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 821 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: £691, Upfront: £10,173, Break-even: 14.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1642 kWh | 657 kWh | 985 kWh | £178 | £99 | £276 | £4,069 | 14.7 yrs | £1,457 |
| 3 kW | 2463 kWh | 985 kWh | 1478 kWh | £267 | £148 | £414 | £6,104 | 14.7 yrs | £2,186 |
| 4 kW | 3285 kWh | 1314 kWh | 1971 kWh | £356 | £197 | £553 | £8,138 | 14.7 yrs | £2,914 |
| 5 kW | 4106 kWh | 1642 kWh | 2463 kWh | £444 | £246 | £691 | £10,173 | 14.7 yrs | £3,643 |
| 6 kW | 4927 kWh | 1971 kWh | 2956 kWh | £533 | £296 | £829 | £12,207 | 14.7 yrs | £4,371 |
| 7 kW | 5748 kWh | 2299 kWh | 3449 kWh | £622 | £345 | £967 | £14,242 | 14.7 yrs | £5,100 |
| 8 kW | 6569 kWh | 2628 kWh | 3942 kWh | £711 | £394 | £1,105 | £16,276 | 14.7 yrs | £5,828 |
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: £831, Upfront: £12,273, Break-even: 14.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1642 kWh | 985 kWh | 657 kWh | £267 | £66 | £332 | £6,169 | 18.6 yrs | £478 |
| 3 kW | 2463 kWh | 1478 kWh | 985 kWh | £400 | £99 | £499 | £8,204 | 16.5 yrs | £1,767 |
| 4 kW | 3285 kWh | 1971 kWh | 1314 kWh | £533 | £131 | £665 | £10,238 | 15.4 yrs | £3,056 |
| 5 kW | 4106 kWh | 2463 kWh | 1642 kWh | £667 | £164 | £831 | £12,273 | 14.8 yrs | £4,344 |
| 6 kW | 4927 kWh | 2956 kWh | 1971 kWh | £800 | £197 | £997 | £14,307 | 14.3 yrs | £5,633 |
| 7 kW | 5748 kWh | 3449 kWh | 2299 kWh | £933 | £230 | £1,163 | £16,342 | 14.0 yrs | £6,922 |
| 8 kW | 6569 kWh | 3942 kWh | 2628 kWh | £1,067 | £263 | £1,329 | £18,376 | 13.8 yrs | £8,211 |
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: £901, Upfront: £13,673, Break-even: 15.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1642 kWh | 1150 kWh | 493 kWh | £311 | £49 | £360 | £7,569 | 21.0 yrs | £-362 |
| 3 kW | 2463 kWh | 1724 kWh | 739 kWh | £467 | £74 | £541 | £9,604 | 17.8 yrs | £1,207 |
| 4 kW | 3285 kWh | 2299 kWh | 985 kWh | £622 | £99 | £721 | £11,638 | 16.1 yrs | £2,776 |
| 5 kW | 4106 kWh | 2874 kWh | 1232 kWh | £778 | £123 | £901 | £13,673 | 15.2 yrs | £4,345 |
| 6 kW | 4927 kWh | 3449 kWh | 1478 kWh | £933 | £148 | £1,081 | £15,707 | 14.5 yrs | £5,914 |
| 7 kW | 5748 kWh | 4024 kWh | 1724 kWh | £1,089 | £172 | £1,261 | £17,742 | 14.1 yrs | £7,483 |
| 8 kW | 6569 kWh | 4598 kWh | 1971 kWh | £1,244 | £197 | £1,441 | £19,776 | 13.7 yrs | £9,053 |
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: £922, Upfront: £15,423, Break-even: 16.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1642 kWh | 1199 kWh | 443 kWh | £324 | £44 | £369 | £9,319 | 25.3 yrs | £-1,944 |
| 3 kW | 2463 kWh | 1798 kWh | 665 kWh | £487 | £67 | £553 | £11,354 | 20.5 yrs | £-291 |
| 4 kW | 3285 kWh | 2398 kWh | 887 kWh | £649 | £89 | £738 | £13,388 | 18.2 yrs | £1,362 |
| 5 kW | 4106 kWh | 2997 kWh | 1109 kWh | £811 | £111 | £922 | £15,423 | 16.7 yrs | £3,016 |
| 6 kW | 4927 kWh | 3597 kWh | 1330 kWh | £973 | £133 | £1,106 | £17,457 | 15.8 yrs | £4,669 |
| 7 kW | 5748 kWh | 4196 kWh | 1552 kWh | £1,135 | £155 | £1,291 | £19,492 | 15.1 yrs | £6,322 |
| 8 kW | 6569 kWh | 4796 kWh | 1774 kWh | £1,298 | £177 | £1,475 | £21,526 | 14.6 yrs | £7,975 |
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: £936, 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 | 1642 kWh | 1232 kWh | 411 kWh | £333 | £41 | £374 | £11,069 | 29.6 yrs | £-3,582 |
| 3 kW | 2463 kWh | 1848 kWh | 616 kWh | £500 | £62 | £562 | £13,104 | 23.3 yrs | £-1,873 |
| 4 kW | 3285 kWh | 2463 kWh | 821 kWh | £667 | £82 | £749 | £15,138 | 20.2 yrs | £-163 |
| 5 kW | 4106 kWh | 3079 kWh | 1026 kWh | £833 | £103 | £936 | £17,173 | 18.3 yrs | £1,546 |
| 6 kW | 4927 kWh | 3695 kWh | 1232 kWh | £1,000 | £123 | £1,123 | £19,207 | 17.1 yrs | £3,255 |
| 7 kW | 5748 kWh | 4311 kWh | 1437 kWh | £1,167 | £144 | £1,310 | £21,242 | 16.2 yrs | £4,964 |
| 8 kW | 6569 kWh | 4927 kWh | 1642 kWh | £1,333 | £164 | £1,497 | £23,276 | 15.5 yrs | £6,673 |
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: £950, Upfront: £19,623, Break-even: 20.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1642 kWh | 1265 kWh | 378 kWh | £342 | £38 | £380 | £13,519 | 35.6 yrs | £-5,920 |
| 3 kW | 2463 kWh | 1897 kWh | 567 kWh | £513 | £57 | £570 | £15,554 | 27.3 yrs | £-4,154 |
| 4 kW | 3285 kWh | 2529 kWh | 755 kWh | £684 | £76 | £760 | £17,588 | 23.1 yrs | £-2,389 |
| 5 kW | 4106 kWh | 3161 kWh | 944 kWh | £855 | £94 | £950 | £19,623 | 20.7 yrs | £-624 |
| 6 kW | 4927 kWh | 3794 kWh | 1133 kWh | £1,027 | £113 | £1,140 | £21,657 | 19.0 yrs | £1,141 |
| 7 kW | 5748 kWh | 4426 kWh | 1322 kWh | £1,198 | £132 | £1,330 | £23,692 | 17.8 yrs | £2,906 |
| 8 kW | 6569 kWh | 5058 kWh | 1511 kWh | £1,369 | £151 | £1,520 | £25,726 | 16.9 yrs | £4,672 |
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.