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 701 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: £590, Upfront: £10,173, Break-even: 17.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1402 kWh | 561 kWh | 841 kWh | £152 | £84 | £236 | £4,069 | 17.2 yrs | £650 |
| 3 kW | 2104 kWh | 841 kWh | 1262 kWh | £228 | £126 | £354 | £6,104 | 17.2 yrs | £975 |
| 4 kW | 2805 kWh | 1122 kWh | 1683 kWh | £304 | £168 | £472 | £8,138 | 17.2 yrs | £1,300 |
| 5 kW | 3506 kWh | 1402 kWh | 2104 kWh | £379 | £210 | £590 | £10,173 | 17.2 yrs | £1,624 |
| 6 kW | 4207 kWh | 1683 kWh | 2524 kWh | £455 | £252 | £708 | £12,207 | 17.2 yrs | £1,949 |
| 7 kW | 4908 kWh | 1963 kWh | 2945 kWh | £531 | £295 | £826 | £14,242 | 17.2 yrs | £2,274 |
| 8 kW | 5610 kWh | 2244 kWh | 3366 kWh | £607 | £337 | £944 | £16,276 | 17.2 yrs | £2,599 |
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: £709, Upfront: £12,273, 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 | 1402 kWh | 841 kWh | 561 kWh | £228 | £56 | £284 | £6,169 | 21.7 yrs | £-493 |
| 3 kW | 2104 kWh | 1262 kWh | 841 kWh | £342 | £84 | £426 | £8,204 | 19.3 yrs | £310 |
| 4 kW | 2805 kWh | 1683 kWh | 1122 kWh | £455 | £112 | £568 | £10,238 | 18.0 yrs | £1,114 |
| 5 kW | 3506 kWh | 2104 kWh | 1402 kWh | £569 | £140 | £709 | £12,273 | 17.3 yrs | £1,917 |
| 6 kW | 4207 kWh | 2524 kWh | 1683 kWh | £683 | £168 | £851 | £14,307 | 16.8 yrs | £2,720 |
| 7 kW | 4908 kWh | 2945 kWh | 1963 kWh | £797 | £196 | £993 | £16,342 | 16.5 yrs | £3,524 |
| 8 kW | 5610 kWh | 3366 kWh | 2244 kWh | £911 | £224 | £1,135 | £18,376 | 16.2 yrs | £4,327 |
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: £769, Upfront: £13,673, Break-even: 17.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1402 kWh | 982 kWh | 421 kWh | £266 | £42 | £308 | £7,569 | 24.6 yrs | £-1,415 |
| 3 kW | 2104 kWh | 1473 kWh | 631 kWh | £398 | £63 | £462 | £9,604 | 20.8 yrs | £-372 |
| 4 kW | 2805 kWh | 1963 kWh | 841 kWh | £531 | £84 | £615 | £11,638 | 18.9 yrs | £671 |
| 5 kW | 3506 kWh | 2454 kWh | 1052 kWh | £664 | £105 | £769 | £13,673 | 17.8 yrs | £1,713 |
| 6 kW | 4207 kWh | 2945 kWh | 1262 kWh | £797 | £126 | £923 | £15,707 | 17.0 yrs | £2,756 |
| 7 kW | 4908 kWh | 3436 kWh | 1473 kWh | £930 | £147 | £1,077 | £17,742 | 16.5 yrs | £3,798 |
| 8 kW | 5610 kWh | 3927 kWh | 1683 kWh | £1,063 | £168 | £1,231 | £19,776 | 16.1 yrs | £4,841 |
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: £787, Upfront: £15,423, 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 | 1402 kWh | 1024 kWh | 379 kWh | £277 | £38 | £315 | £9,319 | 29.6 yrs | £-3,021 |
| 3 kW | 2104 kWh | 1536 kWh | 568 kWh | £416 | £57 | £472 | £11,354 | 24.0 yrs | £-1,907 |
| 4 kW | 2805 kWh | 2048 kWh | 757 kWh | £554 | £76 | £630 | £13,388 | 21.3 yrs | £-792 |
| 5 kW | 3506 kWh | 2559 kWh | 947 kWh | £693 | £95 | £787 | £15,423 | 19.6 yrs | £322 |
| 6 kW | 4207 kWh | 3071 kWh | 1136 kWh | £831 | £114 | £945 | £17,457 | 18.5 yrs | £1,436 |
| 7 kW | 4908 kWh | 3583 kWh | 1325 kWh | £970 | £133 | £1,102 | £19,492 | 17.7 yrs | £2,551 |
| 8 kW | 5610 kWh | 4095 kWh | 1515 kWh | £1,108 | £151 | £1,260 | £21,526 | 17.1 yrs | £3,665 |
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: £799, Upfront: £17,173, Break-even: 21.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1402 kWh | 1052 kWh | 351 kWh | £285 | £35 | £320 | £11,069 | 34.6 yrs | £-4,675 |
| 3 kW | 2104 kWh | 1578 kWh | 526 kWh | £427 | £53 | £480 | £13,104 | 27.3 yrs | £-3,513 |
| 4 kW | 2805 kWh | 2104 kWh | 701 kWh | £569 | £70 | £639 | £15,138 | 23.7 yrs | £-2,351 |
| 5 kW | 3506 kWh | 2630 kWh | 876 kWh | £712 | £88 | £799 | £17,173 | 21.5 yrs | £-1,189 |
| 6 kW | 4207 kWh | 3155 kWh | 1052 kWh | £854 | £105 | £959 | £19,207 | 20.0 yrs | £-26 |
| 7 kW | 4908 kWh | 3681 kWh | 1227 kWh | £996 | £123 | £1,119 | £21,242 | 19.0 yrs | £1,136 |
| 8 kW | 5610 kWh | 4207 kWh | 1402 kWh | £1,138 | £140 | £1,279 | £23,276 | 18.2 yrs | £2,298 |
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: £811, Upfront: £19,623, Break-even: 24.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1402 kWh | 1080 kWh | 323 kWh | £292 | £32 | £324 | £13,519 | 41.7 yrs | £-7,030 |
| 3 kW | 2104 kWh | 1620 kWh | 484 kWh | £438 | £48 | £487 | £15,554 | 32.0 yrs | £-5,820 |
| 4 kW | 2805 kWh | 2160 kWh | 645 kWh | £584 | £65 | £649 | £17,588 | 27.1 yrs | £-4,610 |
| 5 kW | 3506 kWh | 2700 kWh | 806 kWh | £731 | £81 | £811 | £19,623 | 24.2 yrs | £-3,399 |
| 6 kW | 4207 kWh | 3240 kWh | 968 kWh | £877 | £97 | £973 | £21,657 | 22.2 yrs | £-2,189 |
| 7 kW | 4908 kWh | 3779 kWh | 1129 kWh | £1,023 | £113 | £1,136 | £23,692 | 20.9 yrs | £-979 |
| 8 kW | 5610 kWh | 4319 kWh | 1290 kWh | £1,169 | £129 | £1,298 | £25,726 | 19.8 yrs | £231 |
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.