La recherche scientifique face aux défis de l'énergie - BibSciences.org

EXECUTIVE SUMMARY 39
power level. When analyzing such storage solutions, one must also include a
necessary delay time to restore power when a demand comes on line.
In general terms, energy can be stored in a mechanical/chemical/
electrochemical and/or thermal form. Mechanical storage mainly calls for
pumping large amounts of water to high level dams and used later in turbine
generators to produce electricity (PHES). Another possible method is to
compress air and use this at a later time through a gas turbine unit to produce
electricity. A large number of methods also exist to store energy in chemical
form: batteries, production of hydrogen by electrolysis and then recovering the
energy through fuel cell assemblies or through gas turbines, production of
hydrogen to synthesize fuels (liquid or gaseous). Lastly, storage of thermal
energy – well adapted to solar concentration processes – can extend the
possibility to produce electricity beyond the daylight (sun radiation) period. *
Research priorities should be directed to:
(1) Possibilities of implementing PHES facilities in low-elevation
configurations. The reason for this is that PHES’s alone can be used to
easily store energy from which to generate electricity. One can
imagine sea-water lakes installed at the tops of cliffs, near offshore
wind farms or near a land-based power generation station.
(2) Pushing back the physical limits for electro-chemical storage of electric
power to augment the density of the energy stored. Such research is
necessary notably for applications in the domain of transportation systems.
(3) Storage in the form of hydrogen gas, the conversion to electricity
being enabled by both high and low temperature fuel cells or
combustion driven turbines in a combined cycle power plant.
(4) Possibilities of using hydrogen to produce synthetic fuels. Using
hydrogen was first envisaged to provide automotive power for
automotive vehicles, but the difficulties to implement the process are
quite sizable and it may well turn out that this vector could prove more
useful (viz., efficient) in other sectors.
Storing electricity is a major theme necessary in the development and
integration of renewable energy sources, but research in this area does not
match the needs.
* It is worth noting the orders of magnitude of various forms of energy storage: for PHES
(pumped hydro energy storage), 1 m 3 (i.e., 1 000 kg) of water represents 0.8 MJ after a 100 m
drop; combustion of 1 kg of oil fuel releases 42 MJ; combustion of 1 kg of hydrogen, 120 MJ
and, finally, 1 kg of the best batteries today can store 0.72 MJ.