A typical roof here lands around 3.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 936 kWh per year on a south-facing roof. We value self-used electricity at 25.6p 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: £761, 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 | 1871 kWh | 749 kWh | 1123 kWh | £192 | £112 | £304 | £4,069 | 13.4 yrs | £2,016 |
| 3 kW | 2807 kWh | 1123 kWh | 1684 kWh | £288 | £168 | £456 | £6,104 | 13.4 yrs | £3,023 |
| 4 kW | 3743 kWh | 1497 kWh | 2246 kWh | £384 | £225 | £608 | £8,138 | 13.4 yrs | £4,031 |
| 5 kW | 4679 kWh | 1871 kWh | 2807 kWh | £480 | £281 | £761 | £10,173 | 13.4 yrs | £5,039 |
| 6 kW | 5614 kWh | 2246 kWh | 3369 kWh | £576 | £337 | £913 | £12,207 | 13.4 yrs | £6,047 |
| 7 kW | 6550 kWh | 2620 kWh | 3930 kWh | £672 | £393 | £1,065 | £14,242 | 13.4 yrs | £7,054 |
| 8 kW | 7486 kWh | 2994 kWh | 4492 kWh | £768 | £449 | £1,217 | £16,276 | 13.4 yrs | £8,062 |
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: £907, 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 | 1871 kWh | 1123 kWh | 749 kWh | £288 | £75 | £363 | £6,169 | 17.0 yrs | £1,086 |
| 3 kW | 2807 kWh | 1684 kWh | 1123 kWh | £432 | £112 | £544 | £8,204 | 15.1 yrs | £2,680 |
| 4 kW | 3743 kWh | 2246 kWh | 1497 kWh | £576 | £150 | £726 | £10,238 | 14.1 yrs | £4,273 |
| 5 kW | 4679 kWh | 2807 kWh | 1871 kWh | £720 | £187 | £907 | £12,273 | 13.5 yrs | £5,866 |
| 6 kW | 5614 kWh | 3369 kWh | 2246 kWh | £864 | £225 | £1,088 | £14,307 | 13.1 yrs | £7,459 |
| 7 kW | 6550 kWh | 3930 kWh | 2620 kWh | £1,008 | £262 | £1,270 | £16,342 | 12.9 yrs | £9,052 |
| 8 kW | 7486 kWh | 4492 kWh | 2994 kWh | £1,152 | £299 | £1,451 | £18,376 | 12.7 yrs | £10,645 |
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: £980, 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 | 1871 kWh | 1310 kWh | 561 kWh | £336 | £56 | £392 | £7,569 | 19.3 yrs | £272 |
| 3 kW | 2807 kWh | 1965 kWh | 842 kWh | £504 | £84 | £588 | £9,604 | 16.3 yrs | £2,158 |
| 4 kW | 3743 kWh | 2620 kWh | 1123 kWh | £672 | £112 | £784 | £11,638 | 14.8 yrs | £4,043 |
| 5 kW | 4679 kWh | 3275 kWh | 1404 kWh | £840 | £140 | £980 | £13,673 | 14.0 yrs | £5,929 |
| 6 kW | 5614 kWh | 3930 kWh | 1684 kWh | £1,008 | £168 | £1,176 | £15,707 | 13.4 yrs | £7,815 |
| 7 kW | 6550 kWh | 4585 kWh | 1965 kWh | £1,176 | £197 | £1,372 | £17,742 | 12.9 yrs | £9,701 |
| 8 kW | 7486 kWh | 5240 kWh | 2246 kWh | £1,344 | £225 | £1,568 | £19,776 | 12.6 yrs | £11,587 |
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: £1,002, 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 | 1871 kWh | 1366 kWh | 505 kWh | £350 | £51 | £401 | £9,319 | 23.2 yrs | £-1,303 |
| 3 kW | 2807 kWh | 2049 kWh | 758 kWh | £525 | £76 | £601 | £11,354 | 18.9 yrs | £671 |
| 4 kW | 3743 kWh | 2732 kWh | 1011 kWh | £701 | £101 | £802 | £13,388 | 16.7 yrs | £2,645 |
| 5 kW | 4679 kWh | 3415 kWh | 1263 kWh | £876 | £126 | £1,002 | £15,423 | 15.4 yrs | £4,618 |
| 6 kW | 5614 kWh | 4099 kWh | 1516 kWh | £1,051 | £152 | £1,202 | £17,457 | 14.5 yrs | £6,592 |
| 7 kW | 6550 kWh | 4782 kWh | 1769 kWh | £1,226 | £177 | £1,403 | £19,492 | 13.9 yrs | £8,566 |
| 8 kW | 7486 kWh | 5465 kWh | 2021 kWh | £1,401 | £202 | £1,603 | £21,526 | 13.4 yrs | £10,539 |
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: £1,017, 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 | 1871 kWh | 1404 kWh | 468 kWh | £360 | £47 | £407 | £11,069 | 27.2 yrs | £-2,936 |
| 3 kW | 2807 kWh | 2105 kWh | 702 kWh | £540 | £70 | £610 | £13,104 | 21.5 yrs | £-903 |
| 4 kW | 3743 kWh | 2807 kWh | 936 kWh | £720 | £94 | £813 | £15,138 | 18.6 yrs | £1,129 |
| 5 kW | 4679 kWh | 3509 kWh | 1170 kWh | £900 | £117 | £1,017 | £17,173 | 16.9 yrs | £3,161 |
| 6 kW | 5614 kWh | 4211 kWh | 1404 kWh | £1,080 | £140 | £1,220 | £19,207 | 15.7 yrs | £5,193 |
| 7 kW | 6550 kWh | 4913 kWh | 1638 kWh | £1,260 | £164 | £1,423 | £21,242 | 14.9 yrs | £7,226 |
| 8 kW | 7486 kWh | 5614 kWh | 1871 kWh | £1,440 | £187 | £1,627 | £23,276 | 14.3 yrs | £9,258 |
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: £1,031, Upfront: £19,623, Break-even: 19.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1871 kWh | 1441 kWh | 430 kWh | £369 | £43 | £413 | £13,519 | 32.8 yrs | £-5,268 |
| 3 kW | 2807 kWh | 2162 kWh | 646 kWh | £554 | £65 | £619 | £15,554 | 25.1 yrs | £-3,178 |
| 4 kW | 3743 kWh | 2882 kWh | 861 kWh | £739 | £86 | £825 | £17,588 | 21.3 yrs | £-1,087 |
| 5 kW | 4679 kWh | 3603 kWh | 1076 kWh | £924 | £108 | £1,031 | £19,623 | 19.0 yrs | £1,004 |
| 6 kW | 5614 kWh | 4323 kWh | 1291 kWh | £1,108 | £129 | £1,238 | £21,657 | 17.5 yrs | £3,095 |
| 7 kW | 6550 kWh | 5044 kWh | 1507 kWh | £1,293 | £151 | £1,444 | £23,692 | 16.4 yrs | £5,185 |
| 8 kW | 7486 kWh | 5764 kWh | 1722 kWh | £1,478 | £172 | £1,650 | £25,726 | 15.6 yrs | £7,276 |
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.