How to Install Solar on a Van: Full Walkthrough

A van solar install is four jobs: fix the panels down, get the cable through the roof without creating a leak, land it on a charge controller, and connect that controller to the battery through a fuse. The electrical part is straightforward arithmetic. The part that goes wrong is the roof penetration and the mounting, which is why a solar install is as much a sealing job as a wiring job. This guide covers both, in the order you actually do them.

How big should the array be?

Daily solar yield is panel watts multiplied by peak sun hours multiplied by a system derate. Peak sun hours is the number of hours of full-strength sun equivalent your location gets in a day, typically four to six in summer and two to three in winter at mid latitudes. The derate accounts for cell temperature, flat mounting, dust, cable losses and controller efficiency: use 0.75 for a flat roof-mounted array with MPPT and 0.6 with PWM.

Those figures assume five peak sun hours, which is a good summer day and an optimistic winter one. Run your own location and season through the solar array calculator, and check the seasonal swing on the output by sun hours chart before you decide the array is finished. A 200W array that covers everything at midsummer may cover a third of it at midwinter from the same latitude.

On panel choice, a Renogy 200W 12V Solar Panel (N-Type, 16BB) is the standard building block: twice the output of a 100W panel for roughly the same mounting effort and half the roof penetrations per watt. A Renogy 100W 12V Monocrystalline Solar Panel (N-Type, 16BB) is the right shape for filling an awkward gap around a fan or a vent. A Renogy 400W 12V RV Solar Kit (4x100W, 30A PWM Controller) arrives as a complete array with brackets and cables, which removes the part that trips people up, though the bundled controller is PWM and deserves an MPPT upgrade at that array size.

Where do the panels go on the roof?

Lay everything out on the roof before you fix anything. Panels, roof fan, any vents, the rack feet if you have a rack, and the cable entry point. What you are looking for is a layout where no panel is shaded by the fan cowl or a roof rail in the morning or the late afternoon, because partial shading on a series string costs far more output than the shaded area suggests.

Leave an air gap under the panel. A panel bonded flat against a hot roof runs hotter and produces measurably less, and the gap also lets water and grit wash through instead of sitting under the frame. A set of Renogy Solar Panel Mounting Z Brackets (2 sets) is the cheap way to get that gap on a bolted install. The panel mounting guide covers adhesive versus bolted mounting, rack mounting and the tilt question in detail.

Position the cable entry near the panels but not directly under a low point where water pools. A BougeRV Double Cable Entry Gland Box for Roof Solar (ABS, White) bedded in sealant is the correct fitting: it gives the cable a strain relief, a sealed path and a cover that sheds water. Ten dollars of gland box against a headliner full of water is the easiest trade in the whole build.

How do I size the cable from the roof?

Two runs matter and they are sized differently. The panel-to-controller run carries panel current at panel voltage, which is low current, so 10 AWG covers almost every van array. The controller-to-battery run carries full charge current at battery voltage, which is high current over a short distance, so it is usually 8 AWG to 4 AWG depending on the controller.

Voltage drop is calculated as 2 times L times I times R, where L is the one-way run length in feet, I is current in amps and R is the conductor resistance in ohms per foot. The factor of 2 is there because current travels out and comes back, and forgetting it is the single most common sizing error in DIY builds. Copper resistance is 0.000999 ohms per foot for 10 AWG, 0.000628 for 8 AWG, 0.000395 for 6 AWG and 0.000249 for 4 AWG. The 3 percent target on a 12V system is 0.36V.

Use proper PV cable on the roof rather than automotive wire. A 10 AWG Solar Extension Cable, 30 ft Pair with MC4 Connectors is tinned copper rated for UV and roof temperatures, which ordinary primary wire is not, and it comes with the connectors already fitted. Buy a MC4 Solar Connector Set, IP67 Waterproof (10 AWG, 40 pieces) set as well, because every array needs connectors to join panels and the first two crimps are always practice. The wire gauge calculator checks both ampacity and voltage drop for your specific run.

Series or parallel, and which controller?

Series adds voltage and keeps current the same. Parallel adds current and keeps voltage the same. On a van roof with two identical panels and an MPPT controller, series usually wins: doubling the string voltage halves the current, which quarters the voltage drop loss on the roof run and lets you use thinner, cheaper, easier-to-route cable.

The limit is the controller maximum PV input voltage, and the thing that catches people is that panel open circuit voltage rises as cell temperature falls. A string that reads 44V on a warm afternoon can exceed 50V on a cold clear morning, so leave real headroom against the controller rating rather than working to the number on the panel label.

A Victron SmartSolar MPPT 100/30 Solar Charge Controller (Bluetooth) handles 100V of panel input and 30A of charge current, which covers a 440W 12V array and is the default for most van roofs. The Victron SmartSolar MPPT 100/50 Solar Charge Controller (12/24V) takes the same architecture to 50A for arrays up to roughly 700W, and the Renogy Rover Lite 60A MPPT Solar Charge Controller (150V PV) raises the PV ceiling to 150V for a long series-wired run. On a tighter budget the EPEVER 40A MPPT Solar Charge Controller (100V PV, 520W at 12V) gives 40A of genuine MPPT tracking without Bluetooth. The MPPT versus PWM comparison quantifies the difference, and the charge controller roundup sorts the field by array size.

How is a solar array fused?

On the battery side, always. The controller-to-battery cable is connected to a source that can deliver hundreds of amps into a short, so it is fused at the battery end, within a few inches of the terminal or the busbar it lands on, at or below the ampacity of that cable. An 8 AWG run rated at 80A under ABYC ratings outside engine spaces takes a fuse at or below 80A, and in practice a 40A or 50A fuse sized just above the controller output is the right choice.

On the panel side, a fuse or breaker is about isolation and about protecting a string when several panels are wired in parallel. A Young Marine 60A Resettable DC Circuit Breaker, Surface Mount (12 to 48V) doubles as a switch, so you can isolate the array without pulling a fuse in the dark, which you will want on the day you service the controller. A RED WOLF 4 Way ANL Fuse Holder and Distribution Block (12V) at the battery gives fused distribution for the whole system including the solar leg. The wiring and fusing guide has the full ampacity table and the fuse selection logic.

What order do I connect it in?

Mount the panels and run the cable with nothing connected. Cover the array. Mount the controller somewhere with airflow, close to the battery rather than close to the panels, because the short fat run should be the high current one. Land the battery cable on the controller first, with its fuse already fitted at the battery end and the battery disconnected. Then connect the battery. Then, last, connect the panel leads and uncover the array.

That order exists because most controllers detect system voltage from the battery on first power-up. Powering a controller from the panels first can leave it guessing at 24V on a 12V system, and on some units it is a warranty condition. When it comes up, set the charge profile to match your battery datasheet rather than leaving it on the default, which is usually a lead acid profile. A Renogy 12V 100Ah Self-Heating LiFePO4 Battery (DuoHeat, Mini) and a generic AGM profile will charge, but not to the right absorption voltage and not for the right duration.

Then verify. Watch the controller report panel voltage, charge current and battery voltage, and check those against a AstroAI Digital Clamp Meter, AC/DC Current and Voltage (4000 count) on the battery cable. A controller that says it is delivering 14A and a clamp meter that says 4A means a connector problem, not a software one. Once it is running, have the installation inspected by a qualified installer before it carries load, particularly the fusing and the roof sealing. The figures here are researched guidance from published standards and manufacturer documentation, not an electrical certification.