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 860 kWh per year on a south-facing roof. We value self-used electricity at 25.8p 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: £702, Upfront: £10,173, Break-even: 14.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1720 kWh | 688 kWh | 1032 kWh | £178 | £103 | £281 | £4,069 | 14.5 yrs | £1,550 |
| 3 kW | 2580 kWh | 1032 kWh | 1548 kWh | £267 | £155 | £421 | £6,104 | 14.5 yrs | £2,325 |
| 4 kW | 3440 kWh | 1376 kWh | 2064 kWh | £356 | £206 | £562 | £8,138 | 14.5 yrs | £3,100 |
| 5 kW | 4300 kWh | 1720 kWh | 2580 kWh | £444 | £258 | £702 | £10,173 | 14.5 yrs | £3,875 |
| 6 kW | 5160 kWh | 2064 kWh | 3096 kWh | £533 | £310 | £843 | £12,207 | 14.5 yrs | £4,650 |
| 7 kW | 6019 kWh | 2408 kWh | 3612 kWh | £622 | £361 | £983 | £14,242 | 14.5 yrs | £5,425 |
| 8 kW | 6879 kWh | 2752 kWh | 4128 kWh | £711 | £413 | £1,124 | £16,276 | 14.5 yrs | £6,200 |
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: £839, Upfront: £12,273, Break-even: 14.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1720 kWh | 1032 kWh | 688 kWh | £267 | £69 | £335 | £6,169 | 18.4 yrs | £540 |
| 3 kW | 2580 kWh | 1548 kWh | 1032 kWh | £400 | £103 | £503 | £8,204 | 16.3 yrs | £1,860 |
| 4 kW | 3440 kWh | 2064 kWh | 1376 kWh | £533 | £138 | £671 | £10,238 | 15.3 yrs | £3,179 |
| 5 kW | 4300 kWh | 2580 kWh | 1720 kWh | £667 | £172 | £839 | £12,273 | 14.6 yrs | £4,499 |
| 6 kW | 5160 kWh | 3096 kWh | 2064 kWh | £800 | £206 | £1,006 | £14,307 | 14.2 yrs | £5,819 |
| 7 kW | 6019 kWh | 3612 kWh | 2408 kWh | £933 | £241 | £1,174 | £16,342 | 13.9 yrs | £7,139 |
| 8 kW | 6879 kWh | 4128 kWh | 2752 kWh | £1,067 | £275 | £1,342 | £18,376 | 13.7 yrs | £8,459 |
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: £907, Upfront: £13,673, Break-even: 15.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1720 kWh | 1204 kWh | 516 kWh | £311 | £52 | £363 | £7,569 | 20.9 yrs | £-315 |
| 3 kW | 2580 kWh | 1806 kWh | 774 kWh | £467 | £77 | £544 | £9,604 | 17.7 yrs | £1,277 |
| 4 kW | 3440 kWh | 2408 kWh | 1032 kWh | £622 | £103 | £725 | £11,638 | 16.0 yrs | £2,869 |
| 5 kW | 4300 kWh | 3010 kWh | 1290 kWh | £778 | £129 | £907 | £13,673 | 15.1 yrs | £4,461 |
| 6 kW | 5160 kWh | 3612 kWh | 1548 kWh | £933 | £155 | £1,088 | £15,707 | 14.4 yrs | £6,054 |
| 7 kW | 6019 kWh | 4214 kWh | 1806 kWh | £1,089 | £181 | £1,269 | £17,742 | 14.0 yrs | £7,646 |
| 8 kW | 6879 kWh | 4816 kWh | 2064 kWh | £1,244 | £206 | £1,451 | £19,776 | 13.6 yrs | £9,238 |
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: £927, Upfront: £15,423, Break-even: 16.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1720 kWh | 1255 kWh | 464 kWh | £324 | £46 | £371 | £9,319 | 25.1 yrs | £-1,902 |
| 3 kW | 2580 kWh | 1883 kWh | 697 kWh | £487 | £70 | £556 | £11,354 | 20.4 yrs | £-228 |
| 4 kW | 3440 kWh | 2511 kWh | 929 kWh | £649 | £93 | £742 | £13,388 | 18.1 yrs | £1,446 |
| 5 kW | 4300 kWh | 3139 kWh | 1161 kWh | £811 | £116 | £927 | £15,423 | 16.6 yrs | £3,120 |
| 6 kW | 5160 kWh | 3766 kWh | 1393 kWh | £973 | £139 | £1,113 | £17,457 | 15.7 yrs | £4,794 |
| 7 kW | 6019 kWh | 4394 kWh | 1625 kWh | £1,135 | £163 | £1,298 | £19,492 | 15.0 yrs | £6,468 |
| 8 kW | 6879 kWh | 5022 kWh | 1857 kWh | £1,298 | £186 | £1,483 | £21,526 | 14.5 yrs | £8,142 |
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: £941, Upfront: £17,173, Break-even: 18.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1720 kWh | 1290 kWh | 430 kWh | £333 | £43 | £376 | £11,069 | 29.4 yrs | £-3,543 |
| 3 kW | 2580 kWh | 1935 kWh | 645 kWh | £500 | £64 | £564 | £13,104 | 23.2 yrs | £-1,815 |
| 4 kW | 3440 kWh | 2580 kWh | 860 kWh | £667 | £86 | £753 | £15,138 | 20.1 yrs | £-86 |
| 5 kW | 4300 kWh | 3225 kWh | 1075 kWh | £833 | £107 | £941 | £17,173 | 18.3 yrs | £1,642 |
| 6 kW | 5160 kWh | 3870 kWh | 1290 kWh | £1,000 | £129 | £1,129 | £19,207 | 17.0 yrs | £3,371 |
| 7 kW | 6019 kWh | 4515 kWh | 1505 kWh | £1,167 | £150 | £1,317 | £21,242 | 16.1 yrs | £5,099 |
| 8 kW | 6879 kWh | 5160 kWh | 1720 kWh | £1,333 | £172 | £1,505 | £23,276 | 15.5 yrs | £6,828 |
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: £954, Upfront: £19,623, Break-even: 20.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1720 kWh | 1324 kWh | 396 kWh | £342 | £40 | £382 | £13,519 | 35.4 yrs | £-5,884 |
| 3 kW | 2580 kWh | 1986 kWh | 593 kWh | £513 | £59 | £573 | £15,554 | 27.2 yrs | £-4,101 |
| 4 kW | 3440 kWh | 2649 kWh | 791 kWh | £684 | £79 | £763 | £17,588 | 23.0 yrs | £-2,318 |
| 5 kW | 4300 kWh | 3311 kWh | 989 kWh | £855 | £99 | £954 | £19,623 | 20.6 yrs | £-535 |
| 6 kW | 5160 kWh | 3973 kWh | 1187 kWh | £1,027 | £119 | £1,145 | £21,657 | 18.9 yrs | £1,248 |
| 7 kW | 6019 kWh | 4635 kWh | 1384 kWh | £1,198 | £138 | £1,336 | £23,692 | 17.7 yrs | £3,031 |
| 8 kW | 6879 kWh | 5297 kWh | 1582 kWh | £1,369 | £158 | £1,527 | £25,726 | 16.8 yrs | £4,814 |
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.