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 908 kWh per year on a south-facing roof. We value self-used electricity at 25.3p 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 | 1816 kWh | 727 kWh | 1090 kWh | £184 | £109 | £293 | £4,069 | 13.9 yrs | £1,792 |
| 3 kW | 2725 kWh | 1090 kWh | 1635 kWh | £276 | £163 | £440 | £6,104 | 13.9 yrs | £2,687 |
| 4 kW | 3633 kWh | 1453 kWh | 2180 kWh | £368 | £218 | £586 | £8,138 | 13.9 yrs | £3,583 |
| 5 kW | 4541 kWh | 1816 kWh | 2725 kWh | £460 | £272 | £733 | £10,173 | 13.9 yrs | £4,479 |
| 6 kW | 5449 kWh | 2180 kWh | 3270 kWh | £552 | £327 | £879 | £12,207 | 13.9 yrs | £5,375 |
| 7 kW | 6358 kWh | 2543 kWh | 3815 kWh | £644 | £381 | £1,026 | £14,242 | 13.9 yrs | £6,271 |
| 8 kW | 7266 kWh | 2906 kWh | 4360 kWh | £736 | £436 | £1,172 | £16,276 | 13.9 yrs | £7,166 |
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: £872, Upfront: £12,273, Break-even: 14.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1816 kWh | 1090 kWh | 727 kWh | £276 | £73 | £349 | £6,169 | 17.7 yrs | £805 |
| 3 kW | 2725 kWh | 1635 kWh | 1090 kWh | £414 | £109 | £523 | £8,204 | 15.7 yrs | £2,258 |
| 4 kW | 3633 kWh | 2180 kWh | 1453 kWh | £552 | £145 | £697 | £10,238 | 14.7 yrs | £3,711 |
| 5 kW | 4541 kWh | 2725 kWh | 1816 kWh | £690 | £182 | £872 | £12,273 | 14.1 yrs | £5,164 |
| 6 kW | 5449 kWh | 3270 kWh | 2180 kWh | £828 | £218 | £1,046 | £14,307 | 13.7 yrs | £6,616 |
| 7 kW | 6358 kWh | 3815 kWh | 2543 kWh | £966 | £254 | £1,221 | £16,342 | 13.4 yrs | £8,069 |
| 8 kW | 7266 kWh | 4360 kWh | 2906 kWh | £1,104 | £291 | £1,395 | £18,376 | 13.2 yrs | £9,522 |
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: £941, 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 | 1816 kWh | 1272 kWh | 545 kWh | £322 | £54 | £377 | £7,569 | 20.1 yrs | £-38 |
| 3 kW | 2725 kWh | 1907 kWh | 817 kWh | £483 | £82 | £565 | £9,604 | 17.0 yrs | £1,694 |
| 4 kW | 3633 kWh | 2543 kWh | 1090 kWh | £644 | £109 | £753 | £11,638 | 15.5 yrs | £3,425 |
| 5 kW | 4541 kWh | 3179 kWh | 1362 kWh | £805 | £136 | £941 | £13,673 | 14.5 yrs | £5,156 |
| 6 kW | 5449 kWh | 3815 kWh | 1635 kWh | £966 | £163 | £1,130 | £15,707 | 13.9 yrs | £6,887 |
| 7 kW | 6358 kWh | 4450 kWh | 1907 kWh | £1,127 | £191 | £1,318 | £17,742 | 13.5 yrs | £8,618 |
| 8 kW | 7266 kWh | 5086 kWh | 2180 kWh | £1,288 | £218 | £1,506 | £19,776 | 13.1 yrs | £10,350 |
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: £962, 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 | 1816 kWh | 1326 kWh | 490 kWh | £336 | £49 | £385 | £9,319 | 24.2 yrs | £-1,621 |
| 3 kW | 2725 kWh | 1989 kWh | 736 kWh | £504 | £74 | £577 | £11,354 | 19.7 yrs | £194 |
| 4 kW | 3633 kWh | 2652 kWh | 981 kWh | £672 | £98 | £770 | £13,388 | 17.4 yrs | £2,009 |
| 5 kW | 4541 kWh | 3315 kWh | 1226 kWh | £840 | £123 | £962 | £15,423 | 16.0 yrs | £3,824 |
| 6 kW | 5449 kWh | 3978 kWh | 1471 kWh | £1,008 | £147 | £1,155 | £17,457 | 15.1 yrs | £5,638 |
| 7 kW | 6358 kWh | 4641 kWh | 1717 kWh | £1,176 | £172 | £1,347 | £19,492 | 14.5 yrs | £7,453 |
| 8 kW | 7266 kWh | 5304 kWh | 1962 kWh | £1,344 | £196 | £1,540 | £21,526 | 14.0 yrs | £9,268 |
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: £976, Upfront: £17,173, Break-even: 17.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1816 kWh | 1362 kWh | 454 kWh | £345 | £45 | £390 | £11,069 | 28.3 yrs | £-3,259 |
| 3 kW | 2725 kWh | 2044 kWh | 681 kWh | £518 | £68 | £586 | £13,104 | 22.4 yrs | £-1,389 |
| 4 kW | 3633 kWh | 2725 kWh | 908 kWh | £690 | £91 | £781 | £15,138 | 19.4 yrs | £482 |
| 5 kW | 4541 kWh | 3406 kWh | 1135 kWh | £863 | £114 | £976 | £17,173 | 17.6 yrs | £2,352 |
| 6 kW | 5449 kWh | 4087 kWh | 1362 kWh | £1,035 | £136 | £1,171 | £19,207 | 16.4 yrs | £4,223 |
| 7 kW | 6358 kWh | 4768 kWh | 1589 kWh | £1,208 | £159 | £1,367 | £21,242 | 15.5 yrs | £6,093 |
| 8 kW | 7266 kWh | 5449 kWh | 1816 kWh | £1,380 | £182 | £1,562 | £23,276 | 14.9 yrs | £7,963 |
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: £990, Upfront: £19,623, Break-even: 19.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1816 kWh | 1399 kWh | 418 kWh | £354 | £42 | £396 | £13,519 | 34.1 yrs | £-5,598 |
| 3 kW | 2725 kWh | 2098 kWh | 627 kWh | £531 | £63 | £594 | £15,554 | 26.2 yrs | £-3,672 |
| 4 kW | 3633 kWh | 2797 kWh | 836 kWh | £709 | £84 | £792 | £17,588 | 22.2 yrs | £-1,746 |
| 5 kW | 4541 kWh | 3497 kWh | 1044 kWh | £886 | £104 | £990 | £19,623 | 19.8 yrs | £181 |
| 6 kW | 5449 kWh | 4196 kWh | 1253 kWh | £1,063 | £125 | £1,188 | £21,657 | 18.2 yrs | £2,107 |
| 7 kW | 6358 kWh | 4895 kWh | 1462 kWh | £1,240 | £146 | £1,386 | £23,692 | 17.1 yrs | £4,033 |
| 8 kW | 7266 kWh | 5595 kWh | 1671 kWh | £1,417 | £167 | £1,584 | £25,726 | 16.2 yrs | £5,959 |
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.