Solar Thermal Power Plants - Point Focusing Systems Part 4
This is a modal window.
The media could not be loaded, either because the server or network failed or because the format is not supported.
Formal Metadata
| Title |
| |
| Subtitle |
| |
| Title of Series | ||
| Part Number | 4 | |
| Number of Parts | 7 | |
| Author | ||
| License | CC Attribution - ShareAlike 4.0 International: You are free to use, adapt and copy, distribute and transmit the work or content in adapted or unchanged form for any legal purpose as long as the work is attributed to the author in the manner specified by the author or licensor and the work or content is shared also in adapted form only under the conditions of this | |
| Identifiers | 10.5446/65437 (DOI) | |
| Publisher | ||
| Release Date | ||
| Language |
Content Metadata
| Subject Area | |||||
| Genre | |||||
| Abstract |
| ||||
| Keywords |
|
00:00
Computer animationDiagramLecture/Conference
Transcript: English(auto-generated)
00:11
Hello, and welcome back to the fourth subject. In this video, we will now look at complete power tower concepts.
00:20
Here we see again an overall schematic of such a power tower plant. We have already taken a closer look at the heliostat field and at the receiver. And we have also dealt with the efficiency determination of these two subsystems. The power block, which is connected at the end of the conversion process,
00:42
is again a relatively conventional power block. Generally, a storage unit can also be integrated, which type of storage depends on the heat transfer medium used. And I will present different technologies within this chapter. For calculating the total efficiency of the plant,
01:03
the efficiencies of the single subsystems have to be multiplied with each other. On the subject of combining the individual efficiencies, I would like to briefly discuss an opposing effect with respect to temperatures we want to achieve. As we have already learned, the efficiency of a collector
01:23
decreases with increasing temperature. The temperatures can be raised until the heat losses are as high as the heat gains. The efficiency is then zero, and the temperatures cannot be increased anymore. If I still need higher temperatures,
01:41
then I have to switch to another technology with higher concentration ratios, for example, from trough to tower. But if I'm here on a curve of a single technology, for instance, here for a solar tower, then high temperatures always means higher losses
02:01
and a lower receiver efficiency. On the other hand, I would like to increase the temperatures because this increases my power plant efficiency. I can express this via the Carnot efficiency. The Carnot efficiency versus temperature is shown in the next graph.
02:22
Here we see the two opposing trends. The Carnot efficiency increases with temperature. The receiver efficiency decreases. So is a higher temperature now good or bad? I can find the answer to this question if I multiply both efficiencies,
02:41
and the result of this product is shown in the next graph. Here we see the interesting result that the total efficiency has a maximum for each case. Thus, for each technology, there is an optimum temperature, and from then on, it makes no sense to increase the temperature any further.
03:03
It should be noted that these curves are, of course, idealized curves. On the one hand, an ideal black body was assumed for the receiver, and on the other hand, the Carnot efficiency was taken for the power plant efficiency. But nevertheless, the diagram gives a good orientation.
03:23
It shows, for example, that the tower technology has a better overall efficiency than the graph already starting from temperatures of approximately 600 K. The maximum for the tower is about 1,100 K or about 800 degrees C.
03:43
As the following examples will show, none of the current technologies reaches such high temperatures yet. In the following, I will present you some examples of realized tower plant concepts. Let's start with the only plant that is located in Germany, the research power plant in Ullich.
04:04
This plant works with a volumetric air receiver with 18,000 square meters of mirror surface. This solar field is rather small. Air temperatures of 680 degrees C are reached in the receiver. This drives a steam turbine with an electrical output of 1.5 megawatt.
04:24
A thermal storage is also integrated in the system. The storage is composed out of ceramic honeycomb elements like the one I got here. Similar to the receiver, the air flows through the little channels here. During loading, when the air is hot
04:41
and the stone is cold, the heat is transferred to the stone and stored here. During discharging, it is the other way around. Cold air then flows through the hot bricks from the other side and heats up while the bricks are cooling down. The storage here is dimensioned
05:01
to run the turbine for one hour for load. The Ullich facility is not a commercial plant and is for demonstration and research purposes only. In the meantime, a second tower has been built on this site where other receiver technologies can be developed and tested. Next, we see a schematic of a power tower plant
05:22
using salt as the heat transfer fluid. Due to the selected salt mixture, the upper process temperature is limited to about 565 degrees C, but this is, of course, already well above the temperature of a parabolic trough. The big advantage here is that salt is a relatively easy fluid to pump up and down the tower
05:43
and that the widely used two-tank storage concept can also be integrated here. Next, we see a photo and the data of the world's first commercial tower plant using this technology. It's named Hema Solar and is located in Spain.
06:01
The solar field here is about 300,000 square meters and the tower has a height of 140 meter. The receiver is an external tube receiver. The electrical output of the system is 90 megawatts. The salt storage is dimensioned in order to run the turbine for another 15 hours at full load.
06:20
This allows 24 hours operation, at least on sunny days. The plant went into operation in 2011 and has been feeding electricity into the public grid ever since. In the meantime, towers in the 100 megawatt range are also being built. Here, you see the NOR3 plant in Morocco,
06:43
which has an electrical output of 150 megawatts. Of course, the storage system is also integrated here. The storage capacity is seven full load hours in this plant. As a third widespread concept, I would like to present the concept
07:01
with direct steam generation. Here, water is used as heat transfer medium and the water is pumped into the tube receiver where it is evaporated and superheated. The superheated steam can then be fed directly to a steam turbine, therefore the name, diode steam generation.
07:22
This concept saves one cycle compared to the previous concepts. However, the disadvantage here is that there is no large-scale storage technology available for superheated steam and only small buffer storage units can be used.
07:40
Here, you see a photo of such a plant also located in Spain. Two plants of this type have been built at this site, one with the capacity of 11 megawatt and the other with the capacity of 22 megawatts. And here we got the largest plant and the largest complex of plants built with this principle.
08:01
These plants are located in Ivanpah, California. There are three plants with a capacity of about 113 megawatt each. In the external tube receiver, superheated steam is generated at 160 bar and 538 degrees C, which is then fed directly to the turbine.
08:22
The plant does not have any storage. The plant covers an area of 14.2 square kilometers. On this picture, you can see what a gigantic size these three plants have. But if you look at the whole plant from a great height,
08:42
the installation does not take up so much room and there is still a lot of unused space around them. I think these photos have demonstrated how impressive this technology is and that it is quite widespread all over the world. Finally, I would like to make some additional remarks
09:03
about such large scale projects. Whenever such plants are built on an untouched desert, this of course always represents an intervention in nature, which has to be carefully evaluated. For this reason, biological reports on the flora
09:21
and fauna as well as archeological studies have to be prepared at an early stage before a decision on the project is made. In California, for example, where the Ivanpah facilities are located, the desert tortoise presents a particular challenge. The desert tortoise is a protected species
09:41
because it is threatened by extinction. Therefore, before construction begins, the area must be surveyed to determine if a large population of tortoise is living there. If there is a large population, a building permit will usually not be issued. If the population is small, it must be relocated.
10:03
Of course, this is not allowed to happen during the breeding season. After relocation, a protective fence is erected around the area, such as the one shown in this picture here. This should keep the tortoises out of the construction site.
10:22
And of course, there are always people in opposing position when it comes to large scale projects. Even if everything is coordinated with the authorities and the affected communities, there's always a small group of people who are against the project and who protests against it.
10:43
Therefore, you have to try to involve as many interest groups as possible at an early stage of the project. You must also have to deal with this kind of situations even as an engineer, when you are involved in large scale projects.
11:01
And with this stunning photo of the Noor 3 plant in Morocco, I would like to close this chapter on solar tower power plants.