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 957 kWh per year on a south-facing roof. We value self-used electricity at 25.6p 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: £778, Upfront: £10,173, Break-even: 13.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1915 kWh | 766 kWh | 1149 kWh | £196 | £115 | £311 | £4,069 | 13.1 yrs | £2,156 |
| 3 kW | 2872 kWh | 1149 kWh | 1723 kWh | £295 | £172 | £467 | £6,104 | 13.1 yrs | £3,235 |
| 4 kW | 3830 kWh | 1532 kWh | 2298 kWh | £393 | £230 | £623 | £8,138 | 13.1 yrs | £4,313 |
| 5 kW | 4787 kWh | 1915 kWh | 2872 kWh | £491 | £287 | £778 | £10,173 | 13.1 yrs | £5,391 |
| 6 kW | 5744 kWh | 2298 kWh | 3447 kWh | £589 | £345 | £934 | £12,207 | 13.1 yrs | £6,469 |
| 7 kW | 6702 kWh | 2681 kWh | 4021 kWh | £687 | £402 | £1,089 | £14,242 | 13.1 yrs | £7,548 |
| 8 kW | 7659 kWh | 3064 kWh | 4596 kWh | £786 | £460 | £1,245 | £16,276 | 13.1 yrs | £8,626 |
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: £928, Upfront: £12,273, Break-even: 13.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1915 kWh | 1149 kWh | 766 kWh | £295 | £77 | £371 | £6,169 | 16.6 yrs | £1,254 |
| 3 kW | 2872 kWh | 1723 kWh | 1149 kWh | £442 | £115 | £557 | £8,204 | 14.7 yrs | £2,932 |
| 4 kW | 3830 kWh | 2298 kWh | 1532 kWh | £589 | £153 | £742 | £10,238 | 13.8 yrs | £4,609 |
| 5 kW | 4787 kWh | 2872 kWh | 1915 kWh | £736 | £191 | £928 | £12,273 | 13.2 yrs | £6,286 |
| 6 kW | 5744 kWh | 3447 kWh | 2298 kWh | £884 | £230 | £1,114 | £14,307 | 12.8 yrs | £7,963 |
| 7 kW | 6702 kWh | 4021 kWh | 2681 kWh | £1,031 | £268 | £1,299 | £16,342 | 12.6 yrs | £9,640 |
| 8 kW | 7659 kWh | 4596 kWh | 3064 kWh | £1,178 | £306 | £1,485 | £18,376 | 12.4 yrs | £11,317 |
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: £1,003, Upfront: £13,673, Break-even: 13.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1915 kWh | 1340 kWh | 574 kWh | £344 | £57 | £401 | £7,569 | 18.9 yrs | £453 |
| 3 kW | 2872 kWh | 2011 kWh | 862 kWh | £516 | £86 | £602 | £9,604 | 16.0 yrs | £2,430 |
| 4 kW | 3830 kWh | 2681 kWh | 1149 kWh | £687 | £115 | £802 | £11,638 | 14.5 yrs | £4,407 |
| 5 kW | 4787 kWh | 3351 kWh | 1436 kWh | £859 | £144 | £1,003 | £13,673 | 13.6 yrs | £6,383 |
| 6 kW | 5744 kWh | 4021 kWh | 1723 kWh | £1,031 | £172 | £1,203 | £15,707 | 13.1 yrs | £8,360 |
| 7 kW | 6702 kWh | 4691 kWh | 2011 kWh | £1,203 | £201 | £1,404 | £17,742 | 12.6 yrs | £10,337 |
| 8 kW | 7659 kWh | 5361 kWh | 2298 kWh | £1,375 | £230 | £1,604 | £19,776 | 12.3 yrs | £12,313 |
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: £1,025, Upfront: £15,423, Break-even: 15.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1915 kWh | 1398 kWh | 517 kWh | £358 | £52 | £410 | £9,319 | 22.7 yrs | £-1,117 |
| 3 kW | 2872 kWh | 2097 kWh | 776 kWh | £538 | £78 | £615 | £11,354 | 18.5 yrs | £949 |
| 4 kW | 3830 kWh | 2796 kWh | 1034 kWh | £717 | £103 | £820 | £13,388 | 16.3 yrs | £3,016 |
| 5 kW | 4787 kWh | 3495 kWh | 1293 kWh | £896 | £129 | £1,025 | £15,423 | 15.0 yrs | £5,082 |
| 6 kW | 5744 kWh | 4193 kWh | 1551 kWh | £1,075 | £155 | £1,230 | £17,457 | 14.2 yrs | £7,149 |
| 7 kW | 6702 kWh | 4892 kWh | 1810 kWh | £1,254 | £181 | £1,435 | £19,492 | 13.6 yrs | £9,215 |
| 8 kW | 7659 kWh | 5591 kWh | 2068 kWh | £1,434 | £207 | £1,640 | £21,526 | 13.1 yrs | £11,282 |
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: £1,040, Upfront: £17,173, Break-even: 16.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1915 kWh | 1436 kWh | 479 kWh | £368 | £48 | £416 | £11,069 | 26.6 yrs | £-2,747 |
| 3 kW | 2872 kWh | 2154 kWh | 718 kWh | £552 | £72 | £624 | £13,104 | 21.0 yrs | £-621 |
| 4 kW | 3830 kWh | 2872 kWh | 957 kWh | £736 | £96 | £832 | £15,138 | 18.2 yrs | £1,506 |
| 5 kW | 4787 kWh | 3590 kWh | 1197 kWh | £921 | £120 | £1,040 | £17,173 | 16.5 yrs | £3,632 |
| 6 kW | 5744 kWh | 4308 kWh | 1436 kWh | £1,105 | £144 | £1,248 | £19,207 | 15.4 yrs | £5,758 |
| 7 kW | 6702 kWh | 5026 kWh | 1675 kWh | £1,289 | £168 | £1,456 | £21,242 | 14.6 yrs | £7,885 |
| 8 kW | 7659 kWh | 5744 kWh | 1915 kWh | £1,473 | £191 | £1,664 | £23,276 | 14.0 yrs | £10,011 |
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: £1,055, Upfront: £19,623, Break-even: 18.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1915 kWh | 1474 kWh | 440 kWh | £378 | £44 | £422 | £13,519 | 32.0 yrs | £-5,077 |
| 3 kW | 2872 kWh | 2212 kWh | 661 kWh | £567 | £66 | £633 | £15,554 | 24.6 yrs | £-2,891 |
| 4 kW | 3830 kWh | 2949 kWh | 881 kWh | £756 | £88 | £844 | £17,588 | 20.8 yrs | £-705 |
| 5 kW | 4787 kWh | 3686 kWh | 1101 kWh | £945 | £110 | £1,055 | £19,623 | 18.6 yrs | £1,481 |
| 6 kW | 5744 kWh | 4423 kWh | 1321 kWh | £1,134 | £132 | £1,266 | £21,657 | 17.1 yrs | £3,668 |
| 7 kW | 6702 kWh | 5160 kWh | 1541 kWh | £1,323 | £154 | £1,477 | £23,692 | 16.0 yrs | £5,854 |
| 8 kW | 7659 kWh | 5898 kWh | 1762 kWh | £1,512 | £176 | £1,688 | £25,726 | 15.2 yrs | £8,040 |
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.