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PUMPED STORAGE June 2017
8 WWW.WATERPOWERMAGAZINE.COM
Pumped storage Pumped storage
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Innovative pumped storage at Negundo innovation centre
In Froyennes, Belgium, an innovative pumped hydro storage system is being built in the
Negundo innovation centre [5]. The installation uses an existing 1500m3 articial basin for
rainwater collection as the upper reservoir (gure 3) and an underground 625m3 lower
reservoir (gure 4) with the available head ranging from 6 to 10m. Both are connected by a
70m long, 30cm diameter underground polyethylene pipe featuring a 10.5kW Ensival-Moret
single-stage, centrifugal pump t with a variable frequency driver (gure 5) allowing a
hydraulic efciency of 83% in pump mode and 73% in turbine mode. The installation sits well
in the Negundo innovation centre as a demonstrator not only for integrated pumped hydro
but also for an exemplary building complex already t with solar panels, wind turbines, and
batteries. The installation was also designed as a test rig for hydraulic equipment, a place
where manufacturers can bring their own equipment and test it under a variety of conditions.
Looking back at the project which started in 2014, Alessandro Morabito, one of the engineers
behind the project, points out the civil works and the design of the hydraulic machine as the
biggest challenges: “Picking a reversible machine that can work efciently with a variable
head for such small capacities is no easy task and the engineering people did a great job in
tting the lower reservoir among the existing buildings”. Meanwhile, the place is mostly ready,
just waiting for the reservoirs to ll up with rainwater. Then it is just a matter of getting
everything to work together, says Alessandro, one headache at a time.
How small
can you go?
Distributed energy storage in buildings is expected to play an increasing role in the future energy
transition. As pumped hydro is by far the most successful storage technology, Guilherme Silva asks
does this prompt the question: could pumped storage be used on a much smaller scale in buildings?
Representing such an important share
of energy use, it is no surprise that
buildings are one of the first elements
to tackle for fighting climate change and the
dependence on fossil fuels. Inside buildings,
appliances are becoming more efficient, mostly
due to strong energy use standards, while
the buildings themselves enjoy new design
processes that further optimise their behaviour.
Construction technology is also keeping up, with
new materials and techniques that embrace the
transition while renewable energy sources, such
as solar panels for water heating or electricity
production through photovoltaics, are even
allowing for buildings that produce more energy
than what they use on an annual average.
The problem with most renewables is that
their generation is variable in nature. One solution
to solve that variability is to use energy storage,
effectively decoupling the required timely
match between energy generation and use. With
buildings representing such an important share
of energy use and with most renewable energy
sources being of a distributed nature, distributed
energy storage in buildings is expected to play an
increasing role in the future energy transition.
Among the different energy storage
technologies, pumped storage hydro is by far
the most successful technology, representing
most of the installed storage capacity worldwide,
although for large installations. This prompts the
question on whether such technology could be
used on a much smaller scale, namely in buildings,
given its simplicity and possible synergies with
the existing water infrastructure. The physics,
however, are demanding: the limited floor loads
and height of the buildings would lead to low
energy density which means low energy storage
capacity. The economics also seem challenging:
large installations are competitive since, with
minimum civil works, a large storage capacity can
be obtained from a geographically suitable site. In
a building, however, everything would have to be
built and economies of scale would not be present
for such small installations. Therefore, it seems
intuitive that making pumped storage competitive
on a small scale, especially in buildings, would be
challenging but the question still stands on how
small can one go. How small is it still feasible?
Pumped proposals
A few authors have proposed pumped hydro
energy storage for buildings. Fonseca and
Schlueter [2] proposed such a system for an
informal community of 3000 people, occupying an
abandoned complex of five unfinished buildings in
Caracas. They imagined distributed water tanks,
due to load floor limits, through different floors
coupled to the building’s water infrastructure. With
a storage capacity of 85kWh, the system was more
expensive than using lead-acid batteries but the
authors defended that externalities such as water
security of supply and technological simplicity
rendered it the best choice.
Stoppato et al [3] also proposed a small-scale
pumped hydro storage, although not in a building,
coupled to a cogeneration system, batteries, and
PV in order to supply electricity, heat, and water
to a resort of 170 people in Italy. Despite the
optimistic input values, optimisation resulted in
two 175m3 artificial concrete reservoirs, placed
at a height difference of 50m, for a storage
capacity of 24kWh. Using a reversible 7kW pump,
the pumped storage project would increase
the lifetime of the 148kWh lead-acid battery
by reducing the discharge rate and depth-of-
discharge. Again, externalities such as technology
simplicity and greenhouse gas emissions
mitigation were presented as important
externalities, especially for a resort.
Manolakos et al [4] described an existing
pumped storage hydro scheme for a remote
village of 13 homes in a Greek island, coupled
to 18kW photovoltaics and a 100Ah lead-acid
battery. The project consists of two 150m3 water
tanks, at a height difference of 100m, with a
40kWh storage capacity. A multistage centrifugal
pump is used for pumping while another is
reversed and used as a turbine. A variable-
frequency drive adjusts the pump rotation
speed according to the available excess power.
No references are made to the economics of
the project but the system, with an estimated
efficiency of about 30%, is also used for irrigation
and household water supply, with the easy
maintenance being a crucial advantage.
Enter the Goudemand residence
The Goudemand residence is an apartment
building complex located in Arras, France where,
in 2012, part of the common areas were rendered
grid-independent using solar panels, wind
turbines, batteries, and an integrated pumped
storage project [1]. To the author’s knowledge, it is
the first existing installation of its kind. It is part
of a larger renovation where the electricity use in
the common areas (except for the lift) was also
reduced by about 80%, through the replacement
of intercoms for more efficient models and
lighting for more efficient LED models coupled to
presence and light sensors. Electricity generation
is provided by a 2.2kW photovoltaic installation
and two 500W vertical-axis wind turbines which,
meanwhile, have been deactivated and replaced
by different models. The pumped hydro makes
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Figure 1: Upper reservoir of the
Goudemand residence pumped
storage hydro (in 2015).
Figure 2: Lower reservoir and Pelton turbine
of the Goudemand residence pumped storage
hydro (in 2015).
Figure 3: Upper reservoir of the Froyennes project (in 2017).
PUMPED STORAGE June 2017
10
Pumped storage
use of the 30m height of the building to store
water in the 200m2 roof reservoir, up to 60m3
at a depth of 30cm (figure 1). It was built by
waterproofing the roof and existing surrounding
walls with the contractor estimating that such
configuration brought an additional cost of €700
to a typical roof waterproofing of €10000. The
reservoir is only fully emptied for the annual clean
of accumulated plastic bags and dead birds,
increasing the lifetime of the waterproofing and
avoiding trespassers on the wind turbines.
The lower reservoir is located in the basement,
consisting of five rectangular 10m3 plastic water
tanks (figure 2) connected to the upper part by
a 450W Pelton turbine and an 18W electrovalve
while pumping is ensured by a 1.5kW multistage
pump. The 3.5kWh useful energy capacity of
the project is small compared to the 24kWh of
the lead-acid battery, but proves essential in
extending the battery’s lifetime of about 1000
cycles. The system is set to provide local energy
generation to the common areas of the residence,
with the remaining recharging the battery, and
finally the pumped hydro storage. When the local
energy generation is not sufficient to supply the
common areas, the battery starts discharging
down to a certain depth-of-discharge until the
pumped hydro kicks in, feeding the local load and
recharging the battery [1].
The economics of the project are not publically
available but the contractor estimates the entire
renovation at about €150,000. Nevertheless,
contractors and equipment suppliers indicated
lower average cost estimates of €38,000 for the
pumped hydro, €35,000 for the remaining energy
production and storage equipment, and €27,000
for the energy efficiency measures [1].
Getting the numbers right
A pumped storage project requires six basic
components: two reservoirs, a pump, a turbine,
piping, and a control system. For the reservoirs, a
waterproofed structure can be used for low cost,
as seen in the Goudemand residence. Otherwise, a
plastic water tank can be used with an average
cost of €300/m3 for a vertical cylindrical plastic
tank, plus installation. For the hydraulic machinery,
the bigger the better in terms of efficiency and
economies of scale. Efficiency ranges from 50-60%
and cost from €2-4/W for a centrifugal pump with
a head of 5-20m and a hydraulic power capacity
of 0.5-1.0kW. An electronically-controlled pump
could, under the same conditions, raise the
efficiency to 60-70% but, with a cost of €4-6/W, the
increased efficiency does not prove a good trade-
off. On the other hand, small turbines are difficult
to come by. The typical solution is to use a pump
in reverse, an area where some manufacturers
have a large experience but where data is still
scarce. Nevertheless, literature suggests that
peak efficiency in turbine mode is the same as in
pump mode, but for higher head and flow values.
Therefore, round trip efficiency would be around
25-35% which is quite low when compared to
batteries which boast values closer to 90%. But
efficiency itself is only important if the energy
input cost is high, since that would also render the
energy losses expensive. Piping is about €100/m,
while the control system stands for an almost
fixed average cost of €7000. Other costs, such as
certification, are mostly fixed and can reach up
to €3000.
Putting it all together in a 20m height building
with a 200m2 roof surface, one ends up with a
€46,000 pumped storage schem with a 2.2kWh
electrical energy output. The results look grim
knowing that a similar lithium-ion battery
installation would cost less than €4000 and
Author information
The author is a Researcher at Université
Libre de Bruxelles. He has been carrying
out research into the electric power
industry, namely the impact of market
liberalisation and the increased share of
renewable energy sources and storage.
Email: goliveir@ulb.ac.be
have a 90% efficiency, although with a shorter
lifetime. The use of an existing lower reservoir,
for instance for a building close to a canal, would
lower the cost close to €19,000 which is still far
from competitive. Further synergies, namely with
the existing water infrastructure of the building,
are difficult to justify given the very different
dimensioning requirements and the strict potable
water norms. Therefore, despite being technically
feasible, pumped storage is too expensive for
small-scale installations, namely in buildings,
since it misses on the synergies and economies of
scale that render large installations competitive.
Also, while other storage technologies are
quickly getting cheaper, the maturity of pumped
storage hydro contradicts any strong future
improvements which, coupled with its low energy
density, seems to make it a losing contender for
energy storage in buildings. ■
References
[1] G. Silva and P. Hendrick. Pumped hydro
energy storage in buildings. Applied energy
179 (2016) 1242-1250.
[2] J. Fonseca and A. Schlueter. A novel
approach for decentralized energy supply
and energy storage of tall buildings in Latin
America based on renewable energy
sources: Case study - Informal vertical
community Torre David, Caracas - Venezu-
ela. Energy 53 (2013) 93-115.
[3] A. Stoppato et al. A model for the
optimal design and management of a
cogeneration system with energy storage.
Energy and buildings 124 (2016) 241-247.
[4] D. Manolakos et al. A stand-alone
photovoltaic power system for remote
villages using pumped water energy
storage. Energy 29 (2004) 57-69.
[5] A. Morabito et al. Set-up of a pump as
turbine use in micro-pumped hydro energy
storage: a case of study in Froyennes
Belgium. Journal of Physics: Conf. Series
813 (2017) 012033.
Left – Figure 4: Underground lower reservoir of the
Froyennes pumped hydro storage (in 2017).
Above – Figure 5: Reversible hydraulic machine of the
Froyennes project (in 2017).
