Several factors must be addressed when managing an electrical system, key among them is demand and supply alignment as misalignments can result in system collapses. This makes renewable energy integration particularly complex as these sources of energy are inherently intermittent and therefore prone to periods of unavailability.
Managing this risk would require the adoption of energy storage facilities and while it is widely understood that electricity once generated, must be consumed as it cannot be stored, innovations in energy storage technologies such as batteries are constantly being developed.
Energy Storage Systems
Energy storage is the ability to save energy at a given time for later use. Once stored, it can be used to meet future demand or to balance electricity demand and supply in a grid network. While energy cannot be stored in electrical form, it can be converted to other forms that can be stored such as kinetic, chemical, or thermal energy.
Some popular energy storage mechanisms include pumped-storage hydroelectricity, flywheel, compressed-air energy storage (CAES), and lithium-ion batteries.
Existing Energy Storage Mechanisms
These are the existing storage mechanisms and the challenges faced when they are being used.
1. Pumped-storage hydroelectricity: This storage system involves a turbine and two reservoirs, one reservoir at a higher elevation and the other at a lower elevation. When there is excess electricity generated, water is pumped from the lower reservoir to the higher one and stored. Later, when electricity demand is high, the turbine generates enough power to release water from the higher reservoir to the lower reservoir.
2. Flywheel: This storage system is a mechanical machinery that involves a heavy wheel attached to a rotating shaft that spins around when switched on. It is designed to store rotational energy by spinning the wheel. The spinning wheel can be slowed down or sped up depending on how much energy is stored.
3. Compressed Air Energy Storage (CAES): This storage system can be described as a large, secured container or an underground cave where air is squeezed tightly. When there is excess energy available from strong winds, the air is captured and secured. The compressed air is then released and used to generate power when there is increased energy demand.
4. Lithium-ion batteries: These lightweight and high-power batteries work by moving positive and negative electrodes, with an electrolyte in between the two electrodes, making them rechargeable. Note that lithium-ion batteries are different from lithium batteries. This is because lithium batteries contain lithium metal and are not rechargeable.
While these storage mechanisms are currently in use, they have their challenges, requiring further innovation in the energy storage market.
S/N Technology Challenge
1. Pumped-storage hydroelectricity: A key barrier to the implementation of this system is its capital-intensive nature as there are high capital and maintenance costs involved.
2. Flywheel: Since most flywheels work in vacuum buildings, the rotor bearings' thermal management that permits the rotor shaft's rotation typically causes issues in the flywheel. Because of the considerable heat produced during operation, this may have an impact on the bearings' longevity and performance.
3. Compressed Air Energy Storage (CAES): The high capital cost and long period of time, associated with the development of underground cages for CAES, causes a barrier in the widespread adoption of this storage system. There is also a significant risk of damage to lives and property where there is a failure in the optimal design of the storage system.
4. Lithium-ion batteries: While these batteries are increasingly popular and cost-effective in comparison to other technologies, they still cannot discharge electricity for long periods. Even at full power capacity they typically discharge for only four hours at most.
Emerging Technologies for Energy Storage
The following technologies are being developed or piloted to support electricity storage:
1. Hydrogen Caves: Hydrogen storage technologies, such as hydrogen fuel cells and electrolysis, enable the conversion of excess renewable energy into hydrogen. These technologies are emerging as promising solutions for long-duration energy storage and transportation. Once produced, hydrogen can be cooled and stored in large volumes in underground caves or in smaller volumes in storage tanks. During spikes in electricity demand, the stored hydrogen can be used to heat homes, power vehicles, and power generators.
2. Flow batteries: These are electrochemical batteries capable of storing enough electricity to reliably power several homes for days on a single charge. They operate with two tanks filled with chemical substances, primarily redox couples, which undergo reduction and oxidation reactions to store and release energy. Examples of redox couples include zinc-bromine, vanadium, and iron-chromium. Energy stored in the electrolyte solution flows through the battery during charge and discharge cycles. However, the substantial waste produced by these batteries does not degrade over time, posing a challenge to sustainability objectives.
3. Heated Rock Beds: The idea of rock beds was formulated by a solar company called CSolPower, in New Mexico. The company aims to use solar energy to heat rock beds. These rocks act as heat storage when demand is low and are used to generate power when electricity demand is high.
4. Liquid Air or Cryogenic Energy Storage: Here, air from the environment is sucked in and cooled to below -196 degrees Celsius. When electricity demand increases, the air is warmed, pressurized, and used to operate a turbine for electricity production.
5. Gravity Battery: This type of battery relies on potential energy stored in heavy weights. During periods of excess electricity production, the weights are raised to significant heights. When electricity demand increases, these weights are released, converting their potential energy into kinetic energy, which in turn generates electricity.
Conclusion
Energy storage is essential for ensuring the reliability of energy supply by storing surplus electricity for later use, particularly for intermittent sources such as solar and wind. While electricity cannot be directly stored, it can be converted into other forms of energy for future use.
Although current energy storage technologies are relatively new and have limitations, emerging solutions offer promising alternatives for long-term sustainability and energy transition goals. These systems provide two key benefits: supporting grid stability and promoting energy access.
