Concentrating Type Collectors
Concentrating type of collectors are also known as focusing collectors. These type of collectors are used when the temperatures higher than 100° C are required. Therefore in these collectors, it is necessary to concentrate and collect the high intensity of solar radiations on the absorber surface. The collector system comprises of a concentrator and an absorber (receiver). The concentrator is an optical system in the form of reflecting mirrors or refracting lenses.
Due to apparent motion of the sun , the concentrating surface is unable to redirect the sun rays on the absorber throughout the sunshine period if both the collector and absorber are stationary. Therefore the collector is installed with a tracking device for continuously following the sun.
The receiver includes an energy absorbing surface, transparent cover and other accessories. The system receives the solar radiations on the large concentrating area and these radiations are focused on to an absorber having relatively much lesser area.
As a result of energy concentration the fluids can be heated upto a temperature of 500° C or more. In point focusing type of receivers the temperatures even upto 3000° C can be achieved.
Solar concentrators are used for high temperature thermal applications and photovoltaic conversion of solar energy directly into electrical energy.
These systems have high collector efficiency since the losses are much less compared to flat plate type of collectors.
Advantages of solar concentrators :
- High fluid temperatures upto 500°C or more can be achieved.
- It has high collector efficiency.
- The thermal heat losses are reduced due to reduced heat loss since area of collection is less.
- The cost of concentrator system is low compared to flat plate collector since less material is needed.
- The cost of heat storage system is less due to storage of heat at high temperatures.
Disadvantages of solar concentrators :
- Collects only beam radiations in focusing collectors because diffuse radiations cannot be reflected, hence these are lost.
- Needs costly tracking device to track the sun for its round the year application for its high efficiency of operation.
- Needs extensive maintenance to remove dirt from reflecting surfaces.
- Has high initial cost.
- Has non-uniform flux on absorber plate.