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 813 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: £684, Upfront: £10,173, Break-even: 14.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1627 kWh | 651 kWh | 976 kWh | £176 | £98 | £274 | £4,069 | 14.9 yrs | £1,404 |
| 3 kW | 2440 kWh | 976 kWh | 1464 kWh | £264 | £146 | £410 | £6,104 | 14.9 yrs | £2,106 |
| 4 kW | 3253 kWh | 1301 kWh | 1952 kWh | £352 | £195 | £547 | £8,138 | 14.9 yrs | £2,808 |
| 5 kW | 4067 kWh | 1627 kWh | 2440 kWh | £440 | £244 | £684 | £10,173 | 14.9 yrs | £3,511 |
| 6 kW | 4880 kWh | 1952 kWh | 2928 kWh | £528 | £293 | £821 | £12,207 | 14.9 yrs | £4,213 |
| 7 kW | 5693 kWh | 2277 kWh | 3416 kWh | £616 | £342 | £958 | £14,242 | 14.9 yrs | £4,915 |
| 8 kW | 6506 kWh | 2603 kWh | 3904 kWh | £704 | £390 | £1,095 | £16,276 | 14.9 yrs | £5,617 |
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: £823, Upfront: £12,273, Break-even: 14.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1627 kWh | 976 kWh | 651 kWh | £264 | £65 | £329 | £6,169 | 18.7 yrs | £414 |
| 3 kW | 2440 kWh | 1464 kWh | 976 kWh | £396 | £98 | £494 | £8,204 | 16.6 yrs | £1,671 |
| 4 kW | 3253 kWh | 1952 kWh | 1301 kWh | £528 | £130 | £658 | £10,238 | 15.6 yrs | £2,928 |
| 5 kW | 4067 kWh | 2440 kWh | 1627 kWh | £660 | £163 | £823 | £12,273 | 14.9 yrs | £4,186 |
| 6 kW | 4880 kWh | 2928 kWh | 1952 kWh | £792 | £195 | £987 | £14,307 | 14.5 yrs | £5,443 |
| 7 kW | 5693 kWh | 3416 kWh | 2277 kWh | £924 | £228 | £1,152 | £16,342 | 14.2 yrs | £6,700 |
| 8 kW | 6506 kWh | 3904 kWh | 2603 kWh | £1,056 | £260 | £1,317 | £18,376 | 14.0 yrs | £7,957 |
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: £892, Upfront: £13,673, Break-even: 15.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1627 kWh | 1139 kWh | 488 kWh | £308 | £49 | £357 | £7,569 | 21.2 yrs | £-431 |
| 3 kW | 2440 kWh | 1708 kWh | 732 kWh | £462 | £73 | £535 | £9,604 | 17.9 yrs | £1,104 |
| 4 kW | 3253 kWh | 2277 kWh | 976 kWh | £616 | £98 | £714 | £11,638 | 16.3 yrs | £2,638 |
| 5 kW | 4067 kWh | 2847 kWh | 1220 kWh | £770 | £122 | £892 | £13,673 | 15.3 yrs | £4,173 |
| 6 kW | 4880 kWh | 3416 kWh | 1464 kWh | £924 | £146 | £1,071 | £15,707 | 14.7 yrs | £5,708 |
| 7 kW | 5693 kWh | 3985 kWh | 1708 kWh | £1,078 | £171 | £1,249 | £17,742 | 14.2 yrs | £7,242 |
| 8 kW | 6506 kWh | 4555 kWh | 1952 kWh | £1,232 | £195 | £1,428 | £19,776 | 13.9 yrs | £8,777 |
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: £913, Upfront: £15,423, Break-even: 16.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1627 kWh | 1187 kWh | 439 kWh | £321 | £44 | £365 | £9,319 | 25.5 yrs | £-2,014 |
| 3 kW | 2440 kWh | 1781 kWh | 659 kWh | £482 | £66 | £548 | £11,354 | 20.7 yrs | £-396 |
| 4 kW | 3253 kWh | 2375 kWh | 878 kWh | £643 | £88 | £730 | £13,388 | 18.3 yrs | £1,221 |
| 5 kW | 4067 kWh | 2969 kWh | 1098 kWh | £803 | £110 | £913 | £15,423 | 16.9 yrs | £2,839 |
| 6 kW | 4880 kWh | 3562 kWh | 1318 kWh | £964 | £132 | £1,096 | £17,457 | 15.9 yrs | £4,457 |
| 7 kW | 5693 kWh | 4156 kWh | 1537 kWh | £1,125 | £154 | £1,278 | £19,492 | 15.2 yrs | £6,075 |
| 8 kW | 6506 kWh | 4750 kWh | 1757 kWh | £1,285 | £176 | £1,461 | £21,526 | 14.7 yrs | £7,693 |
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: £927, Upfront: £17,173, Break-even: 18.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1627 kWh | 1220 kWh | 407 kWh | £330 | £41 | £371 | £11,069 | 29.9 yrs | £-3,653 |
| 3 kW | 2440 kWh | 1830 kWh | 610 kWh | £495 | £61 | £556 | £13,104 | 23.6 yrs | £-1,980 |
| 4 kW | 3253 kWh | 2440 kWh | 813 kWh | £660 | £81 | £742 | £15,138 | 20.4 yrs | £-307 |
| 5 kW | 4067 kWh | 3050 kWh | 1017 kWh | £825 | £102 | £927 | £17,173 | 18.5 yrs | £1,367 |
| 6 kW | 4880 kWh | 3660 kWh | 1220 kWh | £990 | £122 | £1,112 | £19,207 | 17.3 yrs | £3,040 |
| 7 kW | 5693 kWh | 4270 kWh | 1423 kWh | £1,155 | £142 | £1,298 | £21,242 | 16.4 yrs | £4,714 |
| 8 kW | 6506 kWh | 4880 kWh | 1627 kWh | £1,320 | £163 | £1,483 | £23,276 | 15.7 yrs | £6,387 |
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: £941, Upfront: £19,623, Break-even: 20.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1627 kWh | 1252 kWh | 374 kWh | £339 | £37 | £376 | £13,519 | 35.9 yrs | £-5,992 |
| 3 kW | 2440 kWh | 1879 kWh | 561 kWh | £508 | £56 | £565 | £15,554 | 27.6 yrs | £-4,263 |
| 4 kW | 3253 kWh | 2505 kWh | 748 kWh | £678 | £75 | £753 | £17,588 | 23.4 yrs | £-2,535 |
| 5 kW | 4067 kWh | 3131 kWh | 935 kWh | £847 | £94 | £941 | £19,623 | 20.9 yrs | £-806 |
| 6 kW | 4880 kWh | 3757 kWh | 1122 kWh | £1,017 | £112 | £1,129 | £21,657 | 19.2 yrs | £923 |
| 7 kW | 5693 kWh | 4384 kWh | 1309 kWh | £1,186 | £131 | £1,317 | £23,692 | 18.0 yrs | £2,652 |
| 8 kW | 6506 kWh | 5010 kWh | 1496 kWh | £1,356 | £150 | £1,505 | £25,726 | 17.1 yrs | £4,381 |
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.