A typical roof here lands around 4.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 871 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: £733, Upfront: £10,173, Break-even: 13.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1742 kWh | 697 kWh | 1045 kWh | £189 | £104 | £293 | £4,069 | 13.9 yrs | £1,798 |
| 3 kW | 2612 kWh | 1045 kWh | 1567 kWh | £283 | £157 | £440 | £6,104 | 13.9 yrs | £2,697 |
| 4 kW | 3483 kWh | 1393 kWh | 2090 kWh | £378 | £209 | £587 | £8,138 | 13.9 yrs | £3,596 |
| 5 kW | 4354 kWh | 1742 kWh | 2612 kWh | £472 | £261 | £733 | £10,173 | 13.9 yrs | £4,496 |
| 6 kW | 5225 kWh | 2090 kWh | 3135 kWh | £567 | £313 | £880 | £12,207 | 13.9 yrs | £5,395 |
| 7 kW | 6096 kWh | 2438 kWh | 3657 kWh | £661 | £366 | £1,027 | £14,242 | 13.9 yrs | £6,294 |
| 8 kW | 6967 kWh | 2787 kWh | 4180 kWh | £755 | £418 | £1,173 | £16,276 | 13.9 yrs | £7,193 |
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: £882, Upfront: £12,273, Break-even: 13.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1742 kWh | 1045 kWh | 697 kWh | £283 | £70 | £353 | £6,169 | 17.5 yrs | £890 |
| 3 kW | 2612 kWh | 1567 kWh | 1045 kWh | £425 | £104 | £529 | £8,204 | 15.5 yrs | £2,385 |
| 4 kW | 3483 kWh | 2090 kWh | 1393 kWh | £567 | £139 | £706 | £10,238 | 14.5 yrs | £3,880 |
| 5 kW | 4354 kWh | 2612 kWh | 1742 kWh | £708 | £174 | £882 | £12,273 | 13.9 yrs | £5,375 |
| 6 kW | 5225 kWh | 3135 kWh | 2090 kWh | £850 | £209 | £1,059 | £14,307 | 13.5 yrs | £6,871 |
| 7 kW | 6096 kWh | 3657 kWh | 2438 kWh | £992 | £244 | £1,235 | £16,342 | 13.2 yrs | £8,366 |
| 8 kW | 6967 kWh | 4180 kWh | 2787 kWh | £1,133 | £279 | £1,412 | £18,376 | 13.0 yrs | £9,861 |
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: £957, Upfront: £13,673, Break-even: 14.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1742 kWh | 1219 kWh | 522 kWh | £331 | £52 | £383 | £7,569 | 19.8 yrs | £86 |
| 3 kW | 2612 kWh | 1829 kWh | 784 kWh | £496 | £78 | £574 | £9,604 | 16.7 yrs | £1,879 |
| 4 kW | 3483 kWh | 2438 kWh | 1045 kWh | £661 | £104 | £766 | £11,638 | 15.2 yrs | £3,672 |
| 5 kW | 4354 kWh | 3048 kWh | 1306 kWh | £826 | £131 | £957 | £13,673 | 14.3 yrs | £5,465 |
| 6 kW | 5225 kWh | 3657 kWh | 1567 kWh | £992 | £157 | £1,148 | £15,707 | 13.7 yrs | £7,259 |
| 7 kW | 6096 kWh | 4267 kWh | 1829 kWh | £1,157 | £183 | £1,340 | £17,742 | 13.2 yrs | £9,052 |
| 8 kW | 6967 kWh | 4877 kWh | 2090 kWh | £1,322 | £209 | £1,531 | £19,776 | 12.9 yrs | £10,845 |
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: £979, Upfront: £15,423, 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 | 1742 kWh | 1271 kWh | 470 kWh | £345 | £47 | £392 | £9,319 | 23.8 yrs | £-1,485 |
| 3 kW | 2612 kWh | 1907 kWh | 705 kWh | £517 | £71 | £588 | £11,354 | 19.3 yrs | £397 |
| 4 kW | 3483 kWh | 2543 kWh | 940 kWh | £689 | £94 | £783 | £13,388 | 17.1 yrs | £2,280 |
| 5 kW | 4354 kWh | 3178 kWh | 1176 kWh | £862 | £118 | £979 | £15,423 | 15.7 yrs | £4,162 |
| 6 kW | 5225 kWh | 3814 kWh | 1411 kWh | £1,034 | £141 | £1,175 | £17,457 | 14.9 yrs | £6,045 |
| 7 kW | 6096 kWh | 4450 kWh | 1646 kWh | £1,206 | £165 | £1,371 | £19,492 | 14.2 yrs | £7,927 |
| 8 kW | 6967 kWh | 5086 kWh | 1881 kWh | £1,379 | £188 | £1,567 | £21,526 | 13.7 yrs | £9,810 |
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: £994, Upfront: £17,173, Break-even: 17.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1742 kWh | 1306 kWh | 435 kWh | £354 | £44 | £398 | £11,069 | 27.8 yrs | £-3,116 |
| 3 kW | 2612 kWh | 1959 kWh | 653 kWh | £531 | £65 | £596 | £13,104 | 22.0 yrs | £-1,174 |
| 4 kW | 3483 kWh | 2612 kWh | 871 kWh | £708 | £87 | £795 | £15,138 | 19.0 yrs | £768 |
| 5 kW | 4354 kWh | 3266 kWh | 1089 kWh | £885 | £109 | £994 | £17,173 | 17.3 yrs | £2,710 |
| 6 kW | 5225 kWh | 3919 kWh | 1306 kWh | £1,062 | £131 | £1,193 | £19,207 | 16.1 yrs | £4,653 |
| 7 kW | 6096 kWh | 4572 kWh | 1524 kWh | £1,239 | £152 | £1,392 | £21,242 | 15.3 yrs | £6,595 |
| 8 kW | 6967 kWh | 5225 kWh | 1742 kWh | £1,416 | £174 | £1,591 | £23,276 | 14.6 yrs | £8,537 |
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: £1,009, Upfront: £19,623, Break-even: 19.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1742 kWh | 1341 kWh | 401 kWh | £364 | £40 | £404 | £13,519 | 33.5 yrs | £-5,447 |
| 3 kW | 2612 kWh | 2012 kWh | 601 kWh | £545 | £60 | £605 | £15,554 | 25.7 yrs | £-3,445 |
| 4 kW | 3483 kWh | 2682 kWh | 801 kWh | £727 | £80 | £807 | £17,588 | 21.8 yrs | £-1,443 |
| 5 kW | 4354 kWh | 3353 kWh | 1001 kWh | £909 | £100 | £1,009 | £19,623 | 19.4 yrs | £558 |
| 6 kW | 5225 kWh | 4023 kWh | 1202 kWh | £1,091 | £120 | £1,211 | £21,657 | 17.9 yrs | £2,560 |
| 7 kW | 6096 kWh | 4694 kWh | 1402 kWh | £1,272 | £140 | £1,413 | £23,692 | 16.8 yrs | £4,562 |
| 8 kW | 6967 kWh | 5364 kWh | 1602 kWh | £1,454 | £160 | £1,614 | £25,726 | 15.9 yrs | £6,564 |
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.