Patent Application
20230029351
The present invention relates to a system and a method for generating and storing hydroelectric energy.
The concept of underground pumped hydro energy storage (UPHS) is known in the Prior Art. It is conceptually similar to aboveground pumped hydropower where energy is stored by pumping water from a low-lying reservoir to a water reservoir at a higher elevation. When energy is needed, the water is returned to a turbine/generator combination at a lower level and dropped into the lower reservoir.
In underground pumped hydropower plants, the upper reservoir does not need to be located at high level aboveground, since water is delivered to the turbine at a level below the ground and collected in an underground cavity. This increases vastly the number of locations where pumped hydropower can be used, which is of particular interest in flat land regions and when operated in concert with renewable energy sources such as wind and sun. It also enables local communities to form electrical microgrid networks with increased autonomy and optimized energy trading solutions. A requirement for this is that the amount of water that can be stored in the upper and lower reservoirs is large enough. Depending on the elevation difference between the upper and the lower reservoirs, an energy storage capacity in the range 100 MWh-1 GWh shall imply a required water storage volume in the upper level reservoir to be 104-106 m3, corresponding to a pond or reservoir of surface area 103-105 m2 at a water depth 10 m. The presence of such a body of water represents a problem in many cases, e.g in local communities with high population density, where microgrid storage appears especially attractive but where space is limited and concerns may be raised about safety and visual impact.
Accordingly, it is a major objective of the present invention to introduce novel concepts and techniques for underground pumped hydroelectric energy storage systems with the following characteristics:
The objective is achieved according to the invention by a system and a method according to independent claims. A number of non-exhaustive embodiments, variants or alternatives of the invention are defined by the dependent claims.
A first aspect of the invention is a hydroelectric energy production and storage system comprising an upper reservoir located in a depression or cavity in the ground, a lower reservoir comprising at least one cavity located underground at a lower altitude than the upper reservoir, a shaft extending from a low point of the upper reservoir to the lower reservoir for providing hydraulic connection between the upper and lower reservoir, energy production means comprising a turbine and generator unit arranged to be driven by water in the shaft, and energy storage means comprising pumping means arranged for pumping water from the lower reservoir to the upper reservoir. The system further comprises objects arranged in the depression or cavity forming an aggregate which fills the depression or cavity and comprises hydraulically communicating void volumes between the objects.
Optionally, the energy storage means comprise the turbine and generator unit run in reverse, or a separate pump.
Optionally, the depression or cavity is at least partially a landscape feature of natural origin. Further optionally, the depression or cavity is one of the following: A gully, valley, trench, pond or lake. Even further, the depression or cavity can be at least partially created by excavation or mining.
Optionally, the depression or cavity is one of the following: An open pit mine, tunnel opening, water reservoir, well, trench.
Optionally, the objects are made from incompressible materials. The objects can be of one or more of the following types: Rocks, gravel, sand. Further, the objects can be manufactured by molding, cutting, extrusion or crushing. Optionally, the objects are shaped as one or more of the following: Spheres, rods, pipes, symmetric or asymmetric polyhedra.
Optionally, the aggregate is arranged to present a defined upper surface. The upper surface can be covered by a membrane, and the membrane can be impermeable to gas or water or both. Optionally, the membrane is arranged and configured to collect gas transmitted to or from the aggregate of objects and guide it through a venting chimney to the ambient air.
Optionally, the aggregate contributes to constituting a landfill. The landfill can be providing real estate for one or more of the following: Buildings, industry, agriculture, gardens, leisure activities.
A further aspect of the invention is a method for building and operating a hydroelectric energy production and storage system as described above, comprising the steps of:
Optionally, the objects arranged in the depression or cavity are at least in part rocks and gravel from the excavation or mining performed to create the system.
Embodiments of the present invention will now be described, by way of example only, with reference to the following diagrams wherein:
The following reference numbers refer to the drawings:
The following description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further particular features, structures or characteristics may be combined in any suitable manner or in one or more embodiments.
The basic concept for the energy storage system according to the present invention is illustrated in
The arrangement shown in
Assuming that the volumes of water that need to be stored in the upper and lower reservoirs are roughly equal, the minimum volume of rock and gravel that must be accommodated in the depression holding the upper reservoir shall correspond to that of the lower reservoir, plus an added volume which depends on the void space available to hold water between the individual rocks and gravel particles: If rock and gravel particles constitute a volumetric fraction q of the total rock and gravel volume Vtotal, the available void volume for storing water Vvoid interstitially is
V
void=(1−η)Vtotal. Eq. 1
Thus, for η=0.5, the void space is half the volume occupied by the rocks and gravel, and the minimum volume required for storage in the depression holding the rocks and gravel shall be roughly twice that of the lower reservoir.
The value of η depends on many factors, including the shape and size distribution of the rock and gravel particles, how they are packed, and the presence of earth, clay, sand and organic matter. As a general rule, the rock and gravel particles should be uniform, hard and clean (i.e. free from small particle fractions such as dust and sediments). Solid granite has a density of 2.69 tons/m3, which is reduced to 1.4-1.7 tons/m3 when in crushed or gravel form, corresponding to a volumetric void fraction (1-η)=0.36-0.48.
As shall be clear to a person skilled in the art, the basic principle taught in the present invention may allow any type of fill material that provides communicating internal voids and does not compress too easily. Thus, fill material can include objects of nearly any shape packed in organized or random fashion, either of natural origin (e.g. rocks, gravel) or manmade (e.g. spheres).
| Number | Date | Country | Kind |
|---|---|---|---|
| 20191481 | Dec 2019 | NO | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/NO2020/050313 | 12/14/2020 | WO |
