Page 18 - Innovation in energy management: contribution of railways to sustainable mobility

R.3. Promote the active use of electricity generated by the
braking of trains (in DC systems)

Investment: Nature: Improvement:

Related to:
R.7 R.8 R.10

The active use of regenerated energy from braking on direct current lines will continue
to be a strategic aspect for railway companies, both in terms of the installation of
electronic power converters to inject the energy surplus into the network (reversible
cells) and the installation of grounded storage systems.

The technology is becoming standard, although it is necessary to continue optimising it
as more knowledge is available at the operation phase.

Royal Decree 1011/2009 continues to represent a fundamental tool for the
implementation of reversible cells, as it represents a direct economic incentive for users.
It should be noted that the operating experience has confirmed that the savings produced
are particularly important, with values that can exceed 50% of the total energy consumed
by the substation, providing a return on investment in a few years.

On the other hand, the implementation of grounded storage systems has been scarce,
although this is expected to change as a result of the gradual introduction of new smart
grids. Currently, this solution is considered more expensive than the use of reversible
cells, although it also has other technical advantages associated with the improvement of
energy flows in the network, such as:

 The minimisation of problems caused by undervoltage.

 The continuity of the electricity supply in the event of a fault from the substation
(for example, for a train leaving a tunnel or arriving at a nearby station).

 Limitation of disturbances coming from the installation.

 Improving the quality of energy distribution.

In any case, it is necessary to update, at sector level, the technical and economic
characteristics of the different storage technologies, identifying which ones would be the
most efficient for the current needs of railway companies. These technologies must be
aimed at improving energy capacity as well as the cost ratio per unit of energy for each
charge/discharge cycle.

The experience of use on the ground, although low, identifies that electrochemical storage
is the most interesting at this time compared to purely mechanical storage. Thus, lithium
ion batteries are being improved, and batteries that use titanium are also being
developed. On the other hand, there is ongoing work to optimise redox flow batteries.

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Position paper: Innovation in energy management: contribution of railways to sustainable mobility
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