7
construction costs. In most cases, the mine openings have
collapsed or the water has re-entered the mine floor, mak-
ing dewatering unavoidable 33.
In most cases, access through shafts is advantageous, but
the underground storage space often has to be created first.
Depending on the respective geology, the underground stor-
age volumes can be created either by chamber construction
or as a system of parallel tunnels. Both methods correspond
to the current state of the art in the construction of large
underground storage caverns for underground pumped
storage power plants (UGPSP) in Europe over the last 20
years, as shown in Table 1. The main difference is that a
system of parallel tunnels stores less volume per area than
the adapted Room and Pillar method, which was pioneered
by Clausthal University of Technology in 2011 in a small
project in collaboration with the Barbara iron ore mine 34.
However, a suitable stable rock formation is required for the
localized mining method to offer a higher rate of available
volume per area. In addition, the Harz Energy and Water
Storage (EWAZ) project was developed by a consortium of
universities in Lower Saxony between 2019 and 2022. As
part of the EWAZ project, energy storage was considered
in a holistic concept in which water storage was considered
as a solution to current problems such as flood protection,
low water elevation and ensuring access to drinking water
supplies in the northern German region. The Harz region
is a large water catchment area and supplies the major cities
and municipalities in Lower Saxony with drinking water.
As part of this interdisciplinary project on energy and water
storage, a strategy was proposed for the construction of an
interconnected system of above-ground and underground
waterworks in the western Harz.
The entire workflow of the EWAZ project is shown in
Figure 4 and was designed according to the BM approach.
Table 1. Overview of the most important UGPSP projects of the last 20 years 32 Abbreviations: Austria (AT), Belgium (BE),
Germany (DE), the Netherlands (NL) and Italy (IT)
Project Country Status
Storage
capacity
[m3]
Fall
height
[m] Type Method Year Remarks
Naßfeld AT Operation 160 000 317 New built Parallel adits 2006 Sustainable approach:
Reused excavated rock
for dam expansion
Shale mine
Martelange
BE Research 550 000 500 Subsequent
use
Parallel
storage rooms
2016 Technical feasibility
demonstrated
After-use of
closed coal
mine Prosper
Haniel
DE Research 575 000 530 Subsequent
use
Ring buffer 2012 Technical feasibility
demonstrated.
Investment costs for
reusing infrastructure
After-use of
Grund Ore
Mine
DE Research 320 000 700 Subsequent
use
Parallele adits 2011 Technical feasibility
demonstrated.
Investment costs for
reusing infrastructure
Iron ore Mine
Barbara
DE Research 1 000 000 200–300 Subsequent
use
Adapted
Room and
pillar
2011 Technical feasibility
demonstrated.
Combined with
operating mine
O-PAC NL Research ~192 000 1400 New built Parallel adits 1980
&
2020
Technical feasibility
demonstrated. High
investment costs.
Pfaffenboden in
Molln
AT Authorized 1 240 000 630 New built Parallel adits 2011
&
2021
Project on hold in
initial phase until
2019 for economic
reasons. Under
construction since
2021
Ritten IT Rejected 600 000 900 New built Parallel adits 2009 Not feasible due
to community
disagreements.
construction costs. In most cases, the mine openings have
collapsed or the water has re-entered the mine floor, mak-
ing dewatering unavoidable 33.
In most cases, access through shafts is advantageous, but
the underground storage space often has to be created first.
Depending on the respective geology, the underground stor-
age volumes can be created either by chamber construction
or as a system of parallel tunnels. Both methods correspond
to the current state of the art in the construction of large
underground storage caverns for underground pumped
storage power plants (UGPSP) in Europe over the last 20
years, as shown in Table 1. The main difference is that a
system of parallel tunnels stores less volume per area than
the adapted Room and Pillar method, which was pioneered
by Clausthal University of Technology in 2011 in a small
project in collaboration with the Barbara iron ore mine 34.
However, a suitable stable rock formation is required for the
localized mining method to offer a higher rate of available
volume per area. In addition, the Harz Energy and Water
Storage (EWAZ) project was developed by a consortium of
universities in Lower Saxony between 2019 and 2022. As
part of the EWAZ project, energy storage was considered
in a holistic concept in which water storage was considered
as a solution to current problems such as flood protection,
low water elevation and ensuring access to drinking water
supplies in the northern German region. The Harz region
is a large water catchment area and supplies the major cities
and municipalities in Lower Saxony with drinking water.
As part of this interdisciplinary project on energy and water
storage, a strategy was proposed for the construction of an
interconnected system of above-ground and underground
waterworks in the western Harz.
The entire workflow of the EWAZ project is shown in
Figure 4 and was designed according to the BM approach.
Table 1. Overview of the most important UGPSP projects of the last 20 years 32 Abbreviations: Austria (AT), Belgium (BE),
Germany (DE), the Netherlands (NL) and Italy (IT)
Project Country Status
Storage
capacity
[m3]
Fall
height
[m] Type Method Year Remarks
Naßfeld AT Operation 160 000 317 New built Parallel adits 2006 Sustainable approach:
Reused excavated rock
for dam expansion
Shale mine
Martelange
BE Research 550 000 500 Subsequent
use
Parallel
storage rooms
2016 Technical feasibility
demonstrated
After-use of
closed coal
mine Prosper
Haniel
DE Research 575 000 530 Subsequent
use
Ring buffer 2012 Technical feasibility
demonstrated.
Investment costs for
reusing infrastructure
After-use of
Grund Ore
Mine
DE Research 320 000 700 Subsequent
use
Parallele adits 2011 Technical feasibility
demonstrated.
Investment costs for
reusing infrastructure
Iron ore Mine
Barbara
DE Research 1 000 000 200–300 Subsequent
use
Adapted
Room and
pillar
2011 Technical feasibility
demonstrated.
Combined with
operating mine
O-PAC NL Research ~192 000 1400 New built Parallel adits 1980
&
2020
Technical feasibility
demonstrated. High
investment costs.
Pfaffenboden in
Molln
AT Authorized 1 240 000 630 New built Parallel adits 2011
&
2021
Project on hold in
initial phase until
2019 for economic
reasons. Under
construction since
2021
Ritten IT Rejected 600 000 900 New built Parallel adits 2009 Not feasible due
to community
disagreements.