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 852 kWh per year on a south-facing roof. We value self-used electricity at 25.8p 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: £696, Upfront: £10,173, 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 | 1705 kWh | 682 kWh | 1023 kWh | £176 | £102 | £279 | £4,069 | 14.6 yrs | £1,501 |
| 3 kW | 2557 kWh | 1023 kWh | 1534 kWh | £264 | £153 | £418 | £6,104 | 14.6 yrs | £2,252 |
| 4 kW | 3410 kWh | 1364 kWh | 2046 kWh | £352 | £205 | £557 | £8,138 | 14.6 yrs | £3,003 |
| 5 kW | 4262 kWh | 1705 kWh | 2557 kWh | £441 | £256 | £696 | £10,173 | 14.6 yrs | £3,754 |
| 6 kW | 5115 kWh | 2046 kWh | 3069 kWh | £529 | £307 | £836 | £12,207 | 14.6 yrs | £4,504 |
| 7 kW | 5967 kWh | 2387 kWh | 3580 kWh | £617 | £358 | £975 | £14,242 | 14.6 yrs | £5,255 |
| 8 kW | 6820 kWh | 2728 kWh | 4092 kWh | £705 | £409 | £1,114 | £16,276 | 14.6 yrs | £6,006 |
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: £831, Upfront: £12,273, Break-even: 14.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1705 kWh | 1023 kWh | 682 kWh | £264 | £68 | £333 | £6,169 | 18.6 yrs | £482 |
| 3 kW | 2557 kWh | 1534 kWh | 1023 kWh | £397 | £102 | £499 | £8,204 | 16.4 yrs | £1,773 |
| 4 kW | 3410 kWh | 2046 kWh | 1364 kWh | £529 | £136 | £665 | £10,238 | 15.4 yrs | £3,063 |
| 5 kW | 4262 kWh | 2557 kWh | 1705 kWh | £661 | £170 | £831 | £12,273 | 14.8 yrs | £4,354 |
| 6 kW | 5115 kWh | 3069 kWh | 2046 kWh | £793 | £205 | £998 | £14,307 | 14.3 yrs | £5,645 |
| 7 kW | 5967 kWh | 3580 kWh | 2387 kWh | £925 | £239 | £1,164 | £16,342 | 14.0 yrs | £6,936 |
| 8 kW | 6820 kWh | 4092 kWh | 2728 kWh | £1,057 | £273 | £1,330 | £18,376 | 13.8 yrs | £8,227 |
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: £899, Upfront: £13,673, Break-even: 15.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1705 kWh | 1193 kWh | 511 kWh | £308 | £51 | £360 | £7,569 | 21.1 yrs | £-378 |
| 3 kW | 2557 kWh | 1790 kWh | 767 kWh | £463 | £77 | £539 | £9,604 | 17.8 yrs | £1,183 |
| 4 kW | 3410 kWh | 2387 kWh | 1023 kWh | £617 | £102 | £719 | £11,638 | 16.2 yrs | £2,744 |
| 5 kW | 4262 kWh | 2984 kWh | 1279 kWh | £771 | £128 | £899 | £13,673 | 15.2 yrs | £4,305 |
| 6 kW | 5115 kWh | 3580 kWh | 1534 kWh | £925 | £153 | £1,079 | £15,707 | 14.6 yrs | £5,865 |
| 7 kW | 5967 kWh | 4177 kWh | 1790 kWh | £1,079 | £179 | £1,258 | £17,742 | 14.1 yrs | £7,426 |
| 8 kW | 6820 kWh | 4774 kWh | 2046 kWh | £1,234 | £205 | £1,438 | £19,776 | 13.8 yrs | £8,987 |
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: £919, Upfront: £15,423, 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 | 1705 kWh | 1245 kWh | 460 kWh | £322 | £46 | £368 | £9,319 | 25.3 yrs | £-1,966 |
| 3 kW | 2557 kWh | 1867 kWh | 691 kWh | £482 | £69 | £551 | £11,354 | 20.6 yrs | £-324 |
| 4 kW | 3410 kWh | 2489 kWh | 921 kWh | £643 | £92 | £735 | £13,388 | 18.2 yrs | £1,318 |
| 5 kW | 4262 kWh | 3112 kWh | 1151 kWh | £804 | £115 | £919 | £15,423 | 16.8 yrs | £2,960 |
| 6 kW | 5115 kWh | 3734 kWh | 1381 kWh | £965 | £138 | £1,103 | £17,457 | 15.8 yrs | £4,602 |
| 7 kW | 5967 kWh | 4356 kWh | 1611 kWh | £1,126 | £161 | £1,287 | £19,492 | 15.1 yrs | £6,244 |
| 8 kW | 6820 kWh | 4978 kWh | 1841 kWh | £1,286 | £184 | £1,471 | £21,526 | 14.6 yrs | £7,885 |
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: £933, Upfront: £17,173, Break-even: 18.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1705 kWh | 1279 kWh | 426 kWh | £330 | £43 | £373 | £11,069 | 29.7 yrs | £-3,608 |
| 3 kW | 2557 kWh | 1918 kWh | 639 kWh | £496 | £64 | £560 | £13,104 | 23.4 yrs | £-1,912 |
| 4 kW | 3410 kWh | 2557 kWh | 852 kWh | £661 | £85 | £746 | £15,138 | 20.3 yrs | £-216 |
| 5 kW | 4262 kWh | 3197 kWh | 1066 kWh | £826 | £107 | £933 | £17,173 | 18.4 yrs | £1,480 |
| 6 kW | 5115 kWh | 3836 kWh | 1279 kWh | £991 | £128 | £1,119 | £19,207 | 17.2 yrs | £3,176 |
| 7 kW | 5967 kWh | 4476 kWh | 1492 kWh | £1,156 | £149 | £1,306 | £21,242 | 16.3 yrs | £4,872 |
| 8 kW | 6820 kWh | 5115 kWh | 1705 kWh | £1,322 | £170 | £1,492 | £23,276 | 15.6 yrs | £6,568 |
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: £946, Upfront: £19,623, Break-even: 20.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1705 kWh | 1313 kWh | 392 kWh | £339 | £39 | £378 | £13,519 | 35.7 yrs | £-5,950 |
| 3 kW | 2557 kWh | 1969 kWh | 588 kWh | £509 | £59 | £568 | £15,554 | 27.4 yrs | £-4,200 |
| 4 kW | 3410 kWh | 2626 kWh | 784 kWh | £678 | £78 | £757 | £17,588 | 23.2 yrs | £-2,450 |
| 5 kW | 4262 kWh | 3282 kWh | 980 kWh | £848 | £98 | £946 | £19,623 | 20.7 yrs | £-700 |
| 6 kW | 5115 kWh | 3938 kWh | 1176 kWh | £1,018 | £118 | £1,135 | £21,657 | 19.1 yrs | £1,050 |
| 7 kW | 5967 kWh | 4595 kWh | 1372 kWh | £1,187 | £137 | £1,325 | £23,692 | 17.9 yrs | £2,800 |
| 8 kW | 6820 kWh | 5251 kWh | 1569 kWh | £1,357 | £157 | £1,514 | £25,726 | 17.0 yrs | £4,550 |
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.