A typical roof here lands around 4.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 841 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: £709, Upfront: £10,173, Break-even: 14.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1683 kWh | 673 kWh | 1010 kWh | £182 | £101 | £283 | £4,069 | 14.4 yrs | £1,599 |
| 3 kW | 2524 kWh | 1010 kWh | 1514 kWh | £274 | £151 | £425 | £6,104 | 14.4 yrs | £2,399 |
| 4 kW | 3365 kWh | 1346 kWh | 2019 kWh | £365 | £202 | £567 | £8,138 | 14.4 yrs | £3,198 |
| 5 kW | 4206 kWh | 1683 kWh | 2524 kWh | £456 | £252 | £709 | £10,173 | 14.4 yrs | £3,998 |
| 6 kW | 5048 kWh | 2019 kWh | 3029 kWh | £547 | £303 | £850 | £12,207 | 14.4 yrs | £4,797 |
| 7 kW | 5889 kWh | 2356 kWh | 3533 kWh | £639 | £353 | £992 | £14,242 | 14.4 yrs | £5,597 |
| 8 kW | 6730 kWh | 2692 kWh | 4038 kWh | £730 | £404 | £1,134 | £16,276 | 14.4 yrs | £6,396 |
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: £852, Upfront: £12,273, Break-even: 14.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1683 kWh | 1010 kWh | 673 kWh | £274 | £67 | £341 | £6,169 | 18.1 yrs | £651 |
| 3 kW | 2524 kWh | 1514 kWh | 1010 kWh | £411 | £101 | £511 | £8,204 | 16.0 yrs | £2,026 |
| 4 kW | 3365 kWh | 2019 kWh | 1346 kWh | £547 | £135 | £682 | £10,238 | 15.0 yrs | £3,401 |
| 5 kW | 4206 kWh | 2524 kWh | 1683 kWh | £684 | £168 | £852 | £12,273 | 14.4 yrs | £4,776 |
| 6 kW | 5048 kWh | 3029 kWh | 2019 kWh | £821 | £202 | £1,023 | £14,307 | 14.0 yrs | £6,152 |
| 7 kW | 5889 kWh | 3533 kWh | 2356 kWh | £958 | £236 | £1,193 | £16,342 | 13.7 yrs | £7,527 |
| 8 kW | 6730 kWh | 4038 kWh | 2692 kWh | £1,095 | £269 | £1,364 | £18,376 | 13.5 yrs | £8,902 |
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: £924, Upfront: £13,673, 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 | 1683 kWh | 1178 kWh | 505 kWh | £319 | £50 | £370 | £7,569 | 20.5 yrs | £-174 |
| 3 kW | 2524 kWh | 1767 kWh | 757 kWh | £479 | £76 | £555 | £9,604 | 17.3 yrs | £1,489 |
| 4 kW | 3365 kWh | 2356 kWh | 1010 kWh | £639 | £101 | £740 | £11,638 | 15.7 yrs | £3,153 |
| 5 kW | 4206 kWh | 2944 kWh | 1262 kWh | £798 | £126 | £924 | £13,673 | 14.8 yrs | £4,816 |
| 6 kW | 5048 kWh | 3533 kWh | 1514 kWh | £958 | £151 | £1,109 | £15,707 | 14.2 yrs | £6,479 |
| 7 kW | 5889 kWh | 4122 kWh | 1767 kWh | £1,118 | £177 | £1,294 | £17,742 | 13.7 yrs | £8,142 |
| 8 kW | 6730 kWh | 4711 kWh | 2019 kWh | £1,277 | £202 | £1,479 | £19,776 | 13.4 yrs | £9,805 |
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: £946, Upfront: £15,423, Break-even: 16.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1683 kWh | 1228 kWh | 454 kWh | £333 | £45 | £378 | £9,319 | 24.6 yrs | £-1,751 |
| 3 kW | 2524 kWh | 1842 kWh | 681 kWh | £499 | £68 | £568 | £11,354 | 20.0 yrs | £-1 |
| 4 kW | 3365 kWh | 2456 kWh | 909 kWh | £666 | £91 | £757 | £13,388 | 17.7 yrs | £1,748 |
| 5 kW | 4206 kWh | 3071 kWh | 1136 kWh | £832 | £114 | £946 | £15,423 | 16.3 yrs | £3,498 |
| 6 kW | 5048 kWh | 3685 kWh | 1363 kWh | £999 | £136 | £1,135 | £17,457 | 15.4 yrs | £5,247 |
| 7 kW | 5889 kWh | 4299 kWh | 1590 kWh | £1,165 | £159 | £1,324 | £19,492 | 14.7 yrs | £6,997 |
| 8 kW | 6730 kWh | 4913 kWh | 1817 kWh | £1,332 | £182 | £1,514 | £21,526 | 14.2 yrs | £8,746 |
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: £960, Upfront: £17,173, Break-even: 17.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1683 kWh | 1262 kWh | 421 kWh | £342 | £42 | £384 | £11,069 | 28.8 yrs | £-3,386 |
| 3 kW | 2524 kWh | 1893 kWh | 631 kWh | £513 | £63 | £576 | £13,104 | 22.7 yrs | £-1,579 |
| 4 kW | 3365 kWh | 2524 kWh | 841 kWh | £684 | £84 | £768 | £15,138 | 19.7 yrs | £228 |
| 5 kW | 4206 kWh | 3155 kWh | 1052 kWh | £855 | £105 | £960 | £17,173 | 17.9 yrs | £2,036 |
| 6 kW | 5048 kWh | 3786 kWh | 1262 kWh | £1,026 | £126 | £1,152 | £19,207 | 16.7 yrs | £3,843 |
| 7 kW | 5889 kWh | 4417 kWh | 1472 kWh | £1,197 | £147 | £1,345 | £21,242 | 15.8 yrs | £5,650 |
| 8 kW | 6730 kWh | 5048 kWh | 1683 kWh | £1,368 | £168 | £1,537 | £23,276 | 15.1 yrs | £7,457 |
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: £975, Upfront: £19,623, Break-even: 20.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1683 kWh | 1296 kWh | 387 kWh | £351 | £39 | £390 | £13,519 | 34.7 yrs | £-5,721 |
| 3 kW | 2524 kWh | 1943 kWh | 580 kWh | £527 | £58 | £585 | £15,554 | 26.6 yrs | £-3,856 |
| 4 kW | 3365 kWh | 2591 kWh | 774 kWh | £702 | £77 | £780 | £17,588 | 22.6 yrs | £-1,991 |
| 5 kW | 4206 kWh | 3239 kWh | 967 kWh | £878 | £97 | £975 | £19,623 | 20.1 yrs | £-127 |
| 6 kW | 5048 kWh | 3887 kWh | 1161 kWh | £1,054 | £116 | £1,170 | £21,657 | 18.5 yrs | £1,738 |
| 7 kW | 5889 kWh | 4534 kWh | 1354 kWh | £1,229 | £135 | £1,365 | £23,692 | 17.4 yrs | £3,603 |
| 8 kW | 6730 kWh | 5182 kWh | 1548 kWh | £1,405 | £155 | £1,560 | £25,726 | 16.5 yrs | £5,467 |
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.