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 953 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: £774, Upfront: £10,173, Break-even: 13.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1906 kWh | 762 kWh | 1143 kWh | £195 | £114 | £310 | £4,069 | 13.1 yrs | £2,127 |
| 3 kW | 2858 kWh | 1143 kWh | 1715 kWh | £293 | £172 | £465 | £6,104 | 13.1 yrs | £3,190 |
| 4 kW | 3811 kWh | 1524 kWh | 2287 kWh | £391 | £229 | £620 | £8,138 | 13.1 yrs | £4,253 |
| 5 kW | 4764 kWh | 1906 kWh | 2858 kWh | £489 | £286 | £774 | £10,173 | 13.1 yrs | £5,316 |
| 6 kW | 5717 kWh | 2287 kWh | 3430 kWh | £586 | £343 | £929 | £12,207 | 13.1 yrs | £6,380 |
| 7 kW | 6670 kWh | 2668 kWh | 4002 kWh | £684 | £400 | £1,084 | £14,242 | 13.1 yrs | £7,443 |
| 8 kW | 7622 kWh | 3049 kWh | 4573 kWh | £782 | £457 | £1,239 | £16,276 | 13.1 yrs | £8,506 |
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: £923, Upfront: £12,273, Break-even: 13.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1906 kWh | 1143 kWh | 762 kWh | £293 | £76 | £369 | £6,169 | 16.7 yrs | £1,219 |
| 3 kW | 2858 kWh | 1715 kWh | 1143 kWh | £440 | £114 | £554 | £8,204 | 14.8 yrs | £2,878 |
| 4 kW | 3811 kWh | 2287 kWh | 1524 kWh | £586 | £152 | £739 | £10,238 | 13.9 yrs | £4,537 |
| 5 kW | 4764 kWh | 2858 kWh | 1906 kWh | £733 | £191 | £923 | £12,273 | 13.3 yrs | £6,197 |
| 6 kW | 5717 kWh | 3430 kWh | 2287 kWh | £879 | £229 | £1,108 | £14,307 | 12.9 yrs | £7,856 |
| 7 kW | 6670 kWh | 4002 kWh | 2668 kWh | £1,026 | £267 | £1,293 | £16,342 | 12.6 yrs | £9,515 |
| 8 kW | 7622 kWh | 4573 kWh | 3049 kWh | £1,173 | £305 | £1,478 | £18,376 | 12.4 yrs | £11,175 |
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: £998, Upfront: £13,673, Break-even: 13.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1906 kWh | 1334 kWh | 572 kWh | £342 | £57 | £399 | £7,569 | 19.0 yrs | £415 |
| 3 kW | 2858 kWh | 2001 kWh | 858 kWh | £513 | £86 | £599 | £9,604 | 16.0 yrs | £2,372 |
| 4 kW | 3811 kWh | 2668 kWh | 1143 kWh | £684 | £114 | £798 | £11,638 | 14.6 yrs | £4,330 |
| 5 kW | 4764 kWh | 3335 kWh | 1429 kWh | £855 | £143 | £998 | £13,673 | 13.7 yrs | £6,287 |
| 6 kW | 5717 kWh | 4002 kWh | 1715 kWh | £1,026 | £172 | £1,198 | £15,707 | 13.1 yrs | £8,244 |
| 7 kW | 6670 kWh | 4669 kWh | 2001 kWh | £1,197 | £200 | £1,397 | £17,742 | 12.7 yrs | £10,202 |
| 8 kW | 7622 kWh | 5336 kWh | 2287 kWh | £1,368 | £229 | £1,597 | £19,776 | 12.4 yrs | £12,159 |
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: £1,020, Upfront: £15,423, Break-even: 15.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1906 kWh | 1391 kWh | 515 kWh | £357 | £51 | £408 | £9,319 | 22.8 yrs | £-1,156 |
| 3 kW | 2858 kWh | 2087 kWh | 772 kWh | £535 | £77 | £612 | £11,354 | 18.5 yrs | £890 |
| 4 kW | 3811 kWh | 2782 kWh | 1029 kWh | £713 | £103 | £816 | £13,388 | 16.4 yrs | £2,937 |
| 5 kW | 4764 kWh | 3478 kWh | 1286 kWh | £892 | £129 | £1,020 | £15,423 | 15.1 yrs | £4,984 |
| 6 kW | 5717 kWh | 4173 kWh | 1544 kWh | £1,070 | £154 | £1,224 | £17,457 | 14.3 yrs | £7,031 |
| 7 kW | 6670 kWh | 4869 kWh | 1801 kWh | £1,248 | £180 | £1,428 | £19,492 | 13.6 yrs | £9,078 |
| 8 kW | 7622 kWh | 5564 kWh | 2058 kWh | £1,427 | £206 | £1,633 | £21,526 | 13.2 yrs | £11,124 |
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: £1,035, Upfront: £17,173, Break-even: 16.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1906 kWh | 1429 kWh | 476 kWh | £366 | £48 | £414 | £11,069 | 26.7 yrs | £-2,787 |
| 3 kW | 2858 kWh | 2144 kWh | 715 kWh | £550 | £71 | £621 | £13,104 | 21.1 yrs | £-681 |
| 4 kW | 3811 kWh | 2858 kWh | 953 kWh | £733 | £95 | £828 | £15,138 | 18.3 yrs | £1,426 |
| 5 kW | 4764 kWh | 3573 kWh | 1191 kWh | £916 | £119 | £1,035 | £17,173 | 16.6 yrs | £3,532 |
| 6 kW | 5717 kWh | 4288 kWh | 1429 kWh | £1,099 | £143 | £1,242 | £19,207 | 15.5 yrs | £5,638 |
| 7 kW | 6670 kWh | 5002 kWh | 1667 kWh | £1,283 | £167 | £1,449 | £21,242 | 14.7 yrs | £7,745 |
| 8 kW | 7622 kWh | 5717 kWh | 1906 kWh | £1,466 | £191 | £1,656 | £23,276 | 14.1 yrs | £9,851 |
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: £1,050, Upfront: £19,623, 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 | 1906 kWh | 1467 kWh | 438 kWh | £376 | £44 | £420 | £13,519 | 32.2 yrs | £-5,118 |
| 3 kW | 2858 kWh | 2201 kWh | 657 kWh | £564 | £66 | £630 | £15,554 | 24.7 yrs | £-2,952 |
| 4 kW | 3811 kWh | 2935 kWh | 877 kWh | £752 | £88 | £840 | £17,588 | 20.9 yrs | £-786 |
| 5 kW | 4764 kWh | 3668 kWh | 1096 kWh | £941 | £110 | £1,050 | £19,623 | 18.7 yrs | £1,380 |
| 6 kW | 5717 kWh | 4402 kWh | 1315 kWh | £1,129 | £131 | £1,260 | £21,657 | 17.2 yrs | £3,546 |
| 7 kW | 6670 kWh | 5136 kWh | 1534 kWh | £1,317 | £153 | £1,470 | £23,692 | 16.1 yrs | £5,712 |
| 8 kW | 7622 kWh | 5869 kWh | 1753 kWh | £1,505 | £175 | £1,680 | £25,726 | 15.3 yrs | £7,878 |
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.