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 897 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: £733, Upfront: £10,173, Break-even: 13.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1794 kWh | 717 kWh | 1076 kWh | £185 | £108 | £293 | £4,069 | 13.9 yrs | £1,791 |
| 3 kW | 2690 kWh | 1076 kWh | 1614 kWh | £278 | £161 | £440 | £6,104 | 13.9 yrs | £2,687 |
| 4 kW | 3587 kWh | 1435 kWh | 2152 kWh | £371 | £215 | £586 | £8,138 | 13.9 yrs | £3,582 |
| 5 kW | 4484 kWh | 1794 kWh | 2690 kWh | £463 | £269 | £733 | £10,173 | 13.9 yrs | £4,478 |
| 6 kW | 5381 kWh | 2152 kWh | 3229 kWh | £556 | £323 | £879 | £12,207 | 13.9 yrs | £5,374 |
| 7 kW | 6278 kWh | 2511 kWh | 3767 kWh | £649 | £377 | £1,026 | £14,242 | 13.9 yrs | £6,269 |
| 8 kW | 7175 kWh | 2870 kWh | 4305 kWh | £742 | £430 | £1,172 | £16,276 | 13.9 yrs | £7,165 |
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: £875, Upfront: £12,273, Break-even: 14.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1794 kWh | 1076 kWh | 717 kWh | £278 | £72 | £350 | £6,169 | 17.6 yrs | £828 |
| 3 kW | 2690 kWh | 1614 kWh | 1076 kWh | £417 | £108 | £525 | £8,204 | 15.6 yrs | £2,292 |
| 4 kW | 3587 kWh | 2152 kWh | 1435 kWh | £556 | £143 | £700 | £10,238 | 14.6 yrs | £3,755 |
| 5 kW | 4484 kWh | 2690 kWh | 1794 kWh | £695 | £179 | £875 | £12,273 | 14.0 yrs | £5,219 |
| 6 kW | 5381 kWh | 3229 kWh | 2152 kWh | £834 | £215 | £1,050 | £14,307 | 13.6 yrs | £6,683 |
| 7 kW | 6278 kWh | 3767 kWh | 2511 kWh | £973 | £251 | £1,224 | £16,342 | 13.3 yrs | £8,147 |
| 8 kW | 7175 kWh | 4305 kWh | 2870 kWh | £1,112 | £287 | £1,399 | £18,376 | 13.1 yrs | £9,611 |
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: £946, Upfront: £13,673, 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 | 1794 kWh | 1256 kWh | 538 kWh | £324 | £54 | £378 | £7,569 | 20.0 yrs | £-4 |
| 3 kW | 2690 kWh | 1883 kWh | 807 kWh | £487 | £81 | £567 | £9,604 | 16.9 yrs | £1,744 |
| 4 kW | 3587 kWh | 2511 kWh | 1076 kWh | £649 | £108 | £756 | £11,638 | 15.4 yrs | £3,492 |
| 5 kW | 4484 kWh | 3139 kWh | 1345 kWh | £811 | £135 | £946 | £13,673 | 14.5 yrs | £5,240 |
| 6 kW | 5381 kWh | 3767 kWh | 1614 kWh | £973 | £161 | £1,135 | £15,707 | 13.8 yrs | £6,988 |
| 7 kW | 6278 kWh | 4394 kWh | 1883 kWh | £1,136 | £188 | £1,324 | £17,742 | 13.4 yrs | £8,736 |
| 8 kW | 7175 kWh | 5022 kWh | 2152 kWh | £1,298 | £215 | £1,513 | £19,776 | 13.1 yrs | £10,484 |
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: £967, Upfront: £15,423, Break-even: 16.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1794 kWh | 1309 kWh | 484 kWh | £338 | £48 | £387 | £9,319 | 24.1 yrs | £-1,584 |
| 3 kW | 2690 kWh | 1964 kWh | 726 kWh | £508 | £73 | £580 | £11,354 | 19.6 yrs | £250 |
| 4 kW | 3587 kWh | 2619 kWh | 969 kWh | £677 | £97 | £774 | £13,388 | 17.3 yrs | £2,083 |
| 5 kW | 4484 kWh | 3273 kWh | 1211 kWh | £846 | £121 | £967 | £15,423 | 16.0 yrs | £3,916 |
| 6 kW | 5381 kWh | 3928 kWh | 1453 kWh | £1,015 | £145 | £1,160 | £17,457 | 15.0 yrs | £5,749 |
| 7 kW | 6278 kWh | 4583 kWh | 1695 kWh | £1,184 | £170 | £1,354 | £19,492 | 14.4 yrs | £7,582 |
| 8 kW | 7175 kWh | 5237 kWh | 1937 kWh | £1,353 | £194 | £1,547 | £21,526 | 13.9 yrs | £9,416 |
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: £981, Upfront: £17,173, Break-even: 17.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1794 kWh | 1345 kWh | 448 kWh | £348 | £45 | £392 | £11,069 | 28.2 yrs | £-3,220 |
| 3 kW | 2690 kWh | 2018 kWh | 673 kWh | £521 | £67 | £589 | £13,104 | 22.3 yrs | £-1,330 |
| 4 kW | 3587 kWh | 2690 kWh | 897 kWh | £695 | £90 | £785 | £15,138 | 19.3 yrs | £560 |
| 5 kW | 4484 kWh | 3363 kWh | 1121 kWh | £869 | £112 | £981 | £17,173 | 17.5 yrs | £2,450 |
| 6 kW | 5381 kWh | 4036 kWh | 1345 kWh | £1,043 | £135 | £1,177 | £19,207 | 16.3 yrs | £4,340 |
| 7 kW | 6278 kWh | 4708 kWh | 1569 kWh | £1,217 | £157 | £1,374 | £21,242 | 15.5 yrs | £6,230 |
| 8 kW | 7175 kWh | 5381 kWh | 1794 kWh | £1,390 | £179 | £1,570 | £23,276 | 14.8 yrs | £8,120 |
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: £995, Upfront: £19,623, Break-even: 19.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1794 kWh | 1381 kWh | 413 kWh | £357 | £41 | £398 | £13,519 | 34.0 yrs | £-5,556 |
| 3 kW | 2690 kWh | 2072 kWh | 619 kWh | £535 | £62 | £597 | £15,554 | 26.0 yrs | £-3,609 |
| 4 kW | 3587 kWh | 2762 kWh | 825 kWh | £714 | £83 | £796 | £17,588 | 22.1 yrs | £-1,663 |
| 5 kW | 4484 kWh | 3453 kWh | 1031 kWh | £892 | £103 | £995 | £19,623 | 19.7 yrs | £284 |
| 6 kW | 5381 kWh | 4143 kWh | 1238 kWh | £1,071 | £124 | £1,194 | £21,657 | 18.1 yrs | £2,231 |
| 7 kW | 6278 kWh | 4834 kWh | 1444 kWh | £1,249 | £144 | £1,393 | £23,692 | 17.0 yrs | £4,178 |
| 8 kW | 7175 kWh | 5524 kWh | 1650 kWh | £1,428 | £165 | £1,593 | £25,726 | 16.2 yrs | £6,125 |
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.