How much solar actually fits on a van roof? Every base van, with the fan in

A medium large van (Ducato, Sprinter, Transit, Crafter L2) carries 400–500 W of rigid solar on the flat part of its roof; an L3 carries 500–700 W; an L4/L5 body 600–800 W. Mid-size vans take 300–500 W, compact vans 200–300 W. A roof fan costs one 100 W panel on three vans in four, and a rooftop A/C unit costs one or two more. Those are the physical ceilings. The solar sizing post works out how many watts you need from your loads; this one is the other half of the question — how many watts the roof you bought will actually hold once the fan is in.

The table below covers every base van in the planner: usable roof rectangle, the area ceiling, the realistic panel count at two common rigid panel sizes, and what is left after a fan and after a fan plus an A/C unit. Nothing in it is typed by hand — it is a dump of the same roof clamp the planner uses to place a panel.

The assumptions, so you can adjust them

• Usable roof = the cargo-box roof, minus the rolled edge. Length is the interior cargo length behind the cab (the cab roof is curved, stepped and usually where the aerial and the third brake light live — not counted); width is the interior width between the walls. From that rectangle a 0.20 m band comes off every side, which is where the flat roof skin rolls down into the wall on a panel van and where nothing rigid will sit flat. That band is the planner’s own roof-shoulder rule, the same one that stops you dragging a panel onto the curve in the 3D view.
• Panels: two real rigid sizes, at 180 W/m². A compact 100 W monocrystalline panel at 1,062 × 531 mm and a 200 W rigid at 1,650 × 670 mm — the two gear variants in the planner’s catalogue. Wattage is footprint × 180 W/m², the figure the planner’s power budget uses for any roof panel; the 100 W panel works out to 102 W, the 200 to 199, a 175 W Victron at 1,485 × 668 mm to 179. A flexible thin-film panel reads a bit under that per m², which is directionally right.
• Packing: edge to edge, either orientation, no gaps. Panels are laid in a grid, whichever way round fits more, touching. Real mounts want 20–30 mm between frames, so on a roof where the count is marginal — the table tells you the usable width, check it — you may lose one.
• Obstacles take a full-width strip. A 400 × 400 mm roof fan (the Maxxair / Fiamma class, the catalogue’s roof vent) and a 750 × 650 mm rooftop A/C (the catalogue’s unit) sit on the centreline, so each one breaks the row of panels it lands in: the model removes a strip 0.40 m and 0.75 m long across the whole roof width. That is the worst case. Push the fan to the very back over the rear doors and you sometimes get the row back — the planner will tell you, per van.
• No roof rails, no rack, no Starlink. A rail pair along the edges usually lives inside the 0.20 m band and costs nothing; a full rack platform changes everything and is out of scope.

The table: every base van

One row per body; rebadges in brackets share the row. Ranges run from the shortest variant to the longest. “Area ceiling” is the whole flat rectangle at 180 W/m² — a number no real panel layout reaches, useful only as the upper bound. Counts are 100 W panels; watts in brackets are nameplate at 102 W each.

Across the 85 base variants, 19 hold 700 W or more of 100 W panels on a clear roof (the Sprinter, Transit, Crafter, Master and Daily at L4/L5, plus the Sprinter L3), 82 hold at least 300 W, and only the three shortest compact vans (Caddy SWB, Berlingo M, Transit Connect L1) stop at 200. Rebadged bodies (ProMaster, Boxer, Movano, TGE, Vivaro, ProAce, Metris…) share the donor row exactly.

How to read it

• The area ceiling is not a target. A Ducato L3 has 4.86 m² of flat roof and an 875 W ceiling; the best real grid of 100 W panels puts 609 W on it, 70 %. Every roof is 1.2–1.5 m wide and every panel is 0.53 or 0.67 m wide, so there is always a strip left over. Anyone quoting a roof’s capacity from m² alone is 30 % high.
• Small panels win on nearly every roof. Two 200 W rigids side by side are 1.34 m wide, which fits a 1.36–1.47 m large-van roof and nothing narrower; on the Trafic, Vito, Transporter and Expert (1.23–1.30 m usable) one 200 W panel is the maximum, where four 100 W panels fit. On the large vans the 200 W count jumps from 2 to 4 at L3 (Ducato, Sprinter, Master) or L4 (Transit, Crafter, Daily) — and with a fan in the way it falls back to 2 on the Ducato at every length and on the Master L3, while the Sprinter L3 keeps its 4 because it has 0.6 m more roof. Fewer connections argue for big panels; the roof argues for small ones.
• A fan is one panel. An A/C is two or three. The 400 mm fan strip takes one 100 W panel off 65 of the 85 variants and none off the other 20; the 750 mm A/C strip then takes one more on 45 of them and two more on 40. On a Ducato L2 the sequence is 5 → 4 → 2 panels; on a Sprinter L3, 7 → 6 → 5; on a Transporter, 4 → 3 → 2. The ventilation post says to plan the roof opening early for EN 721 reasons; this is the second reason — the fan fixes the panel layout, not the other way round.
• Length matters more than anything you can buy. Each body length step (L2 → L3 → L4) adds 0.4–1.0 m of roof and one or two panels — 100 W per step on the Ducato (4 → 5 → 6 → 6), 100–200 W on the Sprinter (4 → 5 → 7 → 8). Roof height (H2 vs H3) changes nothing here; the roof is the same rectangle. So a high roof costs you no solar, and a long one buys you a lot.

Match it to what you need

The sizing post lands a two-person van with a compressor fridge, laptops and no electric cooking at about 400 W of array for a European summer — which is what an L2 large van holds after the fan, and one panel more than a mid-size van holds. The full-timer with induction and a heater it sizes at 600 W and up is an L3 clear-roof or an L4-with-fan build, and not achievable on any mid-size body from the roof alone. If your load table says 600 W and your van is a Transporter, the answer is a bigger alternator charger, not a bigger panel; the roof is full at 300–400.

Check your own roof, not the row

The rows are ranges across a body. In the planner, every panel, fan and A/C unit is a real roof item: it clamps to the flat rectangle, refuses to overlap another roof item, and the power panel recomputes the array wattage from the footprint you actually placed. Drag the fan to the back over the rear doors and watch whether the lost panel comes back. The van pages list interior length and width per variant if you want to redo the arithmetic yourself: subtract 0.40 m from each, multiply, and divide by the panel you have in mind. I have not built a van yet; this is the sheet I made when the 200 W panels I had picked turned out to fit my roof one at a time.

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