Resource: gentle intro to solar
Solar power is common for vehicle dwellers, especially those living in cargo vans or other vehicles with large, high, and flat rooflines.
Solar is more challenging for cardwellers due to limited roof space. SUVs are somewhere in the middle.
Portable panels are panels that store away and are deployed as needed.
Pro: Panel can be in sun while car is in shade. Can be secured when not in use. Can be aimed at the sun.
Con: Expensive per watt. Newbies commonly underestimate how much power is required. Voltage drop from long wiring runs. Must be aimed at the sun1), which would require repositioning every couple of hours. Portability increases risk of theft. Can be urinated on by dogs.2)
Each type of portable panel has it's own strengths and weaknesses.
Pro: Cheapest per watt. Toughest panel.
Con: Heaviest portable. Hardest to stow due to frame thickness, panel size, and rigidity.
Pro: Fold for easier storage. Built-in handle makes carrying easier.
Con: Most expensive per watt. Relatively heavy. Can be fiddly. Subject to mechanical wear from setup and teardown. Some have a built-in charge controller, resulting in very long runs between controller and battery.3)
Pro: Very light. Extremely thin, which allows it to be slid into narrow storage.
Con: Can blow away in wind. Much easier to damage than framed panels; consider the lifetime of these panels to be a few years rather than decades. Roughly 2x as expensive as framed panels.
Low yield panels (10w-25w) encased in hard plastic. Most often seen in backpacking scenarios or on dashboard “battery maintainers”.
Pro: Small. Con: Most expensive Watt/$. Lowest output. Can overcharge batteries that are unused.
While roofspace is limited, it is possible to mount a normal framed panel on a roof rack. Your vehicle may already have a rack (or at least rails), making the job easier. A simple two-bar universal rack is about $150, and a nice locking two-bar rack from someone like Inno is about $300-$450.
When rack-mounting panels, mount them flush with or on top of the rack. This will prevent the rack from shading the panels.
To prevent theft the panel could be attached with tamper-proof fasteners.
Pro: Can use normal, inexpensive panels. Greater output due to bigger panel. Greater output because it is always deployed. Flat-mounted panels do not need to be re-aimed at the sun.
Con: Initial installation. Running wires to vehicle interior. Vehicle must remain in the sun.