Many types are available of evacuated tube collectors. The collectors are composed of many tubes and each tube consists of an absorber plate, surrounded by glass tube. The vacuum between plate and tube acts as insulator and has superior efficiency than air. These collectors retain more heat than flat plate collectors because of air-glass space and keeps very high temperature (120°C-180C°) without losses, even in very cold climate.


Glazed flat plate collectors consist of thick (10cm) rectangular boxes (around 2 m²) – containing layers: an absorber plate – a sheet of copper, painted or coated with black-bonded to pipes that contains the heat transfer fluid. The pipes and the copper sheet are placed in an insulated metal frame with a sheet of glass on the top. The glazing is used to protect the absorber plate and creates an insulating space. The insulation is high temperature rigid foam –glass is low iron tempered and frames are made of aluminum. These are the most common used material with variable absorber plates coating- preferably the surface materials that can maximize the heat absorption and retention.


Unglazed flat plate collectors are usually made of durable, cost effective black polymer. These collectors do not have selective coating, frame and insulation at back, so referred as unglazed. These collectors are good to capture the sun energy but do the thermal losses rapidly, especially in windy and cold climate. Therefore, unglazed flat plate collectors are commonly used for the application that requires low temperature (60 – 65°C) like pool heating; make – up water in fish farms and for low temperature space heating.