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 833 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: £680, Upfront: £10,173, Break-even: 15.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1666 kWh | 666 kWh | 1000 kWh | £172 | £100 | £272 | £4,069 | 15.0 yrs | £1,374 |
| 3 kW | 2499 kWh | 1000 kWh | 1499 kWh | £258 | £150 | £408 | £6,104 | 15.0 yrs | £2,062 |
| 4 kW | 3332 kWh | 1333 kWh | 1999 kWh | £344 | £200 | £544 | £8,138 | 15.0 yrs | £2,749 |
| 5 kW | 4165 kWh | 1666 kWh | 2499 kWh | £431 | £250 | £680 | £10,173 | 15.0 yrs | £3,436 |
| 6 kW | 4998 kWh | 1999 kWh | 2999 kWh | £517 | £300 | £817 | £12,207 | 15.0 yrs | £4,123 |
| 7 kW | 5831 kWh | 2333 kWh | 3499 kWh | £603 | £350 | £953 | £14,242 | 15.0 yrs | £4,810 |
| 8 kW | 6664 kWh | 2666 kWh | 3999 kWh | £689 | £400 | £1,089 | £16,276 | 15.0 yrs | £5,498 |
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: £812, Upfront: £12,273, Break-even: 15.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1666 kWh | 1000 kWh | 666 kWh | £258 | £67 | £325 | £6,169 | 19.0 yrs | £330 |
| 3 kW | 2499 kWh | 1499 kWh | 1000 kWh | £387 | £100 | £487 | £8,204 | 16.8 yrs | £1,545 |
| 4 kW | 3332 kWh | 1999 kWh | 1333 kWh | £517 | £133 | £650 | £10,238 | 15.8 yrs | £2,760 |
| 5 kW | 4165 kWh | 2499 kWh | 1666 kWh | £646 | £167 | £812 | £12,273 | 15.1 yrs | £3,975 |
| 6 kW | 4998 kWh | 2999 kWh | 1999 kWh | £775 | £200 | £975 | £14,307 | 14.7 yrs | £5,190 |
| 7 kW | 5831 kWh | 3499 kWh | 2333 kWh | £904 | £233 | £1,137 | £16,342 | 14.4 yrs | £6,405 |
| 8 kW | 6664 kWh | 3999 kWh | 2666 kWh | £1,033 | £267 | £1,300 | £18,376 | 14.1 yrs | £7,620 |
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: £878, Upfront: £13,673, Break-even: 15.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1666 kWh | 1166 kWh | 500 kWh | £301 | £50 | £351 | £7,569 | 21.5 yrs | £-542 |
| 3 kW | 2499 kWh | 1749 kWh | 750 kWh | £452 | £75 | £527 | £9,604 | 18.2 yrs | £937 |
| 4 kW | 3332 kWh | 2333 kWh | 1000 kWh | £603 | £100 | £703 | £11,638 | 16.6 yrs | £2,416 |
| 5 kW | 4165 kWh | 2916 kWh | 1250 kWh | £753 | £125 | £878 | £13,673 | 15.6 yrs | £3,895 |
| 6 kW | 4998 kWh | 3499 kWh | 1499 kWh | £904 | £150 | £1,054 | £15,707 | 14.9 yrs | £5,374 |
| 7 kW | 5831 kWh | 4082 kWh | 1749 kWh | £1,055 | £175 | £1,230 | £17,742 | 14.4 yrs | £6,852 |
| 8 kW | 6664 kWh | 4665 kWh | 1999 kWh | £1,205 | £200 | £1,405 | £19,776 | 14.1 yrs | £8,331 |
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: £898, Upfront: £15,423, Break-even: 17.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1666 kWh | 1216 kWh | 450 kWh | £314 | £45 | £359 | £9,319 | 25.9 yrs | £-2,134 |
| 3 kW | 2499 kWh | 1824 kWh | 675 kWh | £471 | £67 | £539 | £11,354 | 21.1 yrs | £-576 |
| 4 kW | 3332 kWh | 2432 kWh | 900 kWh | £629 | £90 | £719 | £13,388 | 18.6 yrs | £982 |
| 5 kW | 4165 kWh | 3041 kWh | 1125 kWh | £786 | £112 | £898 | £15,423 | 17.2 yrs | £2,540 |
| 6 kW | 4998 kWh | 3649 kWh | 1350 kWh | £943 | £135 | £1,078 | £17,457 | 16.2 yrs | £4,099 |
| 7 kW | 5831 kWh | 4257 kWh | 1574 kWh | £1,100 | £157 | £1,257 | £19,492 | 15.5 yrs | £5,657 |
| 8 kW | 6664 kWh | 4865 kWh | 1799 kWh | £1,257 | £180 | £1,437 | £21,526 | 15.0 yrs | £7,215 |
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: £911, Upfront: £17,173, Break-even: 18.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1666 kWh | 1250 kWh | 417 kWh | £323 | £42 | £365 | £11,069 | 30.4 yrs | £-3,778 |
| 3 kW | 2499 kWh | 1874 kWh | 625 kWh | £484 | £62 | £547 | £13,104 | 24.0 yrs | £-2,167 |
| 4 kW | 3332 kWh | 2499 kWh | 833 kWh | £646 | £83 | £729 | £15,138 | 20.8 yrs | £-557 |
| 5 kW | 4165 kWh | 3124 kWh | 1041 kWh | £807 | £104 | £911 | £17,173 | 18.8 yrs | £1,054 |
| 6 kW | 4998 kWh | 3749 kWh | 1250 kWh | £969 | £125 | £1,094 | £19,207 | 17.6 yrs | £2,665 |
| 7 kW | 5831 kWh | 4373 kWh | 1458 kWh | £1,130 | £146 | £1,276 | £21,242 | 16.6 yrs | £4,276 |
| 8 kW | 6664 kWh | 4998 kWh | 1666 kWh | £1,292 | £167 | £1,458 | £23,276 | 16.0 yrs | £5,887 |
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: £925, Upfront: £19,623, Break-even: 21.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1666 kWh | 1283 kWh | 383 kWh | £331 | £38 | £370 | £13,519 | 36.6 yrs | £-6,123 |
| 3 kW | 2499 kWh | 1924 kWh | 575 kWh | £497 | £57 | £555 | £15,554 | 28.0 yrs | £-4,459 |
| 4 kW | 3332 kWh | 2566 kWh | 766 kWh | £663 | £77 | £740 | £17,588 | 23.8 yrs | £-2,795 |
| 5 kW | 4165 kWh | 3207 kWh | 958 kWh | £829 | £96 | £925 | £19,623 | 21.2 yrs | £-1,132 |
| 6 kW | 4998 kWh | 3849 kWh | 1150 kWh | £994 | £115 | £1,109 | £21,657 | 19.5 yrs | £532 |
| 7 kW | 5831 kWh | 4490 kWh | 1341 kWh | £1,160 | £134 | £1,294 | £23,692 | 18.3 yrs | £2,196 |
| 8 kW | 6664 kWh | 5132 kWh | 1533 kWh | £1,326 | £153 | £1,479 | £25,726 | 17.4 yrs | £3,859 |
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.