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 928 kWh per year on a south-facing roof. We value self-used electricity at 25.4p 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: £751, Upfront: £10,173, Break-even: 13.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1857 kWh | 743 kWh | 1114 kWh | £189 | £111 | £300 | £4,069 | 13.6 yrs | £1,937 |
| 3 kW | 2785 kWh | 1114 kWh | 1671 kWh | £283 | £167 | £450 | £6,104 | 13.6 yrs | £2,905 |
| 4 kW | 3714 kWh | 1485 kWh | 2228 kWh | £378 | £223 | £601 | £8,138 | 13.6 yrs | £3,873 |
| 5 kW | 4642 kWh | 1857 kWh | 2785 kWh | £472 | £279 | £751 | £10,173 | 13.6 yrs | £4,841 |
| 6 kW | 5570 kWh | 2228 kWh | 3342 kWh | £567 | £334 | £901 | £12,207 | 13.6 yrs | £5,810 |
| 7 kW | 6499 kWh | 2599 kWh | 3899 kWh | £661 | £390 | £1,051 | £14,242 | 13.6 yrs | £6,778 |
| 8 kW | 7427 kWh | 2971 kWh | 4456 kWh | £755 | £446 | £1,201 | £16,276 | 13.6 yrs | £7,746 |
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: £894, 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 | 1857 kWh | 1114 kWh | 743 kWh | £283 | £74 | £358 | £6,169 | 17.3 yrs | £983 |
| 3 kW | 2785 kWh | 1671 kWh | 1114 kWh | £425 | £111 | £536 | £8,204 | 15.3 yrs | £2,524 |
| 4 kW | 3714 kWh | 2228 kWh | 1485 kWh | £567 | £149 | £715 | £10,238 | 14.3 yrs | £4,065 |
| 5 kW | 4642 kWh | 2785 kWh | 1857 kWh | £708 | £186 | £894 | £12,273 | 13.7 yrs | £5,606 |
| 6 kW | 5570 kWh | 3342 kWh | 2228 kWh | £850 | £223 | £1,073 | £14,307 | 13.3 yrs | £7,148 |
| 7 kW | 6499 kWh | 3899 kWh | 2599 kWh | £992 | £260 | £1,252 | £16,342 | 13.1 yrs | £8,689 |
| 8 kW | 7427 kWh | 4456 kWh | 2971 kWh | £1,133 | £297 | £1,430 | £18,376 | 12.8 yrs | £10,230 |
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: £966, Upfront: £13,673, Break-even: 14.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1857 kWh | 1300 kWh | 557 kWh | £331 | £56 | £386 | £7,569 | 19.6 yrs | £156 |
| 3 kW | 2785 kWh | 1950 kWh | 836 kWh | £496 | £84 | £579 | £9,604 | 16.6 yrs | £1,983 |
| 4 kW | 3714 kWh | 2599 kWh | 1114 kWh | £661 | £111 | £772 | £11,638 | 15.1 yrs | £3,811 |
| 5 kW | 4642 kWh | 3249 kWh | 1393 kWh | £826 | £139 | £966 | £13,673 | 14.2 yrs | £5,639 |
| 6 kW | 5570 kWh | 3899 kWh | 1671 kWh | £992 | £167 | £1,159 | £15,707 | 13.6 yrs | £7,467 |
| 7 kW | 6499 kWh | 4549 kWh | 1950 kWh | £1,157 | £195 | £1,352 | £17,742 | 13.1 yrs | £9,294 |
| 8 kW | 7427 kWh | 5199 kWh | 2228 kWh | £1,322 | £223 | £1,545 | £19,776 | 12.8 yrs | £11,122 |
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: £987, 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 | 1857 kWh | 1355 kWh | 501 kWh | £345 | £50 | £395 | £9,319 | 23.6 yrs | £-1,423 |
| 3 kW | 2785 kWh | 2033 kWh | 752 kWh | £517 | £75 | £592 | £11,354 | 19.2 yrs | £491 |
| 4 kW | 3714 kWh | 2711 kWh | 1003 kWh | £689 | £100 | £790 | £13,388 | 17.0 yrs | £2,405 |
| 5 kW | 4642 kWh | 3389 kWh | 1253 kWh | £862 | £125 | £987 | £15,423 | 15.6 yrs | £4,319 |
| 6 kW | 5570 kWh | 4066 kWh | 1504 kWh | £1,034 | £150 | £1,184 | £17,457 | 14.7 yrs | £6,232 |
| 7 kW | 6499 kWh | 4744 kWh | 1755 kWh | £1,206 | £175 | £1,382 | £19,492 | 14.1 yrs | £8,146 |
| 8 kW | 7427 kWh | 5422 kWh | 2005 kWh | £1,379 | £201 | £1,579 | £21,526 | 13.6 yrs | £10,060 |
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: £1,001, 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 | 1857 kWh | 1393 kWh | 464 kWh | £354 | £46 | £401 | £11,069 | 27.6 yrs | £-3,058 |
| 3 kW | 2785 kWh | 2089 kWh | 696 kWh | £531 | £70 | £601 | £13,104 | 21.8 yrs | £-1,087 |
| 4 kW | 3714 kWh | 2785 kWh | 928 kWh | £708 | £93 | £801 | £15,138 | 18.9 yrs | £884 |
| 5 kW | 4642 kWh | 3481 kWh | 1160 kWh | £885 | £116 | £1,001 | £17,173 | 17.1 yrs | £2,855 |
| 6 kW | 5570 kWh | 4178 kWh | 1393 kWh | £1,062 | £139 | £1,202 | £19,207 | 16.0 yrs | £4,826 |
| 7 kW | 6499 kWh | 4874 kWh | 1625 kWh | £1,239 | £162 | £1,402 | £21,242 | 15.2 yrs | £6,797 |
| 8 kW | 7427 kWh | 5570 kWh | 1857 kWh | £1,417 | £186 | £1,602 | £23,276 | 14.5 yrs | £8,768 |
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: £1,016, Upfront: £19,623, Break-even: 19.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1857 kWh | 1430 kWh | 427 kWh | £364 | £43 | £406 | £13,519 | 33.3 yrs | £-5,393 |
| 3 kW | 2785 kWh | 2145 kWh | 641 kWh | £545 | £64 | £609 | £15,554 | 25.5 yrs | £-3,365 |
| 4 kW | 3714 kWh | 2859 kWh | 854 kWh | £727 | £85 | £813 | £17,588 | 21.6 yrs | £-1,337 |
| 5 kW | 4642 kWh | 3574 kWh | 1068 kWh | £909 | £107 | £1,016 | £19,623 | 19.3 yrs | £692 |
| 6 kW | 5570 kWh | 4289 kWh | 1281 kWh | £1,091 | £128 | £1,219 | £21,657 | 17.8 yrs | £2,720 |
| 7 kW | 6499 kWh | 5004 kWh | 1495 kWh | £1,273 | £149 | £1,422 | £23,692 | 16.7 yrs | £4,748 |
| 8 kW | 7427 kWh | 5719 kWh | 1708 kWh | £1,454 | £171 | £1,625 | £25,726 | 15.8 yrs | £6,777 |
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.