Hydraulic Rock Storage
A new concept
for storing electricity
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The solution for storing large
amounts of electricity from
renewable energy sources
— Renewable energy from wind and solar sources
is now making a rapidly increasing contribution to global
power supplies. Solar energy in particular is always available
in many regions of the world and this can be converted
relatively cheaply into electricity. In order to ensure a con­
tinuous supply of electrical power it is necessary to have
a highly efficient system capable of storing the day‘s electrical
output for a period of several hours.
The Hydraulic Rock Storage (HRS) can do this.
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The Hydraulic Rock Storage
Using proven technology for
smart storage solutions
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Method of operation
— The HRS consists of a large piston of rock that has
been detached from the surrounding strata using validated and
proven mining techniques. The rock piston and its surrounding
cylinder are sealed by means of a synthetic film liner. This
method is already used by the international tunnel construction
industry.
The sealing ring itself is composed of a rolling bellow
sealing, which works effectively in high stress situations (see
page 9). A pump driven by surplus electricity forces water
beneath the rock piston, causing it to lift. When electri­city is
required the pressu­rised water is directed through a turbine
to generate alternating-current electricity that can then be fed
directly into the supply grid. This process has an efficiency
rating of over 80%.
r
Basic principle
— The HRS operates on the principle of converting
electrical into potential energy by lifting of a large mass
of rock. Here the amount of energy that can be stored is pro­
portional to the rock mass and the height by which it can
be raised. In the case of the HRS this results in the remarkable
characteristic that a piston whose diameter and height are
both doubled exhibits a sixteen-fold energy storage capability.
As the cost of the operation to detach a rock piston of twice
the reference size is only four times the reference amount,
the storage capacity of the system becomes significantly
more cost-effective.
This particular physical law favours the construction
of large HRS units. Economic systems would have a minimum
diameter of some 150 metres, which results in a storage capa­
city of one gigawatt-hour. When used in combination with
photovoltaics the HRS can guarantee stable production costs
for many years on end.
2r
r
Storage Capacity
Mass ~ r 3
Height ~ r
Capacity ~ r4
Construction cost: b ~ r 2
— Cost per kWh ~ 1/r 2
capacity [GWh]
0.20
1.0
2.1
3.2
8.0
124
radius, height [m]
50
75
90
100
125
250
diameter [m]
100
150
180
200
252
500
volume of water [1000 m3 ]
392
1325
2290
3141
6284
49087
21
31
37
41
52
103
pressure [bar]
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Constructing the HRS
— Recognised mining techniques are employed
for the construction of the HRS. A supply tunnel is driven
down to the bottom level of the planned cylinder. The floor
of the cylinder is then detached using mechanised drill and
blast technology and the area is sealed. Conventional drilling
and blasting is also used to excavate down through the sidewalls of the piston from ground level.
All the exposed surfaces are sealed with geomembrane
or metal to protect against environmental effects and
water ingress.
The required infrastructure is also put in place at the same
time, primarily the access tunnel and generator chamber.
The construction work is expected to last 3 to 4 years from
the construction start date.
spiral tunnel
working level
connecting tunnel
working level
base sole
connecting tunnel
150 meter
The construction of the piston is very similar
to projects in the coal mining industry and
tunnel construction.
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A possible application of mining process
4m
Mining process application in Kiruna, Sweden
(View on illustration: unrolled cylinder wall).
— The mining engineering procedures required
for the project are well tested and can be executed by
a number of mining contractor companies.
Various rock bolting techniques can be employed,
according to the type of rock strata encountered, so as to
ensure that the piston and cylinder remain stable in the long
term. This provides for an operating life of some 100 years,
which is comparable with that of today‘s road tunnels.
rock strata
shotcrete
watertight sheeting
concrete slab with mounting
high-grade strata
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The Sealing
The rolling membrane is hidden in the slit
between piston and cylinder. The width of
the slit is about 20 centimeter.
Piston
Detail
Features
— The rolling membrane seal is the preferred tech­­
no­logy to seal the system. With the rolling membrane the
appearance of the cylinder in the countryside can also be
varied according to taste. This means, for example, that lightcoloured concrete can be used instead of a metallic surface.
–
–
–
–
–
ypical pressure at sealing: 40 Bar
T
Forces are absorbed by steel cables
Flexible towards fluctuating position of cylinder
Self-centering
Production similar to steel belted tires
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The Storage in Operation
An example of HRS of one
gigawatt-hour in real scale.
Combining a large PV power plant and
a Hydraulic Rock Storage System results in
a reliable power supply.
— After the HRS has been completed the pumping
operation can commence for the first piston lift. This would
normally take place during daylight hours when the sun is
shining or when there is wind blowing. The piston would then
be lowered during the evening or night-time hours, or when
the wind is light, so that electricity can be generated from the
stored energy. This process would be repeated on a daily basis,
thereby provi­ding a consistent supply of electri­city. The opera­
ting life of the system is therefore practically unlimited, since
the storage facility, i.e. the rock mass, essentially does not wear
out. The operating equipment, and especially the pumps,
turbines and generator, will be designed for a service life of 60
years or more. If necessary, these units can be replaced at the
end of their operating life.
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— The daily cycle of elec­tricity demand
depends on local lifestyle. In most countries the sun
is already settled when a lot of energy is needed.
Therefore, it is useful, to collect and store the solar
energy during the daytime and provide the useful
electric power at the evening and during night time.
This time shift needs efficient and very reliable
storage systems. The Hydraulic Rock Storage does
not wear out, even if it is used for the daily cycle.
Power [MW]
200
PV Electricity for
Storage
180
160
140
Direct Used PV
Electricity
120
100
80
Usage of Stored
Electricity
60
40
20
0
0
1
2
3
4
5
6
7
8
9
10
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Example of the energy supply, that is possible with
a 200 MW peak power PV system and a one gigawatt
hour Hydraulic Rock Storage (150 meter diameter).
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21
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Time [h]
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Location Factors
— The HRS is best built at locations with
a solid bedrock. The most favourable sites comprise
stable, non-faulted rock such as granite or compact
layers of another solid rock material. The initial
situation first has to be assessed in detail by a team
of geologists.
In addition, and depending on the size of the storage
facility, two million cubic metres of water have to
be provided only once and held ready for transfer
in a reservoir.
The HRS is best suited to regions where
– t here is a high solar radiation level and/or a large
wind yield
– power supply security is indispensable
–conventional pumped storage systems cannot
be built due to inadequate elevation.
The necessary water for the hydraulic piston
is stored in a reservoir. No continuous water
supply is necessary.
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Advantages of the
Hydraulic Rock Storage
System
–Cost effectiveness: scaling of costs
with increasing radius, costs fall at 1/r²
– E
fficiency: about 80%
(comparable with pumped storage)
–Project can be constructed using proven
and validated technologies
– Relatively low space requirement
– Long operating life of several decades
–Lower water consumption than pumped
storage systems (about 1/4)
–Black start capability and high
flexibility in various operating modes
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— The concept of the Hydraulic Rock Storage
system was invented by Professor Heindl and is developed
by Stuttgart-based Heindl Energy GmbH. A team of specialists
in geology, geophysics, mining and civil engineering provide
advice and assistance during the development process.
The company is majority-owned by Professor Eduard Heindl
and is financed by Swiss-based HTG Ventures AG.
Contact
Heindl Energy GmbH
Wankelstrasse 14
70563 Stuttgart / Germany
Phone +49 711 46926713 www.heindl-energy.com
info@heindl-energy.com
Picture Credits
©fotolia.com/trekandphoto; ©iStock.com/andreiorlov,
InnaFelker, pavel_klimenko, SoleilC, vallefrias;
Heindl Energy GmbH
Computer Generated Imagery: designconcepts GmbH
Professor Dr. Eduard Heindl, inventor
of the Hydraulic Rock Storage System.
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www.designconcepts.de
Contact
Phone +49 711 46926713 www.heindl-energy.com
info@heindl-energy.com
1/2015
Heindl Energy GmbH
Wankelstrasse 14
70563 Stuttgart / Germany