Vacuum Tube Collectors
Vacuum tube collectors also use absorber sheets or coated copper tubes, but these absorbers are long and thin and placed in a vacuum inside transparent glass tubes coated with special selective materials. The tubes are laid out in parallel rows, and liquid such as water or glycol circulates or is pumped through them. The use of a vacuum enables these systems to operate at higher temperatures – in some cases generating steam rather than just hot water – and reduces thermal losses when the sun is not shining.
Concentrating Thermal Collectors
Concentrating Solar Power (CSP) systems use large reflective surfaces to focus the sun’s energy on vacuum tube collectors, generating much higher temperatures than systems not using concentration. CSP systems can be located on rooftops or on vacant land, and can be ideal for industrial users requiring high-temperature process heat. Because concentrators require direct rather than diffuse light, they work much better in areas having a high number of hours per year of direct sunshine. In some systems the heat is also used to drive a turbine or other generator to produce electricity.
Heat
Solar energy can be a cost-effective alternative or supplement to electricity, natural gas or other fossil fuels for heating water or space in commercial and industrial buildings. There are three main types of thermal collectors. Determining which one is appropriate is dependant on the quantity and temperature of heat needed.
Flat Thermal Collectors
Flat collectors use a thin absorber sheet, usually made from either copper or a polymer and coated with a dark coating to absorb solar radiation. A grid or coil of tubes sits behind the absorber, and fluid such as water or glycol circulates or is pumped through the tubes to carry the heat from the absorber sheet to a storage tank or heat exchanger. Systems using natural convection to cause the fluid to move are called “passive”, while ones using pumps are called “active”.
Solar energy can be a cost-effective alternative or supplement to electricity, natural gas or other fossil fuels for heating water or space in commercial and industrial buildings.
