In order to guarantee grid stability and security of supply, additional generating plants (“special technical equipment pursuant to Section 11(3) EnWG”) are needed as part of the energy transition. EnBW has built such a grid stabilization plant at its power plant site in Marbach am Necker. The plant has been in operation since end of September 2024.
Grid stabilization plant
Project introduction
An important milestone for securing the electricity supply in Germany has been reached: On 30 September 2024, EnBW handed over the new grid stabilization plant on the Marbach power plant site to its client, the transmission system operator TransnetBW. This plant will keep the nationwide power grid stable in the event of any equipment failure. Its use is regulated by law and it may only be put into operation by TransnetBW on demand.
Due to Germany’s phasing out of nuclear power and the increased use of renewable energy sources, it is necessary to expand the German electricity grid. Not least because the electricity generated mainly in the north from renewable sources must also be transported to southern Germany. This grid expansion is only progressing slowly, which means that additional reserve capacity is needed to ensure grid stability.
The Federal Network Agency had therefore decided to have new generating plants built in southern Germany in addition to the existing power plant stock. These grid stabilization plants are only used if one or more plants within the power grid have already failed and there is a specific threat to grid stability. In such cases, the grid stabilization plants serve to ease the load on the power grids on a short-term basis.
The transmission system operators TransnetBW, Amprion and TenneT defined the capacity they each require and issued invitations to tender for the construction of suitable power plants within their control zones to cover this capacity. TransnetBW GmbH has issued an invitation to tender for a capacity of 300 megawatts (MW) for Baden-Württemberg.
EnBW had participated in this tendering process with its Marbach am Neckar power plant site. Having secured the contract in August 2019, a so-called open-cycle gas turbine was then installed there. The advantage of such turbines is their ability to supply a high level of electrical power within a relatively short space of time. Following the completion of the construction phase, the plant has now been in operation since end of September 2024.
Technology
The grid stabilization plant essentially consists of a gas turbine with filter house for air intake, a diffuser for drawing off the hot exhaust gases from the turbine into the separate chimney, a generator and the associated ancillary and auxiliary systems. Occupying a total area of around 14,000 square meters, the plant is located on the existing company site at Thomas-Alva-Edison-Ring.
- The compressor draws in air and compresses it.
- The oil-water emulsified fuel is injected into the combustion chamber and ignited.
- The hot combustion gases drive the turbine.
- The turbine drives the generator, with part of the energy used to compress the intake air.
The gas turbine is fired with light fuel oil. This will avoid any potential difficulties in obtaining the fuel supply to the greatest possible extent. That’s because the large oil storage facility on the power plant site (with a total capacity of approx. 70,000 m³) ensures that the fuel is available all year round. This is especially important in winter, because any threat to grid stability is most likely to occur during cold periods.
Specifications
The plant has been built as an open-cycle gas turbine powered by extra-light fuel oil (LFO). It has a thermal output of 940 MW and an electrical output of 300 MW.
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Operation mode
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Full load
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Max. thermal output
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940 MW
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Electrical efficiency
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>33 %
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Electrical output
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300 MW
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Max. operating hours at full load
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500 h/a
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Time to full load
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30 min
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Fuel
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Extra-light heating oil (standard)
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Heating value
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42,6 MJ/kg
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Mass flow rate of fuel
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79.449 kg/h
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"What is a grid stability system?" explained simply.
Approach
Project phases
This is where we inform you about important events and milestones relating to the planning and construction of the grid stabilization plant on the Marbach site. You will find the latest information here on the timetable for the planning and approval process as well as the progress of the construction work.
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End of September 2024
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Commercial operation of the grid stabilization plant
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Q4 2023
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Work starts on commissioning the grid stabilization plant
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July 2022
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Commissioning of demineralization plant
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April 2022
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Grid connection completed
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December 2021
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Approval change
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July 2020
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Approval granted and start of construction
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3rd quarter 2019
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Start of work on existing 110 kV plant at the site
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3rd quarter 2019
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Application submitted for approval in line with immission control regulations
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August 2019
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Contract awarded to EnBW upon completion of the tendering process
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December 2018
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Scoping meeting* for Stuttgart Regional Council
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29 November 2018
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Citizen information
Energy and technology park at Marbach power plant Reinhold-Würth-Straße 4 / Am alten Kraftwerk, first floor |
* In complex planning processes, a scoping meeting is held by the authority overseeing the process (in this case Stuttgart Regional Council). With the involvement of public agencies and specialist authorities, the meeting is used to formally determine the subject, scope and methodology of the regional impact and environmental impact studies as well as the content of the application documents that need to be drawn up.
Construction diary
September 2024
The plant achieves the desired output of 300 MW at 3000 rpm. After all tests and certification runs are completed, the power plant is placed into operation.
July 2024
The first fire of the turbine is carried out. The moisture in the sound absorbers evaporates due to the resulting heat and creates a cloud of steam.
May 2024
A spray cage test is carried out to test the extinguishing system on the transformer.
April 2024
First rotation of the gas turbine (view of the shaft between the generator (right) and gas turbine (left)).
March 2024
View of the nacelle; the red high-pressure pumps at the front, the enclosed gas turbine at the back.
February 2024
Activation of the control cabinets and step-by-step commissioning of the individual systems.
January 2024
Positioning of the repaired transformer on the foundation.
December 2023
Installation of the generator cable (connection between transformer and generator).
November 2023
Sound enclosure for the fuel pumps in the powerhouse.
October 2023
Overview of the construction site.
September 2023
Gas turbine insulated.
August 2023
Power plant roads asphalted.
July 2023
Ventilation systems installed.
June 2023
Insulation work is carried out on the completed outdoor pipework.
May 2023
The cables are installed and connected to the switchgear.
April 2023
The cable routes are built in the switchgear building.
March 2023
Installation of pipework and pipe skids – the heating oil pumps in the pump house can be seen here.
February 2023
All filter and silencer banks were installed for the air intake.
January 2023
Bringing in and installing the switchgear in the switchgear building.
December 2022
Construction of the pipeline bridge for the oil and cooling water pipes.
November 2022
Completion of the switchgear room interior..
October 2022
Preparation of the air filter plates for the air intake.
September 2022
The pipework in the pump house takes shape.
August 2022
At the start of August, the last of the eight segments were lifted into position on the 80-meter chimney.
July 2022
Installation of the ventilators on the heat exchanger.
June 2022
Chimney segments three, four and five are hoisted into position. All eight segments will be in position by August.
May 2022
At the heart of the power plant, the 300 MW gas turbine, the structural parts are attached.
April 2022
The chimney is made up of eight segments. These silencer units are installed in three segments in order to comply with the low noise immission limits.
March 2022
The concrete formwork helps the switchgear building to take shape. In the foreground is the 220 kV transformer, which is almost fully assembled.
February 2022
The second of eight chimney segments is lifted into position.
January 2022
Completion of the groundwater pumping rooms.
December 2021
Cladding the turbine hall facade.
November 2021
Construction of the plant technology in the water treatment plant is progressing according to plan. Pictured are the different filter lines in the plant used to produce the deionized water.
October 2021
Installing the diffuser, which is located between the gas turbine and the chimney.
September 2021
Works on the portal for the 220 kV connection.
August 2021
Construction work on the turbine hall continues with the gas turbine positioned inside.
July 2021
At the end of July, the three major components arrived by barge: gas turbine, generator and transformer Their journey began back in June on a container ship in Genoa. Traveling via Antwerp, the three large components ultimately continued along the Rhine and Neckar to Marbach on a barge. At the same time, work had been ongoing since mid-July to transform the parking lot of Marbach Technology Park into a temporary harbor to enable two large cranes to be set up. Here, by the quayside, they unloaded the heavy plant components: The generator weighs 378 metric tons, the turbine 317 tons and the machine transformer 270 tons. On the power plant construction site, they were positioned and installed on their respective foundations using special lifting and moving equipment.
June 2021
The gas turbine was loaded onto the ship in Genoa. It is due to arrive in Marbach in July.
May 2021
Concrete formwork for the gas turbine foundations.
April 2021
The 10-meter-long rotor on the 300 MW gas turbine weighing 85 metric tons was subjected to a so-called “balancing run” and “overspeed test” and passed with flying colors. The first rows of blades on the turbine must be capable of withstanding a temperature of over 1000°C at 3000 revolutions per minute during operation.
March 2021
A bird’s eye view reveals the water treatment plant building in the bottom left-hand corner of the picture. In the middle of the picture are the reinforcements and foundations for the power plant’s various buildings, with the large gas turbine foundation in the center.
February 2021
The concrete formwork for the walls is now added to the finished floor slab of the water treatment plant. All against the backdrop of a yellowy Sahara dust sky.
January 2021
The floor slabs for the water treatment plant are completed.
December 2020
Following soil improvement measures on the construction site, the granular subbase is now laid. The foundations are then built.
November 2020
The floor slabs for the water treatment plant are made.
October 2020
Construction work officially began on 12 October 2020 with the symbolic groundbreaking ceremony attended by (from left) Dirk Güsewell, Head of Generation/Portfolio Development at EnBW, Jan Trost, Mayor of Marbach, Hans-Josef Zimmer, EnBW Chief Technology Officer, Franz Untersteller, Minister for the Environment, and Werner Götz, TransnetBW Managing Director.
September 2020
As part of soil improvement measures, a total of around 1,800 gravel and concrete columns are now placed in the subsoil in order to increase the load-bearing capacity in the area of the gas turbine plant and in the area of the demineralization plant.
August 2020
The topsoil is removed from the construction site and the assembly and storage area is graveled.
July 2020
16 July 2020: The Regional Council grants approval in line with the Federal Immission Control Act for the Marbach 4 grid stabilization plant, marking a very important milestone – and even one month ahead of schedule. The approval process took eleven months from the initial application submission date. A decision on the application was made about five months after the application was completed, one month sooner than the statutory period of six months. At the same time, the EnBW container village was installed on the construction site – enabling construction work to begin.
June 2020
The quantity and quality of the well water for the water treatment plant are tested in a large-scale pumping test. Impurities and dirt particles are filtered in the settling tank
May 2020
Work on the power supply for the construction site is completed in May. The 10 kV cable for supplying power to the later water treatment plant has also been laid.
April 2020
The construction disclosure process and subsequent one-month objection period ends on 20 April with no objections.
March 2020
The application for project approval is open to public consultation until 20 March 2020 at Stuttgart Regional Council and the planning office for the town of Marbach am Neckar. Anyone with a legitimate interest may officially participate in the consultation and make suggestions, raise concerns, etc. In addition, we invite you to get in touch directly with the project team. You can do this by sending an email to netzstabilitaetsanlage@enbw.com.
February 2020
Initial work is carried out on the construction site where the new grid stabilization plant is set to be built. The building ground is analyzed, for example, in order to be able to definitively determine the position of the power plant’s foundations. In addition, the site must be examined for possible ordnance because it was shelled with grenades in the Second World War (pictured: excavation of a suspected explosive ordnance case with nothing found).
Frequently asked questions
The power grid can only be stably operated if the energy generated corresponds to the energy consumed at any given moment. A change in consumption must be instantly balanced on the generation side, which is why power plants have balancing reserves and quickly controllable power plants can balance this change in consumption at short notice.
Fluctuating generation from renewable energy sources (such as photovoltaics or wind power) must also be balanced by conventional power plants, nuclear power plants or pumped-storage power plants.
Even if certain equipment (i.e., a system such as a switch, a power line or a transformer) fails, the power grid can still be operated in a stable manner. This is known as (n-1) security. The remaining lines/systems then take on the task of transmitting the electricity. The circuits are usually not overloaded, meaning that the failure is safely controlled – as long as no further equipment fails during this phase. That is why so-called (n-1) security must be restored as soon as possible. This is achieved by easing the load on the power grid locally through generation capacity that can be activated quickly.
In the past, power grids were rarely operated at the limits of (n-1) security because the transmission distances were significantly shorter than they are today due to power being generated close to where it was consumed. Even after the failure of equipment, (n-1) security was often still guaranteed – helped by the grid’s normally unused overload capacity in those days. Today, the grids are increasingly being operated at their technical limits. As a result, the number of interventions required to ease the pressure on the grid has increased significantly in recent years.
The situation on the generation side will change significantly in the future due to the following factors:
- The phaseout of nuclear power
- Further expansion of renewable energy capacity increasingly leading to a generation surplus in northern Germany, which has to be redirected toward southern Germany
- Delayed grid expansion of high-voltage lines between northern and southern Germany
These factors are having a particularly serious impact in southern Germany. Additional generation plants are therefore needed to guarantee grid stability and security of supply. However, these will not be used to compensate for the lost capacity previously provided by nuclear power plants, but will only be used for a relatively brief length of time to support the power grids in the event of problems in the transmission grid if equipment fails (see also question 2).
The capacity of conventional generation plants and pumped-storage plants has been factored into the calculations for new grid stabilization plants when determining the power needed. In an analysis, the Federal Network Agency concluded that an additional 1,200 megawatts (MW) of rapidly accessible generation capacity are needed in southern Germany to guarantee security of supply in the event of a fault in the grid.
The current reserve power plants are used to balance any power deficiency in the power grid and support grid stability as a preventive measure, even if no equipment within the power grid has failed and the grid remains stable.
The new grid stabilization plants, meanwhile, will only be used if one or more system elements (such as a switch, a power line or a transformer) have actually failed within the transmission grid, placing the power grid in a critical condition. Grid stability will then be restored with the help of these new plants. The grid stabilization plants are also available much more quickly than the existing grid reserve, which is usually made up of older plants.
The grid stabilization plant will only be started up in the event of an equipment failure within the transmission grid. In most cases, they are used secondarily to all existing power plants. As such, in our view, a very small number of operating hours can be expected.
However, the operator (in the event of being awarded the contract in the tendering process: EnBW) has no influence on the plant’s use and operating life. This is the responsibility of the transmission system operators, who decide entirely independently how the grid stabilization plant is used.
The operative word “gas” describes the medium that drives the turbine. Steam drives a steam turbine and wind drives a wind turbine. A gas turbine, meanwhile, is driven by hot combustion gas, which is why it is known as a “gas turbine” – regardless of which fuel is used to produce the hot combustion gas.
No, the gas turbine is built as a new block at the Marbach site and will not replace any of the existing plants.
Back in 2013, EnBW applied for the final decommissioning of all generation plants in Marbach. Since the plants have been classified as having system relevance by the transmission system operator since 2013 (most recently in 2018), they have been subject to a decommissioning ban ever since and are started up at the request of the transmission system operator.
The operating license for some of the existing plants (MAR II gas turbine and MAR III boiler and steam turbine) expires at the end of 2023, so we must assume that these plants will be decommissioned at the end of 2023.
The plant will be kept available for a period of ten years.
The emissions and in particular the gas turbine’s impact on the environment have been examined as part of the immission control approval process. Approval will only be granted if operating the gas turbine has no significant impact.
In our view, light fuel oil is more suitable as a fuel than natural gas in Baden-Württemberg. This will avoid any short-term supply bottlenecks, which could occur if natural gas were used. Furthermore, security of supply in southern Germany should not depend on a single primary energy source like natural gas. In conjunction with the large (already existing) oil storage facility in Marbach, we consider light fuel oil to be the ideal fuel for this purpose.
Since the grid stabilization plant is not expected to be used very often, the fuel will have no significant impact on the environment. Gas turbines that run on fuel oil are also subject to much lower emission limits today than they were around 20 years ago.
This will be examined and evaluated in the course of the approval process. We currently do not expect there to be any significant impact on water resources.
Oil will still be supplied by ship via the Neckar. Due to the low number of expected operating hours, we do not currently expect any significant increase in activity.
- During operations:
The impact of the gas turbine power plant on surrounding areas will be examined and evaluated in detail as part of the approval process. Approval will only be granted in accordance with regulations governing emissions if the gas turbine can be operated within the permissible limits.