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 719 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: £605, Upfront: £10,173, 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 | 1438 kWh | 575 kWh | 863 kWh | £156 | £86 | £242 | £4,069 | 16.8 yrs | £770 |
| 3 kW | 2157 kWh | 863 kWh | 1294 kWh | £234 | £129 | £363 | £6,104 | 16.8 yrs | £1,155 |
| 4 kW | 2876 kWh | 1151 kWh | 1726 kWh | £311 | £173 | £484 | £8,138 | 16.8 yrs | £1,541 |
| 5 kW | 3596 kWh | 1438 kWh | 2157 kWh | £389 | £216 | £605 | £10,173 | 16.8 yrs | £1,926 |
| 6 kW | 4315 kWh | 1726 kWh | 2589 kWh | £467 | £259 | £726 | £12,207 | 16.8 yrs | £2,311 |
| 7 kW | 5034 kWh | 2014 kWh | 3020 kWh | £545 | £302 | £847 | £14,242 | 16.8 yrs | £2,696 |
| 8 kW | 5753 kWh | 2301 kWh | 3452 kWh | £623 | £345 | £968 | £16,276 | 16.8 yrs | £3,081 |
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: £728, Upfront: £12,273, 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 | 1438 kWh | 863 kWh | 575 kWh | £234 | £58 | £291 | £6,169 | 21.2 yrs | £-348 |
| 3 kW | 2157 kWh | 1294 kWh | 863 kWh | £350 | £86 | £437 | £8,204 | 18.8 yrs | £528 |
| 4 kW | 2876 kWh | 1726 kWh | 1151 kWh | £467 | £115 | £582 | £10,238 | 17.6 yrs | £1,403 |
| 5 kW | 3596 kWh | 2157 kWh | 1438 kWh | £584 | £144 | £728 | £12,273 | 16.9 yrs | £2,279 |
| 6 kW | 4315 kWh | 2589 kWh | 1726 kWh | £701 | £173 | £873 | £14,307 | 16.4 yrs | £3,155 |
| 7 kW | 5034 kWh | 3020 kWh | 2014 kWh | £817 | £201 | £1,019 | £16,342 | 16.0 yrs | £4,031 |
| 8 kW | 5753 kWh | 3452 kWh | 2301 kWh | £934 | £230 | £1,164 | £18,376 | 15.8 yrs | £4,907 |
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: £789, Upfront: £13,673, Break-even: 17.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1438 kWh | 1007 kWh | 431 kWh | £272 | £43 | £316 | £7,569 | 24.0 yrs | £-1,258 |
| 3 kW | 2157 kWh | 1510 kWh | 647 kWh | £409 | £65 | £473 | £9,604 | 20.3 yrs | £-136 |
| 4 kW | 2876 kWh | 2014 kWh | 863 kWh | £545 | £86 | £631 | £11,638 | 18.4 yrs | £985 |
| 5 kW | 3596 kWh | 2517 kWh | 1079 kWh | £681 | £108 | £789 | £13,673 | 17.3 yrs | £2,106 |
| 6 kW | 4315 kWh | 3020 kWh | 1294 kWh | £817 | £129 | £947 | £15,707 | 16.6 yrs | £3,227 |
| 7 kW | 5034 kWh | 3524 kWh | 1510 kWh | £953 | £151 | £1,105 | £17,742 | 16.1 yrs | £4,349 |
| 8 kW | 5753 kWh | 4027 kWh | 1726 kWh | £1,090 | £173 | £1,262 | £19,776 | 15.7 yrs | £5,470 |
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: £807, Upfront: £15,423, Break-even: 19.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1438 kWh | 1050 kWh | 388 kWh | £284 | £39 | £323 | £9,319 | 28.9 yrs | £-2,860 |
| 3 kW | 2157 kWh | 1575 kWh | 582 kWh | £426 | £58 | £484 | £11,354 | 23.4 yrs | £-1,665 |
| 4 kW | 2876 kWh | 2100 kWh | 777 kWh | £568 | £78 | £646 | £13,388 | 20.7 yrs | £-471 |
| 5 kW | 3596 kWh | 2625 kWh | 971 kWh | £710 | £97 | £807 | £15,423 | 19.1 yrs | £724 |
| 6 kW | 4315 kWh | 3150 kWh | 1165 kWh | £852 | £116 | £969 | £17,457 | 18.0 yrs | £1,919 |
| 7 kW | 5034 kWh | 3675 kWh | 1359 kWh | £994 | £136 | £1,130 | £19,492 | 17.2 yrs | £3,114 |
| 8 kW | 5753 kWh | 4200 kWh | 1553 kWh | £1,136 | £155 | £1,292 | £21,526 | 16.7 yrs | £4,309 |
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: £820, Upfront: £17,173, Break-even: 21.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1438 kWh | 1079 kWh | 360 kWh | £292 | £36 | £328 | £11,069 | 33.8 yrs | £-4,512 |
| 3 kW | 2157 kWh | 1618 kWh | 539 kWh | £438 | £54 | £492 | £13,104 | 26.6 yrs | £-3,268 |
| 4 kW | 2876 kWh | 2157 kWh | 719 kWh | £584 | £72 | £656 | £15,138 | 23.1 yrs | £-2,024 |
| 5 kW | 3596 kWh | 2697 kWh | 899 kWh | £730 | £90 | £820 | £17,173 | 21.0 yrs | £-780 |
| 6 kW | 4315 kWh | 3236 kWh | 1079 kWh | £876 | £108 | £984 | £19,207 | 19.5 yrs | £463 |
| 7 kW | 5034 kWh | 3775 kWh | 1258 kWh | £1,022 | £126 | £1,147 | £21,242 | 18.5 yrs | £1,707 |
| 8 kW | 5753 kWh | 4315 kWh | 1438 kWh | £1,168 | £144 | £1,311 | £23,276 | 17.7 yrs | £2,951 |
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: £832, Upfront: £19,623, Break-even: 23.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1438 kWh | 1107 kWh | 331 kWh | £300 | £33 | £333 | £13,519 | 40.6 yrs | £-6,864 |
| 3 kW | 2157 kWh | 1661 kWh | 496 kWh | £450 | £50 | £499 | £15,554 | 31.2 yrs | £-5,571 |
| 4 kW | 2876 kWh | 2215 kWh | 662 kWh | £599 | £66 | £665 | £17,588 | 26.4 yrs | £-4,278 |
| 5 kW | 3596 kWh | 2769 kWh | 827 kWh | £749 | £83 | £832 | £19,623 | 23.6 yrs | £-2,985 |
| 6 kW | 4315 kWh | 3322 kWh | 992 kWh | £899 | £99 | £998 | £21,657 | 21.7 yrs | £-1,692 |
| 7 kW | 5034 kWh | 3876 kWh | 1158 kWh | £1,049 | £116 | £1,165 | £23,692 | 20.3 yrs | £-399 |
| 8 kW | 5753 kWh | 4430 kWh | 1323 kWh | £1,199 | £132 | £1,331 | £25,726 | 19.3 yrs | £894 |
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.