Collectors for solar hot water and heating systems are typically the most expensive components in the system. I am continually annoyed by self-serving manufacturer’s, distributors and installers that want everyone to believe that their panel fits all occasions and all other panels are worthless.
It’s actually quite simple. Here are a few pointers; a) Different collectors work better for different applications. b) all collectors work best at lower temperatures for their range. Mostly, I am writing about flat plate and evacuated tube collectors. In general flat plate collectors are best for low temperature applications. Such as; domestic hot water for your home (showers, dishwashing, etc.), low temperature radiant heating. Evacuated tube collectors are best for High temperature applications. Such as; commercial water heating (restaurants), high temperature radiant heating.
Next, you need to consider where the collectors will be used. Is it a cold climate or hot climate? is the hot water going to be needed year round. This is where things get a little more interesting. Evacuated tubes perform better than flat plate collectors in cold climates. However, evacuated tubes do not melt snow off of themselves very well. The flat plate collectors operate at their least efficiency in cold climates. In a nutshell, evacuated tube collectors are best suited to cold climates where you are providing high water temperatures. If snow is an issue, be sure to tilt up the panels at least to 45 degrees and to not allow snow to build up around the bottom of the collectors. With the evacuated tubes you will also want to consider whether you need the heat that they generate all year, or only seasonally, like for heating. Here in Colorado, you need to provide a heat dump to keep the evacuated tube collectors from overheating in the summer, when the heat isn’t needed.
To recap. Use the right collector for the right application. This will keep the system more reliable and economical. Feel free to comment if you have any questions or additions!