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 914 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: £769, Upfront: £10,173, Break-even: 13.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1829 kWh | 731 kWh | 1097 kWh | £198 | £110 | £308 | £4,069 | 13.2 yrs | £2,084 |
| 3 kW | 2743 kWh | 1097 kWh | 1646 kWh | £297 | £165 | £462 | £6,104 | 13.2 yrs | £3,126 |
| 4 kW | 3657 kWh | 1463 kWh | 2194 kWh | £396 | £219 | £615 | £8,138 | 13.2 yrs | £4,169 |
| 5 kW | 4572 kWh | 1829 kWh | 2743 kWh | £495 | £274 | £769 | £10,173 | 13.2 yrs | £5,211 |
| 6 kW | 5486 kWh | 2194 kWh | 3292 kWh | £594 | £329 | £923 | £12,207 | 13.2 yrs | £6,253 |
| 7 kW | 6401 kWh | 2560 kWh | 3840 kWh | £693 | £384 | £1,077 | £14,242 | 13.2 yrs | £7,295 |
| 8 kW | 7315 kWh | 2926 kWh | 4389 kWh | £792 | £439 | £1,231 | £16,276 | 13.2 yrs | £8,337 |
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: £925, 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 | 1829 kWh | 1097 kWh | 731 kWh | £297 | £73 | £370 | £6,169 | 16.7 yrs | £1,232 |
| 3 kW | 2743 kWh | 1646 kWh | 1097 kWh | £445 | £110 | £555 | £8,204 | 14.8 yrs | £2,898 |
| 4 kW | 3657 kWh | 2194 kWh | 1463 kWh | £594 | £146 | £740 | £10,238 | 13.8 yrs | £4,565 |
| 5 kW | 4572 kWh | 2743 kWh | 1829 kWh | £742 | £183 | £925 | £12,273 | 13.3 yrs | £6,231 |
| 6 kW | 5486 kWh | 3292 kWh | 2194 kWh | £891 | £219 | £1,110 | £14,307 | 12.9 yrs | £7,897 |
| 7 kW | 6401 kWh | 3840 kWh | 2560 kWh | £1,039 | £256 | £1,295 | £16,342 | 12.6 yrs | £9,563 |
| 8 kW | 7315 kWh | 4389 kWh | 2926 kWh | £1,188 | £293 | £1,480 | £18,376 | 12.4 yrs | £11,229 |
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: £1,003, Upfront: £13,673, Break-even: 13.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1829 kWh | 1280 kWh | 549 kWh | £346 | £55 | £401 | £7,569 | 18.9 yrs | £456 |
| 3 kW | 2743 kWh | 1920 kWh | 823 kWh | £520 | £82 | £602 | £9,604 | 16.0 yrs | £2,434 |
| 4 kW | 3657 kWh | 2560 kWh | 1097 kWh | £693 | £110 | £803 | £11,638 | 14.5 yrs | £4,412 |
| 5 kW | 4572 kWh | 3200 kWh | 1372 kWh | £866 | £137 | £1,003 | £13,673 | 13.6 yrs | £6,391 |
| 6 kW | 5486 kWh | 3840 kWh | 1646 kWh | £1,039 | £165 | £1,204 | £15,707 | 13.0 yrs | £8,369 |
| 7 kW | 6401 kWh | 4480 kWh | 1920 kWh | £1,212 | £192 | £1,404 | £17,742 | 12.6 yrs | £10,347 |
| 8 kW | 7315 kWh | 5120 kWh | 2194 kWh | £1,386 | £219 | £1,605 | £19,776 | 12.3 yrs | £12,325 |
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: £1,027, Upfront: £15,423, 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 | 1829 kWh | 1335 kWh | 494 kWh | £361 | £49 | £411 | £9,319 | 22.7 yrs | £-1,107 |
| 3 kW | 2743 kWh | 2002 kWh | 741 kWh | £542 | £74 | £616 | £11,354 | 18.4 yrs | £965 |
| 4 kW | 3657 kWh | 2670 kWh | 988 kWh | £722 | £99 | £821 | £13,388 | 16.3 yrs | £3,037 |
| 5 kW | 4572 kWh | 3337 kWh | 1234 kWh | £903 | £123 | £1,027 | £15,423 | 15.0 yrs | £5,109 |
| 6 kW | 5486 kWh | 4005 kWh | 1481 kWh | £1,084 | £148 | £1,232 | £17,457 | 14.2 yrs | £7,180 |
| 7 kW | 6401 kWh | 4672 kWh | 1728 kWh | £1,264 | £173 | £1,437 | £19,492 | 13.6 yrs | £9,252 |
| 8 kW | 7315 kWh | 5340 kWh | 1975 kWh | £1,445 | £198 | £1,642 | £21,526 | 13.1 yrs | £11,324 |
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: £1,042, Upfront: £17,173, Break-even: 16.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1829 kWh | 1372 kWh | 457 kWh | £371 | £46 | £417 | £11,069 | 26.6 yrs | £-2,732 |
| 3 kW | 2743 kWh | 2057 kWh | 686 kWh | £557 | £69 | £625 | £13,104 | 21.0 yrs | £-598 |
| 4 kW | 3657 kWh | 2743 kWh | 914 kWh | £742 | £91 | £834 | £15,138 | 18.2 yrs | £1,536 |
| 5 kW | 4572 kWh | 3429 kWh | 1143 kWh | £928 | £114 | £1,042 | £17,173 | 16.5 yrs | £3,671 |
| 6 kW | 5486 kWh | 4115 kWh | 1372 kWh | £1,113 | £137 | £1,251 | £19,207 | 15.4 yrs | £5,805 |
| 7 kW | 6401 kWh | 4800 kWh | 1600 kWh | £1,299 | £160 | £1,459 | £21,242 | 14.6 yrs | £7,939 |
| 8 kW | 7315 kWh | 5486 kWh | 1829 kWh | £1,485 | £183 | £1,667 | £23,276 | 14.0 yrs | £10,073 |
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: £1,058, Upfront: £19,623, Break-even: 18.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1829 kWh | 1408 kWh | 421 kWh | £381 | £42 | £423 | £13,519 | 32.0 yrs | £-5,057 |
| 3 kW | 2743 kWh | 2112 kWh | 631 kWh | £572 | £63 | £635 | £15,554 | 24.5 yrs | £-2,861 |
| 4 kW | 3657 kWh | 2816 kWh | 841 kWh | £762 | £84 | £846 | £17,588 | 20.8 yrs | £-664 |
| 5 kW | 4572 kWh | 3520 kWh | 1052 kWh | £953 | £105 | £1,058 | £19,623 | 18.6 yrs | £1,532 |
| 6 kW | 5486 kWh | 4224 kWh | 1262 kWh | £1,143 | £126 | £1,269 | £21,657 | 17.1 yrs | £3,729 |
| 7 kW | 6401 kWh | 4928 kWh | 1472 kWh | £1,334 | £147 | £1,481 | £23,692 | 16.0 yrs | £5,925 |
| 8 kW | 7315 kWh | 5633 kWh | 1682 kWh | £1,524 | £168 | £1,692 | £25,726 | 15.2 yrs | £8,122 |
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.