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 935 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: £754, Upfront: £10,173, Break-even: 13.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1870 kWh | 748 kWh | 1122 kWh | £189 | £112 | £302 | £4,069 | 13.5 yrs | £1,965 |
| 3 kW | 2805 kWh | 1122 kWh | 1683 kWh | £284 | £168 | £453 | £6,104 | 13.5 yrs | £2,948 |
| 4 kW | 3740 kWh | 1496 kWh | 2244 kWh | £379 | £224 | £603 | £8,138 | 13.5 yrs | £3,930 |
| 5 kW | 4676 kWh | 1870 kWh | 2805 kWh | £474 | £281 | £754 | £10,173 | 13.5 yrs | £4,913 |
| 6 kW | 5611 kWh | 2244 kWh | 3366 kWh | £568 | £337 | £905 | £12,207 | 13.5 yrs | £5,895 |
| 7 kW | 6546 kWh | 2618 kWh | 3928 kWh | £663 | £393 | £1,056 | £14,242 | 13.5 yrs | £6,878 |
| 8 kW | 7481 kWh | 2992 kWh | 4489 kWh | £758 | £449 | £1,207 | £16,276 | 13.5 yrs | £7,860 |
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: £898, Upfront: £12,273, Break-even: 13.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1870 kWh | 1122 kWh | 748 kWh | £284 | £75 | £359 | £6,169 | 17.2 yrs | £1,012 |
| 3 kW | 2805 kWh | 1683 kWh | 1122 kWh | £426 | £112 | £539 | £8,204 | 15.2 yrs | £2,568 |
| 4 kW | 3740 kWh | 2244 kWh | 1496 kWh | £568 | £150 | £718 | £10,238 | 14.3 yrs | £4,124 |
| 5 kW | 4676 kWh | 2805 kWh | 1870 kWh | £711 | £187 | £898 | £12,273 | 13.7 yrs | £5,680 |
| 6 kW | 5611 kWh | 3366 kWh | 2244 kWh | £853 | £224 | £1,077 | £14,307 | 13.3 yrs | £7,236 |
| 7 kW | 6546 kWh | 3928 kWh | 2618 kWh | £995 | £262 | £1,257 | £16,342 | 13.0 yrs | £8,792 |
| 8 kW | 7481 kWh | 4489 kWh | 2992 kWh | £1,137 | £299 | £1,436 | £18,376 | 12.8 yrs | £10,348 |
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: £969, Upfront: £13,673, Break-even: 14.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1870 kWh | 1309 kWh | 561 kWh | £332 | £56 | £388 | £7,569 | 19.5 yrs | £185 |
| 3 kW | 2805 kWh | 1964 kWh | 842 kWh | £497 | £84 | £582 | £9,604 | 16.5 yrs | £2,028 |
| 4 kW | 3740 kWh | 2618 kWh | 1122 kWh | £663 | £112 | £775 | £11,638 | 15.0 yrs | £3,871 |
| 5 kW | 4676 kWh | 3273 kWh | 1403 kWh | £829 | £140 | £969 | £13,673 | 14.1 yrs | £5,713 |
| 6 kW | 5611 kWh | 3928 kWh | 1683 kWh | £995 | £168 | £1,163 | £15,707 | 13.5 yrs | £7,556 |
| 7 kW | 6546 kWh | 4582 kWh | 1964 kWh | £1,161 | £196 | £1,357 | £17,742 | 13.1 yrs | £9,399 |
| 8 kW | 7481 kWh | 5237 kWh | 2244 kWh | £1,326 | £224 | £1,551 | £19,776 | 12.8 yrs | £11,241 |
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: £991, Upfront: £15,423, Break-even: 15.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1870 kWh | 1365 kWh | 505 kWh | £346 | £50 | £396 | £9,319 | 23.5 yrs | £-1,393 |
| 3 kW | 2805 kWh | 2048 kWh | 757 kWh | £519 | £76 | £594 | £11,354 | 19.1 yrs | £536 |
| 4 kW | 3740 kWh | 2731 kWh | 1010 kWh | £692 | £101 | £793 | £13,388 | 16.9 yrs | £2,465 |
| 5 kW | 4676 kWh | 3413 kWh | 1262 kWh | £865 | £126 | £991 | £15,423 | 15.6 yrs | £4,393 |
| 6 kW | 5611 kWh | 4096 kWh | 1515 kWh | £1,037 | £151 | £1,189 | £17,457 | 14.7 yrs | £6,322 |
| 7 kW | 6546 kWh | 4778 kWh | 1767 kWh | £1,210 | £177 | £1,387 | £19,492 | 14.1 yrs | £8,251 |
| 8 kW | 7481 kWh | 5461 kWh | 2020 kWh | £1,383 | £202 | £1,585 | £21,526 | 13.6 yrs | £10,180 |
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: £1,005, Upfront: £17,173, Break-even: 17.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1870 kWh | 1403 kWh | 468 kWh | £355 | £47 | £402 | £11,069 | 27.5 yrs | £-3,028 |
| 3 kW | 2805 kWh | 2104 kWh | 701 kWh | £533 | £70 | £603 | £13,104 | 21.7 yrs | £-1,042 |
| 4 kW | 3740 kWh | 2805 kWh | 935 kWh | £711 | £94 | £804 | £15,138 | 18.8 yrs | £944 |
| 5 kW | 4676 kWh | 3507 kWh | 1169 kWh | £888 | £117 | £1,005 | £17,173 | 17.1 yrs | £2,930 |
| 6 kW | 5611 kWh | 4208 kWh | 1403 kWh | £1,066 | £140 | £1,206 | £19,207 | 15.9 yrs | £4,916 |
| 7 kW | 6546 kWh | 4909 kWh | 1636 kWh | £1,244 | £164 | £1,407 | £21,242 | 15.1 yrs | £6,902 |
| 8 kW | 7481 kWh | 5611 kWh | 1870 kWh | £1,421 | £187 | £1,608 | £23,276 | 14.5 yrs | £8,888 |
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: £1,019, Upfront: £19,623, Break-even: 19.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1870 kWh | 1440 kWh | 430 kWh | £365 | £43 | £408 | £13,519 | 33.2 yrs | £-5,363 |
| 3 kW | 2805 kWh | 2160 kWh | 645 kWh | £547 | £65 | £612 | £15,554 | 25.4 yrs | £-3,320 |
| 4 kW | 3740 kWh | 2880 kWh | 860 kWh | £730 | £86 | £816 | £17,588 | 21.6 yrs | £-1,276 |
| 5 kW | 4676 kWh | 3600 kWh | 1075 kWh | £912 | £108 | £1,019 | £19,623 | 19.2 yrs | £767 |
| 6 kW | 5611 kWh | 4320 kWh | 1290 kWh | £1,094 | £129 | £1,223 | £21,657 | 17.7 yrs | £2,810 |
| 7 kW | 6546 kWh | 5040 kWh | 1506 kWh | £1,277 | £151 | £1,427 | £23,692 | 16.6 yrs | £4,854 |
| 8 kW | 7481 kWh | 5760 kWh | 1721 kWh | £1,459 | £172 | £1,631 | £25,726 | 15.8 yrs | £6,897 |
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.