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 774 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: £651, Upfront: £10,173, Break-even: 15.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1548 kWh | 619 kWh | 929 kWh | £168 | £93 | £260 | £4,069 | 15.6 yrs | £1,141 |
| 3 kW | 2322 kWh | 929 kWh | 1393 kWh | £251 | £139 | £391 | £6,104 | 15.6 yrs | £1,711 |
| 4 kW | 3097 kWh | 1239 kWh | 1858 kWh | £335 | £186 | £521 | £8,138 | 15.6 yrs | £2,281 |
| 5 kW | 3871 kWh | 1548 kWh | 2322 kWh | £419 | £232 | £651 | £10,173 | 15.6 yrs | £2,851 |
| 6 kW | 4645 kWh | 1858 kWh | 2787 kWh | £503 | £279 | £781 | £12,207 | 15.6 yrs | £3,422 |
| 7 kW | 5419 kWh | 2168 kWh | 3251 kWh | £587 | £325 | £912 | £14,242 | 15.6 yrs | £3,992 |
| 8 kW | 6193 kWh | 2477 kWh | 3716 kWh | £670 | £372 | £1,042 | £16,276 | 15.6 yrs | £4,562 |
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: £783, Upfront: £12,273, 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 | 1548 kWh | 929 kWh | 619 kWh | £251 | £62 | £313 | £6,169 | 19.7 yrs | £97 |
| 3 kW | 2322 kWh | 1393 kWh | 929 kWh | £377 | £93 | £470 | £8,204 | 17.5 yrs | £1,196 |
| 4 kW | 3097 kWh | 1858 kWh | 1239 kWh | £503 | £124 | £627 | £10,238 | 16.3 yrs | £2,294 |
| 5 kW | 3871 kWh | 2322 kWh | 1548 kWh | £628 | £155 | £783 | £12,273 | 15.7 yrs | £3,393 |
| 6 kW | 4645 kWh | 2787 kWh | 1858 kWh | £754 | £186 | £940 | £14,307 | 15.2 yrs | £4,491 |
| 7 kW | 5419 kWh | 3251 kWh | 2168 kWh | £880 | £217 | £1,097 | £16,342 | 14.9 yrs | £5,590 |
| 8 kW | 6193 kWh | 3716 kWh | 2477 kWh | £1,006 | £248 | £1,253 | £18,376 | 14.7 yrs | £6,688 |
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: £849, Upfront: £13,673, Break-even: 16.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1548 kWh | 1084 kWh | 464 kWh | £293 | £46 | £340 | £7,569 | 22.3 yrs | £-775 |
| 3 kW | 2322 kWh | 1626 kWh | 697 kWh | £440 | £70 | £510 | £9,604 | 18.8 yrs | £588 |
| 4 kW | 3097 kWh | 2168 kWh | 929 kWh | £587 | £93 | £679 | £11,638 | 17.1 yrs | £1,951 |
| 5 kW | 3871 kWh | 2709 kWh | 1161 kWh | £733 | £116 | £849 | £13,673 | 16.1 yrs | £3,313 |
| 6 kW | 4645 kWh | 3251 kWh | 1393 kWh | £880 | £139 | £1,019 | £15,707 | 15.4 yrs | £4,676 |
| 7 kW | 5419 kWh | 3793 kWh | 1626 kWh | £1,026 | £163 | £1,189 | £17,742 | 14.9 yrs | £6,039 |
| 8 kW | 6193 kWh | 4335 kWh | 1858 kWh | £1,173 | £186 | £1,359 | £19,776 | 14.6 yrs | £7,401 |
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: £869, Upfront: £15,423, 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 | 1548 kWh | 1130 kWh | 418 kWh | £306 | £42 | £348 | £9,319 | 26.8 yrs | £-2,366 |
| 3 kW | 2322 kWh | 1695 kWh | 627 kWh | £459 | £63 | £521 | £11,354 | 21.8 yrs | £-924 |
| 4 kW | 3097 kWh | 2260 kWh | 836 kWh | £612 | £84 | £695 | £13,388 | 19.3 yrs | £518 |
| 5 kW | 3871 kWh | 2826 kWh | 1045 kWh | £765 | £105 | £869 | £15,423 | 17.7 yrs | £1,960 |
| 6 kW | 4645 kWh | 3391 kWh | 1254 kWh | £918 | £125 | £1,043 | £17,457 | 16.7 yrs | £3,402 |
| 7 kW | 5419 kWh | 3956 kWh | 1463 kWh | £1,070 | £146 | £1,217 | £19,492 | 16.0 yrs | £4,843 |
| 8 kW | 6193 kWh | 4521 kWh | 1672 kWh | £1,223 | £167 | £1,391 | £21,526 | 15.5 yrs | £6,285 |
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: £882, Upfront: £17,173, Break-even: 19.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1548 kWh | 1161 kWh | 387 kWh | £314 | £39 | £353 | £11,069 | 31.4 yrs | £-4,011 |
| 3 kW | 2322 kWh | 1742 kWh | 581 kWh | £471 | £58 | £529 | £13,104 | 24.8 yrs | £-2,516 |
| 4 kW | 3097 kWh | 2322 kWh | 774 kWh | £628 | £77 | £706 | £15,138 | 21.4 yrs | £-1,021 |
| 5 kW | 3871 kWh | 2903 kWh | 968 kWh | £786 | £97 | £882 | £17,173 | 19.5 yrs | £474 |
| 6 kW | 4645 kWh | 3484 kWh | 1161 kWh | £943 | £116 | £1,059 | £19,207 | 18.1 yrs | £1,968 |
| 7 kW | 5419 kWh | 4064 kWh | 1355 kWh | £1,100 | £135 | £1,235 | £21,242 | 17.2 yrs | £3,463 |
| 8 kW | 6193 kWh | 4645 kWh | 1548 kWh | £1,257 | £155 | £1,412 | £23,276 | 16.5 yrs | £4,958 |
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: £896, Upfront: £19,623, Break-even: 21.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1548 kWh | 1192 kWh | 356 kWh | £323 | £36 | £358 | £13,519 | 37.7 yrs | £-6,355 |
| 3 kW | 2322 kWh | 1788 kWh | 534 kWh | £484 | £53 | £537 | £15,554 | 28.9 yrs | £-4,807 |
| 4 kW | 3097 kWh | 2384 kWh | 712 kWh | £645 | £71 | £716 | £17,588 | 24.6 yrs | £-3,260 |
| 5 kW | 3871 kWh | 2980 kWh | 890 kWh | £806 | £89 | £896 | £19,623 | 21.9 yrs | £-1,712 |
| 6 kW | 4645 kWh | 3576 kWh | 1068 kWh | £968 | £107 | £1,075 | £21,657 | 20.2 yrs | £-165 |
| 7 kW | 5419 kWh | 4173 kWh | 1246 kWh | £1,129 | £125 | £1,254 | £23,692 | 18.9 yrs | £1,383 |
| 8 kW | 6193 kWh | 4769 kWh | 1424 kWh | £1,290 | £142 | £1,433 | £25,726 | 18.0 yrs | £2,931 |
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.