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 791 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: £665, Upfront: £10,173, 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 | 1582 kWh | 633 kWh | 949 kWh | £171 | £95 | £266 | £4,069 | 15.3 yrs | £1,254 |
| 3 kW | 2373 kWh | 949 kWh | 1424 kWh | £257 | £142 | £399 | £6,104 | 15.3 yrs | £1,880 |
| 4 kW | 3164 kWh | 1265 kWh | 1898 kWh | £342 | £190 | £532 | £8,138 | 15.3 yrs | £2,507 |
| 5 kW | 3955 kWh | 1582 kWh | 2373 kWh | £428 | £237 | £665 | £10,173 | 15.3 yrs | £3,134 |
| 6 kW | 4746 kWh | 1898 kWh | 2847 kWh | £514 | £285 | £798 | £12,207 | 15.3 yrs | £3,761 |
| 7 kW | 5537 kWh | 2215 kWh | 3322 kWh | £599 | £332 | £931 | £14,242 | 15.3 yrs | £4,388 |
| 8 kW | 6327 kWh | 2531 kWh | 3796 kWh | £685 | £380 | £1,065 | £16,276 | 15.3 yrs | £5,014 |
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: £800, Upfront: £12,273, 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 | 1582 kWh | 949 kWh | 633 kWh | £257 | £63 | £320 | £6,169 | 19.3 yrs | £233 |
| 3 kW | 2373 kWh | 1424 kWh | 949 kWh | £385 | £95 | £480 | £8,204 | 17.1 yrs | £1,400 |
| 4 kW | 3164 kWh | 1898 kWh | 1265 kWh | £514 | £127 | £640 | £10,238 | 16.0 yrs | £2,566 |
| 5 kW | 3955 kWh | 2373 kWh | 1582 kWh | £642 | £158 | £800 | £12,273 | 15.3 yrs | £3,733 |
| 6 kW | 4746 kWh | 2847 kWh | 1898 kWh | £770 | £190 | £960 | £14,307 | 14.9 yrs | £4,899 |
| 7 kW | 5537 kWh | 3322 kWh | 2215 kWh | £899 | £221 | £1,120 | £16,342 | 14.6 yrs | £6,066 |
| 8 kW | 6327 kWh | 3796 kWh | 2531 kWh | £1,027 | £253 | £1,280 | £18,376 | 14.4 yrs | £7,232 |
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: £868, Upfront: £13,673, Break-even: 15.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1582 kWh | 1107 kWh | 475 kWh | £300 | £47 | £347 | £7,569 | 21.8 yrs | £-627 |
| 3 kW | 2373 kWh | 1661 kWh | 712 kWh | £449 | £71 | £521 | £9,604 | 18.4 yrs | £809 |
| 4 kW | 3164 kWh | 2215 kWh | 949 kWh | £599 | £95 | £694 | £11,638 | 16.8 yrs | £2,246 |
| 5 kW | 3955 kWh | 2768 kWh | 1186 kWh | £749 | £119 | £868 | £13,673 | 15.8 yrs | £3,682 |
| 6 kW | 4746 kWh | 3322 kWh | 1424 kWh | £899 | £142 | £1,041 | £15,707 | 15.1 yrs | £5,118 |
| 7 kW | 5537 kWh | 3876 kWh | 1661 kWh | £1,049 | £166 | £1,215 | £17,742 | 14.6 yrs | £6,555 |
| 8 kW | 6327 kWh | 4429 kWh | 1898 kWh | £1,199 | £190 | £1,388 | £19,776 | 14.2 yrs | £7,991 |
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: £888, Upfront: £15,423, Break-even: 17.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1582 kWh | 1155 kWh | 427 kWh | £312 | £43 | £355 | £9,319 | 26.2 yrs | £-2,215 |
| 3 kW | 2373 kWh | 1732 kWh | 641 kWh | £469 | £64 | £533 | £11,354 | 21.3 yrs | £-698 |
| 4 kW | 3164 kWh | 2310 kWh | 854 kWh | £625 | £85 | £710 | £13,388 | 18.8 yrs | £819 |
| 5 kW | 3955 kWh | 2887 kWh | 1068 kWh | £781 | £107 | £888 | £15,423 | 17.4 yrs | £2,337 |
| 6 kW | 4746 kWh | 3464 kWh | 1281 kWh | £937 | £128 | £1,066 | £17,457 | 16.4 yrs | £3,854 |
| 7 kW | 5537 kWh | 4042 kWh | 1495 kWh | £1,094 | £149 | £1,243 | £19,492 | 15.7 yrs | £5,372 |
| 8 kW | 6327 kWh | 4619 kWh | 1708 kWh | £1,250 | £171 | £1,421 | £21,526 | 15.2 yrs | £6,889 |
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: £901, Upfront: £17,173, Break-even: 19.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1582 kWh | 1186 kWh | 395 kWh | £321 | £40 | £361 | £11,069 | 30.7 yrs | £-3,857 |
| 3 kW | 2373 kWh | 1780 kWh | 593 kWh | £482 | £59 | £541 | £13,104 | 24.2 yrs | £-2,286 |
| 4 kW | 3164 kWh | 2373 kWh | 791 kWh | £642 | £79 | £721 | £15,138 | 21.0 yrs | £-715 |
| 5 kW | 3955 kWh | 2966 kWh | 989 kWh | £803 | £99 | £901 | £17,173 | 19.0 yrs | £857 |
| 6 kW | 4746 kWh | 3559 kWh | 1186 kWh | £963 | £119 | £1,082 | £19,207 | 17.8 yrs | £2,428 |
| 7 kW | 5537 kWh | 4152 kWh | 1384 kWh | £1,124 | £138 | £1,262 | £21,242 | 16.8 yrs | £3,999 |
| 8 kW | 6327 kWh | 4746 kWh | 1582 kWh | £1,284 | £158 | £1,442 | £23,276 | 16.1 yrs | £5,571 |
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: £915, Upfront: £19,623, Break-even: 21.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1582 kWh | 1218 kWh | 364 kWh | £330 | £36 | £366 | £13,519 | 36.9 yrs | £-6,199 |
| 3 kW | 2373 kWh | 1827 kWh | 546 kWh | £494 | £55 | £549 | £15,554 | 28.3 yrs | £-4,574 |
| 4 kW | 3164 kWh | 2436 kWh | 728 kWh | £659 | £73 | £732 | £17,588 | 24.0 yrs | £-2,949 |
| 5 kW | 3955 kWh | 3045 kWh | 910 kWh | £824 | £91 | £915 | £19,623 | 21.4 yrs | £-1,323 |
| 6 kW | 4746 kWh | 3654 kWh | 1091 kWh | £989 | £109 | £1,098 | £21,657 | 19.7 yrs | £302 |
| 7 kW | 5537 kWh | 4263 kWh | 1273 kWh | £1,154 | £127 | £1,281 | £23,692 | 18.5 yrs | £1,927 |
| 8 kW | 6327 kWh | 4872 kWh | 1455 kWh | £1,318 | £146 | £1,464 | £25,726 | 17.6 yrs | £3,553 |
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.