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 1025 kWh per year on a south-facing roof. We value self-used electricity at 26.5p 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: £850, Upfront: £10,173, Break-even: 12.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2049 kWh | 820 kWh | 1230 kWh | £217 | £123 | £340 | £4,069 | 12.0 yrs | £2,732 |
| 3 kW | 3074 kWh | 1230 kWh | 1844 kWh | £326 | £184 | £510 | £6,104 | 12.0 yrs | £4,098 |
| 4 kW | 4099 kWh | 1640 kWh | 2459 kWh | £434 | £246 | £680 | £8,138 | 12.0 yrs | £5,463 |
| 5 kW | 5124 kWh | 2049 kWh | 3074 kWh | £543 | £307 | £850 | £10,173 | 12.0 yrs | £6,829 |
| 6 kW | 6148 kWh | 2459 kWh | 3689 kWh | £651 | £369 | £1,020 | £12,207 | 12.0 yrs | £8,195 |
| 7 kW | 7173 kWh | 2869 kWh | 4304 kWh | £760 | £430 | £1,190 | £14,242 | 12.0 yrs | £9,561 |
| 8 kW | 8198 kWh | 3279 kWh | 4919 kWh | £868 | £492 | £1,360 | £16,276 | 12.0 yrs | £10,927 |
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: £1,019, Upfront: £12,273, Break-even: 12.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2049 kWh | 1230 kWh | 820 kWh | £326 | £82 | £408 | £6,169 | 15.1 yrs | £1,983 |
| 3 kW | 3074 kWh | 1844 kWh | 1230 kWh | £488 | £123 | £611 | £8,204 | 13.4 yrs | £4,024 |
| 4 kW | 4099 kWh | 2459 kWh | 1640 kWh | £651 | £164 | £815 | £10,238 | 12.6 yrs | £6,065 |
| 5 kW | 5124 kWh | 3074 kWh | 2049 kWh | £814 | £205 | £1,019 | £12,273 | 12.0 yrs | £8,107 |
| 6 kW | 6148 kWh | 3689 kWh | 2459 kWh | £977 | £246 | £1,223 | £14,307 | 11.7 yrs | £10,148 |
| 7 kW | 7173 kWh | 4304 kWh | 2869 kWh | £1,140 | £287 | £1,427 | £16,342 | 11.5 yrs | £12,189 |
| 8 kW | 8198 kWh | 4919 kWh | 3279 kWh | £1,302 | £328 | £1,630 | £18,376 | 11.3 yrs | £14,231 |
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: £1,103, Upfront: £13,673, Break-even: 12.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2049 kWh | 1435 kWh | 615 kWh | £380 | £61 | £441 | £7,569 | 17.1 yrs | £1,258 |
| 3 kW | 3074 kWh | 2152 kWh | 922 kWh | £570 | £92 | £662 | £9,604 | 14.5 yrs | £3,637 |
| 4 kW | 4099 kWh | 2869 kWh | 1230 kWh | £760 | £123 | £883 | £11,638 | 13.2 yrs | £6,016 |
| 5 kW | 5124 kWh | 3586 kWh | 1537 kWh | £950 | £154 | £1,103 | £13,673 | 12.4 yrs | £8,395 |
| 6 kW | 6148 kWh | 4304 kWh | 1844 kWh | £1,140 | £184 | £1,324 | £15,707 | 11.9 yrs | £10,774 |
| 7 kW | 7173 kWh | 5021 kWh | 2152 kWh | £1,330 | £215 | £1,545 | £17,742 | 11.5 yrs | £13,154 |
| 8 kW | 8198 kWh | 5738 kWh | 2459 kWh | £1,520 | £246 | £1,765 | £19,776 | 11.2 yrs | £15,533 |
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: £1,129, Upfront: £15,423, 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 | 2049 kWh | 1496 kWh | 553 kWh | £396 | £55 | £451 | £9,319 | 20.6 yrs | £-289 |
| 3 kW | 3074 kWh | 2244 kWh | 830 kWh | £594 | £83 | £677 | £11,354 | 16.8 yrs | £2,191 |
| 4 kW | 4099 kWh | 2992 kWh | 1107 kWh | £792 | £111 | £903 | £13,388 | 14.8 yrs | £4,672 |
| 5 kW | 5124 kWh | 3740 kWh | 1383 kWh | £990 | £138 | £1,129 | £15,423 | 13.7 yrs | £7,152 |
| 6 kW | 6148 kWh | 4488 kWh | 1660 kWh | £1,188 | £166 | £1,354 | £17,457 | 12.9 yrs | £9,632 |
| 7 kW | 7173 kWh | 5236 kWh | 1937 kWh | £1,387 | £194 | £1,580 | £19,492 | 12.3 yrs | £12,113 |
| 8 kW | 8198 kWh | 5984 kWh | 2213 kWh | £1,585 | £221 | £1,806 | £21,526 | 11.9 yrs | £14,593 |
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: £1,146, Upfront: £17,173, Break-even: 15.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2049 kWh | 1537 kWh | 512 kWh | £407 | £51 | £458 | £11,069 | 24.2 yrs | £-1,904 |
| 3 kW | 3074 kWh | 2306 kWh | 769 kWh | £611 | £77 | £687 | £13,104 | 19.1 yrs | £644 |
| 4 kW | 4099 kWh | 3074 kWh | 1025 kWh | £814 | £102 | £916 | £15,138 | 16.5 yrs | £3,192 |
| 5 kW | 5124 kWh | 3843 kWh | 1281 kWh | £1,018 | £128 | £1,146 | £17,173 | 15.0 yrs | £5,740 |
| 6 kW | 6148 kWh | 4611 kWh | 1537 kWh | £1,221 | £154 | £1,375 | £19,207 | 14.0 yrs | £8,288 |
| 7 kW | 7173 kWh | 5380 kWh | 1793 kWh | £1,425 | £179 | £1,604 | £21,242 | 13.2 yrs | £10,836 |
| 8 kW | 8198 kWh | 6148 kWh | 2049 kWh | £1,628 | £205 | £1,833 | £23,276 | 12.7 yrs | £13,384 |
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: £1,163, Upfront: £19,623, Break-even: 16.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2049 kWh | 1578 kWh | 471 kWh | £418 | £47 | £465 | £13,519 | 29.1 yrs | £-4,219 |
| 3 kW | 3074 kWh | 2367 kWh | 707 kWh | £627 | £71 | £698 | £15,554 | 22.3 yrs | £-1,604 |
| 4 kW | 4099 kWh | 3156 kWh | 943 kWh | £836 | £94 | £930 | £17,588 | 18.9 yrs | £1,012 |
| 5 kW | 5124 kWh | 3945 kWh | 1178 kWh | £1,045 | £118 | £1,163 | £19,623 | 16.9 yrs | £3,627 |
| 6 kW | 6148 kWh | 4734 kWh | 1414 kWh | £1,254 | £141 | £1,395 | £21,657 | 15.5 yrs | £6,243 |
| 7 kW | 7173 kWh | 5523 kWh | 1650 kWh | £1,463 | £165 | £1,628 | £23,692 | 14.6 yrs | £8,858 |
| 8 kW | 8198 kWh | 6312 kWh | 1885 kWh | £1,671 | £189 | £1,860 | £25,726 | 13.8 yrs | £11,474 |
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.