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 838 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: £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 | 1676 kWh | 670 kWh | 1005 kWh | £173 | £101 | £274 | £4,069 | 14.9 yrs | £1,406 |
| 3 kW | 2514 kWh | 1005 kWh | 1508 kWh | £260 | £151 | £411 | £6,104 | 14.9 yrs | £2,109 |
| 4 kW | 3351 kWh | 1341 kWh | 2011 kWh | £346 | £201 | £547 | £8,138 | 14.9 yrs | £2,812 |
| 5 kW | 4189 kWh | 1676 kWh | 2514 kWh | £433 | £251 | £684 | £10,173 | 14.9 yrs | £3,515 |
| 6 kW | 5027 kWh | 2011 kWh | 3016 kWh | £520 | £302 | £821 | £12,207 | 14.9 yrs | £4,218 |
| 7 kW | 5865 kWh | 2346 kWh | 3519 kWh | £606 | £352 | £958 | £14,242 | 14.9 yrs | £4,921 |
| 8 kW | 6703 kWh | 2681 kWh | 4022 kWh | £693 | £402 | £1,095 | £16,276 | 14.9 yrs | £5,624 |
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: £817, Upfront: £12,273, 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 | 1676 kWh | 1005 kWh | 670 kWh | £260 | £67 | £327 | £6,169 | 18.9 yrs | £368 |
| 3 kW | 2514 kWh | 1508 kWh | 1005 kWh | £390 | £101 | £490 | £8,204 | 16.7 yrs | £1,601 |
| 4 kW | 3351 kWh | 2011 kWh | 1341 kWh | £520 | £134 | £654 | £10,238 | 15.7 yrs | £2,835 |
| 5 kW | 4189 kWh | 2514 kWh | 1676 kWh | £650 | £168 | £817 | £12,273 | 15.0 yrs | £4,069 |
| 6 kW | 5027 kWh | 3016 kWh | 2011 kWh | £779 | £201 | £980 | £14,307 | 14.6 yrs | £5,303 |
| 7 kW | 5865 kWh | 3519 kWh | 2346 kWh | £909 | £235 | £1,144 | £16,342 | 14.3 yrs | £6,537 |
| 8 kW | 6703 kWh | 4022 kWh | 2681 kWh | £1,039 | £268 | £1,307 | £18,376 | 14.1 yrs | £7,771 |
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: £883, Upfront: £13,673, Break-even: 15.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1676 kWh | 1173 kWh | 503 kWh | £303 | £50 | £353 | £7,569 | 21.4 yrs | £-502 |
| 3 kW | 2514 kWh | 1760 kWh | 754 kWh | £455 | £75 | £530 | £9,604 | 18.1 yrs | £998 |
| 4 kW | 3351 kWh | 2346 kWh | 1005 kWh | £606 | £101 | £707 | £11,638 | 16.5 yrs | £2,497 |
| 5 kW | 4189 kWh | 2933 kWh | 1257 kWh | £758 | £126 | £883 | £13,673 | 15.5 yrs | £3,996 |
| 6 kW | 5027 kWh | 3519 kWh | 1508 kWh | £909 | £151 | £1,060 | £15,707 | 14.8 yrs | £5,495 |
| 7 kW | 5865 kWh | 4106 kWh | 1760 kWh | £1,061 | £176 | £1,237 | £17,742 | 14.3 yrs | £6,995 |
| 8 kW | 6703 kWh | 4692 kWh | 2011 kWh | £1,212 | £201 | £1,414 | £19,776 | 14.0 yrs | £8,494 |
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: £903, Upfront: £15,423, 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 | 1676 kWh | 1223 kWh | 452 kWh | £316 | £45 | £361 | £9,319 | 25.8 yrs | £-2,092 |
| 3 kW | 2514 kWh | 1835 kWh | 679 kWh | £474 | £68 | £542 | £11,354 | 20.9 yrs | £-513 |
| 4 kW | 3351 kWh | 2447 kWh | 905 kWh | £632 | £90 | £723 | £13,388 | 18.5 yrs | £1,066 |
| 5 kW | 4189 kWh | 3058 kWh | 1131 kWh | £790 | £113 | £903 | £15,423 | 17.1 yrs | £2,644 |
| 6 kW | 5027 kWh | 3670 kWh | 1357 kWh | £948 | £136 | £1,084 | £17,457 | 16.1 yrs | £4,223 |
| 7 kW | 5865 kWh | 4281 kWh | 1584 kWh | £1,106 | £158 | £1,265 | £19,492 | 15.4 yrs | £5,802 |
| 8 kW | 6703 kWh | 4893 kWh | 1810 kWh | £1,264 | £181 | £1,445 | £21,526 | 14.9 yrs | £7,381 |
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: £917, Upfront: £17,173, Break-even: 18.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1676 kWh | 1257 kWh | 419 kWh | £325 | £42 | £367 | £11,069 | 30.2 yrs | £-3,736 |
| 3 kW | 2514 kWh | 1885 kWh | 628 kWh | £487 | £63 | £550 | £13,104 | 23.8 yrs | £-2,104 |
| 4 kW | 3351 kWh | 2514 kWh | 838 kWh | £650 | £84 | £733 | £15,138 | 20.6 yrs | £-472 |
| 5 kW | 4189 kWh | 3142 kWh | 1047 kWh | £812 | £105 | £917 | £17,173 | 18.7 yrs | £1,160 |
| 6 kW | 5027 kWh | 3770 kWh | 1257 kWh | £974 | £126 | £1,100 | £19,207 | 17.5 yrs | £2,792 |
| 7 kW | 5865 kWh | 4399 kWh | 1466 kWh | £1,137 | £147 | £1,283 | £21,242 | 16.6 yrs | £4,424 |
| 8 kW | 6703 kWh | 5027 kWh | 1676 kWh | £1,299 | £168 | £1,467 | £23,276 | 15.9 yrs | £6,056 |
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: £930, Upfront: £19,623, Break-even: 21.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1676 kWh | 1290 kWh | 385 kWh | £333 | £39 | £372 | £13,519 | 36.3 yrs | £-6,080 |
| 3 kW | 2514 kWh | 1935 kWh | 578 kWh | £500 | £58 | £558 | £15,554 | 27.9 yrs | £-4,395 |
| 4 kW | 3351 kWh | 2581 kWh | 771 kWh | £667 | £77 | £744 | £17,588 | 23.6 yrs | £-2,710 |
| 5 kW | 4189 kWh | 3226 kWh | 964 kWh | £834 | £96 | £930 | £19,623 | 21.1 yrs | £-1,025 |
| 6 kW | 5027 kWh | 3871 kWh | 1156 kWh | £1,000 | £116 | £1,116 | £21,657 | 19.4 yrs | £660 |
| 7 kW | 5865 kWh | 4516 kWh | 1349 kWh | £1,167 | £135 | £1,302 | £23,692 | 18.2 yrs | £2,345 |
| 8 kW | 6703 kWh | 5161 kWh | 1542 kWh | £1,334 | £154 | £1,488 | £25,726 | 17.3 yrs | £4,030 |
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.