Whatever happens with the rules, the physics is the physics. Northern Ireland does better on this than either part of Scotland.
| Mounting | Belfast | Against an ideal roof |
|---|---|---|
| Free-standing garden frame, 30 degrees south | 708 kWh | 99 per cent |
| Ideal pitched roof, 35 degrees south | 714 kWh | 100 per cent |
| Vertical south-facing wall | 534 kWh | 75 per cent |
| Vertical east or west wall | 367 kWh | 51 per cent |
Per year, for an 800 W device, unshaded, at Belfast, queried from PVGIS on 13 September 2026.
Belfast at 714 kWh sits ahead of Glasgow and well ahead of Inverness, and behind the English regions. It is a reasonable place to generate, which is part of why the unresolved rules are frustrating rather than academic.
These are ideal conditions: unshaded, correctly angled, at one point standing in for the whole of Northern Ireland. Treat them as a ceiling. And note that a garden frame gets within a per cent of a perfect roof, which is the single most useful thing in the table.
We will keep the numbers current and tell you if the rules catch up with them.
This is not a mailing list and there is nothing to buy. Three questions on this page are still open. If any of them is answered, whether by the department, by the networks or by a change to the specification, you get one email saying which one and what it now says.