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 866 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: £729, Upfront: £10,173, 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 | 1732 kWh | 693 kWh | 1040 kWh | £188 | £104 | £291 | £4,069 | 14.0 yrs | £1,760 |
| 3 kW | 2599 kWh | 1040 kWh | 1559 kWh | £281 | £156 | £437 | £6,104 | 14.0 yrs | £2,641 |
| 4 kW | 3465 kWh | 1386 kWh | 2079 kWh | £375 | £208 | £583 | £8,138 | 14.0 yrs | £3,521 |
| 5 kW | 4331 kWh | 1732 kWh | 2599 kWh | £469 | £260 | £729 | £10,173 | 14.0 yrs | £4,401 |
| 6 kW | 5198 kWh | 2079 kWh | 3118 kWh | £563 | £312 | £874 | £12,207 | 14.0 yrs | £5,281 |
| 7 kW | 6064 kWh | 2426 kWh | 3638 kWh | £656 | £364 | £1,020 | £14,242 | 14.0 yrs | £6,162 |
| 8 kW | 6930 kWh | 2772 kWh | 4158 kWh | £750 | £416 | £1,166 | £16,276 | 14.0 yrs | £7,042 |
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: £876, 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 | 1732 kWh | 1040 kWh | 693 kWh | £281 | £69 | £351 | £6,169 | 17.6 yrs | £843 |
| 3 kW | 2599 kWh | 1559 kWh | 1040 kWh | £422 | £104 | £526 | £8,204 | 15.6 yrs | £2,314 |
| 4 kW | 3465 kWh | 2079 kWh | 1386 kWh | £563 | £139 | £701 | £10,238 | 14.6 yrs | £3,786 |
| 5 kW | 4331 kWh | 2599 kWh | 1732 kWh | £703 | £173 | £876 | £12,273 | 14.0 yrs | £5,257 |
| 6 kW | 5198 kWh | 3118 kWh | 2079 kWh | £844 | £208 | £1,052 | £14,307 | 13.6 yrs | £6,728 |
| 7 kW | 6064 kWh | 3638 kWh | 2426 kWh | £985 | £243 | £1,227 | £16,342 | 13.3 yrs | £8,200 |
| 8 kW | 6930 kWh | 4158 kWh | 2772 kWh | £1,125 | £277 | £1,402 | £18,376 | 13.1 yrs | £9,671 |
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 | 1732 kWh | 1213 kWh | 520 kWh | £328 | £52 | £380 | £7,569 | 19.9 yrs | £34 |
| 3 kW | 2599 kWh | 1819 kWh | 780 kWh | £492 | £78 | £570 | £9,604 | 16.8 yrs | £1,801 |
| 4 kW | 3465 kWh | 2426 kWh | 1040 kWh | £656 | £104 | £760 | £11,638 | 15.3 yrs | £3,568 |
| 5 kW | 4331 kWh | 3032 kWh | 1299 kWh | £820 | £130 | £950 | £13,673 | 14.4 yrs | £5,335 |
| 6 kW | 5198 kWh | 3638 kWh | 1559 kWh | £985 | £156 | £1,140 | £15,707 | 13.8 yrs | £7,102 |
| 7 kW | 6064 kWh | 4245 kWh | 1819 kWh | £1,149 | £182 | £1,331 | £17,742 | 13.3 yrs | £8,869 |
| 8 kW | 6930 kWh | 4851 kWh | 2079 kWh | £1,313 | £208 | £1,521 | £19,776 | 13.0 yrs | £10,636 |
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: £973, 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 | 1732 kWh | 1265 kWh | 468 kWh | £342 | £47 | £389 | £9,319 | 24.0 yrs | £-1,539 |
| 3 kW | 2599 kWh | 1897 kWh | 702 kWh | £513 | £70 | £584 | £11,354 | 19.5 yrs | £317 |
| 4 kW | 3465 kWh | 2529 kWh | 936 kWh | £684 | £94 | £778 | £13,388 | 17.2 yrs | £2,172 |
| 5 kW | 4331 kWh | 3162 kWh | 1169 kWh | £856 | £117 | £973 | £15,423 | 15.9 yrs | £4,028 |
| 6 kW | 5198 kWh | 3794 kWh | 1403 kWh | £1,027 | £140 | £1,167 | £17,457 | 15.0 yrs | £5,884 |
| 7 kW | 6064 kWh | 4427 kWh | 1637 kWh | £1,198 | £164 | £1,362 | £19,492 | 14.3 yrs | £7,739 |
| 8 kW | 6930 kWh | 5059 kWh | 1871 kWh | £1,369 | £187 | £1,556 | £21,526 | 13.8 yrs | £9,595 |
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: £987, 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 | 1732 kWh | 1299 kWh | 433 kWh | £352 | £43 | £395 | £11,069 | 28.0 yrs | £-3,171 |
| 3 kW | 2599 kWh | 1949 kWh | 650 kWh | £527 | £65 | £592 | £13,104 | 22.1 yrs | £-1,256 |
| 4 kW | 3465 kWh | 2599 kWh | 866 kWh | £703 | £87 | £790 | £15,138 | 19.2 yrs | £659 |
| 5 kW | 4331 kWh | 3248 kWh | 1083 kWh | £879 | £108 | £987 | £17,173 | 17.4 yrs | £2,574 |
| 6 kW | 5198 kWh | 3898 kWh | 1299 kWh | £1,055 | £130 | £1,185 | £19,207 | 16.2 yrs | £4,488 |
| 7 kW | 6064 kWh | 4548 kWh | 1516 kWh | £1,231 | £152 | £1,382 | £21,242 | 15.4 yrs | £6,403 |
| 8 kW | 6930 kWh | 5198 kWh | 1732 kWh | £1,406 | £173 | £1,580 | £23,276 | 14.7 yrs | £8,318 |
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: £1,002, 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 | 1732 kWh | 1334 kWh | 398 kWh | £361 | £40 | £401 | £13,519 | 33.7 yrs | £-5,502 |
| 3 kW | 2599 kWh | 2001 kWh | 598 kWh | £541 | £60 | £601 | £15,554 | 25.9 yrs | £-3,528 |
| 4 kW | 3465 kWh | 2668 kWh | 797 kWh | £722 | £80 | £802 | £17,588 | 21.9 yrs | £-1,555 |
| 5 kW | 4331 kWh | 3335 kWh | 996 kWh | £902 | £100 | £1,002 | £19,623 | 19.6 yrs | £419 |
| 6 kW | 5198 kWh | 4002 kWh | 1195 kWh | £1,083 | £120 | £1,203 | £21,657 | 18.0 yrs | £2,393 |
| 7 kW | 6064 kWh | 4669 kWh | 1395 kWh | £1,263 | £139 | £1,403 | £23,692 | 16.9 yrs | £4,367 |
| 8 kW | 6930 kWh | 5336 kWh | 1594 kWh | £1,444 | £159 | £1,603 | £25,726 | 16.0 yrs | £6,341 |
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.