A typical roof here lands around 3.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 996 kWh per year on a south-facing roof. We value self-used electricity at 26.9p 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: £835, Upfront: £10,173, Break-even: 12.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1992 kWh | 797 kWh | 1195 kWh | £215 | £120 | £334 | £4,069 | 12.2 yrs | £2,612 |
| 3 kW | 2988 kWh | 1195 kWh | 1793 kWh | £322 | £179 | £501 | £6,104 | 12.2 yrs | £3,918 |
| 4 kW | 3985 kWh | 1594 kWh | 2391 kWh | £429 | £239 | £668 | £8,138 | 12.2 yrs | £5,224 |
| 5 kW | 4981 kWh | 1992 kWh | 2988 kWh | £536 | £299 | £835 | £10,173 | 12.2 yrs | £6,531 |
| 6 kW | 5977 kWh | 2391 kWh | 3586 kWh | £644 | £359 | £1,002 | £12,207 | 12.2 yrs | £7,837 |
| 7 kW | 6973 kWh | 2789 kWh | 4184 kWh | £751 | £418 | £1,169 | £14,242 | 12.2 yrs | £9,143 |
| 8 kW | 7969 kWh | 3188 kWh | 4781 kWh | £858 | £478 | £1,336 | £16,276 | 12.2 yrs | £10,449 |
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: £1,004, Upfront: £12,273, Break-even: 12.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1992 kWh | 1195 kWh | 797 kWh | £322 | £80 | £401 | £6,169 | 15.4 yrs | £1,861 |
| 3 kW | 2988 kWh | 1793 kWh | 1195 kWh | £483 | £120 | £602 | £8,204 | 13.6 yrs | £3,841 |
| 4 kW | 3985 kWh | 2391 kWh | 1594 kWh | £644 | £159 | £803 | £10,238 | 12.8 yrs | £5,821 |
| 5 kW | 4981 kWh | 2988 kWh | 1992 kWh | £804 | £199 | £1,004 | £12,273 | 12.2 yrs | £7,801 |
| 6 kW | 5977 kWh | 3586 kWh | 2391 kWh | £965 | £239 | £1,204 | £14,307 | 11.9 yrs | £9,782 |
| 7 kW | 6973 kWh | 4184 kWh | 2789 kWh | £1,126 | £279 | £1,405 | £16,342 | 11.6 yrs | £11,762 |
| 8 kW | 7969 kWh | 4781 kWh | 3188 kWh | £1,287 | £319 | £1,606 | £18,376 | 11.4 yrs | £13,742 |
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: £1,088, Upfront: £13,673, Break-even: 12.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1992 kWh | 1395 kWh | 598 kWh | £375 | £60 | £435 | £7,569 | 17.4 yrs | £1,135 |
| 3 kW | 2988 kWh | 2092 kWh | 897 kWh | £563 | £90 | £653 | £9,604 | 14.7 yrs | £3,452 |
| 4 kW | 3985 kWh | 2789 kWh | 1195 kWh | £751 | £120 | £870 | £11,638 | 13.4 yrs | £5,770 |
| 5 kW | 4981 kWh | 3486 kWh | 1494 kWh | £939 | £149 | £1,088 | £13,673 | 12.6 yrs | £8,087 |
| 6 kW | 5977 kWh | 4184 kWh | 1793 kWh | £1,126 | £179 | £1,306 | £15,707 | 12.0 yrs | £10,404 |
| 7 kW | 6973 kWh | 4881 kWh | 2092 kWh | £1,314 | £209 | £1,523 | £17,742 | 11.6 yrs | £12,722 |
| 8 kW | 7969 kWh | 5578 kWh | 2391 kWh | £1,502 | £239 | £1,741 | £19,776 | 11.4 yrs | £15,039 |
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: £1,113, Upfront: £15,423, 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 | 1992 kWh | 1454 kWh | 538 kWh | £392 | £54 | £445 | £9,319 | 20.9 yrs | £-413 |
| 3 kW | 2988 kWh | 2182 kWh | 807 kWh | £587 | £81 | £668 | £11,354 | 17.0 yrs | £2,006 |
| 4 kW | 3985 kWh | 2909 kWh | 1076 kWh | £783 | £108 | £891 | £13,388 | 15.0 yrs | £4,424 |
| 5 kW | 4981 kWh | 3636 kWh | 1345 kWh | £979 | £134 | £1,113 | £15,423 | 13.9 yrs | £6,843 |
| 6 kW | 5977 kWh | 4363 kWh | 1614 kWh | £1,175 | £161 | £1,336 | £17,457 | 13.1 yrs | £9,261 |
| 7 kW | 6973 kWh | 5090 kWh | 1883 kWh | £1,370 | £188 | £1,559 | £19,492 | 12.5 yrs | £11,680 |
| 8 kW | 7969 kWh | 5817 kWh | 2152 kWh | £1,566 | £215 | £1,781 | £21,526 | 12.1 yrs | £14,098 |
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: £1,130, Upfront: £17,173, 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 | 1992 kWh | 1494 kWh | 498 kWh | £402 | £50 | £452 | £11,069 | 24.5 yrs | £-2,028 |
| 3 kW | 2988 kWh | 2241 kWh | 747 kWh | £603 | £75 | £678 | £13,104 | 19.3 yrs | £458 |
| 4 kW | 3985 kWh | 2988 kWh | 996 kWh | £804 | £100 | £904 | £15,138 | 16.7 yrs | £2,944 |
| 5 kW | 4981 kWh | 3735 kWh | 1245 kWh | £1,006 | £125 | £1,130 | £17,173 | 15.2 yrs | £5,430 |
| 6 kW | 5977 kWh | 4483 kWh | 1494 kWh | £1,207 | £149 | £1,356 | £19,207 | 14.2 yrs | £7,916 |
| 7 kW | 6973 kWh | 5230 kWh | 1743 kWh | £1,408 | £174 | £1,582 | £21,242 | 13.4 yrs | £10,401 |
| 8 kW | 7969 kWh | 5977 kWh | 1992 kWh | £1,609 | £199 | £1,808 | £23,276 | 12.9 yrs | £12,887 |
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: £1,147, Upfront: £19,623, Break-even: 17.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1992 kWh | 1534 kWh | 458 kWh | £413 | £46 | £459 | £13,519 | 29.5 yrs | £-4,343 |
| 3 kW | 2988 kWh | 2301 kWh | 687 kWh | £619 | £69 | £688 | £15,554 | 22.6 yrs | £-1,790 |
| 4 kW | 3985 kWh | 3068 kWh | 916 kWh | £826 | £92 | £918 | £17,588 | 19.2 yrs | £763 |
| 5 kW | 4981 kWh | 3835 kWh | 1146 kWh | £1,032 | £115 | £1,147 | £19,623 | 17.1 yrs | £3,317 |
| 6 kW | 5977 kWh | 4602 kWh | 1375 kWh | £1,239 | £137 | £1,376 | £21,657 | 15.7 yrs | £5,870 |
| 7 kW | 6973 kWh | 5369 kWh | 1604 kWh | £1,445 | £160 | £1,606 | £23,692 | 14.8 yrs | £8,423 |
| 8 kW | 7969 kWh | 6136 kWh | 1833 kWh | £1,652 | £183 | £1,835 | £25,726 | 14.0 yrs | £10,977 |
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.