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 1007 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: £836, Upfront: £10,173, Break-even: 12.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2015 kWh | 806 kWh | 1209 kWh | £213 | £121 | £334 | £4,069 | 12.2 yrs | £2,616 |
| 3 kW | 3022 kWh | 1209 kWh | 1813 kWh | £320 | £181 | £501 | £6,104 | 12.2 yrs | £3,924 |
| 4 kW | 4029 kWh | 1612 kWh | 2417 kWh | £427 | £242 | £669 | £8,138 | 12.2 yrs | £5,232 |
| 5 kW | 5036 kWh | 2015 kWh | 3022 kWh | £533 | £302 | £836 | £10,173 | 12.2 yrs | £6,540 |
| 6 kW | 6044 kWh | 2417 kWh | 3626 kWh | £640 | £363 | £1,003 | £12,207 | 12.2 yrs | £7,848 |
| 7 kW | 7051 kWh | 2820 kWh | 4231 kWh | £747 | £423 | £1,170 | £14,242 | 12.2 yrs | £9,157 |
| 8 kW | 8058 kWh | 3223 kWh | 4835 kWh | £854 | £483 | £1,337 | £16,276 | 12.2 yrs | £10,465 |
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: £1,002, Upfront: £12,273, 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 | 2015 kWh | 1209 kWh | 806 kWh | £320 | £81 | £401 | £6,169 | 15.4 yrs | £1,844 |
| 3 kW | 3022 kWh | 1813 kWh | 1209 kWh | £480 | £121 | £601 | £8,204 | 13.7 yrs | £3,816 |
| 4 kW | 4029 kWh | 2417 kWh | 1612 kWh | £640 | £161 | £801 | £10,238 | 12.8 yrs | £5,788 |
| 5 kW | 5036 kWh | 3022 kWh | 2015 kWh | £800 | £201 | £1,002 | £12,273 | 12.3 yrs | £7,760 |
| 6 kW | 6044 kWh | 3626 kWh | 2417 kWh | £960 | £242 | £1,202 | £14,307 | 11.9 yrs | £9,733 |
| 7 kW | 7051 kWh | 4231 kWh | 2820 kWh | £1,120 | £282 | £1,402 | £16,342 | 11.7 yrs | £11,705 |
| 8 kW | 8058 kWh | 4835 kWh | 3223 kWh | £1,280 | £322 | £1,603 | £18,376 | 11.5 yrs | £13,677 |
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: £1,085, Upfront: £13,673, Break-even: 12.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2015 kWh | 1410 kWh | 604 kWh | £373 | £60 | £434 | £7,569 | 17.4 yrs | £1,108 |
| 3 kW | 3022 kWh | 2115 kWh | 907 kWh | £560 | £91 | £651 | £9,604 | 14.8 yrs | £3,412 |
| 4 kW | 4029 kWh | 2820 kWh | 1209 kWh | £747 | £121 | £868 | £11,638 | 13.4 yrs | £5,716 |
| 5 kW | 5036 kWh | 3526 kWh | 1511 kWh | £934 | £151 | £1,085 | £13,673 | 12.6 yrs | £8,020 |
| 6 kW | 6044 kWh | 4231 kWh | 1813 kWh | £1,120 | £181 | £1,302 | £15,707 | 12.1 yrs | £10,325 |
| 7 kW | 7051 kWh | 4936 kWh | 2115 kWh | £1,307 | £212 | £1,519 | £17,742 | 11.7 yrs | £12,629 |
| 8 kW | 8058 kWh | 5641 kWh | 2417 kWh | £1,494 | £242 | £1,735 | £19,776 | 11.4 yrs | £14,933 |
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: £1,110, Upfront: £15,423, 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 | 2015 kWh | 1471 kWh | 544 kWh | £389 | £54 | £444 | £9,319 | 21.0 yrs | £-443 |
| 3 kW | 3022 kWh | 2206 kWh | 816 kWh | £584 | £82 | £666 | £11,354 | 17.1 yrs | £1,961 |
| 4 kW | 4029 kWh | 2941 kWh | 1088 kWh | £779 | £109 | £888 | £13,388 | 15.1 yrs | £4,365 |
| 5 kW | 5036 kWh | 3677 kWh | 1360 kWh | £974 | £136 | £1,110 | £15,423 | 13.9 yrs | £6,768 |
| 6 kW | 6044 kWh | 4412 kWh | 1632 kWh | £1,168 | £163 | £1,331 | £17,457 | 13.1 yrs | £9,172 |
| 7 kW | 7051 kWh | 5147 kWh | 1904 kWh | £1,363 | £190 | £1,553 | £19,492 | 12.5 yrs | £11,576 |
| 8 kW | 8058 kWh | 5883 kWh | 2176 kWh | £1,558 | £218 | £1,775 | £21,526 | 12.1 yrs | £13,980 |
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: £1,126, Upfront: £17,173, Break-even: 15.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2015 kWh | 1511 kWh | 504 kWh | £400 | £50 | £450 | £11,069 | 24.6 yrs | £-2,060 |
| 3 kW | 3022 kWh | 2266 kWh | 755 kWh | £600 | £76 | £676 | £13,104 | 19.4 yrs | £410 |
| 4 kW | 4029 kWh | 3022 kWh | 1007 kWh | £800 | £101 | £901 | £15,138 | 16.8 yrs | £2,880 |
| 5 kW | 5036 kWh | 3777 kWh | 1259 kWh | £1,000 | £126 | £1,126 | £17,173 | 15.2 yrs | £5,350 |
| 6 kW | 6044 kWh | 4533 kWh | 1511 kWh | £1,200 | £151 | £1,351 | £19,207 | 14.2 yrs | £7,821 |
| 7 kW | 7051 kWh | 5288 kWh | 1763 kWh | £1,400 | £176 | £1,577 | £21,242 | 13.5 yrs | £10,291 |
| 8 kW | 8058 kWh | 6044 kWh | 2015 kWh | £1,600 | £201 | £1,802 | £23,276 | 12.9 yrs | £12,761 |
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: £1,143, Upfront: £19,623, Break-even: 17.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2015 kWh | 1551 kWh | 463 kWh | £411 | £46 | £457 | £13,519 | 29.6 yrs | £-4,377 |
| 3 kW | 3022 kWh | 2327 kWh | 695 kWh | £616 | £70 | £686 | £15,554 | 22.7 yrs | £-1,841 |
| 4 kW | 4029 kWh | 3102 kWh | 927 kWh | £822 | £93 | £914 | £17,588 | 19.2 yrs | £696 |
| 5 kW | 5036 kWh | 3878 kWh | 1158 kWh | £1,027 | £116 | £1,143 | £19,623 | 17.2 yrs | £3,232 |
| 6 kW | 6044 kWh | 4654 kWh | 1390 kWh | £1,232 | £139 | £1,371 | £21,657 | 15.8 yrs | £5,769 |
| 7 kW | 7051 kWh | 5429 kWh | 1622 kWh | £1,438 | £162 | £1,600 | £23,692 | 14.8 yrs | £8,305 |
| 8 kW | 8058 kWh | 6205 kWh | 1853 kWh | £1,643 | £185 | £1,828 | £25,726 | 14.1 yrs | £10,842 |
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.