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 746 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: £628, Upfront: £10,173, Break-even: 16.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1492 kWh | 597 kWh | 895 kWh | £162 | £90 | £251 | £4,069 | 16.2 yrs | £952 |
| 3 kW | 2238 kWh | 895 kWh | 1343 kWh | £242 | £134 | £377 | £6,104 | 16.2 yrs | £1,428 |
| 4 kW | 2985 kWh | 1194 kWh | 1791 kWh | £323 | £179 | £502 | £8,138 | 16.2 yrs | £1,904 |
| 5 kW | 3731 kWh | 1492 kWh | 2238 kWh | £404 | £224 | £628 | £10,173 | 16.2 yrs | £2,380 |
| 6 kW | 4477 kWh | 1791 kWh | 2686 kWh | £485 | £269 | £753 | £12,207 | 16.2 yrs | £2,856 |
| 7 kW | 5223 kWh | 2089 kWh | 3134 kWh | £565 | £313 | £879 | £14,242 | 16.2 yrs | £3,332 |
| 8 kW | 5969 kWh | 2388 kWh | 3581 kWh | £646 | £358 | £1,004 | £16,276 | 16.2 yrs | £3,809 |
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: £755, Upfront: £12,273, Break-even: 16.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1492 kWh | 895 kWh | 597 kWh | £242 | £60 | £302 | £6,169 | 20.4 yrs | £-130 |
| 3 kW | 2238 kWh | 1343 kWh | 895 kWh | £363 | £90 | £453 | £8,204 | 18.1 yrs | £856 |
| 4 kW | 2985 kWh | 1791 kWh | 1194 kWh | £485 | £119 | £604 | £10,238 | 17.0 yrs | £1,841 |
| 5 kW | 3731 kWh | 2238 kWh | 1492 kWh | £606 | £149 | £755 | £12,273 | 16.3 yrs | £2,826 |
| 6 kW | 4477 kWh | 2686 kWh | 1791 kWh | £727 | £179 | £906 | £14,307 | 15.8 yrs | £3,811 |
| 7 kW | 5223 kWh | 3134 kWh | 2089 kWh | £848 | £209 | £1,057 | £16,342 | 15.5 yrs | £4,797 |
| 8 kW | 5969 kWh | 3581 kWh | 2388 kWh | £969 | £239 | £1,208 | £18,376 | 15.2 yrs | £5,782 |
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: £819, Upfront: £13,673, Break-even: 16.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1492 kWh | 1045 kWh | 448 kWh | £283 | £45 | £327 | £7,569 | 23.1 yrs | £-1,020 |
| 3 kW | 2238 kWh | 1567 kWh | 672 kWh | £424 | £67 | £491 | £9,604 | 19.6 yrs | £219 |
| 4 kW | 2985 kWh | 2089 kWh | 895 kWh | £565 | £90 | £655 | £11,638 | 17.8 yrs | £1,459 |
| 5 kW | 3731 kWh | 2611 kWh | 1119 kWh | £707 | £112 | £819 | £13,673 | 16.7 yrs | £2,699 |
| 6 kW | 4477 kWh | 3134 kWh | 1343 kWh | £848 | £134 | £982 | £15,707 | 16.0 yrs | £3,939 |
| 7 kW | 5223 kWh | 3656 kWh | 1567 kWh | £989 | £157 | £1,146 | £17,742 | 15.5 yrs | £5,179 |
| 8 kW | 5969 kWh | 4178 kWh | 1791 kWh | £1,131 | £179 | £1,310 | £19,776 | 15.1 yrs | £6,418 |
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: £838, Upfront: £15,423, Break-even: 18.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1492 kWh | 1089 kWh | 403 kWh | £295 | £40 | £335 | £9,319 | 27.8 yrs | £-2,618 |
| 3 kW | 2238 kWh | 1634 kWh | 604 kWh | £442 | £60 | £503 | £11,354 | 22.6 yrs | £-1,301 |
| 4 kW | 2985 kWh | 2179 kWh | 806 kWh | £590 | £81 | £670 | £13,388 | 20.0 yrs | £15 |
| 5 kW | 3731 kWh | 2723 kWh | 1007 kWh | £737 | £101 | £838 | £15,423 | 18.4 yrs | £1,331 |
| 6 kW | 4477 kWh | 3268 kWh | 1209 kWh | £884 | £121 | £1,005 | £17,457 | 17.4 yrs | £2,647 |
| 7 kW | 5223 kWh | 3813 kWh | 1410 kWh | £1,032 | £141 | £1,173 | £19,492 | 16.6 yrs | £3,963 |
| 8 kW | 5969 kWh | 4357 kWh | 1612 kWh | £1,179 | £161 | £1,340 | £21,526 | 16.1 yrs | £5,279 |
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: £850, Upfront: £17,173, Break-even: 20.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1492 kWh | 1119 kWh | 373 kWh | £303 | £37 | £340 | £11,069 | 32.5 yrs | £-4,266 |
| 3 kW | 2238 kWh | 1679 kWh | 560 kWh | £454 | £56 | £510 | £13,104 | 25.7 yrs | £-2,899 |
| 4 kW | 2985 kWh | 2238 kWh | 746 kWh | £606 | £75 | £680 | £15,138 | 22.3 yrs | £-1,532 |
| 5 kW | 3731 kWh | 2798 kWh | 933 kWh | £757 | £93 | £850 | £17,173 | 20.2 yrs | £-165 |
| 6 kW | 4477 kWh | 3358 kWh | 1119 kWh | £909 | £112 | £1,020 | £19,207 | 18.8 yrs | £1,203 |
| 7 kW | 5223 kWh | 3917 kWh | 1306 kWh | £1,060 | £131 | £1,191 | £21,242 | 17.8 yrs | £2,570 |
| 8 kW | 5969 kWh | 4477 kWh | 1492 kWh | £1,211 | £149 | £1,361 | £23,276 | 17.1 yrs | £3,937 |
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: £863, Upfront: £19,623, Break-even: 22.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1492 kWh | 1149 kWh | 343 kWh | £311 | £34 | £345 | £13,519 | 39.2 yrs | £-6,614 |
| 3 kW | 2238 kWh | 1724 kWh | 515 kWh | £466 | £51 | £518 | £15,554 | 30.0 yrs | £-5,196 |
| 4 kW | 2985 kWh | 2298 kWh | 686 kWh | £622 | £69 | £691 | £17,588 | 25.5 yrs | £-3,778 |
| 5 kW | 3731 kWh | 2873 kWh | 858 kWh | £777 | £86 | £863 | £19,623 | 22.7 yrs | £-2,360 |
| 6 kW | 4477 kWh | 3447 kWh | 1030 kWh | £933 | £103 | £1,036 | £21,657 | 20.9 yrs | £-942 |
| 7 kW | 5223 kWh | 4022 kWh | 1201 kWh | £1,088 | £120 | £1,208 | £23,692 | 19.6 yrs | £476 |
| 8 kW | 5969 kWh | 4596 kWh | 1373 kWh | £1,244 | £137 | £1,381 | £25,726 | 18.6 yrs | £1,894 |
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.