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 1096 kWh per year on a south-facing roof. We value self-used electricity at 26.5p 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: £909, Upfront: £10,173, Break-even: 11.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2192 kWh | 877 kWh | 1315 kWh | £232 | £131 | £364 | £4,069 | 11.2 yrs | £3,204 |
| 3 kW | 3287 kWh | 1315 kWh | 1972 kWh | £348 | £197 | £545 | £6,104 | 11.2 yrs | £4,806 |
| 4 kW | 4383 kWh | 1753 kWh | 2630 kWh | £464 | £263 | £727 | £8,138 | 11.2 yrs | £6,408 |
| 5 kW | 5479 kWh | 2192 kWh | 3287 kWh | £580 | £329 | £909 | £10,173 | 11.2 yrs | £8,009 |
| 6 kW | 6575 kWh | 2630 kWh | 3945 kWh | £696 | £394 | £1,091 | £12,207 | 11.2 yrs | £9,611 |
| 7 kW | 7671 kWh | 3068 kWh | 4602 kWh | £812 | £460 | £1,273 | £14,242 | 11.2 yrs | £11,213 |
| 8 kW | 8767 kWh | 3507 kWh | 5260 kWh | £929 | £526 | £1,455 | £16,276 | 11.2 yrs | £12,815 |
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: £1,090, Upfront: £12,273, Break-even: 11.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2192 kWh | 1315 kWh | 877 kWh | £348 | £88 | £436 | £6,169 | 14.2 yrs | £2,549 |
| 3 kW | 3287 kWh | 1972 kWh | 1315 kWh | £522 | £131 | £654 | £8,204 | 12.5 yrs | £4,873 |
| 4 kW | 4383 kWh | 2630 kWh | 1753 kWh | £696 | £175 | £872 | £10,238 | 11.7 yrs | £7,197 |
| 5 kW | 5479 kWh | 3287 kWh | 2192 kWh | £871 | £219 | £1,090 | £12,273 | 11.3 yrs | £9,521 |
| 6 kW | 6575 kWh | 3945 kWh | 2630 kWh | £1,045 | £263 | £1,308 | £14,307 | 10.9 yrs | £11,846 |
| 7 kW | 7671 kWh | 4602 kWh | 3068 kWh | £1,219 | £307 | £1,526 | £16,342 | 10.7 yrs | £14,170 |
| 8 kW | 8767 kWh | 5260 kWh | 3507 kWh | £1,393 | £351 | £1,744 | £18,376 | 10.5 yrs | £16,494 |
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: £1,180, Upfront: £13,673, Break-even: 11.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2192 kWh | 1534 kWh | 657 kWh | £406 | £66 | £472 | £7,569 | 16.0 yrs | £1,871 |
| 3 kW | 3287 kWh | 2301 kWh | 986 kWh | £609 | £99 | £708 | £9,604 | 13.6 yrs | £4,556 |
| 4 kW | 4383 kWh | 3068 kWh | 1315 kWh | £812 | £131 | £944 | £11,638 | 12.3 yrs | £7,242 |
| 5 kW | 5479 kWh | 3835 kWh | 1644 kWh | £1,016 | £164 | £1,180 | £13,673 | 11.6 yrs | £9,927 |
| 6 kW | 6575 kWh | 4602 kWh | 1972 kWh | £1,219 | £197 | £1,416 | £15,707 | 11.1 yrs | £12,613 |
| 7 kW | 7671 kWh | 5370 kWh | 2301 kWh | £1,422 | £230 | £1,652 | £17,742 | 10.7 yrs | £15,298 |
| 8 kW | 8767 kWh | 6137 kWh | 2630 kWh | £1,625 | £263 | £1,888 | £19,776 | 10.5 yrs | £17,984 |
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: £1,207, Upfront: £15,423, Break-even: 12.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2192 kWh | 1600 kWh | 592 kWh | £424 | £59 | £483 | £9,319 | 19.3 yrs | £338 |
| 3 kW | 3287 kWh | 2400 kWh | 888 kWh | £635 | £89 | £724 | £11,354 | 15.7 yrs | £3,131 |
| 4 kW | 4383 kWh | 3200 kWh | 1183 kWh | £847 | £118 | £966 | £13,388 | 13.9 yrs | £5,925 |
| 5 kW | 5479 kWh | 4000 kWh | 1479 kWh | £1,059 | £148 | £1,207 | £15,423 | 12.8 yrs | £8,719 |
| 6 kW | 6575 kWh | 4800 kWh | 1775 kWh | £1,271 | £178 | £1,448 | £17,457 | 12.1 yrs | £11,513 |
| 7 kW | 7671 kWh | 5600 kWh | 2071 kWh | £1,483 | £207 | £1,690 | £19,492 | 11.5 yrs | £14,307 |
| 8 kW | 8767 kWh | 6400 kWh | 2367 kWh | £1,695 | £237 | £1,931 | £21,526 | 11.1 yrs | £17,100 |
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: £1,225, Upfront: £17,173, 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 | 2192 kWh | 1644 kWh | 548 kWh | £435 | £55 | £490 | £11,069 | 22.6 yrs | £-1,268 |
| 3 kW | 3287 kWh | 2466 kWh | 822 kWh | £653 | £82 | £735 | £13,104 | 17.8 yrs | £1,598 |
| 4 kW | 4383 kWh | 3287 kWh | 1096 kWh | £871 | £110 | £980 | £15,138 | 15.4 yrs | £4,464 |
| 5 kW | 5479 kWh | 4109 kWh | 1370 kWh | £1,088 | £137 | £1,225 | £17,173 | 14.0 yrs | £7,330 |
| 6 kW | 6575 kWh | 4931 kWh | 1644 kWh | £1,306 | £164 | £1,470 | £19,207 | 13.1 yrs | £10,196 |
| 7 kW | 7671 kWh | 5753 kWh | 1918 kWh | £1,523 | £192 | £1,715 | £21,242 | 12.4 yrs | £13,062 |
| 8 kW | 8767 kWh | 6575 kWh | 2192 kWh | £1,741 | £219 | £1,960 | £23,276 | 11.9 yrs | £15,928 |
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: £1,243, Upfront: £19,623, Break-even: 15.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2192 kWh | 1688 kWh | 504 kWh | £447 | £50 | £497 | £13,519 | 27.2 yrs | £-3,573 |
| 3 kW | 3287 kWh | 2531 kWh | 756 kWh | £670 | £76 | £746 | £15,554 | 20.9 yrs | £-635 |
| 4 kW | 4383 kWh | 3375 kWh | 1008 kWh | £894 | £101 | £995 | £17,588 | 17.7 yrs | £2,303 |
| 5 kW | 5479 kWh | 4219 kWh | 1260 kWh | £1,117 | £126 | £1,243 | £19,623 | 15.8 yrs | £5,241 |
| 6 kW | 6575 kWh | 5063 kWh | 1512 kWh | £1,341 | £151 | £1,492 | £21,657 | 14.5 yrs | £8,180 |
| 7 kW | 7671 kWh | 5907 kWh | 1764 kWh | £1,564 | £176 | £1,740 | £23,692 | 13.6 yrs | £11,118 |
| 8 kW | 8767 kWh | 6750 kWh | 2016 kWh | £1,787 | £202 | £1,989 | £25,726 | 12.9 yrs | £14,056 |
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.