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.

When it comes to your local climate, there are some factors that can seriously affect your choice of collector type. The worst non-catastrophic climatic event for solar thermal installations is, without any doubt, snow. It's the worst because, unlike rain or total cloud cover, it can physically pile up on top of the collector and block out the sun's light.

Despite all the advances of modern technology, the best solar fluid for use in a solar thermal installation is water. It retains and transfers heat better than any other liquid in the world. However, it has one major drawback: it freezes easily.