The most obvious problem with flat plate collectors is the relatively large sheet of glass taking up one whole side of the construction – glass that can't be insulated without stopping the sunlight from heating the absorber plate. To solve this problem, evacuated tube collectors were invented.
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.
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.
The industry standard for solar fluid is a mix of propylene glycol and water. It's non-toxic, biodegradable and relatively stable. However, you should always mix as much water as possible with your choice of glycol product, as simple water is the ideal solar fluid.
As everyone knows, just about everything expands when it gets hotter. With gases, they can exist in the same space and build up pressure, but liquids have difficulty doing that – when a liquid expands, it needs more space.
When you first set foot in the renewable energy arena, it can look daunting: different technologies, different approaches, net-zero, net-positive, PV arrays, solar thermal, geothermal, wind power... it's a big subject and can be confusing. So where should you start?
There are some things you can do to save energy and money before you install even the simplest renewable energy system. The three simple steps are to reduce losses, increase efficiency and reduce consumption.
