Non Focusing Type Concentrators
As stated earlier, in these type of collectors the solar radiations are allowed to fall on the absorber after using reflection in the mirror. Commonly used non-focusing type concentrators we :
- Flat plate collector with plane reflector
- Compound parabolic concentrator (CPC)
1. Flat Plate Collector with Plane Reflector : It is the modified form of fat plate collector. It uses a flat plate collector with plane mirror reflectors attached on its edges to reflect the additional solar radiations into the receiver. Thus the total solar radiations received by the reciver are increased. The mirrors used called booster mirrors.
A flat plate collector with plane mirror reflectors is shown in Figure A. The flat plate collector facing south is attached with plane mirror reflectors at suitable angles as shown The concentration ratio upto a maximum of can be achieved by such systems.
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| Figure A |
In order that the attached mirror are effective, the angles of mirrors should be adjusted continuously as the sun’s elevation changes. The temperatures upto 140° C can be attained with use of mirror reflectors. However, in practice these types of concentrators are not used commonly except for specific applications.
2. Compound Parabolic Concentrator (CPC) :
The compound parabolic concentrator is non-focusing type collector. It is also called as Winston collector. A CPC is shown in Figure B.
It consists of two facing parabolic mirror segments A and B attached to a flat receiver (absorber). It forms a trough. In this case the solar radiations from all directions are reflected towards the receiver kept at the bottom. It collects both direct and diffused solar radiations with high acceptance angle.
The concentration ratio achieved in this type Optical of collector ranges from 3-7. These collectors require occassional sun tracking with seasonal variations. Parabola.
The absorbers generally used in CPC are mirror either fin type or tubular type of absorbers. The temperatures attained are in the range of 100°C to 150°C . However, temperatures upto 200°C can be attained using evacuated type of tubular absorbers.
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| Figure B |