A typical roof here lands around 6.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 994 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: £824, Upfront: £10,173, Break-even: 12.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1987 kWh | 795 kWh | 1192 kWh | £211 | £119 | £330 | £4,069 | 12.3 yrs | £2,526 |
| 3 kW | 2981 kWh | 1192 kWh | 1789 kWh | £316 | £179 | £495 | £6,104 | 12.3 yrs | £3,789 |
| 4 kW | 3975 kWh | 1590 kWh | 2385 kWh | £421 | £238 | £660 | £8,138 | 12.3 yrs | £5,052 |
| 5 kW | 4969 kWh | 1987 kWh | 2981 kWh | £526 | £298 | £824 | £10,173 | 12.3 yrs | £6,316 |
| 6 kW | 5962 kWh | 2385 kWh | 3577 kWh | £632 | £358 | £989 | £12,207 | 12.3 yrs | £7,579 |
| 7 kW | 6956 kWh | 2782 kWh | 4174 kWh | £737 | £417 | £1,154 | £14,242 | 12.3 yrs | £8,842 |
| 8 kW | 7950 kWh | 3180 kWh | 4770 kWh | £842 | £477 | £1,319 | £16,276 | 12.3 yrs | £10,105 |
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: £988, Upfront: £12,273, 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 | 1987 kWh | 1192 kWh | 795 kWh | £316 | £79 | £395 | £6,169 | 15.6 yrs | £1,736 |
| 3 kW | 2981 kWh | 1789 kWh | 1192 kWh | £474 | £119 | £593 | £8,204 | 13.8 yrs | £3,655 |
| 4 kW | 3975 kWh | 2385 kWh | 1590 kWh | £632 | £159 | £791 | £10,238 | 13.0 yrs | £5,573 |
| 5 kW | 4969 kWh | 2981 kWh | 1987 kWh | £789 | £199 | £988 | £12,273 | 12.4 yrs | £7,491 |
| 6 kW | 5962 kWh | 3577 kWh | 2385 kWh | £947 | £238 | £1,186 | £14,307 | 12.1 yrs | £9,409 |
| 7 kW | 6956 kWh | 4174 kWh | 2782 kWh | £1,105 | £278 | £1,383 | £16,342 | 11.8 yrs | £11,327 |
| 8 kW | 7950 kWh | 4770 kWh | 3180 kWh | £1,263 | £318 | £1,581 | £18,376 | 11.6 yrs | £13,246 |
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: £1,070, Upfront: £13,673, Break-even: 12.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1987 kWh | 1391 kWh | 596 kWh | £368 | £60 | £428 | £7,569 | 17.7 yrs | £991 |
| 3 kW | 2981 kWh | 2087 kWh | 894 kWh | £553 | £89 | £642 | £9,604 | 15.0 yrs | £3,237 |
| 4 kW | 3975 kWh | 2782 kWh | 1192 kWh | £737 | £119 | £856 | £11,638 | 13.6 yrs | £5,483 |
| 5 kW | 4969 kWh | 3478 kWh | 1491 kWh | £921 | £149 | £1,070 | £13,673 | 12.8 yrs | £7,729 |
| 6 kW | 5962 kWh | 4174 kWh | 1789 kWh | £1,105 | £179 | £1,284 | £15,707 | 12.2 yrs | £9,974 |
| 7 kW | 6956 kWh | 4869 kWh | 2087 kWh | £1,289 | £209 | £1,498 | £17,742 | 11.8 yrs | £12,220 |
| 8 kW | 7950 kWh | 5565 kWh | 2385 kWh | £1,474 | £238 | £1,712 | £19,776 | 11.6 yrs | £14,466 |
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: £1,095, Upfront: £15,423, 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 | 1987 kWh | 1451 kWh | 537 kWh | £384 | £54 | £438 | £9,319 | 21.3 yrs | £-562 |
| 3 kW | 2981 kWh | 2176 kWh | 805 kWh | £576 | £80 | £657 | £11,354 | 17.3 yrs | £1,782 |
| 4 kW | 3975 kWh | 2902 kWh | 1073 kWh | £768 | £107 | £876 | £13,388 | 15.3 yrs | £4,126 |
| 5 kW | 4969 kWh | 3627 kWh | 1342 kWh | £960 | £134 | £1,095 | £15,423 | 14.1 yrs | £6,470 |
| 6 kW | 5962 kWh | 4353 kWh | 1610 kWh | £1,153 | £161 | £1,314 | £17,457 | 13.3 yrs | £8,814 |
| 7 kW | 6956 kWh | 5078 kWh | 1878 kWh | £1,345 | £188 | £1,532 | £19,492 | 12.7 yrs | £11,158 |
| 8 kW | 7950 kWh | 5803 kWh | 2146 kWh | £1,537 | £215 | £1,751 | £21,526 | 12.3 yrs | £13,502 |
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: £1,111, Upfront: £17,173, Break-even: 15.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1987 kWh | 1491 kWh | 497 kWh | £395 | £50 | £444 | £11,069 | 24.9 yrs | £-2,181 |
| 3 kW | 2981 kWh | 2236 kWh | 745 kWh | £592 | £75 | £667 | £13,104 | 19.7 yrs | £228 |
| 4 kW | 3975 kWh | 2981 kWh | 994 kWh | £789 | £99 | £889 | £15,138 | 17.0 yrs | £2,638 |
| 5 kW | 4969 kWh | 3727 kWh | 1242 kWh | £987 | £124 | £1,111 | £17,173 | 15.5 yrs | £5,047 |
| 6 kW | 5962 kWh | 4472 kWh | 1491 kWh | £1,184 | £149 | £1,333 | £19,207 | 14.4 yrs | £7,457 |
| 7 kW | 6956 kWh | 5217 kWh | 1739 kWh | £1,381 | £174 | £1,555 | £21,242 | 13.7 yrs | £9,866 |
| 8 kW | 7950 kWh | 5962 kWh | 1987 kWh | £1,579 | £199 | £1,778 | £23,276 | 13.1 yrs | £12,276 |
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: £1,127, Upfront: £19,623, Break-even: 17.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1987 kWh | 1530 kWh | 457 kWh | £405 | £46 | £451 | £13,519 | 30.0 yrs | £-4,500 |
| 3 kW | 2981 kWh | 2296 kWh | 686 kWh | £608 | £69 | £676 | £15,554 | 23.0 yrs | £-2,025 |
| 4 kW | 3975 kWh | 3061 kWh | 914 kWh | £810 | £91 | £902 | £17,588 | 19.5 yrs | £450 |
| 5 kW | 4969 kWh | 3826 kWh | 1143 kWh | £1,013 | £114 | £1,127 | £19,623 | 17.4 yrs | £2,925 |
| 6 kW | 5962 kWh | 4591 kWh | 1371 kWh | £1,216 | £137 | £1,353 | £21,657 | 16.0 yrs | £5,400 |
| 7 kW | 6956 kWh | 5356 kWh | 1600 kWh | £1,418 | £160 | £1,578 | £23,692 | 15.0 yrs | £7,875 |
| 8 kW | 7950 kWh | 6121 kWh | 1828 kWh | £1,621 | £183 | £1,804 | £25,726 | 14.3 yrs | £10,350 |
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.