THE ENERGY INDUSTRY TIMES - AUGUST 2018
Technology 15
Three-way storage breaks the mould
A new energy storage
system capable of
supplying electricity,
heating and cooling
could shape the
future of the thermal
energy storage
market.
Siân Crampsie
The growing need for energy
storage systems in a range of
different applications is driving
new innovation in energy storage
technology, and MAN Energy
Solutions believes it has one such
development: a three-way energy
storage system that can meet largescale
requirements for electricity,
heat and cold.
Germany-based MAN’s so-called
Electro-Thermal Energy Storage
(ETES) system uses surplus renewable
electricity to generate heat and
cold for storage in insulated reservoirs
during a ‘charging cycle’. The
heat and cold can be converted back
into electrical energy on demand, or
distributed to different types of
consumers.
The ability of the system to store
electricity, heat and cold is unique,
according to Prof. Dr. Hans Gut,
Managing Director of MAN Energy
Solutions Schweiz AG, and is also a
factor that will make it appeal to a
broad range of customers. “Due to
the high overall efficiency, the modular
character of the system and its
low impact on the environment,
ETES is a sustainable energy-storage
solution that is suitable for a
wide range of applications worldwide,”
said Gut.
The company also believes that it
will help energy consumers in different
parts of the energy value chain to
play a part in combating climate
change. “The biggest challenge in
building stable, climate-neutral energy
systems is the intermittency of renewable
energy in power generation
and supply,” said Dr. Uwe Lauber,
CEO of MAN Energy Solutions. “To
match an increasing consumer demand
for energy with a fluctuating
supply, the world needs reliable energy
storage systems.”
Energy storage technologies are beginning
to make their mark in the energy
system, helping energy companies
and energy consumers alike
manage intermittent renewable electricity
production and energy costs.
Batteries, in particular, are becoming
increasingly viable in a global energy
storage market estimated at 6 GW in
2017, according to IHS.
There is, however, a growing demand
for thermal energy storage as
governments attempt to electrify and
decarbonise sectors such as HVAC
and district heating. The global demand
for cooling is set to triple by
2050, according to the International
Energy Agency, largely due to the
growth in air conditioning use in
warmer countries. It is in this market
that MAN believes its ETES technology
could play a role.
The ETES system was borne out of
an innovation programme involving
some of MAN’s newest recruits, according
to Patrick Meli, Vice President,
Head of Compressor Engineering
at MAN Energy Solutions.
As Meli explains, MAN runs a
programme, called ‘Future Innovation’,
in which its young engineers
are asked to come up with ideas and
solutions that will be relevant to the
world in 10-15 years’ time. The engineers
have a year to work on their
ideas and build a business plan,
which are then presented to the
company’s board, including the
CTO and CEO.
“ETES came from this programme,”
notes Meli. “We realised it
was an interesting idea and could see
the potential for it, so we started developing
it in further detail.”
Those development plans included
patenting the idea, but MAN hit a
bump in the road when it discovered
that it had already been patented – by
ABB. It was keen to start discussions
with ABB about taking the technology
forward on a commercial basis,
but had to first wait for the Zurichbased
technology firm to resolve legal
issues surrounding its patent.
ABB received the go-ahead in early
2017, and the two companies
started talks over the use of the patent
and developing ETES as a commercial
system. MAN learned that
ABB’s idea was to use ETES for
electricity storage applications only,
but found that the business case was
not exploited to its full potential.
MAN could see the demand for
three-way energy storage, and so the
two companies signed a cooperation
agreement in April 2018.
The cooperation agreement allows
MAN to use the patent under licence
to develop, produce and commercialise
the ETES technology.
The ETES system consists of a turbo
compressor, heat exchange equipment,
hot water storage tanks and ice
storage tanks. It uses carbon dioxide
gas as the medium for energy transfer,
a factor that sets it apart from
some other energy storage systems.
“With CO2, you are talking about a
temperature level of 120°C to -4°C
in the system, temperatures that can
be used directly in most industrial
and commercial applications,” said
Meli. “Other energy storage systems
create much higher and lower temperatures
because they do not use
carbon dioxide, and this creates more
complexity.”
In the charging cycle, MAN’s hermetically
sealed turbo-compressor
HOFIM (High-Speed Oil-Free Integrated
Motor-Compressor) turns surplus
energy from renewable sources
to compress CO2, which is heated to
120°C. The CO2 is fed into a heat exchanger
and heats the water. The hot
water is stored in insulated, isolated
tanks, each one at a separately defined
temperature level. Still under
high pressure, the CO2 is fed into an
expander, which reduces the pressure
so that the CO2 is liquefied and
cooled. The liquefied CO2 is again
pumped through a heat-exchange
system, this time on the cold side of
the system. Heat is taken from the
surrounding water and ice is formed
in the ice storage tank.
In the discharging cycle, gaseous
CO2 enters the heat exchanger on
the cold side of the system where it
condenses because of the cold from
the ice-storage tank. The ice in the
tank melts. The CO2 pump increases
the pressure of the CO2 again. The
CO2 passes through the heat exchanger
and is heated by the water
in the hot-water storage tanks. The
heat from the heated CO2 is fed into
the power turbine where it is converted
back into electrical energy
via a coupled generator. The electricity
flows into the grid and is distributed
to consumers.
According to MAN, there are numerous
uses for the stored heat, including
within the process industries
or for district heating. Among other
possible applications, the cold can be
used to cool data centres, for cold
storage or the air-conditioning of
buildings. “We see this as an energy
management system that can produce
heat, cold and electricity,” said
Meli. “We have been looking at applications
where these three elements
are needed – for example the food
industry and chemicals.”
Data centres are another big draw
for MAN due to their need for cooling
and a need to reduce their carbon
footprint. If they are located close to
cities then they can feed the stored
heat into district heating systems.
“We have presented this idea to data
centre owners and they like it,” noted
Meli.
Mega-cities in regions such as
Southeast Asia and South America
are also an option, according to
MAN, as they have significant requirements
for heat, cooling and
electricity. The ETES system is ideal
in such applications, says Meli, because
of its 5-10 MWe size range.
“ETES can generate 70-80 MWth in
total, and store energy for several
hours, creating a 300 MWh system,”
said Meli.
MAN has not yet demonstrated
ETES at a commercial scale, but has
confidence in the system to work effectively
and reliably. This, in part,
comes from the use of proven technology
that the company has been
using for many years in other industries
such as oil and gas. The challenge
has been the process design.
“We are sure that we have the right
components and the right design,”
said Meli. “We have been through
several design reviews and we are
convinced that the system will work.
“The main challenge for us is on
the customer side, and asking them
to think out of the box and in a different
way from what they are used
to doing.”
Meli added: “Following the Paris
Agreement on climate change, it is
no longer enough to think about your
system on its own; energy users need
to think about the bigger picture and
ETES can help them to do this.”
Potential customers can also be
nervous about the use of CO2, according
to Meli, who points out
when you come from a background
in the oil and gas industries, working
with CO2 is nothing special. “Compressing
CO2 is not so hard,” says
Meli. “We are used to it.”
MAN has yet to sell an ETES unit
but says that it is currently in contact
with a number of potential customers.
“We are sure we will find a partner
soon who sees the advantages of
it,” Meli says.
During the charging cycle the
system uses surplus renewable
electricity to generate heat and
cold for storage
During discharge, heat and cold can be converted back into electrical energy on demand