Set the panels at the winter angle, not the annual optimum. At latitude 52 that is 64.7° rather than 42.9°, because the midday sun is only 14.6° above the horizon in December against 61.4° in June. A cabin runs out of power in the darkest week of the year, not in the average one, so the month that binds is the one to aim at.
It depends on which months you actually use it. A summer cabin wants the annual optimum. A cabin you heat and light through the winter wants the steeper winter angle, which trades a little June output for a lot of December output.
| Latitude | Year-round optimum | Winter angle | Noon sun, December | Noon sun, June |
|---|---|---|---|---|
| 30° (Austin, Jacksonville) | 30.8° | 45.5° | 36.6° | 83.4° |
| 35° (Flagstaff, Chattanooga) | 34.1° | 49.8° | 31.6° | 78.4° |
| 40° (Denver, Pittsburgh) | 37.2° | 54.2° | 26.6° | 73.4° |
| 45° (Bangor, Salem OR) | 39.8° | 58.6° | 21.6° | 68.4° |
| 50° (Cornwall, Winnipeg) | 42.1° | 63.0° | 16.6° | 63.4° |
| 55° (Glasgow, Edmonton) | 44.1° | 67.3° | 11.6° | 58.4° |
The year-round optimum comes from a curve fitted to PVGIS satellite data, and the winter angle from the seasonal formula the city pages use. Both are explained on the methodology page. For the exact figure where your cabin is, look it up by zip code, UK postcode, or town name.
Because there is no grid behind it in the worst week. A house with panels borrows from the grid in December and pays it back in June. A cabin cannot: whatever the array collects on a short, gray day is all there is. Look at the December column above. At latitude 55 the sun climbs to 11.6° at noon and stays there for a few hours, so the same array that runs the place easily in July will not keep up in January.
Steepening the panels recovers part of that. A panel set at 68.5° instead of 44.1° at latitude 55 faces a low winter sun much more squarely, which is the whole reason the winter angle exists.
Panels first, up to the point where one clear December day refills the battery. Battery only carries you across cloudy days. It cannot make power the array never collected, so a big bank behind a small array just runs flat more slowly. Once a sunny midwinter day tops you up, extra storage is what covers the run of gray ones after it.
A shed, a workshop, or a stable runs the same arithmetic with a shorter list of loads: lights, a few tools on charge, maybe a small pump. The angle advice does not change, and neither does the December column. What changes is that the whole job usually fits one panel and one battery rather than a roof full.