2. Figure of the Pumped-Storage Station with four storage rings

 - schematically -

3. Design Feature of the Pumped-Storage Station

The underground pumped-storage station consists of a upper storage ring system, with several storage rings, that could reach each a diameter of several hundred or thousand meter. Furthermore, the pumped-storage station contains a collector system, in which water, in case of opened down pipes flows from the upper storage rings through the turbine house to the distribution device and from there via several down pipes to the lower storage ring system beneath. Storage rings in the lower storage ring system have the same size of diameter and volume as the storage rings above. Water will be pumped via a pump station from the lower storage rings to the upper storage rings.

A temporary water basin for storing accumulated mine water can be build when developing a new underground mining plant. After completion of the upper storage rings, these will be filled with water and the temporary water basin can be removed. Beside of that, a smaller pumped-storage station could be build above ground. These storage systems contain large pipes and the pumped-storage station could be fixed independently on a rigid frame.

4. Field of Application of the Pumped-Storage Station

This inventions applies to a pumped-storage station, which can store energy independently from the place of location. This implies the buildung of pumped-storage station, which rely on the geology of the subsurfaces, in the plains or in the mountains, without permanent upper and lower water basins above ground. The construction of a pumped-storage station, with an upper and lower water basin above ground, implies an important change in nature and landscape. When evaluating a possible site for a plant, many criteria of environment and nature protection had to be taken into account to find the best suitable site for a pumped-storage station, which had to be potentially best accepted by the inhabitants. The main point for building a pumped-storage station, independently form landscape, is a large height difference between the upper storage system and the turbine house. Storage demand depends upon the performance of the pumped-storage station, which is a result from the cross-secctional area of the storage rings, the diameter of the storage rings and the height difference between the upper storage system and the turbine house.

5. Commercial Value

Pumped-storage station offer the possibility to convert the electric power supply, which is, at night or in day times with weak demand, provided at a reduced cost rate, with a time delay to a high priced power supply for peak demand. In this business, selling price of power supply could be a multiple of purchase price, which is commercial reasonable for the business operation of pumped-storage station.

With developing of the renewable energy in the course of energy revolution, pattern of business operation of pumped-storage station have changed clearly. Particularly in summer, when photovoltaics feed-in a great amount of electrical energy into the electrical power supply system, peaks of demand at noon and often great parts of the medium-load range of power supply will be covered by photovoltaic power plants, so that operating times move more and more to the morning and evening hours. Simultanously, the result of developing wind and solar energy leads to a long-term increasing storage demand to balance the volatile generation of electrical power.

Furthermore with the development of electric cars infrastructure to store electrical power becomes more and more important. In addition to that, the behavior of electrical car users, when loading their storage batteries, is not predictable ,so that no one knows the daytime load demand peaks. Because of that, a increasing demand of storage plants in the future is expected, among of them pumped-storage stations.

A pumped-storage station is very flexible in relation to a full stage expansion of storage rings. If one storage ring has a down time, for example in times of maintanance, the other storage rings will be still available for use and generate sales volume.

With extension for example of the storage rings with an inner cross-section area of seven meter, a radius of the storage rings of five kilometers and a heigt of fall of 530 meter and with four storage rings, a storage performance of nearly 1,5 GWh is achieved. The pumped-storage station could easily be extended with a large number of storage rings. 



There is no limitation of an extention of an underground pumped-storage station.

6. Commercialization

Underground pumped-storage stations are appllicable in countries, which have also a high input of base load demand from power plants in the future. They can lead to a better degree of capacity utilisation of nuclear, brown coal and hard coal power plants.

Furthermore the field of application of a underground pumped-storage station can be extended to an on surface pumped-storage station by fixing the station on a rigid frame, which can be used in large scale operations, for example in the chemistry industry or in the metallurgical industry.

An imaginable field of application would be also the construction of underground pumped-storage stations in a raw material extraction area, for instance deserts, in which a high amount of solar power covers the demand for power supply at daytime and with the power surplus to store energy at night in the pumped-storage station to cover demand of power supply at night.

7. Cost Analysis

This sort of pumped-storage station, with subsurface storage systems, had never been realisied in an industrial manner, so there is no empirical value for this application. A feasible study of an underground pumped-storage station for the abondend mining plant Prosper-Haniel has been examined. The possible planned storage-pumped station Prosper-Haniel has in contrast to this invention a storage water basin above ground and a sub-surface storage ring under ground.

Parameter of the Pumped-Storage Station Prosper-Haniel

from Feasible Study*

Extract from journal: Mining Report Glückauf 154 (2018) Nr. 3

Storage Capacity: 750 MWh per storage ring

Discharge Time: 3,75 Std.

Water Storage Capacity 575.000 m³

Hight of fall: ca. 530 m

Length of Storage Rings: 15,5 km

Internal diameter of ring storage facility: 7 m

Investment Costs: 650 Mio. Euro, 3 machine set a 67 MW,

therefrom tunnel construction costs: ca. 359 Mio. Euro

Operating Costs: ca. 7 Mio. Euro/a.

Realisation of an underground pumped-storage station is technical ambitious, but a greater social acceptance, due to less land requirement , is expected. In addition, mining techniques in Europe will be developed anymore.

Authors*

Prof. Dr.-Ing. André Niemann und Jan Peter Balmes M. Eng.,

Institut für Wasserbau und Wasserwirtschaft,

Prof. Dr. rer. nat. Ulrich Schreiber,

Fachgebiet Geologie, Universität Duisburg-Essen

Prof. Dr.-Ing. Hermann-Josef Wagner,

Lehrstuhl Energiesysteme und Energiewirtschaft (LEE), Ruhr-Universität Bochum

Dipl.-Ing. Tobias Friedrich, DMT GmbH & Co. KG, Essen

Mining Report Glückauf 154 (2018) Nr. 3

Figure pumped-storage station german → english

Speicherring 1/2/3/4   - storage ring 1/2/3/4

Verteilerrohre 1/2/3/4 - distributor pipes 1/2/3/4

Steigrohr 1/2                 - ascending pipe ½

Fallrohr 1/2                    - down pipe

Sammler                        - collector

Maschinenhaus            - powerhouse (turbine house)

Pumpenhaus                -  pump station

Verteiler                         - distribution device

Wasserspeicher            - water tank (water reservoir)

Sammelrohr                   - collector pipe

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