Where to put it
The full table, and the balcony problem.
Read moreWhere the numbers come from
Every generation figure comes from PVGIS, the Photovoltaic Geographical Information System published by the European Commission’s Joint Research Centre. It is free, open, needs no registration, and it is the standard reference for this kind of calculation. We are not the source. We just read it and show you the result.
We queried it on 13 September 2026 for an 800 watt device, 14 per cent system losses, at one representative point in each of the thirteen regions the calculator covers. The raw response sits beside this file in our own records and can be checked against a fresh query at any time, because PVGIS is a public tool.
The four mountings
We queried four arrangements for every region, because where a panel goes changes the figure more than which region it is in.
- A free-standing frame in the garden, tilted 30 degrees and facing south.
- An unshaded roof pitch at 35 degrees facing south, the reference case.
- A panel fixed upright to a south-facing wall.
- A panel fixed upright to an east or west facing wall.
Averaged across all thirteen regions, a garden frame comes within about one per cent of the roof figure, a south wall gives about three quarters of it, and an east or west wall gives about half. The full table is on the where to put it page.
| Region | Garden frame | Roof pitch | South wall | East or west wall |
|---|---|---|---|---|
| South East | 890 | 897 | 645 | 424 |
| South West | 816 | 822 | 594 | 417 |
| East of England | 795 | 802 | 594 | 412 |
| Wales | 792 | 798 | 575 | 385 |
| London | 789 | 795 | 582 | 409 |
| East Midlands | 754 | 760 | 564 | 391 |
| West Midlands | 746 | 752 | 555 | 389 |
| Yorkshire | 729 | 736 | 550 | 376 |
| North East | 727 | 734 | 558 | 372 |
| Northern Ireland | 708 | 714 | 534 | 367 |
| North West | 684 | 689 | 505 | 359 |
| Scotland, south | 656 | 661 | 491 | 337 |
| Scotland, north | 623 | 628 | 470 | 321 |
One point, not your postcode
PVGIS was queried at one city per region, not at every postcode. A coastal address and an inland one in the same region will differ, and the figure also assumes nothing shades the panel at any time of day. Treat it as a ceiling under ideal conditions rather than a forecast for your actual roofline, wall or fence.
What the calculator refuses to do
It will not turn a generation figure into pounds saved. That needs a UK price for the kit and an electricity tariff, and we do not have a figure for either that we would put our name to. If you want that worked out for your own house, send us your details and we will talk you through it honestly rather than print a guess.
Why there is no price on this page
Vendor listings quote figures for plug-in kits, but those are vendor claims, not a cited source, so we do not repeat them. Electricity tariffs vary by supplier and by month. Both would need to be sourced properly before a saving figure meant anything, and neither currently is. We would rather leave the box empty than fill it with a plausible number.
Questions about the figures
Can I trust a number this precise?
Trust the method more than the last digit. PVGIS is a recognised European model and the inputs are stated on this page. The precision of the output does not mean your own roof will match it exactly, which is why we call it a ceiling.
Does the calculator know my actual house?
No, and it never claims to. It knows your region and your chosen mounting. Send us your postcode and we will look at your actual address.
Why 14 per cent system losses?
That is a standard PVGIS default for cabling, temperature and inverter losses on a small system. We kept the default rather than choose a flattering number.
More from us
On this page
- Where the numbers come from
- The four mountings
- One point, not your postcode
- Why there is no price on this page
- Questions about the figures
Want your own figure?
Run your region and your surface through the calculator on the home page, then send us your postcode.
Get a quote for my address