The Naturstromspeicher Gaildorf: a green energy storage facility

Total concentration. Everyone is looking up. It is so quiet on the construction site that you could hear a pin drop. The Liebherr 630 EC-H 70 Litronic tower crane is lifting the suspended rotor blade, which measures almost 70 metres in length and weighs 17 tonnes. Very slowly. Right up to the hub of the wind turbine, 178 metres above the ground.

A wind turbine of this size has never been built before. That is why, up in the tower crane, crane drivers Wilhelm Lepertz and Georg Brodwolf are tackling this challenge in tandem. Four eyes see better than two. They are in radio contact with Thomas Ziegenbein. The wind installation project manager for international construction company Max Bögl is the crane drivers' direct link with the ground crew who, from the forest below, are using ropes to control the suspended component and hold it in position. They are all totally focussed on the job in hand. The only sound to be heard is the echo of the radio messages which are being sent back and forth between the construction managers and the cockpit, reverberating across the construction site. There is a feeling in the air that a piece of technological history is being written here today.

We now know how to go about assembling components at these great heights. After this, it will keep getting easier and faster.

Thomas Ziegenbein

Globally acclaimed pilot project

In Gaildorf, located in the Limpurg Hills range of the Swabian-Franconian Forest, Germany's energy transition is being taken to a whole new level. Here, in a globally acclaimed pilot project, the Naturstromspeicher Gaildorf, the wind division of international construction company Max Bögl, supported by the Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety, is building the world's tallest (246.5 metres) onshore wind turbines. The water battery with its four wind turbines – a completely new decentralised storage technology – is also a world first.

Precision work 178 metres above the ground

The rotor blade has now reached the height of the hub and has to be rotated by the crane so that it can be bolted into position. And this has to be done with millimetre precision. The tension among the crane and ground crews is at its peak. At the dizzying height of 178 metres above the ground, specially secured workers are waiting to bolt the metal spindle of the rotor blade to the hub. "This is a critical moment," says Thomas Ziegenbein. "Now, everything has to fit perfectly." As the sound of the rattling of the electronic torque wrenches echoes below, the tension eases. Mission accomplished. "Due to some strong gusts of wind in the early morning, we started a little later than planned today. Lifting the rotor blade, which was secured only with ropes, would otherwise have been too dangerous," says Ziegenbein, visibly relieved. "Tomorrow, the work will continue. We now know how to go about assembling components at these great heights. After this, it will keep getting easier and faster."

The Naturstromspeicher is a combination of a wind farm and a pumped-storage power plant. This allows the wind-generated electricity to be stored, regulated and above all supplied precisely when it is actually needed in the electricity grid.

Johannes Kaltner

A "battery" made of water

The wind turbine which has just been assembled at the "WEA 3" site is no ordinary design. "The water battery is a combination of a wind farm and a pumped-storage power plant. This allows the wind-generated electricity to be stored, regulated and above all supplied precisely when it is actually needed in the electricity grid," explains overall project manager Johannes Kaltner.

Storage is provided by the active and passive reservoirs at the base of the wind turbine. These will later be connected via a pressure pipe to the lower reservoir of water in the valley, as well as to the pumped-storage power plant located between them. "Work on laying the water pipelines will commence in the spring," says Kaltner.

Not run-of-the-mill even for wind power professionals

Since the foundation stone was laid in April 2016, overall project manager Johannes Kaltner has been continuously based at the Gaildorf site with around 35 specialist workers. He says it is the enthusiasm for innovations and what is technically feasible that constantly drives his team on to develop new ideas. "The fact that this construction site is opening a new chapter in Germany's energy transition means that it is not run-of-the-mill work, even for experienced wind-power professionals," stresses Kaltner.

One of these wind-power professionals is Ralf Karras. The Berliner is a crane driver out of sheer passion. Using the joystick, he operates his powerful LTM 11200-9.1 crane, which he has reverentially given the name "Hercules". And with good reason. The 9-axle mobile crane from Liebherr has a 100-metre telescopic boom, one of the longest in the world, and delivers a maximum load capacity of 1,200 tons.

Crane for crane – which is the strongest

  • Mobile powerhouse
    The LTM 11200-9.1 has a 100-metre telescopic boom, the longest in the world, and can lift up to 1,200 tons.

    Mobile powerhouse

    The LTM 11200-9.1 has a 100-metre telescopic boom, the longest in the world, and can lift up to 1,200 tons.

  • Pioneering the way upward
    The mobile crane is helping with the construction of the wind turbine foundations and the water battery.

    Pioneering the way upward

    The mobile crane is helping with the construction of the wind turbine foundations and the water battery.

  • To new heights
    The tower crane arrives at the construction site in 22 truckloads. The mobile crane raises the first sections of the tower crane to a height of 40 metres. After that, the tower crane is then self-climbing. It is fixed to the concrete foundations and later also to the wind-turbine tower. As a result, it remains stable, even in strong winds.

    To new heights

    The tower crane arrives at the construction site in 22 truckloads. The mobile crane raises the first sections of the tower crane to a height of 40 metres. After that, the tower crane is then self-climbing. It is fixed to the concrete foundations and later also to the wind-turbine tower. As a result, it remains stable, even in strong winds.

  • Everything under control
    Crane driver Ralf Karras also often operates the powerful LTM mobile crane by means of remote control. And this has to be done with millimetre precision. "It is all a question of feel," says the Berliner.

    Everything under control

    Crane driver Ralf Karras also often operates the powerful LTM mobile crane by means of remote control. And this has to be done with millimetre precision. "It is all a question of feel," says the Berliner.

  • In safe hands
    Liebherr mobile cranes pick up the concrete shells prefabricated by Max Bögl. They go straight from the low-loader to the construction site. There, the individual components are assembled to form the wind-turbine tower.

    In safe hands

    Liebherr mobile cranes pick up the concrete shells prefabricated by Max Bögl. They go straight from the low-loader to the construction site. There, the individual components are assembled to form the wind-turbine tower.

  • Symbol of the energy transition
    The green energy construction site in Gaildorf towers above the Swabian Alps. The imposing construction is not only attracting interested spectators from across the region. The Naturstromspeicher is also drawing in large numbers of technical specialists and media representatives from all over the world.

    Symbol of the energy transition

    The green energy construction site in Gaildorf towers above the Swabian Alps. The imposing construction is not only attracting interested spectators from across the region. The Naturstromspeicher is also drawing in large numbers of technical specialists and media representatives from all over the world.

  • Real skill: cranes perform a one-two

    The mobile crane performs a clever one-two with the tower crane in Gaildorf. However, initially Karras' crane had to start the work single-handedly. For him, that meant lifting the concrete quarter shells for the base, each weighing 22 tons, from the low loaders, bringing them together on the crane platform and fitting them into the installation with an 88-ton lift. Not until the 40-metre-high active reservoir was in place could the tower crane be mounted on this foundation. Karras had to take delivery of 22 truckloads, including six heavy loads. "I had to lift the first crane modules with my LTM, and after that the tower crane, with its special hydraulic design, erected itself using its self-climbing function," says Karras. Now that the crane is operational, Karras "merely" has to position the large, bulky components so that his colleague up in the crane can lift them up to a great height.

    The pilot project Naturstromspeicher Gaildorf

    Wind turbines with integrated water storage

    The power output of the wind turbines is 3.4 megawatts per turbine. The wind turbines stand on foundations formed of integrated water storage tanks with up to 30 metres of headroom in the active reservoir. A total of 160,000 cubic metres of water are used for storing energy in the active and passive reservoirs. The water storage tank is connected to the generator in the pumped-storage power plant via underground pressure pipes. The height difference between them is 200 metres.

    Pumped-storage power plant with connected lower reservoir

    The water battery works with a variety of power sources and is therefore suitable for a modular concept, with a wind farm as at Gaildorf as well as with a solar power installation or a combined heat and power plant. Three output classes are available: 16, 24 and 32 megawatts.

    In Gaildorf, a 16-megawatt plant is going onstream. The principle behind it is simple: When the wind blows, the surplus power that cannot be taken up by the electricity grid is used to pump water from the lower reservoir to the wind turbines' integrated water reservoirs, using the pumped-storage plant. The switchover from production to storage can be carried out in less than 30 seconds. That's why it's referred to as a "flexible power plant". During periods of calm, the water flowing down from above drives the turbines in the pumped-storage plant. The wind farm can thus continue to generate electricity reliably and predictably and feed it into the grid.

    Planned power supply

    The combination of wind and hydroelectric power ensures that households, businesses and industry are supplied with green electricity in an even and systematic way. In Gaildorf, annual electricity generation from wind can amount to as much as 42 gigawatt hours.

    "The world of wind power is watching Gaildorf"

    Making renewable energy sources flexibly available is seen as one of the biggest challenges of the energy transition. Jürgen Joos, commercial head of wind power in the Max Bögl Group, talks about water batteries and the prospect of making history with them.

    Mr Joos, the idea of generating an endless supply of renewable, clean energy from wind sounds very enticing. If only the wind would blow at the time the energy was needed. Up to now, transporting and storing energy has proved to be difficult and involve heavy losses. What's different here in Gaildorf?

    Jürgen Joos: In our Gaildorf pilot project, we have implemented the world's first water battery, a unique combination of a wind farm and a pumped-storage power plant. Since there is currently no prospect of any viable solution involving high-capacity large-storage facilities for this purpose, we have deliberately opted for decentralised energy-storage systems for use with the water battery. Incidentally, it doesn't matter whether fresh or salt water is used to operate the water battery. The plant could just as easily be located on the coast as in the Swabian Alps.

    How exactly does it work?

    The water battery serves as a short-term storage device that can absorb excess electricity from the power grid and, if required, release it again over a period of four to six hours. It is ideally suited for compensating for fluctuations in the power grid. This method of "peak shaving" enables us to reduce peak loads and save on capacity-related grid fees.

    Faster, higher, more efficient: are 250-metre-high wind turbines the last word in the obsession with height?

    The wind yield is best at great heights. In Gaildorf, we have built turbines with a hub height of 178 metres. I expect that this will soon increase to 200 metres elsewhere. This will make overall heights of 260 to 280 metres realistic. However, the water battery does not only work with wind power. The concept also works in combination with solar power installations or combined heat and power plants. For decentralised systems, pumped-storage technology can to a large extent be easily integrated into the landscape underground. The power plant is then virtually invisible.

    Where will the water battery go from here?

    The world of wind power is watching Gaildorf. Max Bögl Wind AG has therefore already opened another production site in Thailand. Asia and the North American market are increasingly exciting markets for us with potential for the future. This can only be achieved through further innovation and constant product optimization. For the next generation of Max Bögl water batteries, this means that the system will become even more modular, even simpler, even more efficient.

    Batteries from nature

    Ideas and visions regarding how energy could be stored in a natural way

    The apple battery

    Manufacturing electrodes from biological material: this idea was advanced by scientists at the Helmholtz Institute for Electrochemical Energy Storage in Ulm. They ground apple residues until virtually pure carbon was produced. They then added a conductive additive and a binding agent to the powder and applied it to aluminium foil. Their "apple battery" can now manage over 1,000 charging and discharging cycles. The big advantage of this energy storage device is that it does not require mineral raw materials such as lithium and cobalt, but is based on materials that are inexpensive, environmentally friendly and limitlessly renewable. Will the apple-carbon battery catch on? The researchers are still working on it.

    The concrete battery

    Generating electricity from nothing: this is the principle of an undersea concrete battery, which has now been tested for the first time by scientists from the Fraunhofer Institute for Wind Energy and Energy System Technology, at a depth of about 100 metres in Lake Constance. The 20-ton concrete sphere draws its power from the cavity in its interior. It functions like a pumped-storage power plant. The hollow body filled with water is pumped dry using surplus electricity from wind turbines on the shore. In order to convert the stored energy back into electricity at a later date, the researchers allow water to flow back into the air-filled containers. The strong current drives a small generator which generates electricity.

    The rock battery

    Think big. This is the principle which physicist and inventor Professor Eduard Heindl from Stuttgart follows. In order to be able to store electricity from renewable energies temporarily, depending on current electricity prices, he has devised a "gravity storage system". For this purpose, a large rock mass must be removed from its natural environment and made vertically mobile. When water is pumped under the rock mass (at low electricity prices), hydraulic forces lift the rock mass. At high electricity prices, the water is drained away and fed through turbines and generators to generate electricity. The amount of electricity stored depends on the size of the rock piston. The researcher anticipates that where the rock mass diameter exceeds 100 metres, operating a gravity storage system could be worthwhile. Although the mining and tunnelling techniques required for its construction have long been known and tested, no such system has yet been implemented.

    On close terms with nature

    Erecting four wind turbines in the middle of the forest is not only a technical challenge, but also a logistical one. "Just try putting three 70-metre-long rotor blades down in the middle of the forest," says project manager Johannes Kaltner with a wink. "And without clear-felling." He himself is passionate about harmonious interaction between people, nature and large-scale technology: "When organising a construction site like this one here in Gaildorf, we wind people always need a bit of humility and respect for nature." A huge advantage of the tower crane is that it takes up significantly less space than other types of crane. This means that a smaller area has to be cleared in the forest. The fewer traces the construction site leaves in the natural environment, the better," says Kaltner.

    For this reason, geologists, biologists, geo-ecologists and sound insulation experts had tested the environmental compatibility of the turbines beforehand. The inhabitants of Gaildorf were involved in the planning from an early stage and were given extensive information about the individual steps in the process. And what does all this mean for the 70-metre-long rotor blades in the forest? "We have made the construction site as compact and the gravel access roads as narrow as possible. Our logistics must therefore deliver components just-in-time, as we do not have large storage facilities in the forest. At the base of the turbine, there is only room to lift one rotor blade at a time," says Thomas Ziegenbein. After that, the mobile crane has to be brought in again to lift the next heavy blade over the treetops from the site access road and place it in the right position. It's worth the effort," says Ziegenbein. "After we've gone, nature will quickly reclaim the building site."

    A symbol for the environment

    The Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety (BMUB) is supporting the Gaildorf project with funds from the Environmental Innovation Programme to the tune of 7.15 million euros. This is a clear symbol of recognition of this innovative technology, which is being tested out in a large-scale application for the first time.

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