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 1111 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: £932, Upfront: £10,173, Break-even: 10.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2222 kWh | 889 kWh | 1333 kWh | £239 | £133 | £373 | £4,069 | 10.9 yrs | £3,383 |
| 3 kW | 3333 kWh | 1333 kWh | 2000 kWh | £359 | £200 | £559 | £6,104 | 10.9 yrs | £5,075 |
| 4 kW | 4444 kWh | 1778 kWh | 2667 kWh | £479 | £267 | £745 | £8,138 | 10.9 yrs | £6,767 |
| 5 kW | 5555 kWh | 2222 kWh | 3333 kWh | £598 | £333 | £932 | £10,173 | 10.9 yrs | £8,458 |
| 6 kW | 6667 kWh | 2667 kWh | 4000 kWh | £718 | £400 | £1,118 | £12,207 | 10.9 yrs | £10,150 |
| 7 kW | 7778 kWh | 3111 kWh | 4667 kWh | £837 | £467 | £1,304 | £14,242 | 10.9 yrs | £11,841 |
| 8 kW | 8889 kWh | 3555 kWh | 5333 kWh | £957 | £533 | £1,490 | £16,276 | 10.9 yrs | £13,533 |
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: £1,120, Upfront: £12,273, Break-even: 11.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2222 kWh | 1333 kWh | 889 kWh | £359 | £89 | £448 | £6,169 | 13.8 yrs | £2,787 |
| 3 kW | 3333 kWh | 2000 kWh | 1333 kWh | £538 | £133 | £672 | £8,204 | 12.2 yrs | £5,231 |
| 4 kW | 4444 kWh | 2667 kWh | 1778 kWh | £718 | £178 | £896 | £10,238 | 11.4 yrs | £7,675 |
| 5 kW | 5555 kWh | 3333 kWh | 2222 kWh | £897 | £222 | £1,120 | £12,273 | 11.0 yrs | £10,118 |
| 6 kW | 6667 kWh | 4000 kWh | 2667 kWh | £1,077 | £267 | £1,343 | £14,307 | 10.6 yrs | £12,562 |
| 7 kW | 7778 kWh | 4667 kWh | 3111 kWh | £1,256 | £311 | £1,567 | £16,342 | 10.4 yrs | £15,005 |
| 8 kW | 8889 kWh | 5333 kWh | 3555 kWh | £1,436 | £356 | £1,791 | £18,376 | 10.3 yrs | £17,449 |
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: £1,214, Upfront: £13,673, Break-even: 11.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2222 kWh | 1556 kWh | 667 kWh | £419 | £67 | £485 | £7,569 | 15.6 yrs | £2,139 |
| 3 kW | 3333 kWh | 2333 kWh | 1000 kWh | £628 | £100 | £728 | £9,604 | 13.2 yrs | £4,959 |
| 4 kW | 4444 kWh | 3111 kWh | 1333 kWh | £837 | £133 | £971 | £11,638 | 12.0 yrs | £7,778 |
| 5 kW | 5555 kWh | 3889 kWh | 1667 kWh | £1,047 | £167 | £1,214 | £13,673 | 11.3 yrs | £10,598 |
| 6 kW | 6667 kWh | 4667 kWh | 2000 kWh | £1,256 | £200 | £1,456 | £15,707 | 10.8 yrs | £13,418 |
| 7 kW | 7778 kWh | 5444 kWh | 2333 kWh | £1,466 | £233 | £1,699 | £17,742 | 10.4 yrs | £16,237 |
| 8 kW | 8889 kWh | 6222 kWh | 2667 kWh | £1,675 | £267 | £1,942 | £19,776 | 10.2 yrs | £19,057 |
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: £1,242, Upfront: £15,423, Break-even: 12.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2222 kWh | 1622 kWh | 600 kWh | £437 | £60 | £497 | £9,319 | 18.8 yrs | £615 |
| 3 kW | 3333 kWh | 2433 kWh | 900 kWh | £655 | £90 | £745 | £11,354 | 15.2 yrs | £3,547 |
| 4 kW | 4444 kWh | 3244 kWh | 1200 kWh | £873 | £120 | £993 | £13,388 | 13.5 yrs | £6,480 |
| 5 kW | 5555 kWh | 4055 kWh | 1500 kWh | £1,092 | £150 | £1,242 | £15,423 | 12.4 yrs | £9,412 |
| 6 kW | 6667 kWh | 4867 kWh | 1800 kWh | £1,310 | £180 | £1,490 | £17,457 | 11.7 yrs | £12,345 |
| 7 kW | 7778 kWh | 5678 kWh | 2100 kWh | £1,528 | £210 | £1,738 | £19,492 | 11.2 yrs | £15,277 |
| 8 kW | 8889 kWh | 6489 kWh | 2400 kWh | £1,747 | £240 | £1,987 | £21,526 | 10.8 yrs | £18,209 |
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: £1,261, Upfront: £17,173, Break-even: 13.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2222 kWh | 1667 kWh | 556 kWh | £449 | £56 | £504 | £11,069 | 22.0 yrs | £-985 |
| 3 kW | 3333 kWh | 2500 kWh | 833 kWh | £673 | £83 | £756 | £13,104 | 17.3 yrs | £2,023 |
| 4 kW | 4444 kWh | 3333 kWh | 1111 kWh | £897 | £111 | £1,008 | £15,138 | 15.0 yrs | £5,030 |
| 5 kW | 5555 kWh | 4167 kWh | 1389 kWh | £1,122 | £139 | £1,261 | £17,173 | 13.6 yrs | £8,038 |
| 6 kW | 6667 kWh | 5000 kWh | 1667 kWh | £1,346 | £167 | £1,513 | £19,207 | 12.7 yrs | £11,046 |
| 7 kW | 7778 kWh | 5833 kWh | 1944 kWh | £1,570 | £194 | £1,765 | £21,242 | 12.0 yrs | £14,053 |
| 8 kW | 8889 kWh | 6667 kWh | 2222 kWh | £1,795 | £222 | £2,017 | £23,276 | 11.5 yrs | £17,061 |
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: £1,279, Upfront: £19,623, Break-even: 15.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2222 kWh | 1711 kWh | 511 kWh | £461 | £51 | £512 | £13,519 | 26.4 yrs | £-3,284 |
| 3 kW | 3333 kWh | 2567 kWh | 767 kWh | £691 | £77 | £768 | £15,554 | 20.3 yrs | £-202 |
| 4 kW | 4444 kWh | 3422 kWh | 1022 kWh | £921 | £102 | £1,023 | £17,588 | 17.2 yrs | £2,881 |
| 5 kW | 5555 kWh | 4278 kWh | 1278 kWh | £1,152 | £128 | £1,279 | £19,623 | 15.3 yrs | £5,964 |
| 6 kW | 6667 kWh | 5133 kWh | 1533 kWh | £1,382 | £153 | £1,535 | £21,657 | 14.1 yrs | £9,047 |
| 7 kW | 7778 kWh | 5989 kWh | 1789 kWh | £1,612 | £179 | £1,791 | £23,692 | 13.2 yrs | £12,130 |
| 8 kW | 8889 kWh | 6844 kWh | 2044 kWh | £1,842 | £204 | £2,047 | £25,726 | 12.6 yrs | £15,213 |
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.