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Flat Plate Solar Collectors

Flat Plate Solar Collector Design


Photo Credit: Physics World

A glazed flat plate solar collector is an insulated box covered by glass or plastic with a metal absorber plate on the bottom to absorb the sun’s radiation. The weatherproofed collectors are usually glazed with a coating to better retain heat. Heat transfer fluid flows through metal tubes lying below the absorber plate. The fluid then flows through a heat exchanger before entering the storage tank.

Unglazed flat-plate collectors (without insulation or absorber coatings) do not operate in cool or windy climates but are excellent for heating water in a pool.

Efficiency of Flat Plate Solar Collectors

A number of factors influence how well the collector is able to heat water, including the ambient temperature and available sunlight.

Flat plate solar thermal collectors suffer more heat loss than other types of solar collectors, and are thus not the most efficient type. However, flat plate solar water heaters are suited to a wider range of climates. Because these collectors can use a heat transfer fluidsuch as antifreeze, rather than directly heating the domestic water supply, this type of solar thermal panel can be used in colder climates.

A flat plate collector installation. Photo Credit: Viessman

Evacuated tube collectors are often more efficient than flat plate collectors as they are able to reach higher temperatures. However, higher temperature capability should not be the sole characteristic to focus on when choosing a solar water heating system.

Evacuated tube systems are more suited for commercial purposes, when greater amounts of water at higher temperatures are needed, such as at a laundromat.  In most instances, a flat plate system is suitable for heating water for your home.

Cost of Flat Plate Solar Collectors

While they are not the most efficient solar collectors, flat plates last for over 25 years and are one of the most cost-effective options for a residential solar water heating system. Flat plate collectors are the most durable type of collector, and can be cheaper than evacuated tube systems.

Typically, one flat plate collector can supply adequate energy to heat about 40 gallons of water for domestic hot water use. According to, a family of four can obtain about half its hot water from two collectors.


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