Energy Storage in a nutshell

In a recent energy summit, Energy Storage was considered as one of the top 5 technologies that are necessary to delay or postpone climate change. Energy Storage is also an essential ingredient of the Renewable Energy Sources expansion since it is needed to solve the element of unpredictability for some of the renewable green energy sources like Solar and Wind energy sources.

Energy storage is a process where energy is stored in a device or in some form so that this stored energy would be used at a later stage when needed. For instance when the wind blows, wind turbines produce energy and if that energy is not needed at the specific time or at the specific location the produced energy is stored and used when and where needed.

Why is an energy storage system needed and what is its impact on the environment and the economy?  The need and impact of Energy storage can be summarized in 3 main points:

• Energy Storage reduces the need of standby energy plants and enables the implementation of a distributed electricity network since the storage can be used to store energy produced off-peak when it is not much needed and use it as and when the need arises at peak times. This means that no electricity turbines are needed to be in standby mode so as to enable authorities to meet peak demands.
• Energy storage can be used as a bridge to fill in the gap that may arise when a plant failure occurs for a short period thus avoiding power interruptions in the network which are costly to the economy. Electricity outages cost and given the fact that such outages are only for a short period, under 5 mins, the existence of electricity storage ensures a source of electricity that can be used at the time of need. It is the same idea that it is implemented when a UPS device is installed in an installation.
• Energy storage is a Renewable Energy Sources, RES, enabler especially for solar and wind energy sources. Both sources are intermittent and their production varies significantly within the day but with the electricity storage units connected to them the peaks can be shaved and excess energy can be stored to be used when the ‘’production valleys’’ occur.

What kind of energy storage systems exist? What are the energy storage technologies currently available? What kind of energy storage devices exist?  In order to understand these systems, the energy storage technologies behind them and the type of energy storage devices that exist we have to have in mind that all forms of energy fall in one of the categories:  Potential Energy or Kinetic energy.  An example of potential energy is gravitational energy and an example of kinetic energy is thermal energy.

There are currently 6 energy storage systems that are widely used which fall into one of the two different forms of energy and are using different energy storage technologies. These are:

• Pumped Hydropower which is a mechanical storage
• Flywheel Energy Storage, FES, a mechanical storage form
• Compressed Air Energy Storage, CAES, another form of a mechanical storage form
• Batteries - which are an electrochemical storage form
• Superconducting Magnetic Energy Storage, SMES, an electrical energy storage form
• Capacitors which are an electrical form energy storage form

A short analysis of each energy storage system will enable us to understand the concept behind each energy storage system.

Pumped Hydropower: The idea behind this energy storage system is simple. During the times of low electricity demand and/or when electricity is inexpensive water is pumped at a water reservoir at a high elevation and it is kept there. When demand of electricity increases, the stored water is released and powers the hydroelectric turbines which are there for the specific purpose to produce electricity. This is the oldest and most widely used form of energy storage not only in the USA but in the whole world.

Flywheel Energy Storage: Energy in flywheels is stored in a spinning disk which is attached on a metal shaft. The amount of energy stored is related to:  the speed of rotation, the mass of the disk and the amount of mass on the rim of the disk. Flywheels are used at places where short discharge time is required. Flywheels can be networked to form a larger energy storage system but they are costly.

Compressed Air Energy Storage, CAES. In this type of energy storage, compressed air is kept in underground reservoirs such as caves and when the need arises, the compressed air is released to the atmosphere by letting the air pass through electric generators which produce electricity and supply it to the grid at the time of need.

Batteries: Batteries as an electricity storage is perhaps the most well-known energy storage. Due their portability, scalability and ease of use they are used in many energy storage systems. There are many Battery technologies used now such as lithium and lead-acid.

Superconducting Magnetic Energy Storage, SMES. Storage in these systems is stored in superconducting windings and the energy stored depends on the size of the windings. Energy is discharged almost instantly and for a short period.

Electrochemical Capacitors: They store electricity in electrodes which are oppositely charged. The capacitors are used to provide electricity as backup devices during short electricity shortages. They also have the capability to stabilize the voltage and frequency of electricity.

From the above we can safely conclude that energy storage systems are necessary for the smooth operations of the power grid and that they are a necessary component for the expansion of Renewable Green Energy Sources such as solar and wind energy.