Solar Panel Placement on a Van Roof: Layout Guide
Planning where to put your solar panels before you drill anything saves you from expensive regrets. Here's how to lay out your roof.
Know your roof dimensions first
Common van roof usable lengths (approx):
- Standard wheelbase Sprinter/Transit/Promaster: ~130–145" usable length
- Extended wheelbase: ~165–175" usable length
- Roof width (between raised gutters): ~65–75" on most full-size vans
Subtract space for:
- Fan/vent cutouts: typically 14×14" each
- Roof rack if installed
- Roof-mount AC unit if planned
- Required clearance around obstacles: 4–6" minimum
Sketch your roof to scale (graph paper or a simple drawing tool) before ordering panels.
Panel sizing options
100W panels (approx 40"×20" / 100×50cm): The smallest practical rigid panel. Good for tight roofs or mixed layouts. Lower Voc (~20–22V) so two in series gives ideal 40V for most MPPT controllers.
200W panels (approx 58"×27" / 147×67cm): Most common choice. Two panels on a standard SWB van is often the practical limit; three on an extended.
175W panels (approx 58"×26"): Similar to 200W but slightly smaller, popular on Sprinters where millimeters matter.
Placement priorities
1. Avoid east-west shadows from roof features
A vent fan, antenna, or rack leg casting a shadow on a panel reduces output — and in series wiring, shadows on one panel reduce the entire string's current. Place panels so roof features shadow them as little as possible during 9am–3pm peak hours.
Sun angle mid-morning and mid-afternoon comes from slightly south and east or west. Shadows from raised roof features extend toward the front or rear of the van depending on time of day. Panels placed away from shadows' paths during peak hours matter most.
2. Front vs rear placement
Front placement is most common. The cable entry gland installs near the front of the roof, cables drop down the front wall or behind the dash area, and run back to the MPPT controller. Short runs.
Rear placement works if your controller and battery are in the rear — cable runs stay short but your entry gland is near the rear doors.
Mid-roof placement around the fan: if you have one panel on each side of a center fan, each cable drops down separately. Requires two entry glands or one large multi-cable gland.
3. Minimize cable run length
Every foot of MC4 cable between panel and controller is a potential voltage drop. At 5A (common for a 100W panel), 20' of 10 AWG cable adds only 0.1V drop — acceptable. But routing cables across the entire roof adds up. Place the entry gland as close to the panels as practical.
Sample layouts by van model
Ford Transit 148" High Roof:
- Option A: 3× 100W panels in a row longitudinally (leaving room for fan and front clearance)
- Option B: 2× 200W panels side by side, transverse
- Option C: 4× 100W panels (2×2 grid) on an extended wheelbase
Mercedes Sprinter 144" High Roof:
- The Sprinter roof is relatively narrow (~64") — transverse mounting of a full 200W panel is tight but possible
- Most builders run panels longitudinally: 2× 175W or 2× 200W front to rear with fan between
Ram Promaster 159" High Roof:
- Wider roof than Sprinter (~72") — full 200W transverse panels work well
- Common: 2× 200W panels transverse, fan between or fore/aft of panel row
Pre-drilling checklist
- Verified panel locations won't shade each other at mid-morning and mid-afternoon
- Located all vent fans, antennas, roof vents — marked on layout
- Confirmed entry gland location and cable run path
- Checked inside for ribs, wiring, or structures at every planned drill point
- Ordered appropriate bracket hardware (Z-brackets or tilt feet)