Mushroom vents have a lot of possibilities. This one we spotted on the side wall of a shower in a poptop motorhome. The small solar cell was mounted on the roof with no regulator. There are other types on the market with cells built in but these do not move much air due to the limited size of the solar cells. Whitworths the marine suppliers have a wonderful range of vents and many are of better quality than the RV types we are all used to. The website is a bit sad and your best bet could be to order a free catalogue online as it is excellent.