Much like flat plate collectors, evacuated tube collectors have a solid, durable, insulated frame with one glazed side which contains absorbers. In this case, the absorbers are individual transparent tubes rather than a single, flat plate under a pane of glass.

No matter which manufacturer you ask, they'll all tell you they have the best solar collector. They may even tell you that theirs is the most efficient. There's a good chance that they're right, too – and wrong at the same time.

As you should already know, choosing the most efficient collector for your solar thermal installation is more about your situation, location and climate than it is about just picking the top-rated one off a list.

As you are probably aware, the SRCC (www.solar-rating.org) rates both efficiency and durability from the results of ASHRAE's (www.ashrae.org) tests. Thankfully, durability is less of an issue when you're comparing solar collectors because the vast majority of manufacturers build their products to last.