Solar Thermal Power Plants - Point Focusing Systems Part 5
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00:00
Computer animationLecture/ConferenceMeeting/InterviewProgram flowchart
Transcript: English(auto-generated)
00:12
Hello and welcome to our virtual tour to an existing solar thermal power plant. We are here at a very exciting place. We are at the solar thermal experimental power plant in Jülich.
00:26
This plant here is not a commercial power plant, but serves as a research and demonstration platform, operated by the German Aerospace Center DLR. New innovative components and processes for solar power plants are tested and qualified here.
00:44
As you can see here in the background, the solar power plant consists out of two towers. This is quite unusual. Commercial tower plants only have one tower, but this is different here at this research facility.
01:01
The first tower here on the right was built already in 2009. It is about 60 meters tall and contains a volumetric solar receiver at the top. We have already learned about this concept in our class. It uses the concentrated solar radiation to heat up air up to 700 degrees C.
01:24
The hot air is then provided to a water steam cycle and to a ceramic heat storage inside the tower. The ceramic storage can store heat from the volumetric air receiver temporarily and releases it at a later point when needed.
01:41
The turbine in the water steam cycle provides electricity at a rated electrical output of 1.5 megawatts. We have also learned in class that there are several other concepts of towers on the market and under development. Besides the working fluid air, which is used here in Jülich, there are
02:02
also tower concepts using water, particles or molten salt as heat transfer media. In honor to develop such alternatives, the second tower here on the right was built recently in 2020. It is called the Multifocus Tower because the tower contains three test chambers that are used to conduct different experiments.
02:26
Let us now take a closer look at the individual components of this facility and let's first head towards the Heliostat field. Here we are in the middle of the Heliostat field. All together the field consists of more than 2000 individual Heliostats.
02:43
The geographic location of the field is approximately at the 51st latitude north and the field therefore has a northern orientation. Each Heliostat has a two-axis drive that allows the flexible positioning of the reflector to track the sun.
03:02
The drives are the two hydraulic cylinders, which you can see here. That allows the Heliostat to move into two directions, the solar athemos and the solar elevation. During regular operation, each reflector is tracked so that the sun rays are always reflected onto our target on the top of the tower.
03:27
As we discussed in class, each Heliostat has a different distance and radial position towards the tower and therefore needs to be tracked individually. If we have a closer look at the mirrors, we see that a single Heliostat consists of four individual mirror segments.
03:44
The segmentation of the mirror surface into individual elements has two reasons. On the one hand, this is production related because most production lines are limited in size. On the other hand, this is related to the quality of the focus. The shape and position of the focal point on the target of the tower can
04:04
be optimized by a slightly different alignment of the mirror segments, the so-called canting. The mirror segments are connected to the steel structure with strong adhesive pads. This ensures precise and low stress attachment of the mirrors to the steel structure.
04:22
The size of the Heliostat in the solar field is about 8 square meters. Compared to commercial Heliostats, this represents a rather small reflective surface area. We have learned that commercial Heliostats can reach sizes of 100 square meters and more.
04:40
Usually, the investment costs decrease with a larger surface area per Heliostat. But on the other hand, small Heliostats have the advantage of a higher structural rigidity, lower sensitivity to wind forces, and therefore it is easier to achieve a high accuracy. This solar field here consists of more than 2000 of such Heliostats and they have all one goal.
05:05
To concentrate the solar radiation onto the receiver. Below the volumetric air receiver, there is a white area which is used for the calibration of individual Heliostats. If Heliostats are not aligned perfectly, the reflected radiation will fail the receiver.
05:24
This we call the spillage losses. Even small angular deviations lead to a considerable shift of the aim point on the solar receiver. For example, an angular deviation of 1 milliwatt of a Heliostat located 1 kilometer away from the solar tower already leads to a shift of the aiming point by 2 meters.
05:45
This is why the Heliostat's aiming points must be checked regularly and corrected if necessary. For calibration, individual Heliostats are moved out of the focus and their reflection is directed onto the white test surface.
06:00
By measuring the exact position of the reflected light spot on this test surface, the actual position can be compared to the desired target position and the Heliostat can be corrected if necessary. Then we can see a third window that is located directly below the calibration target. This is the test chamber.
06:23
The test chamber is designed to easily accommodate experimental setups. During experiments, the setup receives concentrated solar radiation from the Heliostat field. Various components can be tested here with concentrated solar radiation. For this purpose, the aim point of the Heliostat field or of a selection of Heliostats is directed to the experimental setup instead of the receiver.
06:51
So this one test chamber is relatively small and allows only limited testing. To extend the test capabilities, a second tower was erected, the so-called Multi Focus Tower.
07:04
It contains three more test chambers. With a total of four test chambers, it is now possible to set up and conduct more experiments in the same period of time. This is important because the test periods over the year are usually limited to the number of days with good solar irradiation.
07:23
In addition, the infrastructure of the individual test chambers is designed to flexibly integrate specific test components at existing interfaces. For example, the top chamber is specifically designed for the test of particle receivers while the middle chamber
07:40
is suited to test components with high temperature solar thermal processes such as the production of synthetic fuels. And the third one is specifically designed for molten salt experiments. After the look from outside, I would like now to head inside the solar tower and to show you some of the main components including the power block and the receiver.
08:04
Let's now go and have a look together. Let's now go inside.
08:29
We are now here at the top of the tower where the receiver is located. We are at a height of 52.10 meters and will now go inside the receiver room.
08:42
We are now here in the receiver room and I'm standing directly behind the receiver. The receiver cannot be seen from here, can only be seen from outside as the absorber caps are facing the outside towards the solar field.
09:00
What we can see from here, however, are the large air ducts which collect the hot air from the receiver and feed it into the ceramic storage and to the evaporator of the water steam cycle which are installed on the level further below this level. The huge blue ducts here are the hot air pipes.
09:22
You might have expected to see insulated pipes here, but the approach is different here. The pipes are thermally insulated from the inside so that the outside stays relatively cool. The smaller insulated grey pipes here are the cold air pipes where the air is fed back after it has been cooled down in the power cycle.
09:47
Cool in this case means about 200 degrees C. As mentioned before, they use a volumetric air receiver here at this plant. It consists out of individual ceramic absorber caps like the one we got here.
10:03
Each element has an internal hollow structure with numerous air channels. Due to the high absorption coefficient as well as the porous structure with internal air channels, the absorber caps act as a radiation trap and effectively convert solar radiation into thermal energy.
10:24
The thermal energy is transferred from the ceramic absorber caps to the incoming ambient air which is heated up and then fed into the cycle via these blue air ducts. We are now here one level below the receiver area on the level of the steam generator.
10:47
The steam generator which you can see behind me is a standard heat recovery boiler where preheater, steam generator and super heater are integrated in one large vessel. In the vessel, many pipes are immersed into the water through which the hot air passes.
11:04
In the boiler, steam is generated at 485 degrees C at 27 bar. Technically, higher parameters are possible but in this installation these are limited by the design of the steam turbine. On the level below us which you cannot see very well from here is the thermal energy storage.
11:26
The storage consists out of four chambers that can be operated individually. The chambers are filled with such ceramic bricks. The bricks have an internal hollow channel structure and during charging,
11:42
hot air is passing through these channels and heat up these stones. The storage is then discharged by sending cold air through the ceramic bricks from the other side and then the heat is transferred back again from the hot bricks to the cold air. The capacity of the storage is enough to operate the turbine for another 1.5 hours at nominal load.
12:08
And here we are in the machine room where the turbine is located. This is the lowest level of the tower. The turbine coming from Siemens has a capacity of 1.5 MW.
12:23
It is fed with the steam coming here from the pipes above and the steam enters the turbine here from the side. And there the steam is expanded and the energy of the steam is converted into rotational energy.
12:41
Due to the small size of the turbine, this turbine does not have any reheat or steam extraction. Connected to the turbine is the generator, the blue system behind. And in the generator, the rotational energy is converted into electricity.
13:06
We now have seen all main components of the plant inside the tower. And next we will take a look at the control room from where the power plant is monitored and controlled. We are now in the control room of the solar tower plant.
13:22
And we are here together with Mr. Felix Goering from the German Aerospace Center. Hello Mr. Goering. Mr. Goering, please tell us what we can see here in the control room. This is the control room of the solar tower and therefore we have all the control systems we need for operating the power plant.
13:43
And this means beginning here on the left side we have the control system of our heliostat field. Here the heliostat operator controls the heliostat field. This means he can choose which heliostats he for example wants to focus at a special target.
14:01
This is controlled here. This control system here was developed in DLR. This means that we have the full control about the development process. For example, if we have new receiver systems, new systems here that we test, then we can implement new functionalities for the whole control system.
14:25
It's a very complex matter and we can integrate a lot of optimization into this system and test many things for the heliostat control. Then the next system here is an infrared camera which monitors the temperature of the surface of the receiver,
14:49
of the main receiver of the solar power plant. Right now you can't see anything as we are not operating the power plant, but during operation you see the surface temperatures and if there is an overheating,
15:02
even if it's only a small overheated spot, then the power plant is shut down. Then the next system here is, let's say, a regular wind CC. It's for the basic part more or less of the power plant.
15:20
It's the control system for the air cycle, for the water steam cycle, for the feed water, for example, and the turbine. So this means the more or less conventional parts. Then the next monitor shows the heat storage and gives us insight into our heat storage,
15:41
which is here a packed bed storage which is loaded with the hot air from the receiver and can be discharged of course for heating the water steam cycle. Then another system which you can see here on the right side is our material station. Of course it's very important for operating a solar power plant to know if the sun is shining
16:04
and how strong it is shining. This we see here, of course we see the normal ambient temperature too, but the main interesting thing here is the DNI, the direct normal irradiation. Very interesting Mr. Goering, this looks really complex here.
16:20
Can you explain a little bit what your daily routine looks like? Yeah, actually there is no daily routine as we are not operating the power plant on a commercial base and it's not our purpose to produce electricity. Our purpose is research and research normally has no routine. But if we are operating the power plant or test systems,
16:43
normally it looks like that we have let's say two meetings each week where we discuss with all the corresponding projects, which need power from the heliostat field, who is ready. And then we know, okay, who is ready the next days.
17:01
We know the weather forecast, it's difficult actually in Germany with a weather forecast to really have reliable information about the sunshine during the next days. And then the heliostat operator of course starts up the heliostat field, brings all the heliostats to a standby position, starts focusing with for example
17:22
100, 200 heliostats to heat the system up. And the second engineer looks for the operation of the normal power plant, that everything is fine. And then we heat up the receiver, we go up to the desired temperatures for the power plant, for example up to temperatures of 680 degrees.
17:42
And then depending on the state of the power plant and the weather, the operation can be quite different from day to day. Maybe during mid of the day we have enough power from the heliostat field
18:00
to put a part of the energy into the heat storage and at the same time heat up the water steam cycle. Then if we have the right steam conditions, we can start up the turbine. And then during the afternoon we can use a part of the energy which we put into the heat storage to let the water steam cycle run a little bit longer
18:23
than it would just be possible without the heat storage. That's how a daily work here with a solar power plant can look like. Talking about heliostats, you have a lot of mirrors out there.
18:40
Do you have any issues with soiling? Do you have to clean the mirrors? Yeah, actually of course we have soiling, no question, but it's not a real problem as we are not producing electricity commercially. The thing is if we for example run a test and we think we need 1000 heliostats
19:02
and then we see during operation R the mirrors are soiled or soiled a little bit too much, then we just use 50 heliostats more. More or less it works like this. So we don't really have a problem here at the research power plant with soiling. But anyway, let's say we clean the mirrors, let's say one time a year,
19:23
but it's manual work. It's the same process like cleaning windows. We use demineralized water from our power plant. That's one thing, but then it's manual work. And a very special thing about Jülich is that if in the winter snow,
19:42
snow is falling and we have let's say 5 cm snow, then we let the snow fall on the horizontal mirrors and then we move the mirrors and the snow cleans the mirrors almost perfectly. But of course this is not applicable in summer. Okay, that's interesting to learn that snow is a very good cleaning measure
20:03
for heliostats and for solar mirrors. Interesting. So another thing we have observed out there is that we have seen on the ground a lot of grass. How do you deal with the grass? Because grass is growing and there's not much room that
20:21
more machines can pass through the mirrors. Yeah, that's right. We have two measures to deal with it. We have one thing is let's say one time a year, we have sheep here, but anyway that's not enough sometimes.
20:41
And then one time during late spring and one time in autumn, normally we cut the grass, but it's manual work. Like you said, it's very difficult with machines. So people are running through the field with motorized cutters
21:01
and they cut the grass. Okay, so sheep and humans have to work together? Yes, that's right. Not at the same time, but during the year. One last question, Mr. Goering. What do you most like about your job? It's not one special thing, but I like most the variety of tasks
21:23
which are necessary to do the research here, to run the power plant, to work with colleagues and with external staff because we have many partners. And so there are a lot of different tasks, technical tasks,
21:41
organizational tasks and of course communication with different people, very different people. Thank you very much, Mr. Goering. These were very interesting insights into your daily work at this solar power plant. Thank you, Mr. Goering. Thank you, too. We are now here at the last station of our tour.
22:03
We are at the cooling system. The cooling system is a dry cooler and it belongs to the water steam cycle. The water vapor is cooled and condensed here in this cooling system after the expansion in the turbine.
22:20
The liquid water is then fed back into the evaporator. From large conventional power plants, you may be more familiar with large cooling towers with rising steam clouds, also called condensation cooling towers. The advantage of dry cooling is that no cooling water is required and lost to the atmosphere through evaporation.
22:42
However, there are some disadvantages. A disadvantage of dry cooling is that the specific cooling power required is usually higher compared to condensation cooling towers and also the cooling temperature is a little higher which affects the efficiency of the steam cycle.
23:03
We are now at the end of our tour to the solar power plant in Jülich. I hope you gained some interesting insights into solar concentrating technologies. Many thanks to the German Aerospace Center for letting us shoot here today and also many thanks to Mr. Goering for giving us some insights into his daily work.
23:27
I hope you have enjoyed the video. Thank you and goodbye.