Volkswagen has licensed thin-film solar panel technology from ICP Solar and will offer a private label solar chargers.
ICP's solar panels can prevent batteries from losing their charge, which can happen during extreme temperatures or if the vehicles are not started for lengthy periods of time.
I'm guessing you would periodically recharge your battery to keep it from unexpectedly dying, as opposed to waiting for enough daylight once your battery is already kaput. ICP offers a charger for small cars for $35, and a larger version for $90.
