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 741 kWh per year on a south-facing roof. We value self-used electricity at 27.1p 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: £623, Upfront: £10,173, Break-even: 16.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1481 kWh | 593 kWh | 889 kWh | £160 | £89 | £249 | £4,069 | 16.3 yrs | £915 |
| 3 kW | 2222 kWh | 889 kWh | 1333 kWh | £241 | £133 | £374 | £6,104 | 16.3 yrs | £1,373 |
| 4 kW | 2963 kWh | 1185 kWh | 1778 kWh | £321 | £178 | £498 | £8,138 | 16.3 yrs | £1,831 |
| 5 kW | 3703 kWh | 1481 kWh | 2222 kWh | £401 | £222 | £623 | £10,173 | 16.3 yrs | £2,289 |
| 6 kW | 4444 kWh | 1778 kWh | 2666 kWh | £481 | £267 | £748 | £12,207 | 16.3 yrs | £2,746 |
| 7 kW | 5185 kWh | 2074 kWh | 3111 kWh | £561 | £311 | £872 | £14,242 | 16.3 yrs | £3,204 |
| 8 kW | 5925 kWh | 2370 kWh | 3555 kWh | £641 | £356 | £997 | £16,276 | 16.3 yrs | £3,662 |
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: £749, Upfront: £12,273, Break-even: 16.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1481 kWh | 889 kWh | 593 kWh | £241 | £59 | £300 | £6,169 | 20.6 yrs | £-174 |
| 3 kW | 2222 kWh | 1333 kWh | 889 kWh | £361 | £89 | £450 | £8,204 | 18.2 yrs | £790 |
| 4 kW | 2963 kWh | 1778 kWh | 1185 kWh | £481 | £119 | £600 | £10,238 | 17.1 yrs | £1,753 |
| 5 kW | 3703 kWh | 2222 kWh | 1481 kWh | £601 | £148 | £749 | £12,273 | 16.4 yrs | £2,716 |
| 6 kW | 4444 kWh | 2666 kWh | 1778 kWh | £722 | £178 | £899 | £14,307 | 15.9 yrs | £3,679 |
| 7 kW | 5185 kWh | 3111 kWh | 2074 kWh | £842 | £207 | £1,049 | £16,342 | 15.6 yrs | £4,642 |
| 8 kW | 5925 kWh | 3555 kWh | 2370 kWh | £962 | £237 | £1,199 | £18,376 | 15.3 yrs | £5,605 |
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: £813, Upfront: £13,673, Break-even: 16.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1481 kWh | 1037 kWh | 444 kWh | £281 | £44 | £325 | £7,569 | 23.3 yrs | £-1,068 |
| 3 kW | 2222 kWh | 1555 kWh | 667 kWh | £421 | £67 | £488 | £9,604 | 19.7 yrs | £148 |
| 4 kW | 2963 kWh | 2074 kWh | 889 kWh | £561 | £89 | £650 | £11,638 | 17.9 yrs | £1,364 |
| 5 kW | 3703 kWh | 2592 kWh | 1111 kWh | £701 | £111 | £813 | £13,673 | 16.8 yrs | £2,579 |
| 6 kW | 4444 kWh | 3111 kWh | 1333 kWh | £842 | £133 | £975 | £15,707 | 16.1 yrs | £3,795 |
| 7 kW | 5185 kWh | 3629 kWh | 1555 kWh | £982 | £156 | £1,138 | £17,742 | 15.6 yrs | £5,011 |
| 8 kW | 5925 kWh | 4148 kWh | 1778 kWh | £1,122 | £178 | £1,300 | £19,776 | 15.2 yrs | £6,227 |
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: £832, Upfront: £15,423, Break-even: 18.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1481 kWh | 1081 kWh | 400 kWh | £293 | £40 | £333 | £9,319 | 28.0 yrs | £-2,667 |
| 3 kW | 2222 kWh | 1622 kWh | 600 kWh | £439 | £60 | £499 | £11,354 | 22.8 yrs | £-1,375 |
| 4 kW | 2963 kWh | 2163 kWh | 800 kWh | £585 | £80 | £665 | £13,388 | 20.1 yrs | £-83 |
| 5 kW | 3703 kWh | 2703 kWh | 1000 kWh | £732 | £100 | £832 | £15,423 | 18.5 yrs | £1,209 |
| 6 kW | 4444 kWh | 3244 kWh | 1200 kWh | £878 | £120 | £998 | £17,457 | 17.5 yrs | £2,500 |
| 7 kW | 5185 kWh | 3785 kWh | 1400 kWh | £1,024 | £140 | £1,164 | £19,492 | 16.7 yrs | £3,792 |
| 8 kW | 5925 kWh | 4326 kWh | 1600 kWh | £1,170 | £160 | £1,330 | £21,526 | 16.2 yrs | £5,084 |
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: £844, Upfront: £17,173, Break-even: 20.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1481 kWh | 1111 kWh | 370 kWh | £301 | £37 | £338 | £11,069 | 32.8 yrs | £-4,315 |
| 3 kW | 2222 kWh | 1667 kWh | 556 kWh | £451 | £56 | £507 | £13,104 | 25.9 yrs | £-2,973 |
| 4 kW | 2963 kWh | 2222 kWh | 741 kWh | £601 | £74 | £675 | £15,138 | 22.4 yrs | £-1,631 |
| 5 kW | 3703 kWh | 2778 kWh | 926 kWh | £752 | £93 | £844 | £17,173 | 20.3 yrs | £-289 |
| 6 kW | 4444 kWh | 3333 kWh | 1111 kWh | £902 | £111 | £1,013 | £19,207 | 19.0 yrs | £1,054 |
| 7 kW | 5185 kWh | 3889 kWh | 1296 kWh | £1,052 | £130 | £1,182 | £21,242 | 18.0 yrs | £2,396 |
| 8 kW | 5925 kWh | 4444 kWh | 1481 kWh | £1,203 | £148 | £1,351 | £23,276 | 17.2 yrs | £3,738 |
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: £857, Upfront: £19,623, Break-even: 22.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1481 kWh | 1141 kWh | 341 kWh | £309 | £34 | £343 | £13,519 | 39.4 yrs | £-6,664 |
| 3 kW | 2222 kWh | 1711 kWh | 511 kWh | £463 | £51 | £514 | £15,554 | 30.3 yrs | £-5,272 |
| 4 kW | 2963 kWh | 2281 kWh | 681 kWh | £617 | £68 | £685 | £17,588 | 25.7 yrs | £-3,879 |
| 5 kW | 3703 kWh | 2852 kWh | 852 kWh | £772 | £85 | £857 | £19,623 | 22.9 yrs | £-2,486 |
| 6 kW | 4444 kWh | 3422 kWh | 1022 kWh | £926 | £102 | £1,028 | £21,657 | 21.1 yrs | £-1,093 |
| 7 kW | 5185 kWh | 3992 kWh | 1192 kWh | £1,080 | £119 | £1,200 | £23,692 | 19.8 yrs | £300 |
| 8 kW | 5925 kWh | 4563 kWh | 1363 kWh | £1,235 | £136 | £1,371 | £25,726 | 18.8 yrs | £1,692 |
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.