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 769 kWh per year on a south-facing roof. We value self-used electricity at 27.1p 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: £647, Upfront: £10,173, Break-even: 15.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1539 kWh | 615 kWh | 923 kWh | £167 | £92 | £259 | £4,069 | 15.7 yrs | £1,108 |
| 3 kW | 2308 kWh | 923 kWh | 1385 kWh | £250 | £138 | £388 | £6,104 | 15.7 yrs | £1,663 |
| 4 kW | 3077 kWh | 1231 kWh | 1846 kWh | £333 | £185 | £518 | £8,138 | 15.7 yrs | £2,217 |
| 5 kW | 3847 kWh | 1539 kWh | 2308 kWh | £416 | £231 | £647 | £10,173 | 15.7 yrs | £2,771 |
| 6 kW | 4616 kWh | 1846 kWh | 2770 kWh | £500 | £277 | £777 | £12,207 | 15.7 yrs | £3,325 |
| 7 kW | 5386 kWh | 2154 kWh | 3231 kWh | £583 | £323 | £906 | £14,242 | 15.7 yrs | £3,880 |
| 8 kW | 6155 kWh | 2462 kWh | 3693 kWh | £666 | £369 | £1,035 | £16,276 | 15.7 yrs | £4,434 |
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: £778, Upfront: £12,273, Break-even: 15.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1539 kWh | 923 kWh | 615 kWh | £250 | £62 | £311 | £6,169 | 19.8 yrs | £58 |
| 3 kW | 2308 kWh | 1385 kWh | 923 kWh | £375 | £92 | £467 | £8,204 | 17.6 yrs | £1,138 |
| 4 kW | 3077 kWh | 1846 kWh | 1231 kWh | £500 | £123 | £623 | £10,238 | 16.4 yrs | £2,217 |
| 5 kW | 3847 kWh | 2308 kWh | 1539 kWh | £625 | £154 | £778 | £12,273 | 15.8 yrs | £3,296 |
| 6 kW | 4616 kWh | 2770 kWh | 1846 kWh | £749 | £185 | £934 | £14,307 | 15.3 yrs | £4,375 |
| 7 kW | 5386 kWh | 3231 kWh | 2154 kWh | £874 | £215 | £1,090 | £16,342 | 15.0 yrs | £5,455 |
| 8 kW | 6155 kWh | 3693 kWh | 2462 kWh | £999 | £246 | £1,246 | £18,376 | 14.8 yrs | £6,534 |
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: £844, Upfront: £13,673, Break-even: 16.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1539 kWh | 1077 kWh | 462 kWh | £291 | £46 | £338 | £7,569 | 22.4 yrs | £-817 |
| 3 kW | 2308 kWh | 1616 kWh | 692 kWh | £437 | £69 | £506 | £9,604 | 19.0 yrs | £525 |
| 4 kW | 3077 kWh | 2154 kWh | 923 kWh | £583 | £92 | £675 | £11,638 | 17.2 yrs | £1,867 |
| 5 kW | 3847 kWh | 2693 kWh | 1154 kWh | £729 | £115 | £844 | £13,673 | 16.2 yrs | £3,209 |
| 6 kW | 4616 kWh | 3231 kWh | 1385 kWh | £874 | £138 | £1,013 | £15,707 | 15.5 yrs | £4,550 |
| 7 kW | 5386 kWh | 3770 kWh | 1616 kWh | £1,020 | £162 | £1,182 | £17,742 | 15.0 yrs | £5,892 |
| 8 kW | 6155 kWh | 4308 kWh | 1846 kWh | £1,166 | £185 | £1,351 | £19,776 | 14.6 yrs | £7,234 |
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: £864, Upfront: £15,423, Break-even: 17.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1539 kWh | 1123 kWh | 415 kWh | £304 | £42 | £346 | £9,319 | 27.0 yrs | £-2,409 |
| 3 kW | 2308 kWh | 1685 kWh | 623 kWh | £456 | £62 | £518 | £11,354 | 21.9 yrs | £-988 |
| 4 kW | 3077 kWh | 2247 kWh | 831 kWh | £608 | £83 | £691 | £13,388 | 19.4 yrs | £432 |
| 5 kW | 3847 kWh | 2808 kWh | 1039 kWh | £760 | £104 | £864 | £15,423 | 17.9 yrs | £1,853 |
| 6 kW | 4616 kWh | 3370 kWh | 1246 kWh | £912 | £125 | £1,037 | £17,457 | 16.8 yrs | £3,273 |
| 7 kW | 5386 kWh | 3931 kWh | 1454 kWh | £1,064 | £145 | £1,209 | £19,492 | 16.1 yrs | £4,694 |
| 8 kW | 6155 kWh | 4493 kWh | 1662 kWh | £1,216 | £166 | £1,382 | £21,526 | 15.6 yrs | £6,114 |
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: £877, Upfront: £17,173, Break-even: 19.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1539 kWh | 1154 kWh | 385 kWh | £312 | £38 | £351 | £11,069 | 31.6 yrs | £-4,054 |
| 3 kW | 2308 kWh | 1731 kWh | 577 kWh | £468 | £58 | £526 | £13,104 | 24.9 yrs | £-2,581 |
| 4 kW | 3077 kWh | 2308 kWh | 769 kWh | £625 | £77 | £702 | £15,138 | 21.6 yrs | £-1,108 |
| 5 kW | 3847 kWh | 2885 kWh | 962 kWh | £781 | £96 | £877 | £17,173 | 19.6 yrs | £365 |
| 6 kW | 4616 kWh | 3462 kWh | 1154 kWh | £937 | £115 | £1,052 | £19,207 | 18.3 yrs | £1,838 |
| 7 kW | 5386 kWh | 4039 kWh | 1346 kWh | £1,093 | £135 | £1,228 | £21,242 | 17.3 yrs | £3,311 |
| 8 kW | 6155 kWh | 4616 kWh | 1539 kWh | £1,249 | £154 | £1,403 | £23,276 | 16.6 yrs | £4,784 |
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: £890, Upfront: £19,623, Break-even: 22.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1539 kWh | 1185 kWh | 354 kWh | £321 | £35 | £356 | £13,519 | 38.0 yrs | £-6,399 |
| 3 kW | 2308 kWh | 1777 kWh | 531 kWh | £481 | £53 | £534 | £15,554 | 29.1 yrs | £-4,873 |
| 4 kW | 3077 kWh | 2370 kWh | 708 kWh | £641 | £71 | £712 | £17,588 | 24.7 yrs | £-3,348 |
| 5 kW | 3847 kWh | 2962 kWh | 885 kWh | £802 | £88 | £890 | £19,623 | 22.0 yrs | £-1,822 |
| 6 kW | 4616 kWh | 3554 kWh | 1062 kWh | £962 | £106 | £1,068 | £21,657 | 20.3 yrs | £-297 |
| 7 kW | 5386 kWh | 4147 kWh | 1239 kWh | £1,122 | £124 | £1,246 | £23,692 | 19.0 yrs | £1,229 |
| 8 kW | 6155 kWh | 4739 kWh | 1416 kWh | £1,282 | £142 | £1,424 | £25,726 | 18.1 yrs | £2,754 |
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.