A typical roof here lands around 4.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 937 kWh per year on a south-facing roof. We value self-used electricity at 27.7p 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: £800, Upfront: £10,173, Break-even: 12.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1873 kWh | 749 kWh | 1124 kWh | £208 | £112 | £320 | £4,069 | 12.7 yrs | £2,333 |
| 3 kW | 2810 kWh | 1124 kWh | 1686 kWh | £312 | £169 | £480 | £6,104 | 12.7 yrs | £3,499 |
| 4 kW | 3746 kWh | 1499 kWh | 2248 kWh | £415 | £225 | £640 | £8,138 | 12.7 yrs | £4,666 |
| 5 kW | 4683 kWh | 1873 kWh | 2810 kWh | £519 | £281 | £800 | £10,173 | 12.7 yrs | £5,832 |
| 6 kW | 5620 kWh | 2248 kWh | 3372 kWh | £623 | £337 | £960 | £12,207 | 12.7 yrs | £6,999 |
| 7 kW | 6556 kWh | 2623 kWh | 3934 kWh | £727 | £393 | £1,120 | £14,242 | 12.7 yrs | £8,165 |
| 8 kW | 7493 kWh | 2997 kWh | 4496 kWh | £831 | £450 | £1,280 | £16,276 | 12.7 yrs | £9,332 |
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: £966, Upfront: £12,273, Break-even: 12.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1873 kWh | 1124 kWh | 749 kWh | £312 | £75 | £386 | £6,169 | 16.0 yrs | £1,561 |
| 3 kW | 2810 kWh | 1686 kWh | 1124 kWh | £467 | £112 | £580 | £8,204 | 14.2 yrs | £3,391 |
| 4 kW | 3746 kWh | 2248 kWh | 1499 kWh | £623 | £150 | £773 | £10,238 | 13.2 yrs | £5,221 |
| 5 kW | 4683 kWh | 2810 kWh | 1873 kWh | £779 | £187 | £966 | £12,273 | 12.7 yrs | £7,052 |
| 6 kW | 5620 kWh | 3372 kWh | 2248 kWh | £935 | £225 | £1,159 | £14,307 | 12.3 yrs | £8,882 |
| 7 kW | 6556 kWh | 3934 kWh | 2623 kWh | £1,090 | £262 | £1,353 | £16,342 | 12.1 yrs | £10,713 |
| 8 kW | 7493 kWh | 4496 kWh | 2997 kWh | £1,246 | £300 | £1,546 | £18,376 | 11.9 yrs | £12,543 |
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: £1,049, 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 | 1873 kWh | 1311 kWh | 562 kWh | £363 | £56 | £420 | £7,569 | 18.0 yrs | £825 |
| 3 kW | 2810 kWh | 1967 kWh | 843 kWh | £545 | £84 | £630 | £9,604 | 15.3 yrs | £2,987 |
| 4 kW | 3746 kWh | 2623 kWh | 1124 kWh | £727 | £112 | £839 | £11,638 | 13.9 yrs | £5,149 |
| 5 kW | 4683 kWh | 3278 kWh | 1405 kWh | £909 | £140 | £1,049 | £13,673 | 13.0 yrs | £7,311 |
| 6 kW | 5620 kWh | 3934 kWh | 1686 kWh | £1,090 | £169 | £1,259 | £15,707 | 12.5 yrs | £9,474 |
| 7 kW | 6556 kWh | 4589 kWh | 1967 kWh | £1,272 | £197 | £1,469 | £17,742 | 12.1 yrs | £11,636 |
| 8 kW | 7493 kWh | 5245 kWh | 2248 kWh | £1,454 | £225 | £1,679 | £19,776 | 11.8 yrs | £13,798 |
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: £1,074, Upfront: £15,423, Break-even: 14.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1873 kWh | 1367 kWh | 506 kWh | £379 | £51 | £430 | £9,319 | 21.7 yrs | £-726 |
| 3 kW | 2810 kWh | 2051 kWh | 759 kWh | £569 | £76 | £644 | £11,354 | 17.6 yrs | £1,536 |
| 4 kW | 3746 kWh | 2735 kWh | 1012 kWh | £758 | £101 | £859 | £13,388 | 15.6 yrs | £3,798 |
| 5 kW | 4683 kWh | 3419 kWh | 1264 kWh | £948 | £126 | £1,074 | £15,423 | 14.4 yrs | £6,059 |
| 6 kW | 5620 kWh | 4102 kWh | 1517 kWh | £1,137 | £152 | £1,289 | £17,457 | 13.5 yrs | £8,321 |
| 7 kW | 6556 kWh | 4786 kWh | 1770 kWh | £1,327 | £177 | £1,504 | £19,492 | 13.0 yrs | £10,583 |
| 8 kW | 7493 kWh | 5470 kWh | 2023 kWh | £1,516 | £202 | £1,719 | £21,526 | 12.5 yrs | £12,845 |
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: £1,091, 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 | 1873 kWh | 1405 kWh | 468 kWh | £389 | £47 | £436 | £11,069 | 25.4 yrs | £-2,343 |
| 3 kW | 2810 kWh | 2107 kWh | 702 kWh | £584 | £70 | £654 | £13,104 | 20.0 yrs | £-15 |
| 4 kW | 3746 kWh | 2810 kWh | 937 kWh | £779 | £94 | £873 | £15,138 | 17.3 yrs | £2,313 |
| 5 kW | 4683 kWh | 3512 kWh | 1171 kWh | £974 | £117 | £1,091 | £17,173 | 15.7 yrs | £4,641 |
| 6 kW | 5620 kWh | 4215 kWh | 1405 kWh | £1,168 | £140 | £1,309 | £19,207 | 14.7 yrs | £6,970 |
| 7 kW | 6556 kWh | 4917 kWh | 1639 kWh | £1,363 | £164 | £1,527 | £21,242 | 13.9 yrs | £9,298 |
| 8 kW | 7493 kWh | 5620 kWh | 1873 kWh | £1,558 | £187 | £1,745 | £23,276 | 13.3 yrs | £11,626 |
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 | 1873 kWh | 1442 kWh | 431 kWh | £400 | £43 | £443 | £13,519 | 30.5 yrs | £-4,661 |
| 3 kW | 2810 kWh | 2164 kWh | 646 kWh | £600 | £65 | £664 | £15,554 | 23.4 yrs | £-2,266 |
| 4 kW | 3746 kWh | 2885 kWh | 862 kWh | £800 | £86 | £886 | £17,588 | 19.9 yrs | £129 |
| 5 kW | 4683 kWh | 3606 kWh | 1077 kWh | £1,000 | £108 | £1,107 | £19,623 | 17.7 yrs | £2,523 |
| 6 kW | 5620 kWh | 4327 kWh | 1293 kWh | £1,199 | £129 | £1,329 | £21,657 | 16.3 yrs | £4,918 |
| 7 kW | 6556 kWh | 5048 kWh | 1508 kWh | £1,399 | £151 | £1,550 | £23,692 | 15.3 yrs | £7,313 |
| 8 kW | 7493 kWh | 5770 kWh | 1723 kWh | £1,599 | £172 | £1,772 | £25,726 | 14.5 yrs | £9,707 |
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.