Difference between Flat Plate Collectors and Evacuated Tubes Collectors

The Flat Plate Collector is, as the name suggests, flat. It is also stationary. This means that its effective surface area changes with the time of day. Maximum radiation is received when the collectors face the sun directly. Less energy is collected when the sun is at an angle. A Flat Plate Collector heating liquid contains a transparent cover (glass or plastic), an absorber plate, insulation, and an enclosure. The transparent cover, usually glass or plastic, admits solar radiation. The absorber plate, a flat panel with tubing through which the water is circulated and heated, collects the radiant energy. The plate and tubing are typically steel, aluminium, plastic or copper, and are often black to increase energy absorption. The solar radiation that passes through the transparent cover has a short wavelength. The absorber plate reradiates some of the received energy outward in a longer wavelength, which in turn does not pass back through the cover plate. The transparent cover also minimizes convected heat loss to the surrounding air. Insulation surrounds the other sides of the absorber plate to reduce heat losses there.

Evacuated Tube Collectors are composed of smaller tubes inside larger tubes. Solar radiation is transmitted through the outer, transparent tube. Liquid circulates in the inner tube, waiting to be heated. The space between the two tubes is a vacuum that reduces convection heat losses from the collector. And has the capability to heat water to temperatures exceeding 300 F and absorb 93% of the sun's energy with minimal heat loss. They are unaffected by factors such as wind chill or ambient air temperatures due to the vacuumed structure, allowing them to absorb whatever solar energy that is available even on cold / dull days. This enables the system to provide hot water for eight months of the year and assist your existing water heating during the winter months.

How do Solar Collectors heat your water?

Put simply, the solar thermals system absorbs the sun's energy turning it into water for domestic use.

 

In a standard system, as shown above, the solar collectors that are mounted onto the roofs of houses, or in arrays, absorb solar energy from the sun. They work best when they are tilted at angles of approximately 30 degrees. The collectors have specialized solar fluid (propylene Glycol) in them, located inside risers, which heats up from the absorbed solar energy. When this fluid reaches its optimum temperature it is pumped from the risers within the collector into the twin coil solar cylinder, or water tank, where - in conjunction with a household bolier - it heats the water for general household use. The solar fluid is then pumped back up to the collector to reheat. The whole system is automated by a controller. In summer weather the boiler does not need to be active as the solar colector can absorb enough sunlight to heat the domestic water by itself.

The map below shows annual irradiation (the amount of energy available for collection) at 30degrees south facing in the UK in kwh/m2.       

   

 

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