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 901 kWh per year on a south-facing roof. We value self-used electricity at 25.3p 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: £727, Upfront: £10,173, Break-even: 14.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1802 kWh | 721 kWh | 1081 kWh | £183 | £108 | £291 | £4,069 | 14.0 yrs | £1,745 |
| 3 kW | 2703 kWh | 1081 kWh | 1622 kWh | £274 | £162 | £436 | £6,104 | 14.0 yrs | £2,617 |
| 4 kW | 3604 kWh | 1441 kWh | 2162 kWh | £365 | £216 | £581 | £8,138 | 14.0 yrs | £3,489 |
| 5 kW | 4505 kWh | 1802 kWh | 2703 kWh | £456 | £270 | £727 | £10,173 | 14.0 yrs | £4,361 |
| 6 kW | 5406 kWh | 2162 kWh | 3243 kWh | £548 | £324 | £872 | £12,207 | 14.0 yrs | £5,234 |
| 7 kW | 6307 kWh | 2523 kWh | 3784 kWh | £639 | £378 | £1,017 | £14,242 | 14.0 yrs | £6,106 |
| 8 kW | 7207 kWh | 2883 kWh | 4324 kWh | £730 | £432 | £1,163 | £16,276 | 14.0 yrs | £6,978 |
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: £865, Upfront: £12,273, Break-even: 14.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1802 kWh | 1081 kWh | 721 kWh | £274 | £72 | £346 | £6,169 | 17.8 yrs | £749 |
| 3 kW | 2703 kWh | 1622 kWh | 1081 kWh | £411 | £108 | £519 | £8,204 | 15.8 yrs | £2,174 |
| 4 kW | 3604 kWh | 2162 kWh | 1441 kWh | £548 | £144 | £692 | £10,238 | 14.8 yrs | £3,599 |
| 5 kW | 4505 kWh | 2703 kWh | 1802 kWh | £685 | £180 | £865 | £12,273 | 14.2 yrs | £5,024 |
| 6 kW | 5406 kWh | 3243 kWh | 2162 kWh | £822 | £216 | £1,038 | £14,307 | 13.8 yrs | £6,448 |
| 7 kW | 6307 kWh | 3784 kWh | 2523 kWh | £958 | £252 | £1,211 | £16,342 | 13.5 yrs | £7,873 |
| 8 kW | 7207 kWh | 4324 kWh | 2883 kWh | £1,095 | £288 | £1,384 | £18,376 | 13.3 yrs | £9,298 |
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: £934, Upfront: £13,673, Break-even: 14.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1802 kWh | 1261 kWh | 541 kWh | £319 | £54 | £374 | £7,569 | 20.3 yrs | £-98 |
| 3 kW | 2703 kWh | 1892 kWh | 811 kWh | £479 | £81 | £560 | £9,604 | 17.1 yrs | £1,603 |
| 4 kW | 3604 kWh | 2523 kWh | 1081 kWh | £639 | £108 | £747 | £11,638 | 15.6 yrs | £3,304 |
| 5 kW | 4505 kWh | 3153 kWh | 1351 kWh | £799 | £135 | £934 | £13,673 | 14.6 yrs | £5,005 |
| 6 kW | 5406 kWh | 3784 kWh | 1622 kWh | £958 | £162 | £1,121 | £15,707 | 14.0 yrs | £6,706 |
| 7 kW | 6307 kWh | 4415 kWh | 1892 kWh | £1,118 | £189 | £1,307 | £17,742 | 13.6 yrs | £8,406 |
| 8 kW | 7207 kWh | 5045 kWh | 2162 kWh | £1,278 | £216 | £1,494 | £19,776 | 13.2 yrs | £10,107 |
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: £955, Upfront: £15,423, Break-even: 16.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1802 kWh | 1315 kWh | 487 kWh | £333 | £49 | £382 | £9,319 | 24.4 yrs | £-1,682 |
| 3 kW | 2703 kWh | 1973 kWh | 730 kWh | £500 | £73 | £573 | £11,354 | 19.8 yrs | £101 |
| 4 kW | 3604 kWh | 2631 kWh | 973 kWh | £666 | £97 | £764 | £13,388 | 17.5 yrs | £1,885 |
| 5 kW | 4505 kWh | 3288 kWh | 1216 kWh | £833 | £122 | £955 | £15,423 | 16.2 yrs | £3,669 |
| 6 kW | 5406 kWh | 3946 kWh | 1460 kWh | £1,000 | £146 | £1,145 | £17,457 | 15.2 yrs | £5,453 |
| 7 kW | 6307 kWh | 4604 kWh | 1703 kWh | £1,166 | £170 | £1,336 | £19,492 | 14.6 yrs | £7,237 |
| 8 kW | 7207 kWh | 5261 kWh | 1946 kWh | £1,333 | £195 | £1,527 | £21,526 | 14.1 yrs | £9,020 |
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: £968, Upfront: £17,173, Break-even: 17.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1802 kWh | 1351 kWh | 450 kWh | £342 | £45 | £387 | £11,069 | 28.6 yrs | £-3,322 |
| 3 kW | 2703 kWh | 2027 kWh | 676 kWh | £513 | £68 | £581 | £13,104 | 22.6 yrs | £-1,483 |
| 4 kW | 3604 kWh | 2703 kWh | 901 kWh | £685 | £90 | £775 | £15,138 | 19.5 yrs | £356 |
| 5 kW | 4505 kWh | 3378 kWh | 1126 kWh | £856 | £113 | £968 | £17,173 | 17.7 yrs | £2,195 |
| 6 kW | 5406 kWh | 4054 kWh | 1351 kWh | £1,027 | £135 | £1,162 | £19,207 | 16.5 yrs | £4,034 |
| 7 kW | 6307 kWh | 4730 kWh | 1577 kWh | £1,198 | £158 | £1,356 | £21,242 | 15.7 yrs | £5,873 |
| 8 kW | 7207 kWh | 5406 kWh | 1802 kWh | £1,369 | £180 | £1,549 | £23,276 | 15.0 yrs | £7,712 |
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: £982, Upfront: £19,623, 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 | 1802 kWh | 1387 kWh | 414 kWh | £351 | £41 | £393 | £13,519 | 34.4 yrs | £-5,661 |
| 3 kW | 2703 kWh | 2081 kWh | 622 kWh | £527 | £62 | £589 | £15,554 | 26.4 yrs | £-3,767 |
| 4 kW | 3604 kWh | 2775 kWh | 829 kWh | £703 | £83 | £786 | £17,588 | 22.4 yrs | £-1,873 |
| 5 kW | 4505 kWh | 3469 kWh | 1036 kWh | £879 | £104 | £982 | £19,623 | 20.0 yrs | £21 |
| 6 kW | 5406 kWh | 4162 kWh | 1243 kWh | £1,054 | £124 | £1,179 | £21,657 | 18.4 yrs | £1,916 |
| 7 kW | 6307 kWh | 4856 kWh | 1450 kWh | £1,230 | £145 | £1,375 | £23,692 | 17.2 yrs | £3,810 |
| 8 kW | 7207 kWh | 5550 kWh | 1658 kWh | £1,406 | £166 | £1,572 | £25,726 | 16.4 yrs | £5,704 |
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.