SOLAR THERMAL SYSTEM

LINEAR FFRSNEL LENS COLLECTOR

In this collector one side consists of linear grooves on the surface of the refracting material and flat on the other side.

The angle of each groove make the optical behavior similar to spherical lens.

The beam radiation which is incident normally, it converges on the focal line, where a receiver tube is to absorb the radiation.

Concentration ratio-10 to 30Temperature-150-300

• Types: Imaging and Non-imaging

• Imaging lens- Segments used with curved cross section and produce sharp image.

• Ex: Spherical,Cylindrical.

• Non-imaging-Segments used with flat cross section and do not produce sharp image.

• Application: In solar power such as focusing sun light on a solar panel.

CIRCULAR FRESNEL LENS CONCENTRATOR

CIRCULAR FRESNEL LENS CONCENTRATOR

• The lenses are used in silicon solar cells or gallium arsenide solar cells as receiver where high flux is desired.

• The lens is divided into a number of thin circular zones.• The lens approximates a thin spherical lens by the adjusted each

zones.• Concentration ratio-as high as 2000• If less than 2000 that obtained from a paraboloidal reflector.

Application-Traking is required to keep the small solar image centered on the receiver.

CENTRAL TOWER RECEIVER

CENTRAL TOWER RECEIVER

• The solar power tower is also known as central tower power plant or heliostat power plants.

• It is a type of solar furnance using a tower to receive the focussedsunlight.

• They have flat movable mirrors, to focus sun’s rays.

• Material: 40% potashium nitrate,60% sodium nitrate. They have high heat capacity.

• Design: Flat glass, thermal storage to store the heat in molten salt containers to continue producing electricity while the sun is not shining.

• Steam is heated to 500°C to drive turbines that are coupled to generators which produce electricity.

• Advantages: Higher temperature, lower receiver losses requirment of flat mirrors,suitable for high temperature process heat application.

HEMISPERICAL MIRROR CONCENTRATOR

HEMISPERICAL MIRROR CONCENTRATOR

• Spherical mirrors are the simplest type of concentrator and are easily to build and use.

• It consist of a hemispherical fixed mirror a tracking observer and supporting structures .

• All rays entering the hemisphere .• After reflection cross the paraxial line between focus and mirror surface.• The absorber at the center of curvature intercept all reflected rays.• So its axis is aligned with solar rays passing through the center of the

sphere.

• Advantage: It helps in reducing the cost by replacing an expensive large receiver by a less expansive reflecting or refracting area.

• It increases the intensity by concentrating the energy available over a large surface into a smaller surface.

Disadvantage: A number of complications arise because of non uniform flux on absorber, wide variation in shape, temperature and heat behavior of absorbing.