A typical roof here lands around 6.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 818 kWh per year on a south-facing roof. We value self-used electricity at 25.8p 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: £668, Upfront: £10,173, Break-even: 15.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1637 kWh | 655 kWh | 982 kWh | £169 | £98 | £267 | £4,069 | 15.2 yrs | £1,278 |
| 3 kW | 2455 kWh | 982 kWh | 1473 kWh | £254 | £147 | £401 | £6,104 | 15.2 yrs | £1,917 |
| 4 kW | 3273 kWh | 1309 kWh | 1964 kWh | £338 | £196 | £535 | £8,138 | 15.2 yrs | £2,556 |
| 5 kW | 4091 kWh | 1637 kWh | 2455 kWh | £423 | £245 | £668 | £10,173 | 15.2 yrs | £3,195 |
| 6 kW | 4910 kWh | 1964 kWh | 2946 kWh | £507 | £295 | £802 | £12,207 | 15.2 yrs | £3,834 |
| 7 kW | 5728 kWh | 2291 kWh | 3437 kWh | £592 | £344 | £936 | £14,242 | 15.2 yrs | £4,473 |
| 8 kW | 6546 kWh | 2618 kWh | 3928 kWh | £677 | £393 | £1,069 | £16,276 | 15.2 yrs | £5,112 |
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: £798, Upfront: £12,273, Break-even: 15.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1637 kWh | 982 kWh | 655 kWh | £254 | £65 | £319 | £6,169 | 19.3 yrs | £215 |
| 3 kW | 2455 kWh | 1473 kWh | 982 kWh | £381 | £98 | £479 | £8,204 | 17.1 yrs | £1,372 |
| 4 kW | 3273 kWh | 1964 kWh | 1309 kWh | £507 | £131 | £638 | £10,238 | 16.0 yrs | £2,530 |
| 5 kW | 4091 kWh | 2455 kWh | 1637 kWh | £634 | £164 | £798 | £12,273 | 15.4 yrs | £3,687 |
| 6 kW | 4910 kWh | 2946 kWh | 1964 kWh | £761 | £196 | £958 | £14,307 | 14.9 yrs | £4,844 |
| 7 kW | 5728 kWh | 3437 kWh | 2291 kWh | £888 | £229 | £1,117 | £16,342 | 14.6 yrs | £6,002 |
| 8 kW | 6546 kWh | 3928 kWh | 2618 kWh | £1,015 | £262 | £1,277 | £18,376 | 14.4 yrs | £7,159 |
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: £863, Upfront: £13,673, 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 | 1637 kWh | 1146 kWh | 491 kWh | £296 | £49 | £345 | £7,569 | 21.9 yrs | £-667 |
| 3 kW | 2455 kWh | 1718 kWh | 736 kWh | £444 | £74 | £518 | £9,604 | 18.6 yrs | £750 |
| 4 kW | 3273 kWh | 2291 kWh | 982 kWh | £592 | £98 | £690 | £11,638 | 16.9 yrs | £2,167 |
| 5 kW | 4091 kWh | 2864 kWh | 1227 kWh | £740 | £123 | £863 | £13,673 | 15.8 yrs | £3,583 |
| 6 kW | 4910 kWh | 3437 kWh | 1473 kWh | £888 | £147 | £1,035 | £15,707 | 15.2 yrs | £5,000 |
| 7 kW | 5728 kWh | 4010 kWh | 1718 kWh | £1,036 | £172 | £1,208 | £17,742 | 14.7 yrs | £6,416 |
| 8 kW | 6546 kWh | 4582 kWh | 1964 kWh | £1,184 | £196 | £1,380 | £19,776 | 14.3 yrs | £7,833 |
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: £882, Upfront: £15,423, Break-even: 17.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1637 kWh | 1195 kWh | 442 kWh | £309 | £44 | £353 | £9,319 | 26.4 yrs | £-2,261 |
| 3 kW | 2455 kWh | 1792 kWh | 663 kWh | £463 | £66 | £529 | £11,354 | 21.4 yrs | £-767 |
| 4 kW | 3273 kWh | 2389 kWh | 884 kWh | £617 | £88 | £706 | £13,388 | 19.0 yrs | £728 |
| 5 kW | 4091 kWh | 2987 kWh | 1105 kWh | £772 | £110 | £882 | £15,423 | 17.5 yrs | £2,222 |
| 6 kW | 4910 kWh | 3584 kWh | 1326 kWh | £926 | £133 | £1,059 | £17,457 | 16.5 yrs | £3,716 |
| 7 kW | 5728 kWh | 4181 kWh | 1547 kWh | £1,080 | £155 | £1,235 | £19,492 | 15.8 yrs | £5,211 |
| 8 kW | 6546 kWh | 4779 kWh | 1767 kWh | £1,235 | £177 | £1,412 | £21,526 | 15.2 yrs | £6,705 |
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: £895, Upfront: £17,173, Break-even: 19.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1637 kWh | 1227 kWh | 409 kWh | £317 | £41 | £358 | £11,069 | 30.9 yrs | £-3,908 |
| 3 kW | 2455 kWh | 1841 kWh | 614 kWh | £476 | £61 | £537 | £13,104 | 24.4 yrs | £-2,361 |
| 4 kW | 3273 kWh | 2455 kWh | 818 kWh | £634 | £82 | £716 | £15,138 | 21.1 yrs | £-815 |
| 5 kW | 4091 kWh | 3069 kWh | 1023 kWh | £793 | £102 | £895 | £17,173 | 19.2 yrs | £731 |
| 6 kW | 4910 kWh | 3682 kWh | 1227 kWh | £951 | £123 | £1,074 | £19,207 | 17.9 yrs | £2,277 |
| 7 kW | 5728 kWh | 4296 kWh | 1432 kWh | £1,110 | £143 | £1,253 | £21,242 | 16.9 yrs | £3,824 |
| 8 kW | 6546 kWh | 4910 kWh | 1637 kWh | £1,269 | £164 | £1,432 | £23,276 | 16.3 yrs | £5,370 |
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: £908, Upfront: £19,623, Break-even: 21.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1637 kWh | 1260 kWh | 376 kWh | £326 | £38 | £363 | £13,519 | 37.2 yrs | £-6,254 |
| 3 kW | 2455 kWh | 1890 kWh | 565 kWh | £488 | £56 | £545 | £15,554 | 28.5 yrs | £-4,656 |
| 4 kW | 3273 kWh | 2520 kWh | 753 kWh | £651 | £75 | £727 | £17,588 | 24.2 yrs | £-3,058 |
| 5 kW | 4091 kWh | 3150 kWh | 941 kWh | £814 | £94 | £908 | £19,623 | 21.6 yrs | £-1,460 |
| 6 kW | 4910 kWh | 3780 kWh | 1129 kWh | £977 | £113 | £1,090 | £21,657 | 19.9 yrs | £139 |
| 7 kW | 5728 kWh | 4410 kWh | 1317 kWh | £1,140 | £132 | £1,271 | £23,692 | 18.6 yrs | £1,737 |
| 8 kW | 6546 kWh | 5041 kWh | 1506 kWh | £1,302 | £151 | £1,453 | £25,726 | 17.7 yrs | £3,335 |
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.