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 918 kWh per year on a south-facing roof. We value self-used electricity at 25.4p 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: £742, Upfront: £10,173, 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 | 1835 kWh | 734 kWh | 1101 kWh | £187 | £110 | £297 | £4,069 | 13.7 yrs | £1,867 |
| 3 kW | 2753 kWh | 1101 kWh | 1652 kWh | £280 | £165 | £445 | £6,104 | 13.7 yrs | £2,801 |
| 4 kW | 3671 kWh | 1468 kWh | 2202 kWh | £373 | £220 | £594 | £8,138 | 13.7 yrs | £3,734 |
| 5 kW | 4588 kWh | 1835 kWh | 2753 kWh | £467 | £275 | £742 | £10,173 | 13.7 yrs | £4,668 |
| 6 kW | 5506 kWh | 2202 kWh | 3304 kWh | £560 | £330 | £890 | £12,207 | 13.7 yrs | £5,601 |
| 7 kW | 6424 kWh | 2569 kWh | 3854 kWh | £653 | £385 | £1,039 | £14,242 | 13.7 yrs | £6,535 |
| 8 kW | 7341 kWh | 2937 kWh | 4405 kWh | £747 | £440 | £1,187 | £16,276 | 13.7 yrs | £7,469 |
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: £884, Upfront: £12,273, 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 | 1835 kWh | 1101 kWh | 734 kWh | £280 | £73 | £353 | £6,169 | 17.5 yrs | £900 |
| 3 kW | 2753 kWh | 1652 kWh | 1101 kWh | £420 | £110 | £530 | £8,204 | 15.5 yrs | £2,400 |
| 4 kW | 3671 kWh | 2202 kWh | 1468 kWh | £560 | £147 | £707 | £10,238 | 14.5 yrs | £3,900 |
| 5 kW | 4588 kWh | 2753 kWh | 1835 kWh | £700 | £184 | £884 | £12,273 | 13.9 yrs | £5,400 |
| 6 kW | 5506 kWh | 3304 kWh | 2202 kWh | £840 | £220 | £1,060 | £14,307 | 13.5 yrs | £6,900 |
| 7 kW | 6424 kWh | 3854 kWh | 2569 kWh | £980 | £257 | £1,237 | £16,342 | 13.2 yrs | £8,400 |
| 8 kW | 7341 kWh | 4405 kWh | 2937 kWh | £1,120 | £294 | £1,414 | £18,376 | 13.0 yrs | £9,900 |
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: £954, Upfront: £13,673, Break-even: 14.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1835 kWh | 1285 kWh | 551 kWh | £327 | £55 | £382 | £7,569 | 19.8 yrs | £66 |
| 3 kW | 2753 kWh | 1927 kWh | 826 kWh | £490 | £83 | £573 | £9,604 | 16.8 yrs | £1,849 |
| 4 kW | 3671 kWh | 2569 kWh | 1101 kWh | £653 | £110 | £764 | £11,638 | 15.2 yrs | £3,633 |
| 5 kW | 4588 kWh | 3212 kWh | 1376 kWh | £817 | £138 | £954 | £13,673 | 14.3 yrs | £5,416 |
| 6 kW | 5506 kWh | 3854 kWh | 1652 kWh | £980 | £165 | £1,145 | £15,707 | 13.7 yrs | £7,199 |
| 7 kW | 6424 kWh | 4497 kWh | 1927 kWh | £1,143 | £193 | £1,336 | £17,742 | 13.3 yrs | £8,982 |
| 8 kW | 7341 kWh | 5139 kWh | 2202 kWh | £1,307 | £220 | £1,527 | £19,776 | 13.0 yrs | £10,765 |
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: £976, Upfront: £15,423, 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 | 1835 kWh | 1340 kWh | 496 kWh | £341 | £50 | £390 | £9,319 | 23.9 yrs | £-1,514 |
| 3 kW | 2753 kWh | 2010 kWh | 743 kWh | £511 | £74 | £585 | £11,354 | 19.4 yrs | £354 |
| 4 kW | 3671 kWh | 2680 kWh | 991 kWh | £681 | £99 | £781 | £13,388 | 17.2 yrs | £2,222 |
| 5 kW | 4588 kWh | 3349 kWh | 1239 kWh | £852 | £124 | £976 | £15,423 | 15.8 yrs | £4,090 |
| 6 kW | 5506 kWh | 4019 kWh | 1487 kWh | £1,022 | £149 | £1,171 | £17,457 | 14.9 yrs | £5,959 |
| 7 kW | 6424 kWh | 4689 kWh | 1734 kWh | £1,192 | £173 | £1,366 | £19,492 | 14.3 yrs | £7,827 |
| 8 kW | 7341 kWh | 5359 kWh | 1982 kWh | £1,363 | £198 | £1,561 | £21,526 | 13.8 yrs | £9,695 |
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: £990, Upfront: £17,173, Break-even: 17.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1835 kWh | 1376 kWh | 459 kWh | £350 | £46 | £396 | £11,069 | 28.0 yrs | £-3,151 |
| 3 kW | 2753 kWh | 2065 kWh | 688 kWh | £525 | £69 | £594 | £13,104 | 22.1 yrs | £-1,226 |
| 4 kW | 3671 kWh | 2753 kWh | 918 kWh | £700 | £92 | £792 | £15,138 | 19.1 yrs | £699 |
| 5 kW | 4588 kWh | 3441 kWh | 1147 kWh | £875 | £115 | £990 | £17,173 | 17.3 yrs | £2,624 |
| 6 kW | 5506 kWh | 4129 kWh | 1376 kWh | £1,050 | £138 | £1,188 | £19,207 | 16.2 yrs | £4,548 |
| 7 kW | 6424 kWh | 4818 kWh | 1606 kWh | £1,225 | £161 | £1,386 | £21,242 | 15.3 yrs | £6,473 |
| 8 kW | 7341 kWh | 5506 kWh | 1835 kWh | £1,400 | £184 | £1,584 | £23,276 | 14.7 yrs | £8,398 |
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: £1,004, Upfront: £19,623, Break-even: 19.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1835 kWh | 1413 kWh | 422 kWh | £359 | £42 | £402 | £13,519 | 33.7 yrs | £-5,487 |
| 3 kW | 2753 kWh | 2120 kWh | 633 kWh | £539 | £63 | £602 | £15,554 | 25.8 yrs | £-3,506 |
| 4 kW | 3671 kWh | 2826 kWh | 844 kWh | £719 | £84 | £803 | £17,588 | 21.9 yrs | £-1,525 |
| 5 kW | 4588 kWh | 3533 kWh | 1055 kWh | £898 | £106 | £1,004 | £19,623 | 19.5 yrs | £457 |
| 6 kW | 5506 kWh | 4240 kWh | 1266 kWh | £1,078 | £127 | £1,205 | £21,657 | 18.0 yrs | £2,438 |
| 7 kW | 6424 kWh | 4946 kWh | 1477 kWh | £1,258 | £148 | £1,406 | £23,692 | 16.9 yrs | £4,420 |
| 8 kW | 7341 kWh | 5653 kWh | 1688 kWh | £1,438 | £169 | £1,606 | £25,726 | 16.0 yrs | £6,401 |
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.