Three different Solar Collector Comparison. The Unglazed Flat Panel, Glazed Flat Panel and Evacuated Tubes. In colder areas you would want to use Evacuated Tubes and in areas with more cloud cover. In warmer areas when freezing does not occur - then Glazed Flat Panels would be better. Of course, if you have more cloud cover - then Evacuated Tubes may still be better because they do better in higher cloud levels.