Solar Concentrator Classification: Advantages of Solar Concentrator

Introduction: Definition of Solar Concentrators:

Solar Concentrator is a device which concentrates the solar energy incident over a large surface onto a smaller surface. The concentration is achieved by the use of suitable reflecting or refracting elements, which results in a increased flux density on the absorber surface compared to that existing on the concentrator aperture. In order to get a maximum concentration an arrangement for tracking the sun’s virtual motion is required.  An accurate focusing device is also required. Thus a solar concentrator consists of a focusing device, a receiver system and a tracking arrangement. Temperature as high as 3000 degrees Celsius can be got from a solar concentrator. So they have potential applications in both thermal and photovoltaic utilization of solar power at high temperatures.

Solar concentrating devices have been used for a long time. In Florence as early as 1695, a diamond could be melted by solar energy. Lavoisier carried out a number of experiments with his double-lens concentrator. The knowledge concentrator dates back even time of Archimedes, whose book "On Burning Mirrors" is an evidence of this fact. Many uses of concentrators were reported in the eighteenth and nineteenth centuries, particularly in heat engines and steam production. The advantages of concentrator are as follows: 

The advantages of solar concentrator

1. It increases the intensity by concentrating the energy available over a large surface onto a smaller surface (absorber)

2. Due to concentration on a smaller area, the heat loss area is reduced. Further, the thermal mass us much smaller than that of a flat plate collector and hence transient effects are small.

3. The delivery temperatures being high, a thermodynamic match between the temperature level the task occurs.

4. It helps in reducing the cost by replacing an expensive large receiver by a less expensive reflecting or refracting area.

Disadvantages of Solar Concentrator

However, concentrator is a optical system and hence the optical loss terms become significant. Further it works on beam component of solar radiation, resulting in loss of diffuse component. Although the basic concepts of flat plate collectors are applicable to concentrating systems, a number of complications arise because of non-uniform flux on absorbers, wide variations in shape, temperature and heat loss behavior of absorbers and finally the optical considerations in the energy balance conditions. It may be noted that higher the concentration of the collector, higher is the precision of optics and more is the cost of the unit. In addition to the complexity of the system, the maintenance requirements are also increased.

Classification of solar concentrator

Solar concentrators may be classified as (i) tracking type and (ii) non-tracking type. Tracking may be continuous or intermittent and may be one-axis or two -axes. As the sun may be followed by moving either the focusing part or receiver or both; concentrators can be classified accordingly. Further the system may have distributed receiver or central receiver.

The concentrators may also be classified on the basis of optical components. 

They may be 

1. Reflecting or refractory type

2. Imaging or non-imaging type

3. Line focusing or point focusing type

The reflecting or refracting surface may be one piece or a composite surface, it may be a single stage or two stage type system and may be symmetric or asymmetric. In practice however hybrid and multistage systems, incorporating various levels of the features, occur frequently.

Types of solar concentrators

There are a number of methods by which the flux radiation on receivers can be increased. Some of them have been discussed here:

• Tracking Concentrators
• Non-tracking Concentrators 

   Tracking Concentrators classification: 

   Tracking Concentrators can be further classified as

• One-axis tracking concentrators (Follow the link for the description)
• Two-axes tracking concentrators (Follow the link and know about all types of two-axes tracking concentrators) 

    Concentrators with one axis tracking 

    These are used to achieve moderate concentration. A few of them have been described below.

i.    Fixed Mirror Solar Concentrator (FMSC)

ii.  Cylindrical Parabolic Concentrator

iii.  Linear Fresnel Lens/reflector
         (Follow the link of one axis tracking concentrator for getting the description of all three concentrators)

Concentrators with two-axes tracking 

           In order to achieve a high concentrators for high temperatures solar processes, concentrators with double curvatures are used. These requires two axes tracking of the sun. Some of these have been described below: 

i. Paraboloidal dish concentrators 

ii. Central Tower Receivers 

iii. Circular Fresnel Lens 

iv. Hemispherical bowl mirror

Non-tracking concentrators classification 

These are classified as follows: 

i. Flat Receiver with booster mirror 

ii. Tabor- Zeimer Circular Cylinder 

iii. Compound Parabolic Concentrator 

iv. V- tough  

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