Parabolic trough collector

Among the applications of concentrating solar power, one of the most important is the parabolic trough collector. Below, we will tell you about the characteristics and operation of this type of technology.

A parabolic trough collector is a type of solar concentrator that concentrates the sun's radiation on a receiver that passes through the system, formed by tubes. The purpose of this is to heat the fluid inside and use that energy to transform it into electricity or another application that uses heat.

How does this type of solar collector work?

The principle of operation is based on the parabolic shape of the collectors, since they have a focal point where the rays are directed in a concentrated way. Therefore, by reflecting these rays towards the receiver with the capacity to absorb heat, thermal energy is obtained that will be transformed later.

This receiver is a system of pipes that pass through the system. A heat transfer fluid circulates through these pipes, which will be used to generate electricity.

Solar concentration through the collectors

In order for the energy from the sun to be concentrated, the parabolic collectors must have a special shape. This is the surface of a part of the parabola.

Thus, the energy can be concentrated at a point, known as the focal point. This point depends on the shape and constitution of the collector. Mainly, what defines this is the aperture of the parabola (or width between the ends of the collector), the angle and the length.

Parabolic solar concentrator material

What you are looking for in the material that makes up the collector is that it has reflective properties. That is to say, that it reflects the incident sunlight appropriately. Mainly silver-plated glass is used, because it fulfills these properties perfectly. In addition, it includes other copper layers and protective materials in lower layers.

The main drawback is the high cost of this material, so other alternatives that are cheaper and have similar properties are currently being sought.

Solar tracking of parabolic trough collectors

To achieve acceptable efficiency, it is necessary to track the sun throughout the day. For this purpose, a structure supporting the mirrors with a motor capable of performing solar tracking is available.

In this case, one axis is tracked, taking as a reference of rotation the straight line passing through the vertex of the parabola. The sun can be tracked by calculating the position of the sun and a control system that tells the motor when and to which side to move.

Receiver and heat transfer fluid of the system

The receiver is responsible for transforming the concentrated radiation into heat. It is also the element that transports the fluid inside the receiver to the power block, where the steam needed to generate electricity is generated. To carry out its work efficiently, it must have special properties so as not to lose heat and have the capacity to absorb it.

On the other hand, the fluid inside it must also have these properties, in addition to the following:

- It must be a liquid so that it can absorb heat and be transported.

- Its boiling point must be high, so that it does not turn into a gas.

- Low freezing point, so that it does not turn into a solid.

- Thermally stable, so that it does not suffer damage at high temperatures.

- Low viscosity, so that its transport is more efficient and hydraulic pumps work less.

- Low risk of ignition or explosion, so that operation is safe.

Examples of this fluid could be synthetic oils, salts or liquid sodium. Another way would be to directly evaporate the water, saving the subsequent transformation process. This method has many advantages due to the savings in components, although it is more complex in the control of the system and is currently under development or used in low-power installations.

Energy transformation in parabolic trough collectors

Once the thermal energy is available in the fluid, which is heated throughout the piping system, it is circulated to a heat exchanger. This heat exchanger is able to generate water vapor due to the energy supplied.

The steam will now be used to transport it to a turbine coupled to a generator, so that electricity can be obtained.

In addition, a cooling tower is available to return the water to the liquid state and thus start a new cycle.

Auxiliary Storage System

Additionally, a storage system can be incorporated so that in case there is not enough radiation, energy can continue to be generated. This is done by storing the heat for a certain period of time, although it is a system that is not very efficient.

Parabolic trough collector tracking system

To maximize the efficiency of the system, the collectors incorporate a solar tracking system. Typically, a single-axis system is used because it has been shown to be more efficient than a dual-axis system.