A typical roof here lands around 6.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 901 kWh per year on a south-facing roof. We value self-used electricity at 25.8p 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: £736, Upfront: £10,173, Break-even: 13.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1801 kWh | 720 kWh | 1081 kWh | £186 | £108 | £294 | £4,069 | 13.8 yrs | £1,816 |
| 3 kW | 2702 kWh | 1081 kWh | 1621 kWh | £279 | £162 | £441 | £6,104 | 13.8 yrs | £2,723 |
| 4 kW | 3602 kWh | 1441 kWh | 2161 kWh | £372 | £216 | £588 | £8,138 | 13.8 yrs | £3,631 |
| 5 kW | 4503 kWh | 1801 kWh | 2702 kWh | £465 | £270 | £736 | £10,173 | 13.8 yrs | £4,539 |
| 6 kW | 5403 kWh | 2161 kWh | 3242 kWh | £558 | £324 | £883 | £12,207 | 13.8 yrs | £5,447 |
| 7 kW | 6304 kWh | 2522 kWh | 3782 kWh | £652 | £378 | £1,030 | £14,242 | 13.8 yrs | £6,355 |
| 8 kW | 7204 kWh | 2882 kWh | 4323 kWh | £745 | £432 | £1,177 | £16,276 | 13.8 yrs | £7,262 |
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: £878, Upfront: £12,273, Break-even: 14.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1801 kWh | 1081 kWh | 720 kWh | £279 | £72 | £351 | £6,169 | 17.6 yrs | £857 |
| 3 kW | 2702 kWh | 1621 kWh | 1081 kWh | £419 | £108 | £527 | £8,204 | 15.6 yrs | £2,335 |
| 4 kW | 3602 kWh | 2161 kWh | 1441 kWh | £558 | £144 | £703 | £10,238 | 14.6 yrs | £3,814 |
| 5 kW | 4503 kWh | 2702 kWh | 1801 kWh | £698 | £180 | £878 | £12,273 | 14.0 yrs | £5,292 |
| 6 kW | 5403 kWh | 3242 kWh | 2161 kWh | £838 | £216 | £1,054 | £14,307 | 13.6 yrs | £6,770 |
| 7 kW | 6304 kWh | 3782 kWh | 2522 kWh | £977 | £252 | £1,230 | £16,342 | 13.3 yrs | £8,249 |
| 8 kW | 7204 kWh | 4323 kWh | 2882 kWh | £1,117 | £288 | £1,405 | £18,376 | 13.1 yrs | £9,727 |
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: £950, Upfront: £13,673, Break-even: 14.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1801 kWh | 1261 kWh | 540 kWh | £326 | £54 | £380 | £7,569 | 19.9 yrs | £27 |
| 3 kW | 2702 kWh | 1891 kWh | 811 kWh | £489 | £81 | £570 | £9,604 | 16.9 yrs | £1,791 |
| 4 kW | 3602 kWh | 2522 kWh | 1081 kWh | £652 | £108 | £760 | £11,638 | 15.3 yrs | £3,555 |
| 5 kW | 4503 kWh | 3152 kWh | 1351 kWh | £814 | £135 | £950 | £13,673 | 14.4 yrs | £5,318 |
| 6 kW | 5403 kWh | 3782 kWh | 1621 kWh | £977 | £162 | £1,139 | £15,707 | 13.8 yrs | £7,082 |
| 7 kW | 6304 kWh | 4413 kWh | 1891 kWh | £1,140 | £189 | £1,329 | £17,742 | 13.3 yrs | £8,846 |
| 8 kW | 7204 kWh | 5043 kWh | 2161 kWh | £1,303 | £216 | £1,519 | £19,776 | 13.0 yrs | £10,610 |
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: £971, Upfront: £15,423, Break-even: 15.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1801 kWh | 1315 kWh | 486 kWh | £340 | £49 | £388 | £9,319 | 24.0 yrs | £-1,551 |
| 3 kW | 2702 kWh | 1972 kWh | 729 kWh | £510 | £73 | £583 | £11,354 | 19.5 yrs | £298 |
| 4 kW | 3602 kWh | 2630 kWh | 973 kWh | £679 | £97 | £777 | £13,388 | 17.2 yrs | £2,147 |
| 5 kW | 4503 kWh | 3287 kWh | 1216 kWh | £849 | £122 | £971 | £15,423 | 15.9 yrs | £3,996 |
| 6 kW | 5403 kWh | 3944 kWh | 1459 kWh | £1,019 | £146 | £1,165 | £17,457 | 15.0 yrs | £5,846 |
| 7 kW | 6304 kWh | 4602 kWh | 1702 kWh | £1,189 | £170 | £1,359 | £19,492 | 14.3 yrs | £7,695 |
| 8 kW | 7204 kWh | 5259 kWh | 1945 kWh | £1,359 | £195 | £1,554 | £21,526 | 13.9 yrs | £9,544 |
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: £985, Upfront: £17,173, Break-even: 17.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1801 kWh | 1351 kWh | 450 kWh | £349 | £45 | £394 | £11,069 | 28.1 yrs | £-3,187 |
| 3 kW | 2702 kWh | 2026 kWh | 675 kWh | £524 | £68 | £591 | £13,104 | 22.2 yrs | £-1,281 |
| 4 kW | 3602 kWh | 2702 kWh | 901 kWh | £698 | £90 | £788 | £15,138 | 19.2 yrs | £625 |
| 5 kW | 4503 kWh | 3377 kWh | 1126 kWh | £873 | £113 | £985 | £17,173 | 17.4 yrs | £2,532 |
| 6 kW | 5403 kWh | 4053 kWh | 1351 kWh | £1,047 | £135 | £1,182 | £19,207 | 16.2 yrs | £4,438 |
| 7 kW | 6304 kWh | 4728 kWh | 1576 kWh | £1,222 | £158 | £1,379 | £21,242 | 15.4 yrs | £6,344 |
| 8 kW | 7204 kWh | 5403 kWh | 1801 kWh | £1,396 | £180 | £1,576 | £23,276 | 14.8 yrs | £8,251 |
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: £999, Upfront: £19,623, Break-even: 19.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1801 kWh | 1387 kWh | 414 kWh | £358 | £41 | £400 | £13,519 | 33.8 yrs | £-5,523 |
| 3 kW | 2702 kWh | 2080 kWh | 621 kWh | £538 | £62 | £600 | £15,554 | 25.9 yrs | £-3,560 |
| 4 kW | 3602 kWh | 2774 kWh | 829 kWh | £717 | £83 | £800 | £17,588 | 22.0 yrs | £-1,596 |
| 5 kW | 4503 kWh | 3467 kWh | 1036 kWh | £896 | £104 | £999 | £19,623 | 19.6 yrs | £367 |
| 6 kW | 5403 kWh | 4161 kWh | 1243 kWh | £1,075 | £124 | £1,199 | £21,657 | 18.1 yrs | £2,330 |
| 7 kW | 6304 kWh | 4854 kWh | 1450 kWh | £1,254 | £145 | £1,399 | £23,692 | 16.9 yrs | £4,294 |
| 8 kW | 7204 kWh | 5547 kWh | 1657 kWh | £1,433 | £166 | £1,599 | £25,726 | 16.1 yrs | £6,257 |
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.