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190

I S S U E S E V E N

H O R I Z O N 2 0 2 0 P R O J E C T S : P O R TA L

www.horizon2020projects.com

P R O F I L E

S O C I E TA L C H A L L E N G E S : E N E R G Y

T

he growing production of renewable energy by wind

turbines and photovoltaic panels and its progressive

integration in the centralised grid have created new

energy management issues due to the intermittent and

unpredictable nature of these production means. A restructuring

of the electrical grid is therefore necessary to ensure that

electricity is reliably delivered to consumers. Energy storage is

critical in order to compensate for the imbalance between

consumers and producers. The fragmentation of the grid into

more local, self-sustainable electricity networks – comprising

both producers and consumers of electricity – also requires the

installation of energy storage units to provide a stable electricity

supply. Indeed, as power networks grow smaller, the need for

energy storage increases.

Batteries for the electrical grid

Energy storage systems may be broadly categorised according to

the amount of time energy will be stored for: long term (days),

intermediate (hours), and short term (seconds to minutes). The

intermediate and long term energy storage technologies are

currently limited to hydropower and compressed air energy

storage, which are practically restricted to specific geographical

locations (e.g. existing lakes/reservoirs and underground caverns).

In the last ten years, advances in megawatt-scale batteries have

thrust these technologies to the foreground of the field, and

demonstration projects for renewable energy storage continue to

emerge. Batteries provide major advantages such as flexibility in

terms of location, capacity and power scales. Their characteristic

fast response time (typically less than a second for starting a

charge or discharge), low maintenance requirements and

reliability favour their use for intermediate scale energy storage,

particularly in the case of a delocalised electricity network. For

instance, they are suitable for storing the electricity needed for a

group of houses or an apartment building during the peak

demand periods when the production is insufficient for supplying

the required energy.

Redox flow batteries

In the large family of batteries, redox flow batteries (RFB) are

particularly interesting for the hour-range storage of renewable

energy. These batteries are based on two liquids which are

pumped through a central electrochemical cell – where the energy

is stored/released – and stored in separate, external reservoirs.

The advantage of this approach compared to classical solid-state

batteries is the independence between the energy and power

ratings, which is widening the range of applications. As a result,

these systems may be included in a local grid for compensating

for peak electricity demand, which requires high power for a short

Clean hydrogen on demand

The Laboratory of Physical and Analytical Electrochemistry explains its innovative

battery concept. By generating hydrogen, its redox flow battery offers new

opportunities in renewable energy storage

Fig. 1 Concept of an external chemical discharge of an RFB: the charged liquids stored in the tanks can be discharged in the catalytic bed to

generate hydrogen and oxygen, for instance