What type of system is best; drainback or glycol?
Neither is “best”; the topology chosen depends on the building design, collector orientation, pipe chase locations, whether the array is ground mounted, etc. Drainback systems are more efficient in collection, and don’t have overheating issues that are associated with glycol in the summertime. However, they are susceptible to freezing if not installed by an experienced professional. Glycol based systems allow more flexibility in pipe runs, and minimize concerns about running pipes through unconditioned (unheated) spaces. They can also be powered with PV powered circulators, for a true “zero energy use system”, which is harder (though not impossible) to do with a drainback system. Despite which type of system design is chosen, they should be installed by, or in consultation with, a professional solar installer, as there are many “gotchas” that can cause serious damage to your home if not proactively addressed.
