The Voith Group is a Germany-based multinational corporation with more than 19,000 employees worldwide. One of its primary divisions is Voith Hydro, a complete system supplier that produces turbines and generators for the world’s largest hydropower stations. Voith Hydro’s expertise also extends to pumped storage hydroelectric projects. In this interview, we speak with Dr. Klaus Krüger, Voith Hydro’s senior expert in plant safety and energy storage solutions, about his research and the key factors to keep in mind when planning a pumped storage facility. 



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Hydro Leader: Please tell our readers about your background, education, and work experience with Voith. 

Klaus Krüger: I studied electrical engineering at the Technical University of Karlsruhe in Germany and graduated in 1987 and then earned a PhD at the same university in 1991. By 1992, I was employed with ABB’s thermal power plant automation division in Mannheim, Germany, gaining professional experience in national and international power plant automation and optimization projects and in different management positions. In 2004, I joined Voith Hydro Holding in Heidenheim, Germany. From 2004 until 2016, I was the head of research and development at Voith’s Corporate Technology Center. From 2016 onward, I was responsible for product and plant safety, innovation management, and trend scouting. Since 2017, I have been a member of the executive board of the European Association for Storage of Energy (EASE) in Brussels. My current position at Voith Hydro, which I have held since 2019, is senior expert in plant safety and energy storage. 

Hydro Leader: Would you describe your comparative research on battery storage versus pumped storage for bulk energy storage? 

Klaus Krüger: The research work compares the marginal costs resulting from the specific raw material costs of a representative stationary lithium-ion battery storage facility and a pumped storage scheme, each with a bulk energy capacity of 13.4 gigawatt-hours (GWh) and a lifetime of 100 years. It is evident that the two systems need completely different types and quantities of resources, leading to substantial differences in their specific raw material costs. In addition to the raw material costs, we examined the annual lifetime investment costs and land requirements for each technology. Finally, we analyzed the different contributions to the overall carbon footprint. This research work contributes to the ongoing and controversial discussions around the economic efficiency and environmental effect of different storage technologies for stationary applications. 

Hydro Leader: What were your findings? 

Klaus Krüger: In terms of raw material costs, pumped storage plants use relatively cheap raw materials, such as steel and concrete, whereas certain components of battery cells, such as mercury, binder, and electrolytic solvents, are highly costly. As a consequence, the overall raw material costs of the initial installation of a battery storage project are about 3.7 times higher than the costs of the initial installation of a pumped storage project of the same power and energy storage capacity. Over a lifetime of 100 years, the overall raw material costs are about 18 times higher for a battery storage project. The capital investment and operating costs of a battery storage are 18 times higher than those of a pumped hydro plant. Finally, due to the high greenhouse gas potential of certain raw materials used in battery cells, the carbon footprint of a battery storage system turns out to be double the footprint of the pumped storage hydro plant. 

Hydro Leader: What is your advice to anyone considering a pumped storage project? What are the most important factors to consider? 

Klaus Krüger: Probably the most important factor is the appropriate siting of the project. Pumped storage solutions work best when you have a significant difference in elevation between the upper and lower reservoirs—a typical project would be in the 200–700 meter (656–2,296 foot) head range. The amount of energy that can be generated or stored is proportional to this elevation difference and to the volume of water being stored. 

The variation in level of the lower reservoir should be kept to a minimum. This can be accomplished by making sure that the downstream reservoir has a larger surface area. In many cases, it is advantageous to make use of a large existing lake with a natural inflow as the upstream reservoir or a river as the downstream reservoir to mitigate the variation in level. The ratio of maximum head to minimum head throughout a pumping cycle should ideally not exceed 1.3. The volume of water required depends on the amount of energy that needs to be stored. 

Most pumped storage schemes involve underground power plants because of the submergence requirements for pumped storage units. This means that the geology of the site must also be stable. A further consideration is that the site should have good access and connectivity to the power grid. Optimizing these main factors is key to the economic viability of the project. 

For more details, I invite your readers to refer to “Pumped Hydroelectric Storage,” a piece I wrote that will appear as chapter 4.2 in the forthcoming book Thermal, Mechanical, and Hybrid Chemical Energy Storage by K. Brun, T. Allison, and R. Dennis, which will be published at the end of 2020 by Elsevier. 

Hydro Leader: If people have questions about their potential project, can they contact you directly? 

Klaus Krüger: Yes, of course. My e-mail address is For North American projects, please contact our head of sales, Carl Atkinson, at 

Hydro Leader: What should everyone know about Voith? 

Klaus Krüger: We are focused on being the ideal partner for hydropower energy producers. Voith is known for being a full-line, water-to-wire supplier of hydroelectric equipment, but we have found customers to be impressed by our breadth of offerings in services and areas such as small hydro and digital solutions. Voith and Voith legacy companies, which include Allis-Chalmers Hydroelectric, S. Morgan Smith, and Westinghouse Hydro, have been manufacturing in the United States since 1877. Even today, Voith’s York, Pennsylvania, location is one of the world’s largest dedicated hydropower turbine equipment manufacturing facilities and is the only one in the United States to feature a hydraulic laboratory. 

Dr. Klaus Krüger is the senior expert in plant safety and energy storage solutions at Voith Hydro.