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 780 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: £656, Upfront: £10,173, Break-even: 15.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1560 kWh | 624 kWh | 936 kWh | £169 | £94 | £262 | £4,069 | 15.5 yrs | £1,179 |
| 3 kW | 2339 kWh | 936 kWh | 1404 kWh | £253 | £140 | £394 | £6,104 | 15.5 yrs | £1,768 |
| 4 kW | 3119 kWh | 1248 kWh | 1872 kWh | £338 | £187 | £525 | £8,138 | 15.5 yrs | £2,358 |
| 5 kW | 3899 kWh | 1560 kWh | 2339 kWh | £422 | £234 | £656 | £10,173 | 15.5 yrs | £2,947 |
| 6 kW | 4679 kWh | 1872 kWh | 2807 kWh | £506 | £281 | £787 | £12,207 | 15.5 yrs | £3,537 |
| 7 kW | 5459 kWh | 2184 kWh | 3275 kWh | £591 | £328 | £918 | £14,242 | 15.5 yrs | £4,126 |
| 8 kW | 6239 kWh | 2495 kWh | 3743 kWh | £675 | £374 | £1,050 | £16,276 | 15.5 yrs | £4,716 |
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: £789, Upfront: £12,273, 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 | 1560 kWh | 936 kWh | 624 kWh | £253 | £62 | £316 | £6,169 | 19.5 yrs | £143 |
| 3 kW | 2339 kWh | 1404 kWh | 936 kWh | £380 | £94 | £473 | £8,204 | 17.3 yrs | £1,265 |
| 4 kW | 3119 kWh | 1872 kWh | 1248 kWh | £506 | £125 | £631 | £10,238 | 16.2 yrs | £2,386 |
| 5 kW | 3899 kWh | 2339 kWh | 1560 kWh | £633 | £156 | £789 | £12,273 | 15.6 yrs | £3,508 |
| 6 kW | 4679 kWh | 2807 kWh | 1872 kWh | £760 | £187 | £947 | £14,307 | 15.1 yrs | £4,630 |
| 7 kW | 5459 kWh | 3275 kWh | 2184 kWh | £886 | £218 | £1,105 | £16,342 | 14.8 yrs | £5,751 |
| 8 kW | 6239 kWh | 3743 kWh | 2495 kWh | £1,013 | £250 | £1,262 | £18,376 | 14.6 yrs | £6,873 |
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: £856, Upfront: £13,673, Break-even: 16.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1560 kWh | 1092 kWh | 468 kWh | £295 | £47 | £342 | £7,569 | 22.1 yrs | £-725 |
| 3 kW | 2339 kWh | 1638 kWh | 702 kWh | £443 | £70 | £513 | £9,604 | 18.7 yrs | £663 |
| 4 kW | 3119 kWh | 2184 kWh | 936 kWh | £591 | £94 | £684 | £11,638 | 17.0 yrs | £2,051 |
| 5 kW | 3899 kWh | 2729 kWh | 1170 kWh | £739 | £117 | £856 | £13,673 | 16.0 yrs | £3,438 |
| 6 kW | 4679 kWh | 3275 kWh | 1404 kWh | £886 | £140 | £1,027 | £15,707 | 15.3 yrs | £4,826 |
| 7 kW | 5459 kWh | 3821 kWh | 1638 kWh | £1,034 | £164 | £1,198 | £17,742 | 14.8 yrs | £6,214 |
| 8 kW | 6239 kWh | 4367 kWh | 1872 kWh | £1,182 | £187 | £1,369 | £19,776 | 14.4 yrs | £7,602 |
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: £876, Upfront: £15,423, Break-even: 17.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1560 kWh | 1139 kWh | 421 kWh | £308 | £42 | £350 | £9,319 | 26.6 yrs | £-2,315 |
| 3 kW | 2339 kWh | 1708 kWh | 632 kWh | £462 | £63 | £525 | £11,354 | 21.6 yrs | £-847 |
| 4 kW | 3119 kWh | 2277 kWh | 842 kWh | £616 | £84 | £700 | £13,388 | 19.1 yrs | £620 |
| 5 kW | 3899 kWh | 2846 kWh | 1053 kWh | £770 | £105 | £876 | £15,423 | 17.6 yrs | £2,088 |
| 6 kW | 4679 kWh | 3416 kWh | 1263 kWh | £924 | £126 | £1,051 | £17,457 | 16.6 yrs | £3,555 |
| 7 kW | 5459 kWh | 3985 kWh | 1474 kWh | £1,078 | £147 | £1,226 | £19,492 | 15.9 yrs | £5,023 |
| 8 kW | 6239 kWh | 4554 kWh | 1684 kWh | £1,232 | £168 | £1,401 | £21,526 | 15.4 yrs | £6,490 |
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: £889, Upfront: £17,173, Break-even: 19.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1560 kWh | 1170 kWh | 390 kWh | £317 | £39 | £356 | £11,069 | 31.1 yrs | £-3,959 |
| 3 kW | 2339 kWh | 1755 kWh | 585 kWh | £475 | £58 | £533 | £13,104 | 24.6 yrs | £-2,438 |
| 4 kW | 3119 kWh | 2339 kWh | 780 kWh | £633 | £78 | £711 | £15,138 | 21.3 yrs | £-917 |
| 5 kW | 3899 kWh | 2924 kWh | 975 kWh | £791 | £97 | £889 | £17,173 | 19.3 yrs | £604 |
| 6 kW | 4679 kWh | 3509 kWh | 1170 kWh | £950 | £117 | £1,067 | £19,207 | 18.0 yrs | £2,124 |
| 7 kW | 5459 kWh | 4094 kWh | 1365 kWh | £1,108 | £136 | £1,244 | £21,242 | 17.1 yrs | £3,645 |
| 8 kW | 6239 kWh | 4679 kWh | 1560 kWh | £1,266 | £156 | £1,422 | £23,276 | 16.4 yrs | £5,166 |
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: £902, Upfront: £19,623, Break-even: 21.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1560 kWh | 1201 kWh | 359 kWh | £325 | £36 | £361 | £13,519 | 37.5 yrs | £-6,302 |
| 3 kW | 2339 kWh | 1801 kWh | 538 kWh | £487 | £54 | £541 | £15,554 | 28.7 yrs | £-4,728 |
| 4 kW | 3119 kWh | 2402 kWh | 717 kWh | £650 | £72 | £722 | £17,588 | 24.4 yrs | £-3,154 |
| 5 kW | 3899 kWh | 3002 kWh | 897 kWh | £812 | £90 | £902 | £19,623 | 21.8 yrs | £-1,580 |
| 6 kW | 4679 kWh | 3603 kWh | 1076 kWh | £975 | £108 | £1,083 | £21,657 | 20.0 yrs | £-6 |
| 7 kW | 5459 kWh | 4203 kWh | 1256 kWh | £1,137 | £126 | £1,263 | £23,692 | 18.8 yrs | £1,568 |
| 8 kW | 6239 kWh | 4804 kWh | 1435 kWh | £1,300 | £143 | £1,443 | £25,726 | 17.8 yrs | £3,142 |
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.