We know that solar collectors are used to transform primary solar radiations into thermal energy. In this article let us learn about the differences between flat plate and concentrating type solar collectors.
Flat Plate Solar Collector :
Flat plate collectors are solar energy collectors that absorb solar radiations, which in turn they can be employed for heating the fluid by flowing through it. Flat plate collectors are designed in such a way that, they have high absorption and low emission. A schematic representation of a flat plate collector is shown below.
It consists of a flat or grooved absorber plate with pipelines attached to its surface. The absorber plate is attached inside an insulated metallic frame usually made up of aluminum alloy and is closed from above with one or more toughened glass frames. The flat plate solar collectors are also called non-concentrating type collectors.
They are used for temperature requirements, ranging from 50°C to 100°C, and are widely used because of their simple construction and easy installation. These collectors absorb both direct and diffuse solar radiations.
Hence, these collectors can work effectively on cloudy days. Based on the type of fluid to be heated, these collectors are divided into two types. They are liquid heating flat plate collectors and air or gas heating flat plate collectors.
Concentrating Type Solar Collector :
When there is a requirement for higher temperatures (more than 100°C), concentrating solar collectors are used. In this type of solar collector reflecting arrangement of mirrors is made that directs solar radiation onto an absorber of a smaller area as shown below.
As compared to flat plate collectors, the construction, design, and maintenance of concentrating type collectors are not easy. Due to the presence of the optical system, there are some reflection or absorption losses in the mirrors in addition to the losses in radiation while through the passing cover. Also, these type of collectors has to track the sun so that the beam radiations are directed to the absorber.
The concentrating solar collectors are available in different types. Some of them use reflecting type mirrors, while some of them use refracting type mirrors to concentrate radiations on to the absorber.
Difference Between Flat Plate Solar Collector and Concentrating Type Solar Collector :
| Flat Plate Solar Collector | Concentrating Solar Collector |
|---|---|
| These collectors are also called non-concentrating type solar collectors. | These collectors are also called focusing type solar collectors. |
| In this type of solar collector, the collector area is equal to the absorber area. | In this type of solar collector, the collector area is very large sometimes hundreds of times more than that of the absorber area. |
| The intensity of insolation is small. | The intensity of insolation is very large. |
| The reflecting surfaces require more material. | The reflecting surface requires less material. |
| The working fluid in this type of collector does not attain a high temperature. | The working fluid in this type of collector attains very high temperatures. |
| There is no use of mirrors and lenses to concentrate the sun's rays. | For focusing the sun's radiation, an arrangement of lenses and mirrors is designed. |
| The efficiency of the flat plate collector is low. | The efficiency of concentrating type collector is high. |
| These collectors are cheaper. | These collectors are expensive. |
| Surface treatment required to reduce heat losses and to improve collector efficiency is not economical. | Surface treatment required to reduce heat losses, and to improve the collector efficiency is economical. |
| The absorber gets uniform solar flux. | The absorber gets non-uniform solar flux. |