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 779 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 | 1559 kWh | 624 kWh | 935 kWh | £169 | £94 | £262 | £4,069 | 15.5 yrs | £1,176 |
| 3 kW | 2338 kWh | 935 kWh | 1403 kWh | £253 | £140 | £393 | £6,104 | 15.5 yrs | £1,764 |
| 4 kW | 3118 kWh | 1247 kWh | 1871 kWh | £337 | £187 | £524 | £8,138 | 15.5 yrs | £2,352 |
| 5 kW | 3897 kWh | 1559 kWh | 2338 kWh | £422 | £234 | £656 | £10,173 | 15.5 yrs | £2,940 |
| 6 kW | 4676 kWh | 1871 kWh | 2806 kWh | £506 | £281 | £787 | £12,207 | 15.5 yrs | £3,528 |
| 7 kW | 5456 kWh | 2182 kWh | 3273 kWh | £591 | £327 | £918 | £14,242 | 15.5 yrs | £4,116 |
| 8 kW | 6235 kWh | 2494 kWh | 3741 kWh | £675 | £374 | £1,049 | £16,276 | 15.5 yrs | £4,704 |
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 | 1559 kWh | 935 kWh | 624 kWh | £253 | £62 | £315 | £6,169 | 19.6 yrs | £140 |
| 3 kW | 2338 kWh | 1403 kWh | 935 kWh | £380 | £94 | £473 | £8,204 | 17.3 yrs | £1,260 |
| 4 kW | 3118 kWh | 1871 kWh | 1247 kWh | £506 | £125 | £631 | £10,238 | 16.2 yrs | £2,379 |
| 5 kW | 3897 kWh | 2338 kWh | 1559 kWh | £633 | £156 | £789 | £12,273 | 15.6 yrs | £3,499 |
| 6 kW | 4676 kWh | 2806 kWh | 1871 kWh | £759 | £187 | £946 | £14,307 | 15.1 yrs | £4,619 |
| 7 kW | 5456 kWh | 3273 kWh | 2182 kWh | £886 | £218 | £1,104 | £16,342 | 14.8 yrs | £5,739 |
| 8 kW | 6235 kWh | 3741 kWh | 2494 kWh | £1,012 | £249 | £1,262 | £18,376 | 14.6 yrs | £6,859 |
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: £855, 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 | 1559 kWh | 1091 kWh | 468 kWh | £295 | £47 | £342 | £7,569 | 22.1 yrs | £-728 |
| 3 kW | 2338 kWh | 1637 kWh | 701 kWh | £443 | £70 | £513 | £9,604 | 18.7 yrs | £657 |
| 4 kW | 3118 kWh | 2182 kWh | 935 kWh | £591 | £94 | £684 | £11,638 | 17.0 yrs | £2,043 |
| 5 kW | 3897 kWh | 2728 kWh | 1169 kWh | £738 | £117 | £855 | £13,673 | 16.0 yrs | £3,429 |
| 6 kW | 4676 kWh | 3273 kWh | 1403 kWh | £886 | £140 | £1,026 | £15,707 | 15.3 yrs | £4,815 |
| 7 kW | 5456 kWh | 3819 kWh | 1637 kWh | £1,033 | £164 | £1,197 | £17,742 | 14.8 yrs | £6,200 |
| 8 kW | 6235 kWh | 4365 kWh | 1871 kWh | £1,181 | £187 | £1,368 | £19,776 | 14.5 yrs | £7,586 |
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: £875, 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 | 1559 kWh | 1138 kWh | 421 kWh | £308 | £42 | £350 | £9,319 | 26.6 yrs | £-2,319 |
| 3 kW | 2338 kWh | 1707 kWh | 631 kWh | £462 | £63 | £525 | £11,354 | 21.6 yrs | £-853 |
| 4 kW | 3118 kWh | 2276 kWh | 842 kWh | £616 | £84 | £700 | £13,388 | 19.1 yrs | £612 |
| 5 kW | 3897 kWh | 2845 kWh | 1052 kWh | £770 | £105 | £875 | £15,423 | 17.6 yrs | £2,078 |
| 6 kW | 4676 kWh | 3414 kWh | 1263 kWh | £924 | £126 | £1,050 | £17,457 | 16.6 yrs | £3,543 |
| 7 kW | 5456 kWh | 3983 kWh | 1473 kWh | £1,078 | £147 | £1,225 | £19,492 | 15.9 yrs | £5,009 |
| 8 kW | 6235 kWh | 4552 kWh | 1683 kWh | £1,232 | £168 | £1,400 | £21,526 | 15.4 yrs | £6,474 |
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: £888, 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 | 1559 kWh | 1169 kWh | 390 kWh | £316 | £39 | £355 | £11,069 | 31.2 yrs | £-3,963 |
| 3 kW | 2338 kWh | 1754 kWh | 585 kWh | £475 | £58 | £533 | £13,104 | 24.6 yrs | £-2,444 |
| 4 kW | 3118 kWh | 2338 kWh | 779 kWh | £633 | £78 | £711 | £15,138 | 21.3 yrs | £-925 |
| 5 kW | 3897 kWh | 2923 kWh | 974 kWh | £791 | £97 | £888 | £17,173 | 19.3 yrs | £594 |
| 6 kW | 4676 kWh | 3507 kWh | 1169 kWh | £949 | £117 | £1,066 | £19,207 | 18.0 yrs | £2,112 |
| 7 kW | 5456 kWh | 4092 kWh | 1364 kWh | £1,107 | £136 | £1,244 | £21,242 | 17.1 yrs | £3,631 |
| 8 kW | 6235 kWh | 4676 kWh | 1559 kWh | £1,265 | £156 | £1,421 | £23,276 | 16.4 yrs | £5,150 |
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 | 1559 kWh | 1200 kWh | 359 kWh | £325 | £36 | £361 | £13,519 | 37.5 yrs | £-6,306 |
| 3 kW | 2338 kWh | 1800 kWh | 538 kWh | £487 | £54 | £541 | £15,554 | 28.8 yrs | £-4,734 |
| 4 kW | 3118 kWh | 2401 kWh | 717 kWh | £650 | £72 | £721 | £17,588 | 24.4 yrs | £-3,162 |
| 5 kW | 3897 kWh | 3001 kWh | 896 kWh | £812 | £90 | £902 | £19,623 | 21.8 yrs | £-1,590 |
| 6 kW | 4676 kWh | 3601 kWh | 1076 kWh | £974 | £108 | £1,082 | £21,657 | 20.0 yrs | £-19 |
| 7 kW | 5456 kWh | 4201 kWh | 1255 kWh | £1,137 | £125 | £1,262 | £23,692 | 18.8 yrs | £1,553 |
| 8 kW | 6235 kWh | 4801 kWh | 1434 kWh | £1,299 | £143 | £1,443 | £25,726 | 17.8 yrs | £3,125 |
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.