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 873 kWh per year on a south-facing roof. We value self-used electricity at 0.0p 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: £262, Upfront: £10,173, Break-even: 38.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1745 kWh | 698 kWh | 1047 kWh | £0 | £105 | £105 | £4,069 | 38.9 yrs | £-1,975 |
| 3 kW | 2618 kWh | 1047 kWh | 1571 kWh | £0 | £157 | £157 | £6,104 | 38.9 yrs | £-2,962 |
| 4 kW | 3490 kWh | 1396 kWh | 2094 kWh | £0 | £209 | £209 | £8,138 | 38.9 yrs | £-3,950 |
| 5 kW | 4363 kWh | 1745 kWh | 2618 kWh | £0 | £262 | £262 | £10,173 | 38.9 yrs | £-4,937 |
| 6 kW | 5235 kWh | 2094 kWh | 3141 kWh | £0 | £314 | £314 | £12,207 | 38.9 yrs | £-5,925 |
| 7 kW | 6108 kWh | 2443 kWh | 3665 kWh | £0 | £366 | £366 | £14,242 | 38.9 yrs | £-6,912 |
| 8 kW | 6980 kWh | 2792 kWh | 4188 kWh | £0 | £419 | £419 | £16,276 | 38.9 yrs | £-7,900 |
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: £175, Upfront: £12,273, Break-even: 70.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1745 kWh | 1047 kWh | 698 kWh | £0 | £70 | £70 | £6,169 | 88.4 yrs | £-4,773 |
| 3 kW | 2618 kWh | 1571 kWh | 1047 kWh | £0 | £105 | £105 | £8,204 | 78.4 yrs | £-6,109 |
| 4 kW | 3490 kWh | 2094 kWh | 1396 kWh | £0 | £140 | £140 | £10,238 | 73.3 yrs | £-7,446 |
| 5 kW | 4363 kWh | 2618 kWh | 1745 kWh | £0 | £175 | £175 | £12,273 | 70.3 yrs | £-8,782 |
| 6 kW | 5235 kWh | 3141 kWh | 2094 kWh | £0 | £209 | £209 | £14,307 | 68.3 yrs | £-10,119 |
| 7 kW | 6108 kWh | 3665 kWh | 2443 kWh | £0 | £244 | £244 | £16,342 | 66.9 yrs | £-11,455 |
| 8 kW | 6980 kWh | 4188 kWh | 2792 kWh | £0 | £279 | £279 | £18,376 | 65.8 yrs | £-12,792 |
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: £131, Upfront: £13,673, Break-even: 104.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1745 kWh | 1222 kWh | 524 kWh | £0 | £52 | £52 | £7,569 | 144.6 yrs | £-6,522 |
| 3 kW | 2618 kWh | 1832 kWh | 785 kWh | £0 | £79 | £79 | £9,604 | 122.3 yrs | £-8,033 |
| 4 kW | 3490 kWh | 2443 kWh | 1047 kWh | £0 | £105 | £105 | £11,638 | 111.2 yrs | £-9,544 |
| 5 kW | 4363 kWh | 3054 kWh | 1309 kWh | £0 | £131 | £131 | £13,673 | 104.5 yrs | £-11,055 |
| 6 kW | 5235 kWh | 3665 kWh | 1571 kWh | £0 | £157 | £157 | £15,707 | 100.0 yrs | £-12,566 |
| 7 kW | 6108 kWh | 4275 kWh | 1832 kWh | £0 | £183 | £183 | £17,742 | 96.8 yrs | £-14,077 |
| 8 kW | 6980 kWh | 4886 kWh | 2094 kWh | £0 | £209 | £209 | £19,776 | 94.4 yrs | £-15,588 |
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: £118, Upfront: £15,423, Break-even: 130.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1745 kWh | 1274 kWh | 471 kWh | £0 | £47 | £47 | £9,319 | 197.8 yrs | £-8,377 |
| 3 kW | 2618 kWh | 1911 kWh | 707 kWh | £0 | £71 | £71 | £11,354 | 160.6 yrs | £-9,940 |
| 4 kW | 3490 kWh | 2548 kWh | 942 kWh | £0 | £94 | £94 | £13,388 | 142.1 yrs | £-11,503 |
| 5 kW | 4363 kWh | 3185 kWh | 1178 kWh | £0 | £118 | £118 | £15,423 | 130.9 yrs | £-13,067 |
| 6 kW | 5235 kWh | 3822 kWh | 1413 kWh | £0 | £141 | £141 | £17,457 | 123.5 yrs | £-14,630 |
| 7 kW | 6108 kWh | 4459 kWh | 1649 kWh | £0 | £165 | £165 | £19,492 | 118.2 yrs | £-16,193 |
| 8 kW | 6980 kWh | 5096 kWh | 1885 kWh | £0 | £188 | £188 | £21,526 | 114.2 yrs | £-17,757 |
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: £109, Upfront: £17,173, Break-even: 157.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1745 kWh | 1309 kWh | 436 kWh | £0 | £44 | £44 | £11,069 | 253.7 yrs | £-10,196 |
| 3 kW | 2618 kWh | 1963 kWh | 654 kWh | £0 | £65 | £65 | £13,104 | 200.2 yrs | £-11,795 |
| 4 kW | 3490 kWh | 2618 kWh | 873 kWh | £0 | £87 | £87 | £15,138 | 173.5 yrs | £-13,393 |
| 5 kW | 4363 kWh | 3272 kWh | 1091 kWh | £0 | £109 | £109 | £17,173 | 157.5 yrs | £-14,991 |
| 6 kW | 5235 kWh | 3926 kWh | 1309 kWh | £0 | £131 | £131 | £19,207 | 146.8 yrs | £-16,589 |
| 7 kW | 6108 kWh | 4581 kWh | 1527 kWh | £0 | £153 | £153 | £21,242 | 139.1 yrs | £-18,188 |
| 8 kW | 6980 kWh | 5235 kWh | 1745 kWh | £0 | £175 | £175 | £23,276 | 133.4 yrs | £-19,786 |
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: £100, Upfront: £19,623, Break-even: 195.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1745 kWh | 1344 kWh | 401 kWh | £0 | £40 | £40 | £13,519 | 336.8 yrs | £-12,716 |
| 3 kW | 2618 kWh | 2016 kWh | 602 kWh | £0 | £60 | £60 | £15,554 | 258.3 yrs | £-14,349 |
| 4 kW | 3490 kWh | 2687 kWh | 803 kWh | £0 | £80 | £80 | £17,588 | 219.1 yrs | £-15,983 |
| 5 kW | 4363 kWh | 3359 kWh | 1003 kWh | £0 | £100 | £100 | £19,623 | 195.6 yrs | £-17,616 |
| 6 kW | 5235 kWh | 4031 kWh | 1204 kWh | £0 | £120 | £120 | £21,657 | 179.9 yrs | £-19,249 |
| 7 kW | 6108 kWh | 4703 kWh | 1405 kWh | £0 | £140 | £140 | £23,692 | 168.7 yrs | £-20,882 |
| 8 kW | 6980 kWh | 5375 kWh | 1605 kWh | £0 | £161 | £161 | £25,726 | 160.2 yrs | £-22,515 |
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.