What a 200 W flat van-roof solar panel makes per day in December and June, in nine places

Our own pull of the EU Joint Research Centre's PVGIS 5.2 model, 2026-10-30 (https://re.jrc.ec.europa.eu/pvg_tools/en/): sunlight measured by satellite, averaged over 2005-2020; a crystalline panel flat on a roof (it runs hotter, as on a van), 14% system loss, terrain horizon on. Tilted = the same panel at PVGIS's best fixed angle. We asked for 1 kWp and scaled to 200 W. Checks: each place's 12 months add up to its yearly total; Lisbon's flat roof panel is 3.34% below the same panel free-standing.

Key results:

• December v June, Wh per day from one 200 W flat panel: Tarifa 372 v 1,159; Lisbon 319 v 1,101; Moab, Utah 341 v 1,176; Lyon 169 v 942; Portland, Oregon 131 v 847; Munich 140 v 819; Amsterdam 74 v 840; Edinburgh 46 v 722; Tromso 0 v 685.
• Size for winter: June gives 3.5 times December in Lisbon, 11.3 times in Amsterdam, 15.8 times in Edinburgh.
• Tilting to the best angle adds 18% to 27% over the year in eight of the nine places (36% in Tromso); in December it adds 77% in Tarifa, 133% in Munich, 154% in Amsterdam and 255% in Edinburgh.
• A US desert winter matches southern Europe: Moab (341 Wh) sits between Lisbon (319) and Tarifa (372) in December.

What this cannot tell you: a run of grey days (these are 15-year averages); shade, snow or dust beyond the 14% loss; a van parked on a slope or facing away from the sun; losses in a cheap charge controller.