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 1005 kWh per year on a south-facing roof. We value self-used electricity at 25.6p 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: £817, Upfront: £10,173, Break-even: 12.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2010 kWh | 804 kWh | 1206 kWh | £206 | £121 | £327 | £4,069 | 12.5 yrs | £2,465 |
| 3 kW | 3015 kWh | 1206 kWh | 1809 kWh | £309 | £181 | £490 | £6,104 | 12.5 yrs | £3,697 |
| 4 kW | 4020 kWh | 1608 kWh | 2412 kWh | £412 | £241 | £653 | £8,138 | 12.5 yrs | £4,929 |
| 5 kW | 5025 kWh | 2010 kWh | 3015 kWh | £515 | £302 | £817 | £10,173 | 12.5 yrs | £6,161 |
| 6 kW | 6030 kWh | 2412 kWh | 3618 kWh | £618 | £362 | £980 | £12,207 | 12.5 yrs | £7,394 |
| 7 kW | 7035 kWh | 2814 kWh | 4221 kWh | £721 | £422 | £1,143 | £14,242 | 12.5 yrs | £8,626 |
| 8 kW | 8040 kWh | 3216 kWh | 4824 kWh | £824 | £482 | £1,307 | £16,276 | 12.5 yrs | £9,858 |
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: £974, Upfront: £12,273, 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 | 2010 kWh | 1206 kWh | 804 kWh | £309 | £80 | £390 | £6,169 | 15.8 yrs | £1,621 |
| 3 kW | 3015 kWh | 1809 kWh | 1206 kWh | £464 | £121 | £584 | £8,204 | 14.0 yrs | £3,482 |
| 4 kW | 4020 kWh | 2412 kWh | 1608 kWh | £618 | £161 | £779 | £10,238 | 13.1 yrs | £5,342 |
| 5 kW | 5025 kWh | 3015 kWh | 2010 kWh | £773 | £201 | £974 | £12,273 | 12.6 yrs | £7,203 |
| 6 kW | 6030 kWh | 3618 kWh | 2412 kWh | £927 | £241 | £1,169 | £14,307 | 12.2 yrs | £9,064 |
| 7 kW | 7035 kWh | 4221 kWh | 2814 kWh | £1,082 | £281 | £1,363 | £16,342 | 12.0 yrs | £10,924 |
| 8 kW | 8040 kWh | 4824 kWh | 3216 kWh | £1,236 | £322 | £1,558 | £18,376 | 11.8 yrs | £12,785 |
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: £1,052, Upfront: £13,673, Break-even: 13.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2010 kWh | 1407 kWh | 603 kWh | £361 | £60 | £421 | £7,569 | 18.0 yrs | £850 |
| 3 kW | 3015 kWh | 2111 kWh | 905 kWh | £541 | £90 | £631 | £9,604 | 15.2 yrs | £3,024 |
| 4 kW | 4020 kWh | 2814 kWh | 1206 kWh | £721 | £121 | £842 | £11,638 | 13.8 yrs | £5,199 |
| 5 kW | 5025 kWh | 3518 kWh | 1508 kWh | £902 | £151 | £1,052 | £13,673 | 13.0 yrs | £7,374 |
| 6 kW | 6030 kWh | 4221 kWh | 1809 kWh | £1,082 | £181 | £1,263 | £15,707 | 12.4 yrs | £9,549 |
| 7 kW | 7035 kWh | 4925 kWh | 2111 kWh | £1,262 | £211 | £1,473 | £17,742 | 12.0 yrs | £11,724 |
| 8 kW | 8040 kWh | 5628 kWh | 2412 kWh | £1,443 | £241 | £1,684 | £19,776 | 11.7 yrs | £13,898 |
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: £1,076, Upfront: £15,423, Break-even: 14.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2010 kWh | 1467 kWh | 543 kWh | £376 | £54 | £430 | £9,319 | 21.7 yrs | £-712 |
| 3 kW | 3015 kWh | 2201 kWh | 814 kWh | £564 | £81 | £646 | £11,354 | 17.6 yrs | £1,557 |
| 4 kW | 4020 kWh | 2935 kWh | 1085 kWh | £752 | £109 | £861 | £13,388 | 15.6 yrs | £3,826 |
| 5 kW | 5025 kWh | 3668 kWh | 1357 kWh | £940 | £136 | £1,076 | £15,423 | 14.3 yrs | £6,095 |
| 6 kW | 6030 kWh | 4402 kWh | 1628 kWh | £1,128 | £163 | £1,291 | £17,457 | 13.5 yrs | £8,364 |
| 7 kW | 7035 kWh | 5136 kWh | 1900 kWh | £1,316 | £190 | £1,506 | £19,492 | 12.9 yrs | £10,633 |
| 8 kW | 8040 kWh | 5869 kWh | 2171 kWh | £1,504 | £217 | £1,721 | £21,526 | 12.5 yrs | £12,902 |
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: £1,092, Upfront: £17,173, Break-even: 15.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2010 kWh | 1508 kWh | 503 kWh | £386 | £50 | £437 | £11,069 | 25.4 yrs | £-2,336 |
| 3 kW | 3015 kWh | 2261 kWh | 754 kWh | £580 | £75 | £655 | £13,104 | 20.0 yrs | £-4 |
| 4 kW | 4020 kWh | 3015 kWh | 1005 kWh | £773 | £101 | £873 | £15,138 | 17.3 yrs | £2,328 |
| 5 kW | 5025 kWh | 3769 kWh | 1256 kWh | £966 | £126 | £1,092 | £17,173 | 15.7 yrs | £4,659 |
| 6 kW | 6030 kWh | 4523 kWh | 1508 kWh | £1,159 | £151 | £1,310 | £19,207 | 14.7 yrs | £6,991 |
| 7 kW | 7035 kWh | 5276 kWh | 1759 kWh | £1,352 | £176 | £1,528 | £21,242 | 13.9 yrs | £9,323 |
| 8 kW | 8040 kWh | 6030 kWh | 2010 kWh | £1,546 | £201 | £1,747 | £23,276 | 13.3 yrs | £11,655 |
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: £1,107, Upfront: £19,623, Break-even: 17.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2010 kWh | 1548 kWh | 462 kWh | £397 | £46 | £443 | £13,519 | 30.5 yrs | £-4,661 |
| 3 kW | 3015 kWh | 2322 kWh | 693 kWh | £595 | £69 | £664 | £15,554 | 23.4 yrs | £-2,266 |
| 4 kW | 4020 kWh | 3096 kWh | 925 kWh | £793 | £92 | £886 | £17,588 | 19.9 yrs | £129 |
| 5 kW | 5025 kWh | 3869 kWh | 1156 kWh | £992 | £116 | £1,107 | £19,623 | 17.7 yrs | £2,524 |
| 6 kW | 6030 kWh | 4643 kWh | 1387 kWh | £1,190 | £139 | £1,329 | £21,657 | 16.3 yrs | £4,918 |
| 7 kW | 7035 kWh | 5417 kWh | 1618 kWh | £1,388 | £162 | £1,550 | £23,692 | 15.3 yrs | £7,313 |
| 8 kW | 8040 kWh | 6191 kWh | 1849 kWh | £1,587 | £185 | £1,772 | £25,726 | 14.5 yrs | £9,708 |
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.