A typical roof here lands around 4.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 944 kWh per year on a south-facing roof. We value self-used electricity at 25.3p 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: £762, Upfront: £10,173, Break-even: 13.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1888 kWh | 755 kWh | 1133 kWh | £191 | £113 | £305 | £4,069 | 13.4 yrs | £2,024 |
| 3 kW | 2833 kWh | 1133 kWh | 1700 kWh | £287 | £170 | £457 | £6,104 | 13.4 yrs | £3,035 |
| 4 kW | 3777 kWh | 1511 kWh | 2266 kWh | £383 | £227 | £609 | £8,138 | 13.4 yrs | £4,047 |
| 5 kW | 4721 kWh | 1888 kWh | 2833 kWh | £478 | £283 | £762 | £10,173 | 13.4 yrs | £5,059 |
| 6 kW | 5665 kWh | 2266 kWh | 3399 kWh | £574 | £340 | £914 | £12,207 | 13.4 yrs | £6,071 |
| 7 kW | 6609 kWh | 2644 kWh | 3966 kWh | £670 | £397 | £1,066 | £14,242 | 13.4 yrs | £7,083 |
| 8 kW | 7553 kWh | 3021 kWh | 4532 kWh | £765 | £453 | £1,219 | £16,276 | 13.4 yrs | £8,094 |
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: £906, Upfront: £12,273, Break-even: 13.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1888 kWh | 1133 kWh | 755 kWh | £287 | £76 | £363 | £6,169 | 17.0 yrs | £1,082 |
| 3 kW | 2833 kWh | 1700 kWh | 1133 kWh | £430 | £113 | £544 | £8,204 | 15.1 yrs | £2,672 |
| 4 kW | 3777 kWh | 2266 kWh | 1511 kWh | £574 | £151 | £725 | £10,238 | 14.1 yrs | £4,263 |
| 5 kW | 4721 kWh | 2833 kWh | 1888 kWh | £717 | £189 | £906 | £12,273 | 13.5 yrs | £5,854 |
| 6 kW | 5665 kWh | 3399 kWh | 2266 kWh | £861 | £227 | £1,088 | £14,307 | 13.2 yrs | £7,445 |
| 7 kW | 6609 kWh | 3966 kWh | 2644 kWh | £1,004 | £264 | £1,269 | £16,342 | 12.9 yrs | £9,035 |
| 8 kW | 7553 kWh | 4532 kWh | 3021 kWh | £1,148 | £302 | £1,450 | £18,376 | 12.7 yrs | £10,626 |
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: £979, Upfront: £13,673, Break-even: 14.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1888 kWh | 1322 kWh | 567 kWh | £335 | £57 | £391 | £7,569 | 19.3 yrs | £260 |
| 3 kW | 2833 kWh | 1983 kWh | 850 kWh | £502 | £85 | £587 | £9,604 | 16.4 yrs | £2,141 |
| 4 kW | 3777 kWh | 2644 kWh | 1133 kWh | £670 | £113 | £783 | £11,638 | 14.9 yrs | £4,021 |
| 5 kW | 4721 kWh | 3305 kWh | 1416 kWh | £837 | £142 | £979 | £13,673 | 14.0 yrs | £5,901 |
| 6 kW | 5665 kWh | 3966 kWh | 1700 kWh | £1,004 | £170 | £1,174 | £15,707 | 13.4 yrs | £7,781 |
| 7 kW | 6609 kWh | 4626 kWh | 1983 kWh | £1,172 | £198 | £1,370 | £17,742 | 12.9 yrs | £9,662 |
| 8 kW | 7553 kWh | 5287 kWh | 2266 kWh | £1,339 | £227 | £1,566 | £19,776 | 12.6 yrs | £11,542 |
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: £1,000, Upfront: £15,423, Break-even: 15.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1888 kWh | 1379 kWh | 510 kWh | £349 | £51 | £400 | £9,319 | 23.3 yrs | £-1,316 |
| 3 kW | 2833 kWh | 2068 kWh | 765 kWh | £524 | £76 | £600 | £11,354 | 18.9 yrs | £651 |
| 4 kW | 3777 kWh | 2757 kWh | 1020 kWh | £698 | £102 | £800 | £13,388 | 16.7 yrs | £2,618 |
| 5 kW | 4721 kWh | 3446 kWh | 1275 kWh | £873 | £127 | £1,000 | £15,423 | 15.4 yrs | £4,585 |
| 6 kW | 5665 kWh | 4136 kWh | 1530 kWh | £1,048 | £153 | £1,200 | £17,457 | 14.5 yrs | £6,553 |
| 7 kW | 6609 kWh | 4825 kWh | 1785 kWh | £1,222 | £178 | £1,401 | £19,492 | 13.9 yrs | £8,520 |
| 8 kW | 7553 kWh | 5514 kWh | 2039 kWh | £1,397 | £204 | £1,601 | £21,526 | 13.4 yrs | £10,487 |
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: £1,015, Upfront: £17,173, Break-even: 16.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1888 kWh | 1416 kWh | 472 kWh | £359 | £47 | £406 | £11,069 | 27.3 yrs | £-2,950 |
| 3 kW | 2833 kWh | 2124 kWh | 708 kWh | £538 | £71 | £609 | £13,104 | 21.5 yrs | £-925 |
| 4 kW | 3777 kWh | 2833 kWh | 944 kWh | £717 | £94 | £812 | £15,138 | 18.6 yrs | £1,100 |
| 5 kW | 4721 kWh | 3541 kWh | 1180 kWh | £897 | £118 | £1,015 | £17,173 | 16.9 yrs | £3,125 |
| 6 kW | 5665 kWh | 4249 kWh | 1416 kWh | £1,076 | £142 | £1,218 | £19,207 | 15.8 yrs | £5,150 |
| 7 kW | 6609 kWh | 4957 kWh | 1652 kWh | £1,256 | £165 | £1,421 | £21,242 | 15.0 yrs | £7,175 |
| 8 kW | 7553 kWh | 5665 kWh | 1888 kWh | £1,435 | £189 | £1,624 | £23,276 | 14.3 yrs | £9,200 |
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: £1,029, Upfront: £19,623, Break-even: 19.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1888 kWh | 1454 kWh | 434 kWh | £368 | £43 | £412 | £13,519 | 32.8 yrs | £-5,284 |
| 3 kW | 2833 kWh | 2181 kWh | 651 kWh | £552 | £65 | £618 | £15,554 | 25.2 yrs | £-3,201 |
| 4 kW | 3777 kWh | 2908 kWh | 869 kWh | £737 | £87 | £823 | £17,588 | 21.4 yrs | £-1,118 |
| 5 kW | 4721 kWh | 3635 kWh | 1086 kWh | £921 | £109 | £1,029 | £19,623 | 19.1 yrs | £964 |
| 6 kW | 5665 kWh | 4362 kWh | 1303 kWh | £1,105 | £130 | £1,235 | £21,657 | 17.5 yrs | £3,047 |
| 7 kW | 6609 kWh | 5089 kWh | 1520 kWh | £1,289 | £152 | £1,441 | £23,692 | 16.4 yrs | £5,130 |
| 8 kW | 7553 kWh | 5816 kWh | 1737 kWh | £1,473 | £174 | £1,647 | £25,726 | 15.6 yrs | £7,213 |
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.