565 |
| 3 kW | 2066 kWh | 826 kWh | 1239 kWh | £224 | £124 | £348 | £6,104 | 17.6 yrs | £847 |
| 4 kW | 2754 kWh | 1102 kWh | 1653 kWh | £298 | £165 | £463 | £8,138 | 17.6 yrs | £1,129 |
| 5 kW | 3443 kWh | 1377 kWh | 2066 kWh | £373 | £207 | £579 | £10,173 | 17.6 yrs | £1,412 |
| 6 kW | 4131 kWh | 1653 kWh | 2479 kWh | £447 | £248 | £695 | £12,207 | 17.6 yrs | £1,694 |
| 7 kW | 4820 kWh | 1928 kWh | 2892 kWh | £522 | £289 | £811 | £14,242 | 17.6 yrs | £1,976 |
| 8 kW | 5508 kWh | 2203 kWh | 3305 kWh | £596 | £331 | £927 | £16,276 | 17.6 yrs | £2,259 |
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: £697, Upfront: £12,273, Break-even: 17.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1377 kWh | 826 kWh | 551 kWh | £224 | £55 | £279 | £6,169 | 22.1 yrs | £-596 |
| 3 kW | 2066 kWh | 1239 kWh | 826 kWh | £335 | £83 | £418 | £8,204 | 19.6 yrs | £157 |
| 4 kW | 2754 kWh | 1653 kWh | 1102 kWh | £447 | £110 | £557 | £10,238 | 18.4 yrs | £909 |
| 5 kW | 3443 kWh | 2066 kWh | 1377 kWh | £559 | £138 | £697 | £12,273 | 17.6 yrs | £1,661 |
| 6 kW | 4131 kWh | 2479 kWh | 1653 kWh | £671 | £165 | £836 | £14,307 | 17.1 yrs | £2,413 |
| 7 kW | 4820 kWh | 2892 kWh | 1928 kWh | £783 | £193 | £975 | £16,342 | 16.8 yrs | £3,165 |
| 8 kW | 5508 kWh | 3305 kWh | 2203 kWh | £894 | £220 | £1,115 | £18,376 | 16.5 yrs | £3,918 |
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: £755, Upfront: £13,673, Break-even: 18.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1377 kWh | 964 kWh | 413 kWh | £261 | £41 | £302 | £7,569 | 25.0 yrs | £-1,526 |
| 3 kW | 2066 kWh | 1446 kWh | 620 kWh | £391 | £62 | £453 | £9,604 | 21.2 yrs | £-539 |
| 4 kW | 2754 kWh | 1928 kWh | 826 kWh | £522 | £83 | £604 | £11,638 | 19.3 yrs | £448 |
| 5 kW | 3443 kWh | 2410 kWh | 1033 kWh | £652 | £103 | £755 | £13,673 | 18.1 yrs | £1,436 |
| 6 kW | 4131 kWh | 2892 kWh | 1239 kWh | £783 | £124 | £906 | £15,707 | 17.3 yrs | £2,423 |
| 7 kW | 4820 kWh | 3374 kWh | 1446 kWh | £913 | £145 | £1,058 | £17,742 | 16.8 yrs | £3,410 |
| 8 kW | 5508 kWh | 3856 kWh | 1653 kWh | £1,043 | £165 | £1,209 | £19,776 | 16.4 yrs | £4,397 |
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: £773, Upfront: £15,423, Break-even: 20.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1377 kWh | 1005 kWh | 372 kWh | £272 | £37 | £309 | £9,319 | 30.1 yrs | £-3,135 |
| 3 kW | 2066 kWh | 1508 kWh | 558 kWh | £408 | £56 | £464 | £11,354 | 24.5 yrs | £-2,077 |
| 4 kW | 2754 kWh | 2011 kWh | 744 kWh | £544 | £74 | £618 | £13,388 | 21.6 yrs | £-1,020 |
| 5 kW | 3443 kWh | 2513 kWh | 930 kWh | £680 | £93 | £773 | £15,423 | 20.0 yrs | £38 |
| 6 kW | 4131 kWh | 3016 kWh | 1115 kWh | £816 | £112 | £928 | £17,457 | 18.8 yrs | £1,096 |
| 7 kW | 4820 kWh | 3518 kWh | 1301 kWh | £952 | £130 | £1,082 | £19,492 | 18.0 yrs | £2,153 |
| 8 kW | 5508 kWh | 4021 kWh | 1487 kWh | £1,088 | £149 | £1,237 | £21,526 | 17.4 yrs | £3,211 |
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: £785, Upfront: £17,173, Break-even: 21.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1377 kWh | 1033 kWh | 344 kWh | £279 | £34 | £314 | £11,069 | 35.3 yrs | £-4,791 |
| 3 kW | 2066 kWh | 1549 kWh | 516 kWh | £419 | £52 | £471 | £13,104 | 27.8 yrs | £-3,686 |
| 4 kW | 2754 kWh | 2066 kWh | 689 kWh | £559 | £69 | £628 | £15,138 | 24.1 yrs | £-2,582 |
| 5 kW | 3443 kWh | 2582 kWh | 861 kWh | £699 | £86 | £785 | £17,173 | 21.9 yrs | £-1,477 |
| 6 kW | 4131 kWh | 3098 kWh | 1033 kWh | £838 | £103 | £942 | £19,207 | 20.4 yrs | £-372 |
| 7 kW | 4820 kWh | 3615 kWh | 1205 kWh | £978 | £120 | £1,099 | £21,242 | 19.3 yrs | £732 |
| 8 kW | 5508 kWh | 4131 kWh | 1377 kWh | £1,118 | £138 | £1,256 | £23,276 | 18.5 yrs | £1,837 |
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: £797, Upfront: £19,623, Break-even: 24.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1377 kWh | 1060 kWh | 317 kWh | £287 | £32 | £319 | £13,519 | 42.4 yrs | £-7,147 |
| 3 kW | 2066 kWh | 1591 kWh | 475 kWh | £430 | £48 | £478 | £15,554 | 32.5 yrs | £-5,995 |
| 4 kW | 2754 kWh | 2121 kWh | 633 kWh | £574 | £63 | £637 | £17,588 | 27.6 yrs | £-4,844 |
| 5 kW | 3443 kWh | 2651 kWh | 792 kWh | £717 | £79 | £797 | £19,623 | 24.6 yrs | £-3,692 |
| 6 kW | 4131 kWh | 3181 kWh | 950 kWh | £861 | £95 | £956 | £21,657 | 22.7 yrs | £-2,541 |
| 7 kW | 4820 kWh | 3711 kWh | 1109 kWh | £1,004 | £111 | £1,115 | £23,692 | 21.2 yrs | £-1,389 |
| 8 kW | 5508 kWh | 4241 kWh | 1267 kWh | £1,148 | £127 | £1,274 | £25,726 | 20.2 yrs | £-237 |
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.