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 871 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: £733, Upfront: £10,173, Break-even: 13.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1741 kWh | 696 kWh | 1045 kWh | £189 | £104 | £293 | £4,069 | 13.9 yrs | £1,796 |
| 3 kW | 2612 kWh | 1045 kWh | 1567 kWh | £283 | £157 | £440 | £6,104 | 13.9 yrs | £2,694 |
| 4 kW | 3482 kWh | 1393 kWh | 2089 kWh | £378 | £209 | £587 | £8,138 | 13.9 yrs | £3,593 |
| 5 kW | 4353 kWh | 1741 kWh | 2612 kWh | £472 | £261 | £733 | £10,173 | 13.9 yrs | £4,491 |
| 6 kW | 5223 kWh | 2089 kWh | 3134 kWh | £566 | £313 | £880 | £12,207 | 13.9 yrs | £5,389 |
| 7 kW | 6094 kWh | 2437 kWh | 3656 kWh | £661 | £366 | £1,026 | £14,242 | 13.9 yrs | £6,287 |
| 8 kW | 6964 kWh | 2786 kWh | 4179 kWh | £755 | £418 | £1,173 | £16,276 | 13.9 yrs | £7,185 |
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: £882, Upfront: £12,273, Break-even: 13.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1741 kWh | 1045 kWh | 696 kWh | £283 | £70 | £353 | £6,169 | 17.5 yrs | £888 |
| 3 kW | 2612 kWh | 1567 kWh | 1045 kWh | £425 | £104 | £529 | £8,204 | 15.5 yrs | £2,382 |
| 4 kW | 3482 kWh | 2089 kWh | 1393 kWh | £566 | £139 | £706 | £10,238 | 14.5 yrs | £3,876 |
| 5 kW | 4353 kWh | 2612 kWh | 1741 kWh | £708 | £174 | £882 | £12,273 | 13.9 yrs | £5,370 |
| 6 kW | 5223 kWh | 3134 kWh | 2089 kWh | £850 | £209 | £1,059 | £14,307 | 13.5 yrs | £6,864 |
| 7 kW | 6094 kWh | 3656 kWh | 2437 kWh | £991 | £244 | £1,235 | £16,342 | 13.2 yrs | £8,357 |
| 8 kW | 6964 kWh | 4179 kWh | 2786 kWh | £1,133 | £279 | £1,411 | £18,376 | 13.0 yrs | £9,851 |
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: £957, Upfront: £13,673, Break-even: 14.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1741 kWh | 1219 kWh | 522 kWh | £330 | £52 | £383 | £7,569 | 19.8 yrs | £84 |
| 3 kW | 2612 kWh | 1828 kWh | 783 kWh | £496 | £78 | £574 | £9,604 | 16.7 yrs | £1,875 |
| 4 kW | 3482 kWh | 2437 kWh | 1045 kWh | £661 | £104 | £765 | £11,638 | 15.2 yrs | £3,667 |
| 5 kW | 4353 kWh | 3047 kWh | 1306 kWh | £826 | £131 | £957 | £13,673 | 14.3 yrs | £5,459 |
| 6 kW | 5223 kWh | 3656 kWh | 1567 kWh | £991 | £157 | £1,148 | £15,707 | 13.7 yrs | £7,251 |
| 7 kW | 6094 kWh | 4266 kWh | 1828 kWh | £1,156 | £183 | £1,339 | £17,742 | 13.2 yrs | £9,043 |
| 8 kW | 6964 kWh | 4875 kWh | 2089 kWh | £1,322 | £209 | £1,531 | £19,776 | 12.9 yrs | £10,835 |
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: £979, Upfront: £15,423, 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 | 1741 kWh | 1271 kWh | 470 kWh | £345 | £47 | £392 | £9,319 | 23.8 yrs | £-1,488 |
| 3 kW | 2612 kWh | 1906 kWh | 705 kWh | £517 | £71 | £587 | £11,354 | 19.3 yrs | £394 |
| 4 kW | 3482 kWh | 2542 kWh | 940 kWh | £689 | £94 | £783 | £13,388 | 17.1 yrs | £2,275 |
| 5 kW | 4353 kWh | 3177 kWh | 1175 kWh | £861 | £118 | £979 | £15,423 | 15.8 yrs | £4,156 |
| 6 kW | 5223 kWh | 3813 kWh | 1410 kWh | £1,034 | £141 | £1,175 | £17,457 | 14.9 yrs | £6,037 |
| 7 kW | 6094 kWh | 4448 kWh | 1645 kWh | £1,206 | £165 | £1,370 | £19,492 | 14.2 yrs | £7,918 |
| 8 kW | 6964 kWh | 5084 kWh | 1880 kWh | £1,378 | £188 | £1,566 | £21,526 | 13.7 yrs | £9,799 |
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: £994, Upfront: £17,173, Break-even: 17.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1741 kWh | 1306 kWh | 435 kWh | £354 | £44 | £398 | £11,069 | 27.8 yrs | £-3,118 |
| 3 kW | 2612 kWh | 1959 kWh | 653 kWh | £531 | £65 | £596 | £13,104 | 22.0 yrs | £-1,178 |
| 4 kW | 3482 kWh | 2612 kWh | 871 kWh | £708 | £87 | £795 | £15,138 | 19.0 yrs | £763 |
| 5 kW | 4353 kWh | 3264 kWh | 1088 kWh | £885 | £109 | £994 | £17,173 | 17.3 yrs | £2,704 |
| 6 kW | 5223 kWh | 3917 kWh | 1306 kWh | £1,062 | £131 | £1,193 | £19,207 | 16.1 yrs | £4,645 |
| 7 kW | 6094 kWh | 4570 kWh | 1523 kWh | £1,239 | £152 | £1,391 | £21,242 | 15.3 yrs | £6,585 |
| 8 kW | 6964 kWh | 5223 kWh | 1741 kWh | £1,416 | £174 | £1,590 | £23,276 | 14.6 yrs | £8,526 |
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: £1,009, Upfront: £19,623, Break-even: 19.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1741 kWh | 1341 kWh | 400 kWh | £363 | £40 | £403 | £13,519 | 33.5 yrs | £-5,449 |
| 3 kW | 2612 kWh | 2011 kWh | 601 kWh | £545 | £60 | £605 | £15,554 | 25.7 yrs | £-3,449 |
| 4 kW | 3482 kWh | 2681 kWh | 801 kWh | £727 | £80 | £807 | £17,588 | 21.8 yrs | £-1,449 |
| 5 kW | 4353 kWh | 3352 kWh | 1001 kWh | £909 | £100 | £1,009 | £19,623 | 19.5 yrs | £552 |
| 6 kW | 5223 kWh | 4022 kWh | 1201 kWh | £1,090 | £120 | £1,210 | £21,657 | 17.9 yrs | £2,552 |
| 7 kW | 6094 kWh | 4692 kWh | 1402 kWh | £1,272 | £140 | £1,412 | £23,692 | 16.8 yrs | £4,552 |
| 8 kW | 6964 kWh | 5362 kWh | 1602 kWh | £1,454 | £160 | £1,614 | £25,726 | 15.9 yrs | £6,553 |
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.