ESSAY: ENERGY STORAGE

The energy storage is mainly an economic decision. Without storage, an industry must develop and maintain an entire delivery network capable of meeting the highest peak of the year at any given moment. It means that the generation and consumption of the energy would be ‘just-in-time’, whereas with storage the industry must build up just what is considered to be a heavy but possible load.

Although electricity can not be directly stored, it can be transformed in other forms and converted back to electricity when needed. The additional value of the electricity during the peaks of demand must, therefore, cover the cost of the storage. Therefore, not all the systems for storing energy are suitable at any point.

As the electricity demand is expected to continue growing up, storage can be a key point to give flexibility to the electricity market. In addition, energy storage plays an important role in the development of the renewable energies. The production of renewable energy is desirable because of the environmental improvements, the increase in the energy security (supply becomes more independent from third countries with low political stability) and the improvement in the competitiveness. However, renewable energy resources have two problems. Firstly, most of the renewable energy sources usually take place in locations far away from the centers of consumption (especially those concerning to wind farms) being necessary the construction of new grids. The construction of the grids takes much longer that the construction of the wind farms and this Lag-time opens a door to the storage technologies to use locally the energy generated. Secondly, the generation of power, generally speaking, occurs when the power demand is low.  By storing this power, it can be released during the peaks of demand. Both facts will make renewable energy more cost-effective and promote its acceptance in the coming years

Without storage, the electricity market is threatened with

a)      Raised volatility: higher and more unpredictable prices which lead to reduced investment by manufacturing and service industries in that region

b)      Reduced reliability: lower assurance that high quality power will be continually available rises the cost of the electricity and the risk of damaging the facilities

c)       Threatened security: problems of secury of supply where backups are much likely to occur and increase the damage of sabotage

However, if the energy storage technologies are further developed and successfully applied, those previous challenges can be overcome and a more efficient market that costs less to operate and that is more responsive to market changes and reliable in the event of disruption is achieved.

As commented, not all the locations should be provided with the same energy storage. At present, a number of technologies are commercially viable, while others are expected to be in the next future.

Pumped-hydro storage is the oldest and largest of all the storage technologies. It consists of two reservoirs, one located at a low level and other at higher level. During the off-peak the water is pumped from the lower reservoir to the higher one, where it is stored. During the on-peaks, water is released producing electricity in the water-turbines placed under the waterfall. Due to the high construction cost, long construction times and the requirement of large amounts of land, this technology is only suitable in certain locations.

Compressed air energy storage consists in compressing air into a underground reservoir during the off-peaks and releasing this air during the on-peaks. The air goes through a gas turbine generating the electricity. This technology together with the pumped-hydro storage is the only one that is commercially available to provide large capacity of storage

Regenerative fuel cells are capable of storing and releasing energy through a reversible electrochemical reaction between the two electrolytes. In this technology the electricity is stored into chemical energy and the release of the potential energy occurs within an electrochemical cell with a separate compartment for each electrolyte (separated by an ion-exchange membrane).

Battery is a technology used as utility-scale energy storage and that relies on different electrochemical reactions. However, all of them are composed of two electrodes separated by an electrolyte. During the discharge, ions from the anode (first electrode) are released into the solution and deposit oxides on the cathode (second electrode).

Superconducting magnetic energy storage is an emerging technology where the energy is stored in the magnetic fields created by the flow of direct and current in a coil of cryogenically cooled, superconducting material. It has a high operating cost and therefore best suited to provide constant, deep discharges and constant activity.

Flywheels stores energy through accelerating a rotor up to a high rate of speed and maintaining the energy in the system as inertial energy. Advanced composite materials needed to lower the weight of the rotor. The energy stored in the rotor is proportional to its momentum but the square of the angular momentum. The advantages of this system are the compactness of the system and the lower operate and maintenance costs.

Thermal systems are high-technologies based in the storage of energy either as ice-based systems to cool down commercial and buildings during the high temperatures or as a molten-salt based for steam production. Both kind of systems are not yet fully developed and seems to be the most suitable ones to extend the ability of solar and other renewable energy resources.

Hydrogen is still in the development stages as well, but will be an integral component of any future economy. The hydrogen can be stored in a gas, liquid or carbon-based form, which is then released through a chemical or physical reaction to power a fuel cell. Most storage systems can be used for both stationary and vehicle applications.

Independently of the energy storage technology they bring competitiveness to the market. Especially the large scaled storage facilities are expected to improve the reliability of the grid, allow a faster recoup of the investments and decrease the market risks. Due to the capacity of absorb energy during the off-peaks and release while it is needed the beneficial effects of the energy storage technologies will be accumulated as long as they are incorporated into the market. These benefits will be, among others:

-          Better energy management allocating the energy between the low-cost off-peak and the high-cost peaks

-          Provide power to assure a continuity of service during the switch-on and switch-off of the power facilities

-          Maintain the grid stability, voltage, power quality and reliability

To sum up, the development and implementation of the most suitable energy storage technology for each location is a must in the coming years. This implementation should be carried out at the same time that the energy network is renovated or construction and it will bring down the electricity prices by improving the management of the energy market, increase the security of supply and its quality in terms of stability, power and reliability, and allow the development of the renewable energy sources.

Acknowledgement

I thank all of you who want to post a comment!! ;-)

Sources
Enery storage, ESC white paper of the energy storage council, 2002, among others...