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 1029 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: £855, Upfront: £10,173, Break-even: 11.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2059 kWh | 823 kWh | 1235 kWh | £218 | £124 | £342 | £4,069 | 11.9 yrs | £2,771 |
| 3 kW | 3088 kWh | 1235 kWh | 1853 kWh | £328 | £185 | £513 | £6,104 | 11.9 yrs | £4,156 |
| 4 kW | 4117 kWh | 1647 kWh | 2470 kWh | £437 | £247 | £684 | £8,138 | 11.9 yrs | £5,541 |
| 5 kW | 5147 kWh | 2059 kWh | 3088 kWh | £546 | £309 | £855 | £10,173 | 11.9 yrs | £6,926 |
| 6 kW | 6176 kWh | 2470 kWh | 3706 kWh | £655 | £371 | £1,026 | £12,207 | 11.9 yrs | £8,312 |
| 7 kW | 7205 kWh | 2882 kWh | 4323 kWh | £765 | £432 | £1,197 | £14,242 | 11.9 yrs | £9,697 |
| 8 kW | 8234 kWh | 3294 kWh | 4941 kWh | £874 | £494 | £1,368 | £16,276 | 11.9 yrs | £11,082 |
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: £1,025, 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 | 2059 kWh | 1235 kWh | 823 kWh | £328 | £82 | £410 | £6,169 | 15.0 yrs | £2,032 |
| 3 kW | 3088 kWh | 1853 kWh | 1235 kWh | £492 | £124 | £615 | £8,204 | 13.3 yrs | £4,098 |
| 4 kW | 4117 kWh | 2470 kWh | 1647 kWh | £655 | £165 | £820 | £10,238 | 12.5 yrs | £6,163 |
| 5 kW | 5147 kWh | 3088 kWh | 2059 kWh | £819 | £206 | £1,025 | £12,273 | 12.0 yrs | £8,229 |
| 6 kW | 6176 kWh | 3706 kWh | 2470 kWh | £983 | £247 | £1,230 | £14,307 | 11.6 yrs | £10,295 |
| 7 kW | 7205 kWh | 4323 kWh | 2882 kWh | £1,147 | £288 | £1,435 | £16,342 | 11.4 yrs | £12,361 |
| 8 kW | 8234 kWh | 4941 kWh | 3294 kWh | £1,311 | £329 | £1,640 | £18,376 | 11.2 yrs | £14,427 |
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: £1,110, Upfront: £13,673, 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 | 2059 kWh | 1441 kWh | 618 kWh | £382 | £62 | £444 | £7,569 | 17.0 yrs | £1,312 |
| 3 kW | 3088 kWh | 2162 kWh | 926 kWh | £573 | £93 | £666 | £9,604 | 14.4 yrs | £3,718 |
| 4 kW | 4117 kWh | 2882 kWh | 1235 kWh | £765 | £124 | £888 | £11,638 | 13.1 yrs | £6,125 |
| 5 kW | 5147 kWh | 3603 kWh | 1544 kWh | £956 | £154 | £1,110 | £13,673 | 12.3 yrs | £8,531 |
| 6 kW | 6176 kWh | 4323 kWh | 1853 kWh | £1,147 | £185 | £1,332 | £15,707 | 11.8 yrs | £10,937 |
| 7 kW | 7205 kWh | 5044 kWh | 2162 kWh | £1,338 | £216 | £1,554 | £17,742 | 11.4 yrs | £13,343 |
| 8 kW | 8234 kWh | 5764 kWh | 2470 kWh | £1,529 | £247 | £1,776 | £19,776 | 11.1 yrs | £15,749 |
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: £1,136, Upfront: £15,423, 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 | 2059 kWh | 1503 kWh | 556 kWh | £399 | £56 | £454 | £9,319 | 20.5 yrs | £-234 |
| 3 kW | 3088 kWh | 2254 kWh | 834 kWh | £598 | £83 | £681 | £11,354 | 16.7 yrs | £2,275 |
| 4 kW | 4117 kWh | 3006 kWh | 1112 kWh | £797 | £111 | £909 | £13,388 | 14.7 yrs | £4,783 |
| 5 kW | 5147 kWh | 3757 kWh | 1390 kWh | £997 | £139 | £1,136 | £15,423 | 13.6 yrs | £7,291 |
| 6 kW | 6176 kWh | 4508 kWh | 1667 kWh | £1,196 | £167 | £1,363 | £17,457 | 12.8 yrs | £9,799 |
| 7 kW | 7205 kWh | 5260 kWh | 1945 kWh | £1,395 | £195 | £1,590 | £19,492 | 12.3 yrs | £12,308 |
| 8 kW | 8234 kWh | 6011 kWh | 2223 kWh | £1,595 | £222 | £1,817 | £21,526 | 11.8 yrs | £14,816 |
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: £1,153, Upfront: £17,173, Break-even: 14.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2059 kWh | 1544 kWh | 515 kWh | £410 | £51 | £461 | £11,069 | 24.0 yrs | £-1,847 |
| 3 kW | 3088 kWh | 2316 kWh | 772 kWh | £614 | £77 | £692 | £13,104 | 18.9 yrs | £729 |
| 4 kW | 4117 kWh | 3088 kWh | 1029 kWh | £819 | £103 | £922 | £15,138 | 16.4 yrs | £3,305 |
| 5 kW | 5147 kWh | 3860 kWh | 1287 kWh | £1,024 | £129 | £1,153 | £17,173 | 14.9 yrs | £5,881 |
| 6 kW | 6176 kWh | 4632 kWh | 1544 kWh | £1,229 | £154 | £1,383 | £19,207 | 13.9 yrs | £8,458 |
| 7 kW | 7205 kWh | 5404 kWh | 1801 kWh | £1,434 | £180 | £1,614 | £21,242 | 13.2 yrs | £11,034 |
| 8 kW | 8234 kWh | 6176 kWh | 2059 kWh | £1,638 | £206 | £1,844 | £23,276 | 12.6 yrs | £13,610 |
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: £1,170, Upfront: £19,623, Break-even: 16.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2059 kWh | 1585 kWh | 473 kWh | £421 | £47 | £468 | £13,519 | 28.9 yrs | £-4,161 |
| 3 kW | 3088 kWh | 2378 kWh | 710 kWh | £631 | £71 | £702 | £15,554 | 22.2 yrs | £-1,517 |
| 4 kW | 4117 kWh | 3170 kWh | 947 kWh | £841 | £95 | £936 | £17,588 | 18.8 yrs | £1,127 |
| 5 kW | 5147 kWh | 3963 kWh | 1184 kWh | £1,051 | £118 | £1,170 | £19,623 | 16.8 yrs | £3,772 |
| 6 kW | 6176 kWh | 4755 kWh | 1420 kWh | £1,262 | £142 | £1,404 | £21,657 | 15.4 yrs | £6,416 |
| 7 kW | 7205 kWh | 5548 kWh | 1657 kWh | £1,472 | £166 | £1,638 | £23,692 | 14.5 yrs | £9,060 |
| 8 kW | 8234 kWh | 6341 kWh | 1894 kWh | £1,682 | £189 | £1,872 | £25,726 | 13.7 yrs | £11,705 |
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.