Altbach/Deizisau combined heat and power plant generates reliable and cost-effective energy for the mid-Neckar region. Industrial pioneer Heinrich Mayer built the first coal power plant – known as the “Kraftcentrale” – on the site in 1899. Today, three gas turbine plants and two hard coal-fired blocks produce electricity and district heating in combined heat and power mode. Combined heat and power plant 1 has been part of the grid reserve since 2017 and guarantees grid stability. Combined heat and power plant 2 has been in operation since 1997. EnBW has set itself the goal of phasing out coal-fired power generation before the legally mandated phase-out, provided regulatory and economic conditions allow for it. As part of this strategy, the site will be converted to run on hydrogen in the future (known as a fuel switch): A new combined cycle gas turbine plant will initially be operated using natural gas to generate electricity and district heating and can be converted to run on hydrogen as a fuel at a later date.
We offer free guided tours of Altbach/Deizisau combined heat and power plant all year round – with expert information provided by our employees.
Fuel Switch
Project introduction
EnBW is consistently continuing the decarbonization of its generation portfolio with the expansion of renewable energies. Due to legal requirements, all coal power plants in Germany must also be shut down by no later than 2038, including the plant in Altbach/Deizisau. The most important consideration in the region, however, is guaranteeing security of supply for electricity and district heating, which is why EnBW is building a controllable, hydrogen-ready combined cycle gas turbine (CCGT) plant at the site:
- The new, gas-fired plant has an electrical output of 665 megawatts (MW) and a thermal output of around 180 MW.
- In addition, a hot water boiler system with three boilers and a thermal output of around 120 MW will secure the district heating supply in the mid-Neckar region.
- This fuel switch to natural gas can reduce greenhouse gas emissions by more than half compared to coal-fired power generation.
As soon as hydrogen is available in sufficient quantities and the supply infrastructure has been converted accordingly, the power plant can operate on hydrogen, which would allow for an even greater reduction in CO₂ emissions from electricity and district heating generation compared to coal-fired power generation. That’s because, like the plant itself, the natural gas pipeline that supplies the CCGT is hydrogen-ready, which means that the switch to hydrogen can be made at a later date with no major hurdles. Find out more about the fuel switch here.
Technology
A combined cycle gas turbine (CCGT) plant marries the principles of a gas turbine and a steam power plant:
- A gas-fired turbine produces electricity via a generator. The very hot exhaust gases from the gas turbine are then channeled through a waste heat boiler.
- The resulting steam is used to power another turbine. This steam turbine also drives a generator to produce electricity.
- By combining both principles, the energy from gas combustion is used twice, increasing the efficiency level to as high as 60 percent.
The district heating produced in the course of electricity generation is fed into the „Mittlere Neckarschiene“ district heating network, which is also connected to the Stuttgart-Gaisburg combined heat and power plant and the Stuttgart-Münster waste-to-energy plant. It is used to supply many industrial companies, private households and public buildings in Altbach, Deizisau, Esslingen, Plochingen and Stuttgart.
Approach
Project phases
This is where we inform you about important events and milestones relating to the planning and construction of a combined cycle gas turbine (CCGT) plant on the Altbach/Deizisau 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.
|
Provisionally Q2 2027
|
Commercial commissioning
|
|
2026/2027
|
Start-up phase
|
|
2025/2026
|
Main construction activities
|
|
November 2024
|
Start of plant construction work
|
|
August 2024
|
Start of delivery of major components
|
|
March 2024
|
Start of shell construction work
|
|
January 2024
|
Receipt of the 1st partial permit
|
|
6 November 2023
|
Official groundbreaking ceremony
|
|
11 October 2023
|
Stuttgart Regional Council meeting to discuss the project
|
|
8 September 2023
|
Approval for advance construction work to begin
|
|
May 2023
|
Approval application submitted
|
|
2022/2023
|
Early public consultation process, presentation to the Municipal Council, expert reports produced
|
Construction diary
July 2026: Installation of the air intake system
The air intake system for the new combined cycle gas turbine plant was installed in July. In the future, the system will draw in the fresh air needed for the combustion process from the environment and feed it to the gas turbine. Various transition pieces are used to connect the large intake on the outer facade to the much smaller opening on the gas turbine. Besides the filter elements, the air intake also features silencers and devices for adapting the air to different weather conditions. These include a water injection system for cooling the air when outside temperatures are high and an electric heating unit for cold weather conditions. Weather louvers on the outer facade also protect the system from rain and the ingress of foreign objects.
June 2026: Construction of the stair tower
Further visible progress has been achieved on the construction site following the building of the new combined cycle gas turbine plant’s stair tower, which has already reached its final height of around 45 meters. The stair tower will play a key role in the future operation, maintenance and safety of the plant because it will provide access to the various levels of the plant as well as house a firefighter’s elevator. The imposing structure is being built using the so-called slip form method, whereby the formwork is continuously moved upwards while the concrete is poured in without interruption, creating a continuous, particularly stable concrete tower with no horizontal joints within a short space of time. Once the outer walls have been completed, the precast concrete staircase elements and the technology required for the elevator will be installed inside the stair tower.
May 2026: Cladding of the facades
By May, work on the construction site of the new HKW3 combined heat and power plant had reached an advanced stage. Large parts of the plant are already complete, making it increasingly recognizable as a coherent building complex. The design is intentionally based on the architectural concept of the existing power plant facilities. Thanks to clear and calm facade structures, which are color-coordinated, the new power plant harmoniously blends into the existing surroundings, reducing the visual impact on the landscape and creating a consistent look. Besides visual integration, the building envelope fulfills important technical functions: The multilayer box profile sheet metal structure and the insulation provide effective soundproofing as well as protection from the weather and heat, forming the basis for energy-efficient operation. Individual structures – such as the boiler house and the chimney, which is currently still scaffolded – are still being completed.
April 2026: Alignment of the generator and turbine shafts in the turbine hall
Once the rotor for the low-pressure steam turbine had been lifted into position, work on aligning the entire power train in the turbine hall could continue in April. The new plant features a single-shaft design, with all the main components arranged on a shared shaft and operated at the same speed. The power train essentially consists of a gas turbine, generator and the three steam turbine stages for high, medium and low pressure. At a utility frequency of 50 hertz, all components rotate at 3,000 revolutions per minute. The alignment process requires the utmost precision, taking into account both operational loads and thermal expansion. Even the smallest deviations could lead to vibrations and increased wear. This process takes several months, starting with coarse adjustments and culminating in precise fine adjustments. The aim is to achieve absolute straightness (“alignment”) of all components. That’s because they are mechanically connected to each other during later operation. Exact alignment is therefore essential for guaranteeing safe and efficient plant operation with maximum reliability.
March 2026: Rotor for the low-pressure steam turbine lifted into position
An important milestone in the construction of the new combined cycle gas turbine plant was reached at the end of March when the rotor for the low-pressure steam turbine, which weighs around 90 metric tons, was successfully lifted into position. It has been designed as a single-shaft power plant, with the gas turbine, steam turbines and generator arranged on a shared shaft – the so-called power train. The rotor on the low-pressure steam turbine is a key component of the power plant’s turbine system and has now been installed in the associated turbine housing. The entire steam turbine consists of three turbine parts connected in series – a high- and medium-pressure turbine as well as the aforementioned low-pressure turbine. Generated steam flows through one rotor after another, with the pressure and temperature of the steam gradually dropping. This staged approach significantly increases overall efficiency. The successful lifting into position of the rotor for the low-pressure steam turbine thus marks a decisive step on the way to commissioning the plant.
February 2026: Pipe installation and welding work
In February, work on the extensive pipework for the new combined cycle gas turbine plant reached its peak. Several kilometers of pipes are being installed and welded in almost all areas of the plant over the course of many months. They will later transport water, steam, natural gas and cooling water, connecting key parts of the plant, including boilers, gas and steam turbines, heat exchangers and auxiliary equipment. The diameter, material and wall thickness of the pipelines vary considerably depending on what will flow through them. Later on, they will have to withstand very high pressures and temperatures. The individual pipe sections are therefore lined up and fixed into place with millimeter precision before they are welded. Several thousand joints are welded before being visually inspected and, in some cases, checked using nondestructive methods such as X-ray or ultrasonic testing in line with the subsequent demands placed on them. The joints are only approved once testing is successful and documentation is complete.
January 2026: First fire of the burner in the hot water boiler system
Another significant milestone was reached at the site in January when the burners of all three boilers in the newly built hot water boiler system were successfully ignited for the first time. This so-called “first fire” marked a major step on the way to commissioning the plant further down the line. The boilers were installed in the existing district heating building of HKW 1. This posed a particular challenge, not least because the fitting of the heavy components and the installation of the extensive pipework and cable systems had to be carried out under cramped conditions. The team nonetheless succeeded in precisely assembling all components and fully integrating them into the existing infrastructure. With the first fire a success, work can now begin on the technical drying of the boilers, followed by the first firing tests. This work prepares the ground for the hot startup phase and the subsequent test operations. The new hot water boiler system has a thermal output of around 120 megawatts and will play a key role in supplying secure and flexible district heating to the region in the future.
December 2025: Testing the fire water tank
The new combined cycle gas turbine plant has an independent extinguishing system consisting of a large fire water tank with a capacity of around 4,000 cubic meters and an extensive network of fire water supply pipes. In the event of an incident, the entire power plant can be supplied with water from this tank. For maximum safety, two fully independent pumps are available: one electrically powered and a second fitted with a diesel engine. This means that the system will remain operational even in the event of a power failure. In November, work lasting several weeks began on filling the fire water tank to test its leak tightness under real conditions. The test was continuously monitored over the course of about three weeks and gradually brought to a conclusion. December’s successful leak test confirmed that the tank and the connected systems function reliably, which means that a key element of the new power plant’s fire protection and safety architecture has been successfully verified.
November 2025: Integration of the cooling water connection
The existing HKW 1 hybrid cooling tower will continue to be used for the new combined cycle gas turbine plant. The large cooling water pipes therefore had to be exposed and opened to enable the new pipe to be integrated using a tee connector. Two large concrete shaft structures were built for this purpose, one for the supply and one for the return of the cooling water between HKW 3 and the cooling tower. This work can only be carried out during planned downtimes at the existing power plant, so-called overhauls. Since the time frames are very tight, all work steps must be precisely planned and coordinated. All teams therefore had to work closely together and adhere exactly to the schedule to make sure that everything went smoothly.
November 2025: Visible progress
In November, during the overhaul of the existing HKW 1, there was a rare opportunity to take a look at the construction site from the 250-meter-high chimney at Altbach/Deizisau power plant. This perspective reveals the progress achieved across the entire construction site, showing what up to 450 employees manage to accomplish every day. The roof and facade work on all buildings is also in full swing to guarantee the best possible weather protection for the upcoming winter months.
October 2025: Boiler pressure test
A particularly important milestone was reached in October when the large heat recovery steam generator – the heart of the new plant – sailed through the extensive pressure test. The boiler, which weighs about 4,400 metric tons and was delivered in modules by ship, was tested in five stages. It was gradually subjected to very high pressure to check whether all welded joints and components were completely tight and stable. Tests were conducted across several stages up to a test pressure of 345 bars. This proves how robust the system is. The successful pressure test is confirmation that the more than 4,000 joints have been perfectly welded and the boiler is ready for the next steps in the commissioning process. In operation, the boiler uses the hot exhaust gases from the gas turbine to generate steam. This in turn drives a steam turbine, also producing electricity and significantly increasing the overall efficiency of the power plant.
September 2025: Installation of the two gantry cranes in the turbine hall
In September, two overhead cranes, each with a lifting capacity of 70 metric tons, were installed in the turbine hall of the combined cycle gas turbine (CCGT) plant. These gantry cranes have already been used in the construction of the CCGT plant and will later be needed during operation for major maintenance and overhaul work. The crane runways extend over a length of 86 meters directly beneath the turbine hall’s roof at a height of around 23 meters, making it possible to reach almost every area of the plant. For particularly heavy components, both cranes can be used together in a so-called tandem lift to move up to 140 metric tons. The cranes were delivered in individual parts and assembled on-site. The heavy double-girder crane runways were lifted into position using a 650-ton mobile crane, with every step requiring careful coordination. The installation of the gantry cranes represents another important step toward the completion and subsequent operation of the new plant.
August 2025: Modernization of the control room
In August, a significant milestone was reached at the Altbach/Deizisau site when the fully modernized HKW 2 control room was successfully commissioned. It will serve as the main control center for the existing plants as well as the new HKW 3 in the future. The modernization work was carried out during ongoing power plant operation, so electricity and district heating were still being generated at all times. This meant that the individual steps had to be carefully planned and closely coordinated with the team operating the plant to ensure that the control room was still able to perform safety-related tasks. Ceilings, lighting, flooring, furniture, control panels and all technical equipment in the room were all modernized as part of the measures. The control room now features advanced visualization technology, ergonomic workstations and an updated control environment. It is thus perfectly prepared for the alternating operations between HKW 1 and HKW 3 later on. At the same time, the operating personnel moved into the new main control room, which will now be used as the joint control center for every plant at the site. Following these modernization measures, Altbach/Deizisau power plant now has one of the most technically advanced control centers within EnBW’s generation network, representing an important step toward the future commissioning of the new combined cycle gas turbine plant.
July 2025: Delivery and installation of the auxiliary transformer and generator transformer
In July, two important transformers were moved into their final positions at the power plant: the 380 kV generator transformer and the 110 kV auxiliary transformer (kV = kilovolts). The generator transformer, which was already being stored on the site, will later connect the generator in the combined cycle gas turbine block to the 380 kV switchgear and step up the generated energy to the extra-high-voltage level. Weighing over 400 metric tons with all the components fitted, this transformer is a real heavyweight and yet had to be positioned very precisely. The somewhat smaller auxiliary transformer provides the 110 kV connection needed for auxiliary equipment and startup operations at the power plant. This also stands on specially prepared foundations with an oil catchment pit and cable routes to the switchgear. The installation of both high-voltage transformers means that the power plant’s main connections to the high- and extra-high-voltage network are now fully prepared. (Photographer: Markus Völter)
June 2025: Third hot water boiler moved into position
In June, the third and last of the three planned hot water boilers was moved into position in the building constructed for the district heating system. These boilers are the beating heart of the new hot water boiler system being built as part of the fuel switch project. It plays a key role in securing the district heating supply, especially at times when the new combined cycle gas turbine plant is unavailable or only available to a limited extent – during maintenance work, for example, in the event of failures or when there is a particularly high demand for heat. Each of the three boilers holds around 65,000 liters of water and is powered by gas. Together, they can produce around 120 megawatts of generated heat, reliably supplying high flow temperatures for the district heating grid. Each boiler is equipped with two burners and can be flexibly operated between partial load and full load, enabling the plant to cover peak loads when there is a particularly high demand for heat. Everything is controlled and monitored centrally from the control room. Following the installation of the new hot water boiler system, the Altbach/Deizisau site now has a second, independent technology to generate district heating. This improves security of supply and generally makes the power plant site more flexible.
May 2025: Construction of the chimney (for the CCGT plant)
In May, the new chimney for the combined cycle gas turbine (CCGT) plant was successfully built. The six modules that make up the chimney had already been prefabricated outside the power plant site a few weeks earlier. After being transported to the construction site, the individual segments were carefully placed on top of one another and professionally welded together.
The next step involves insulating the chimney before it is finally given a white protective coat of paint. This not only protects the chimney from corrosion, but also ensures that it harmoniously blends into the overall look of the plant. At a height of 83 meters, the new chimney is the tallest structure in the entire CCGT plant – and a symbol of how well our project is progressing!
April 2025: New district heating pipe network created
The new district heating pipe network – measuring around 600 meters in total (300 meters for supply and the same for return) – has been completed on schedule. It connects the state-of-the-art combined cycle gas turbine plant with the existing district heating grid in Altbach/Deizisau and will play a central role in supplying district heating to the “Mittlere Neckar Line” in the future. Construction work started in June 2024. A particular highlight was the targeted installation of sections of the pipe network beneath HKW 1, which is currently operating as part of the grid reserve. As a result, the existing infrastructure could be optimally integrated and still be used. The new district heating pipe network will play an essential role in maintaining security of supply – representing another step toward achieving efficient and sustainable heat supply.
March 2025: Gas turbine and generator installed
Another milestone was reached following the granting of the second partial permit in March 2025 when two major components – the gas turbine and generator – were successfully positioned on their foundations in the turbine hall using a large crane. (Photographer: Markus Völter)
February 2025: Erection of steelwork ramped up
The project is making very good progress with the laying of the foundations and the accompanying excavation work. Structural steelwork activity is also in full swing, with the heat recovery steam generator slowly taking shape. The construction site is growing visibly taller.
January 2025: Heat recovery steam generator fitted
The building works in Altbach/Deizisau are progressing. The heat recovery steam generator for the gas and steam turbine power station was fitted in January. This heat exchanger uses the heat from the gas turbine’s flue gases to generate hot steam, which in turn drives a downstream steam turbine to generate further power. (Photographer: Markus Völter)
November 2024: Hot water boilers moved into position
In November, two of the three planned hot water boilers were already moved into position in the building constructed for the district heating system. The boilers are the main component of the hot water boiler system that is being constructed as part of the fuel switch project to guarantee the supply of district heating. Each boiler holds 65,000 liters of water and together they have a total heating output of 120 megawatts.
October 2024: Construction site open day
On 25 October 2024, EnBW opened the doors of its power plant site in Altbach/Deizisau to the public: Visitors were able to attend the inauguration ceremony for the new exhibition in the information center and participate in live tours of the fuel switch construction site. Lots of interested people had the chance to learn all about the preparations for the construction work for the fuel switch project during a one-hour tour of the power plant grounds. An H₂-ready combined cycle gas turbine power plant is currently being constructed at the site. It will provide EnBW with the flexibility and controllable output necessary to secure the energy supply on a daily basis and support the expansion of renewable energies.
September 2024: Ongoing shell construction work
The shell construction work involves the foundations, base plates and concrete buildings. Work on the shell construction already began in early 2024 and significant progress can now be seen. The first foundations are ready for the next construction phase, namely the construction of the steel structures for the hall and also for the waste heat boiler and chimney.
August 2024: Gas turbine hub
The heart of the power plant was delivered in August: the 400 MW gas turbine. It was initially delivered to Belfort in France and then transported by ship to our jetty in Altbach/Deizisau. After being unloading from the ship, it is now being temporarily stored on site before it is moved into its final position in the power plant building.
July 2024: Installation of a rental boiler system
A rental boiler system will be installed and operated at the power plant site on a temporary basis to secure the supply of district heating to the “Mittlere Neckar Line”. The first pipework for the boiler was started in July 2024 and the system will be ready for operation from October 2024 onwards. It is anticipated that the system will be needed for a maximum of 6 months up until March 2025. Its operating hours are expected to be very low as it will only be used as additional backup for the district heating supply. The rental boiler system consists of 4 shell boilers and 2 heating oil storage tanks. It has a heating capacity of around 40 megawatts (MW).
May 2024: Construction of the chimney (for the hot water boiler system)
A natural gas-fired hot water boiler system is being built to help secure the district heating supply together with combined heat and power plant 3. It consists of three shell boilers with a rated thermal input of up to 45 MW each so that the hot water boiler system has a total rated thermal input of 135 MW. The boiler system is being installed in the existing district heating building and will be connected to the existing infrastructure. A new 110-meter-high chimney with three flues is now being constructed for the hot water boiler system. It was delivered in six sections and installed in May.
April 2024: Start of excavation of the building pit
A total of 28,000 m³ of soil is being removed from the site every day by diggers and HGVs during the excavation of the construction pit. Despite the confined space, heavy floor slabs for e.g. the boiler house and gas compressor building are being constructed at the site without any disruption to ongoing operations. Work on the concrete structure is scheduled to be completed by the middle of 2024.
March 2024: Start of structural work (construction of the foundations)
The anchor cage for the chimney of the hot water boiler system is being installed. The sections of the 110-meter-high steel chimney will later be attached to the anchor cage. The flue gases from the three hot water boilers will be discharged via three chimney stacks. The hot water boiler systems will be used to provide district heating when, for example, the combined heat and power plant is not running or during times of peak demand.
January 2024: Constructing the bored pile foundations
Work to construct the around 1,200 bored pile foundations began in January. Pile foundations are deep foundations where the loads of supporting structures are transferred to deeper soil layers with a higher load-bearing capacity. Soil layers with poor load-bearing capacity are thus bridged using piles. With so-called pile foundations, the piles are driven into the ground with a pile driver until a soil layer sufficiently capable of bearing the load has been reached. Concrete is then poured into them.
November 2023: Ground-breaking ceremony and official opening of the construction site
The symbolic ground-breaking ceremony was held at the traditional EnBW power plant in Altbach/Deizisau on 6 November 2023. Thomas Matrohs, Mayor of Deizisau, Thekla Walker, Minister for the Environment, Climate and Energy of the State of Baden-Württemberg, Dr. Georg Nikolaus Stamatelopoulos, Member of the EnBW Board of Management, and Martin Funk, Mayor of Altbach (from left), heralded the start of construction work on the fuel switch project.
October 2023: Pre-construction measures
The construction site becomes visible: careful planning and implementation of the pre-construction measures is crucial for a smooth and efficient conversion project. This includes setting up areas on the construction site for temporary facilities such as construction offices and carrying out dismantling work to create space for the conversion project and for storage areas. This stage of the project also includes dismantling facilities and buildings that are no longer required, such as the foundations of coal storage facility 3.
Frequently asked questions
The groundbreaking ceremony for the construction project was held on 6 November 2023. Construction work began in September 2023 because a permit had been obtained to start early. The main construction activities are expected to be completed by 2026, followed by the start-up phase and commercial commissioning.
Unfortunately, it is difficult to fully avoid construction work being noticeable in the area. However, EnBW is making every effort to minimize the impact. Most of the work is carried out during the day, with heavy haulage moved to nighttime whenever possible.
All measures will be carried out as per the approval process and in close consultation with Stuttgart Regional Council and the municipalities in the surrounding area. EnBW also continues to engage in dialogue with residents to address their concerns and questions.
The existing power plants will remain in operation until all new power plant and district heating facilities have been fully commissioned, ensuring that the power supplied by the power plant and the district heating supply in Altbach, Deizisau and the surrounding region is reliably maintained at all times.
As an additional district heating backup plan for the 2024/2025 and 2025/2026 heating periods, EnBW has already installed a temporary rented boiler system during the construction phase.
Before the two old HKW 1 and HKW 2 blocks are finally shut down, a hot water boiler system will be built in addition to the existing combined cycle gas turbine (CCGT) plant in order to ensure a secure district heating supply even during times when the CCGT plant is not in operation. The “Mittlere Neckar Line” pipe network can also be used to supply heat from Stuttgart’s power plants to the district of Esslingen.
If you have any questions, suggestions or criticism, please contact altbach-deizisau@enbw.com at any time.
EnBW provides regular information on the progress of the project and current milestones. This is done via the project page, which can be found at www.enbw.com/altbach-deizisau, and by distributing leaflets. Media outlets also report on the progress on the construction site at regular intervals.
As part of the approval process, noise reports and similar reports are produced to assess the impact of the new building on the surrounding area.
Once the new combined cycle gas turbine (CCGT) plant has been commissioned, blocks HKW 1 and HKW 2 are scheduled to shut down. Only a few large components – such as the gas turbine plants, the HKW 1 cooling tower and the water treatment plant – are expected to remain in operation. Since the decommissioned plants previously made a significant contribution to the noise emissions at the site, the overall noise situation may improve.
The CCGT will be fitted with the latest generation of silencers and sound traps in order to comply with the legal limits laid down by noise control regulations (TA Lärm). In addition, there will no longer be any disposal of residues or delivery of additives associated with the coal blocks’ flue gas cleaning system, which in turn could reduce the volume of traffic.
As part of the approval process, reports such as an air pollutant forecast are produced to assess the impact of the new combined cycle gas turbine (CCGT) plant on the surrounding area.
The switch from coal to natural gas will change the emissions of the entire plant. According to current plans, CO₂ emissions can be significantly reduced compared to the current coal-fired power plant. For the Altbach/Deizisau site, a reduction of over two million metric tons of CO₂ per year is expected. This corresponds to approximately 40% of the coal-fired power plant’s current CO₂ emissions.
Lower emissions are also projected for other air pollutants. For example, emissions of nitrogen oxides (NOx) are expected to decrease by about 25% compared to the existing power plant, and emissions of sulfur oxides (SOx) by more than 75%. In addition, significantly lower dust pollution levels are expected, and that heavy metal emissions – which can result from coal-fired power generation – will be eliminated.
As part of the approval process, reports are produced, including a survey on the impact on water pollution control, in order to assess the impact of the new building on the surrounding area.
According to current plans, the commissioning of the combined cycle gas turbine (CCGT) plant and the subsequent decommissioning of the old plants will result in significantly less heat being released into the Neckar, which borders the power plant site, compared with today. This can contribute to an improvement in water pollution control compared to the current situation.
There are three parts to the approval process for the combined cycle gas turbine (CCGT) plant pursuant to the Federal Immission Control Act (BImSchG):
- The first part of the application was submitted in May 2023. EnBW was granted the partial permit for this in January 2024.
- The second part of the application was submitted in spring 2025. The plant is expected to be commissioned in 2026.
- The third and final part of the application is currently being prepared and will then go through the approval process.
Stuttgart Regional Council is the approval authority.
EnBW currently estimates that a mid-three-digit million euro amount will be invested in the construction project.
Two new main structures are being built on the existing power plant site:
- The combined cycle gas turbine (CCGT) plant and its auxiliary facilities are being built in the area situated to the south of the HKW 1 cooling tower.
- A hot water boiler system is also being built, which will be located in the existing HKW 1 district heating building.
- The HKW 1 hybrid cooling tower will also be used by the new CCGT plant. The water treatment facilities will also be upgraded and remain in operation.
Plans for the future use of the freed up areas are currently still open and will be decided at a later date.
The decision in favor of a combined cycle gas turbine (CCGT) plant is based on its high degree of efficiency:
- For a reliable energy supply, it is essential to use the fuel as efficiently as possible in order to generate as much electricity and heat as possible from a given amount.
- By combining electricity and heat generation in the combined heat and power process, a CCGT plant can achieve a fuel utilization rate with an efficiency level of over 60% based on the current state of the art.
In the field of heat generation in particular, renewable energies are currently not in a position to fully replace fossil fuel within a matter of years and in all applications.
Natural gas is therefore considered a temporary solution, not least because it has the potential to reduce greenhouse gas emissions compared to coal. It is important to remember that natural gas is only intended to be used for a transitional period.
The gas turbines are flexible and can later be converted to burn other gases such as green hydrogen. Green hydrogen is produced by means of electrolysis using electricity from renewable energy sources.
As soon as the combined cycle gas turbine (CCGT) plant is commissioned, it will be possible to add up to 20% hydrogen to the natural gas according to current plans, which can further reduce greenhouse gas emissions. The switch to natural gas thus represents a transitional step culminating in a future energy supply with hydrogen.
The new combined cycle gas turbine (CCGT) plant supports the security of supply and can complement the fluctuating energy production from renewable energy sources. In the initial phase, the CCGT plant will provide electricity and district heating with lower CO₂ emissions than coal-fired power generation.
In the long term, the plant could contribute to a further reduction in CO₂ emissions if it operates using hydrogen as fuel. Based on current technology, a combined-cycle gas turbine plant produces lower emissions of certain air pollutants than older fossil-fuel-fired power plants.
Not directly and not all the time. Converting an urban area to run on regional renewables is a complex challenge. This is mainly due to the fact that renewable energy sources such as wind power and photovoltaics require a lot of space because their energy density is comparatively low.
What’s more, these energy sources are not dispatchable – they generate electricity when the wind or sun is available, and not necessarily when energy demand is at its highest. In order to compensate for these fluctuations, flexibly dispatchable power plants are needed to meet demand.
A combined cycle gas turbine (CCGT) plant consists of a gas turbine, a steam turbine and heat exchangers for the production of hot water. It utilizes the energy generated during the combustion of natural gas in a particularly efficient manner by using the produced heat three times:
1. Electricity generated by the gas turbine: The hot combustion gases produced during the combustion of natural gas firstly drive a gas turbine. This is connected to a generator that converts the turbine’s mechanical energy into electrical energy.
2. Additional electricity generated by the steam turbine: The exhaust gases from the gas turbine are still very hot. This heat is used in a waste heat boiler to evaporate water. The steam drives a steam turbine, which also generates electricity.
3. Further use made of the residual heat: Part of the steam that has already been used to generate electricity is withdrawn from the steam turbine and used to generate district heating. This process is much more efficient compared to direct heat generation in boiler systems.
This combined heat and power generation enables the CCGT plant to achieve a fuel utilization rate of over 70% based on current state-of-the-art technology. With this approach, CO₂ emissions can be reduced by about 50% compared to those produced by a coal power plant according to current plans. Switching from coal to natural gas is therefore viewed as a transitional step that can contribute to a reduction in greenhouse gas emissions.
The combined heat and power generated by the combined cycle gas turbine (CCGT) plant allows the particularly efficient use of natural gas as a fuel and offers the possibility of fully switching to hydrogen in the future.
In the initial phase, a blend of natural gas and up to 20% hydrogen would be used, provided that it is available in sufficient quantities. Starting around the late 2030s, adjustments would then make it possible to operate on 100% hydrogen.
The combined cycle gas turbine (CCGT) plant could offer the following advantages over the hard coal blocks that have been used until now in Altbach/Deizisau
- The gas-fired plant can be controlled more flexibly than a coal-fired power plant and can therefore better compensate for fluctuations in wind and solar power.
- Combined heat and power (CHP) in the gas-and-steam (GuD) plant contributes to efficient fuel utilization. In the future, conversion for the use of hydrogen is possible, provided the technical and economic requirements are met.
- Natural gas produces lower direct CO₂ emissions compared to hard coal. According to current plans, emissions per kilowatt-hour of electricity generated could fall by more than 50% starting in 2027 – depending on the operating mode.
- According to forecasts, a reduction in air pollutants is expected: nitrogen oxide emissions (NOₓ) could drop by about 25%, while sulfur oxide emissions (SOₓ) and particulate matter could be significantly lower. Heavy metal emissions from coal combustion will be eliminated.
- With the decommissioning of the coal-fired units, the existing coal storage facility will be eliminated, thereby eliminating the dust and noise emissions previously associated with it.
- Traffic volume may decrease, as coal deliveries will no longer be necessary and additional transport for flue gas cleaning will largely be eliminated.
- The plant’s noise level is to be limited through modern noise reduction technology. In addition, coal-fired boilers, auxiliary steam generators, and flue gas cleaning systems will be taken out of service.