Details of Hot Water System Types

Description of Solar Hot Water System Types

Active Direct – The water in the water heater is cycled between the tank and the collector. A controller monitors the temperature of the water heater and the collector. When required, the pump operates to heat the water in the tank and to circulate water when the collector temperature falls below the set point to prevent freezing. A back-up electrical element is located in the tank to heat the water when the sun is not available.

Active Indirect – The water heater has an internal heat exchanger. The heat exchanger is plumbed to the collector and charged with propylene glycol (a food grade antifreeze). The glycol provides freeze protection. The pump only operates when there is a need to heat the tank. A back-up electrical element is located in the tank to heat the water when the sun is not available.

Passive Integrated Collector Storage (ICS) – This system stores 30-40 gallons of water on your roof and heats the water the sun. When a hot water fixture is turned, the preheated water is supplied to the water heater.

Drain Back – This system is similar to the Active Indirect except a second small tank is used as a heat exchanger and to store the water that is supplied to the collector when it is not in use. When the main tank requires heat, two pumps activate. One directs the water to the collector and the other circulates water from the water heater to the heat exchanger in the smaller tank. A back-up electrical element is located in the tank to heat the water when the sun is not available.

Active Plastic – Similar to the Drain back except the heat exchanger and drain back unit are separated. This system uses an unglazed plastic collector.

Thermosyphon – This system is similar to a drain back system in operation except the heat exchanger is integrated into the collector located on the roof. This system does not have a pump and relies on the hot liquid to rise and force the colder solution into the bottom of the collector. An antifreeze solution is used.

Evacuated Tube – The evacuated tube collectors contain a copper heated pipe, which is attached to an absorber plate, inside a glass vacuum sealed tube. The hollow and the space inside is hollow and space inside is evacuated or in a vacuum. Inside the heat pipe is a small quantity of liquid. The vacuum enables the liquid to boil at lower temperatures. When sunlight heats the absorber, the liquid in the heat tube turns to hot vapor and rises to the top of the pipe. Glycol flows through a manifold and picks up the heat.