We had 2 solar tubes in our CYV already installed in the 2 baths when we purchased it in 2009. It was built in '04 but I'm not sure when the tubes were actually installed after that date. At any rate, we've had zero problems with them and just got a 3rd installed by the Solar Guys earlier today.
While talking with him about solar fans and their value, he agreed that the most bang for the buck would be blowing in additional insulation to bring it up to R40 over the house and garage, then doing the fan(s) if necessary.
He referred me to the
FL Solar Energy Center website for some interesting publications and studies. In the midst of doing that now...