Solar Thermal Power Plants - Point Focusing Systems Part 1
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00:00
Computer animationMeeting/InterviewLecture/Conference
Transcript: English(auto-generated)
00:12
Hello everybody and welcome back to the third chapter of the lecture on solar thermal power plants. The topic of today are point focusing technologies
00:22
like the one you can see here in the back. This is the largest test site in Germany for solar thermal technologies and it's located in Jülich. What are we going to do in this lecture? We will start with an introduction into point focusing systems.
00:42
We will then look in detail at MIROS, the so-called heliostats, and then at the different receiver technologies. Next, in subchapter 3.4, we will learn about power tower plants as a complete system. And finally, in the last chapter, I will briefly introduce other point focusing technologies.
01:06
In the last chapter, we got to know already the distinction between the different focusing systems. On the left side of this picture are the technologies which we have discussed in the chapter two, the linear focusing systems,
01:21
such as parabolic troughs and Fresnel collectors. In terms of point focusing systems, we will now learn about the so-called power tower and then briefly about the parabolic dish. In the literature, you will find various terms
01:40
for power tower plants. Besides power tower, they are also called solar tower plants or central receiver systems, which basically all describes the same type of technology. At the beginning, I would like to raise the question,
02:03
why do we want to use point focusing systems in the first place? Why we don't stick to the very, very successful parabolic trough technology? We learned in chapter one that the motivation for concentrating solar radiation is related to the fact that we can improve the efficiency through concentration.
02:24
This we have discussed by means of the corresponding equation. High concentration means low relative heat loss, which then leads to a higher efficiency of the solar system. If the efficiency is higher, then as a result,
02:42
we can also reach higher temperatures in the solar receiver and consequently in the power plant process. And from power plant processes, we know that they like high temperatures. If the upper temperature goes up, also the efficiency of the power cycle goes up. This can be described as we know by the Carnot efficiency.
03:04
Consequently, by increasing the concentration ratio, I can improve both the efficiency of the solar system and the efficiency of the power cycle. And this is a motivation to go up with the temperature and the concentration as high as possible,
03:23
which is the driver for developing point focusing technologies. The concept of the power tower is shown here in this general scheme. We got here the individual reflectors, the so-called heliostarts,
03:41
which are mounted on the ground. And these heliostarts then concentrate the solar radiation on the top of the tower that you can see here. On the top of this tower, the solar receiver is located. Each heliostart can be moved individually to track the sun.
04:01
The distance to the tower and the radial position of each heliostart is different, and also the position relative to the sun is different for each heliostart, and therefore it has to be controlled separately to follow the path of the sun. Since the heliostarts are concentrating the radiation
04:21
on a point target, they have to be moved on two axes. The mirrors are placed on the ground around the tower as can be seen here. In the receiver on the top, the heat transfer fluid is heated up and the heat is then transported to the bottom
04:43
where the power cycle is located. Also, the thermal storage is usually located on the ground. The power tower differs from the power bullet trough, particular by the fact that the concentrator and the receiver are completely separated from each other.
05:02
In terms of parabolic troughs, mirrors and receivers are mounted on one common frame and have to be moved as a whole to follow the sun. For the power tower, the mirror field is not connected to the receiver, and these components can be operated separately,
05:21
they can be exchanged individually, and they can be optimized individually. The schematic of a tower plan process is shown in this simplified cycle diagram. The scheme can be divided into four subsystems. On the left, we got the first subsystem, the array of heliostarts.
05:42
Secondly, we got the receiver here, then the third subsystem is the storage, and the fourth is the power plan process. We will discuss the individual subsystems in the following subchapters.