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Over-production in periods of excess requires the adoption of ad hoc storage systems

The introduction of renewable energy has increased this criticality of the already delicate system.

Magazine: AMBIENTE
Publishing house: Publindustria srl.
Number 6
July 2011
Article: Energy must be stored
Summary by: Roberto Reffo
Institute: La Meccanica

The electricity production scheme envisages basic coverage by large non-flexible power stations (large thermal power plants and nuclear power plants) and rapid-start power plants (gas turbine power plants) for demand points. The production system lacks the possibility of accumulating electricity in times of low demand (apart from the pumping stations).

The introduction of renewable energy has increased this criticality of the already delicate system. In fact the problem of energies from wind and PV is their seasonal and night discontinuity which overlaps, in the long term, the meteorological unpredictability. Paradoxically, a study by the German energy agency (DENA) in 2005 already provided for major problems with possible blackouts due to overcapacity due to the introduction of renewable energies and indicated in the 15% quota the maximum limit of intermittent energy that a network conventional can tolerate.

Energy must be stored
In anticipation of the so-called "smart grids" (smart electricity distribution networks), the "energy storage" systems would be ideal.
Below we illustrate some of the possible storage systems:

In Japan, new NaS iodine sulphide battery systems have been developed capable of storing large amounts of energy, even though very light lithium-ion batteries with up to 97% efficiency or electrolyte-flow batteries are expected in the future. base of vanadium salts.

A well-known technology for leveling the supply demand is represented by the pumping of water or air: during the day the water from a basin is used for the production of energy while at night the water is returned to the same basin: the yield however, the system is very low even if effective.

Compressed Air Energy Storage (CAES) compressed air system: excess energy is used to compress air into subterranean cavities. The compressed air is then used as a comburent to increase the efficiency of gas turbines. Large sites where to store large quantities of compressed air. however, they are not readily available and in any case the layout is very expensive.

Advanced accumulation systems based on the accumulation of thermal energy: by molten salts or diathermic oil
Flywheel systems: guarantee rapid intervention and efficiency up to 96%. The mechanical energy obtained from an electric motor is used to start a flywheel which makes the energy accumulated at the right moment.

Hydrogen production: excess energy is used in the production of hydrogen by thermal splitting or electrolytic cleavage. There is no gas distribution network and pressure build-up is expensive.

The use of hydrogen for the production of methane is interesting, reacting with CO2 on ruthenium based catalysts.