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 1021 kWh per year on a south-facing roof. We value self-used electricity at 26.9p 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: £856, 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 | 2043 kWh | 817 kWh | 1226 kWh | £220 | £123 | £343 | £4,069 | 11.9 yrs | £2,782 |
| 3 kW | 3064 kWh | 1226 kWh | 1839 kWh | £330 | £184 | £514 | £6,104 | 11.9 yrs | £4,173 |
| 4 kW | 4086 kWh | 1634 kWh | 2452 kWh | £440 | £245 | £685 | £8,138 | 11.9 yrs | £5,565 |
| 5 kW | 5107 kWh | 2043 kWh | 3064 kWh | £550 | £306 | £856 | £10,173 | 11.9 yrs | £6,956 |
| 6 kW | 6129 kWh | 2452 kWh | 3677 kWh | £660 | £368 | £1,028 | £12,207 | 11.9 yrs | £8,347 |
| 7 kW | 7150 kWh | 2860 kWh | 4290 kWh | £770 | £429 | £1,199 | £14,242 | 11.9 yrs | £9,738 |
| 8 kW | 8172 kWh | 3269 kWh | 4903 kWh | £880 | £490 | £1,370 | £16,276 | 11.9 yrs | £11,129 |
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: £1,029, Upfront: £12,273, 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 | 2043 kWh | 1226 kWh | 817 kWh | £330 | £82 | £412 | £6,169 | 15.0 yrs | £2,065 |
| 3 kW | 3064 kWh | 1839 kWh | 1226 kWh | £495 | £123 | £618 | £8,204 | 13.3 yrs | £4,147 |
| 4 kW | 4086 kWh | 2452 kWh | 1634 kWh | £660 | £163 | £823 | £10,238 | 12.4 yrs | £6,230 |
| 5 kW | 5107 kWh | 3064 kWh | 2043 kWh | £825 | £204 | £1,029 | £12,273 | 11.9 yrs | £8,312 |
| 6 kW | 6129 kWh | 3677 kWh | 2452 kWh | £990 | £245 | £1,235 | £14,307 | 11.6 yrs | £10,395 |
| 7 kW | 7150 kWh | 4290 kWh | 2860 kWh | £1,155 | £286 | £1,441 | £16,342 | 11.3 yrs | £12,477 |
| 8 kW | 8172 kWh | 4903 kWh | 3269 kWh | £1,320 | £327 | £1,647 | £18,376 | 11.2 yrs | £14,560 |
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: £1,116, 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 | 2043 kWh | 1430 kWh | 613 kWh | £385 | £61 | £446 | £7,569 | 17.0 yrs | £1,356 |
| 3 kW | 3064 kWh | 2145 kWh | 919 kWh | £577 | £92 | £669 | £9,604 | 14.3 yrs | £3,784 |
| 4 kW | 4086 kWh | 2860 kWh | 1226 kWh | £770 | £123 | £893 | £11,638 | 13.0 yrs | £6,213 |
| 5 kW | 5107 kWh | 3575 kWh | 1532 kWh | £962 | £153 | £1,116 | £13,673 | 12.3 yrs | £8,641 |
| 6 kW | 6129 kWh | 4290 kWh | 1839 kWh | £1,155 | £184 | £1,339 | £15,707 | 11.7 yrs | £11,069 |
| 7 kW | 7150 kWh | 5005 kWh | 2145 kWh | £1,347 | £215 | £1,562 | £17,742 | 11.4 yrs | £13,497 |
| 8 kW | 8172 kWh | 5720 kWh | 2452 kWh | £1,540 | £245 | £1,785 | £19,776 | 11.1 yrs | £15,925 |
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: £1,142, Upfront: £15,423, 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 | 2043 kWh | 1491 kWh | 552 kWh | £401 | £55 | £457 | £9,319 | 20.4 yrs | £-186 |
| 3 kW | 3064 kWh | 2237 kWh | 827 kWh | £602 | £83 | £685 | £11,354 | 16.6 yrs | £2,345 |
| 4 kW | 4086 kWh | 2983 kWh | 1103 kWh | £803 | £110 | £913 | £13,388 | 14.7 yrs | £4,877 |
| 5 kW | 5107 kWh | 3728 kWh | 1379 kWh | £1,004 | £138 | £1,142 | £15,423 | 13.5 yrs | £7,409 |
| 6 kW | 6129 kWh | 4474 kWh | 1655 kWh | £1,204 | £165 | £1,370 | £17,457 | 12.7 yrs | £9,941 |
| 7 kW | 7150 kWh | 5220 kWh | 1931 kWh | £1,405 | £193 | £1,598 | £19,492 | 12.2 yrs | £12,473 |
| 8 kW | 8172 kWh | 5965 kWh | 2206 kWh | £1,606 | £221 | £1,827 | £21,526 | 11.8 yrs | £15,005 |
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: £1,159, Upfront: £17,173, Break-even: 14.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2043 kWh | 1532 kWh | 511 kWh | £412 | £51 | £464 | £11,069 | 23.9 yrs | £-1,798 |
| 3 kW | 3064 kWh | 2298 kWh | 766 kWh | £619 | £77 | £695 | £13,104 | 18.8 yrs | £803 |
| 4 kW | 4086 kWh | 3064 kWh | 1021 kWh | £825 | £102 | £927 | £15,138 | 16.3 yrs | £3,404 |
| 5 kW | 5107 kWh | 3831 kWh | 1277 kWh | £1,031 | £128 | £1,159 | £17,173 | 14.8 yrs | £6,005 |
| 6 kW | 6129 kWh | 4597 kWh | 1532 kWh | £1,237 | £153 | £1,391 | £19,207 | 13.8 yrs | £8,606 |
| 7 kW | 7150 kWh | 5363 kWh | 1788 kWh | £1,444 | £179 | £1,622 | £21,242 | 13.1 yrs | £11,207 |
| 8 kW | 8172 kWh | 6129 kWh | 2043 kWh | £1,650 | £204 | £1,854 | £23,276 | 12.6 yrs | £13,808 |
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: £1,176, Upfront: £19,623, Break-even: 16.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2043 kWh | 1573 kWh | 470 kWh | £423 | £47 | £470 | £13,519 | 28.7 yrs | £-4,110 |
| 3 kW | 3064 kWh | 2360 kWh | 705 kWh | £635 | £70 | £706 | £15,554 | 22.0 yrs | £-1,440 |
| 4 kW | 4086 kWh | 3146 kWh | 940 kWh | £847 | £94 | £941 | £17,588 | 18.7 yrs | £1,230 |
| 5 kW | 5107 kWh | 3933 kWh | 1175 kWh | £1,059 | £117 | £1,176 | £19,623 | 16.7 yrs | £3,901 |
| 6 kW | 6129 kWh | 4719 kWh | 1410 kWh | £1,270 | £141 | £1,411 | £21,657 | 15.3 yrs | £6,571 |
| 7 kW | 7150 kWh | 5506 kWh | 1645 kWh | £1,482 | £164 | £1,647 | £23,692 | 14.4 yrs | £9,241 |
| 8 kW | 8172 kWh | 6292 kWh | 1880 kWh | £1,694 | £188 | £1,882 | £25,726 | 13.7 yrs | £11,911 |
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.