Peter VanDerWal wrote:If you only have 4-5 freezing nights per year, then the simplest solution is just to pump water through the panel on those days. Granted the water in you tank will get colder, but it will keep the panel from freezing and is a small price to pay for those few nights.
Drain back systems work when designed properly, but they require a much more powerful (and expensive) pump and it might not be worth it for the few times it's needed. If you already have a suitable pump, then definitely go with drain back. But if you don't then wasting some warm water a few nights per year is probably more economical.