4.4 light technologies
Evacuated tubes convert the sun's energy into heat for purposes of heating water. Each evacuated tube consists of two glass tubes. The space between the two glass tubes is a vacuum. The vacuum helps to retain the heat from the sun. The insulation properties are so good that while the inside tube may be 150oC / 304oF, the outer tube is cold to touch. As a result, evacuated tube water heaters can perform well even in cold weather. A set of 20 glass tubes provide all the domestic hot water needed for the house. The tubes are easy to install and may be part of the building skin or, as in this house, part of the outdoor landscape.
