An evacuated tube solar collector is composed of hollow glass tubes. All the air is removed from the tubes to create a vacuum that acts as an excellent insulator. An absorber coating inside the tube absorbs the solar radiation. This energy is transferred to the fluid moving through the collector and then to the hot water storage tank. In cooler climates a heat exchanger is used to separate the potable water from the non-toxic anti-freeze in the collector.
The vacuum prevents heat loss, making these the most efficient collectors. An evacuated tube collector can work well in cloudy conditions and in temperatures as low as -40°F. This characteristic is most advantageous in colder climates, or during the winter, where other solar collectors may not produce as much energy.
Cost and Durability
Photo Credit: Solar Colorado
Depending on the brand, evacuated tube collectors can cost more than flat plate collectors – though the additional up-front cost may be made up for in utility bill savings. Flat plate collectors are usually more cost-effective for residential solar water heating systems. Thus evacuated tube collectors are more commonly used for commercial applications. The added winter and cold climate efficiency makes them a good choice for solar space heating.
Evacuated tube technology has been around since the 1980’s and most evacuated tube collectors have a similar warranty to flat plate collectors. A major benefit is that individual tubes can be replaced as needed, rather than replacing the whole collector.
If you’re considering a solar water heating system, we highly recommend you purchase this comprehensive guide to solar water heating systems by Bob Ramlow.