Evolution and Classification of Energy Storage Systems

Evolution and Classification of Energy Storage Systems

  1. Introduction

The upswing in worldwide energy consumption, driven by industrialization, technological advancements, and economic expansion, led to a 4.5% surge in energy demand and a 5% increase in CO2 emissions in 2021. The established threshold for discussions surrounding global climate change is set at a 1.5-degree Celsius increase, representing the average global temperature rise since pre-industrial times. With the crossing of the 1-degree Celsius mark, deliberations at the COP28 world climate summit in Dubai focused on capping the remaining half-degree rise. However, the current commitments from global entities to reduce emissions are deemed insufficient for this purpose. Present projections indicate that in order to restrain warming to the 1.5-degree Celsius limit, the world needs to develop three times more renewable energy capacity by 2030, equating to at least 11,000 GW. At the COP-28 Dubai Summit, a significant development occurred as 118 countries endorsed the commitment to enhance global renewables and energy efficiency.

However, in the past years, the adoption of renewable energy has been notable, reflecting an anticipated 8% surge in electricity generation from renewable sources, reaching a substantial 8,300 TWh in 2021. The International Renewable Energy Agency has set an ambitious target of achieving a global non-fossil fuel-based generation share of 57% by 2030. Despite renewables making up a commendable 30% of the power mix in 2021, persistent challenges, such as intermittency, highlight the necessity for innovative solutions. For instance, solar panels exhibit inefficiency during cloudy weather and remain inactive at night or during prolonged winter periods with persistent fog. Similarly, wind turbines face inefficiency in calm weather, and at times, renewable energy sources generate excess energy, leading to system overload and wastage. In this context, the emergence of energy storage systems (ESSs) becomes crucial, providing practical and effective mechanisms to optimise energy management and alleviate the risks associated with system overload. ESSs operate by adeptly harvesting, transforming, and storing energy from diverse sources, significantly contributing to maintaining a balance between energy generation and demand.

  1. Evolution of Energy Storage Systems

The evolution of Energy Storage Systems spans over centuries, marked by significant milestones in the development of various technologies. In 1839, Sir William Robert Grove introduced the first simple fuel cell, a groundbreaking invention that mixed hydrogen and oxygen to generate electricity and water. Gaston Planté’s lead-acid battery in 1859 marked a crucial advancement, providing the foundation for practical rechargeable batteries. The year 1883 saw John A. Howell’s development of the first Flywheel Energy Storage (FES), initially designed for military applications.

As the 20th century progressed, innovations continued with the introduction of the nickel-cadmium battery by Waldemar Jungner in 1899 and the deployment of pumped hydro energy storage in 1907 in Switzerland. The 1960s witnessed the creation of the Sodium Sulphur battery by the Ford Motor Company, while in 1969, Ferrier introduced the concept of Superconducting Magnetic Energy Storage to address diurnal variations in power demands. The late 20th century saw the advent of diverse technologies, including Borehole Thermal Energy Storage in 1977, Compressed Air Energy Storage in 1978, and the Supercapacitor in 1982. The 1980s also witnessed pioneering work on flow batteries, such as the Vanadium Redox Flow Battery in 1983 and the Polysulfide Bromide Flow Battery reported in the same year. Advancements continued into the 1990s with the commercial release of the Li-ion battery by Sony in 1991, representing a major breakthrough in portable energy storage. In 2007, the concept of a Paper Battery was introduced by Dr. Robert Linhardt, Dr. Omkaram Nalamasu, and Dr. Pulickel Ajayan, showcasing ongoing efforts to innovate and diversify ESS technologies.

This historical progression underscores the dynamic nature of ESS evolution, driven by the pursuit of more efficient, reliable, and sustainable energy storage solutions across diverse applications and industries.

  1. Classification

These energy storage systems have been systematically categorised based on the underlying mechanisms employed. The primary classifications include the following.

3.1 Thermal Storage

In thermal storage, the preservation of heat in materials forms the basis for subsequent electricity generation. Sensible heat storage involves directly storing heat in the material, such as molten salt or concrete. Latent heat storage, employing phase change materials (PCM), facilitates the storage and release of heat during phase transitions. Thermochemical storage, another subtype, operates through reversible chemical reactions, providing a pathway for achieving high energy density in thermal energy storage systems. The nuanced subcategories within thermal storage highlight the versatility of this approach in meeting diverse energy storage needs.

3.2 Mechanical Storage

Mechanical storage systems capture and release energy in the forms of kinetic or potential energy, showcasing a spectrum of technologies. Flywheels store energy in rotational motion, offering a means of rapid discharge when needed. Pumped hydroelectric storage, leveraging gravitational potential energy, involves lifting and lowering massive volumes of water to store and release energy. Compressed air energy storage utilises the potential energy of compressed air. The subtypes within mechanical storage, spanning gravitational potential energy storage, elastic potential energy storage, and kinetic energy storage, underscore the breadth of mechanical systems in the energy storage domain.

3.3 Electrochemical Storage

Electrochemical energy storage (EcES) systems store energy in the form of chemical bonds and convert it into electrical energy when needed. EcES systems include battery energy storage (BES), flow battery energy storage (FBES), paper battery, and flexible battery.

BES systems use solid electrodes and electrolytes to store and release electrical energy through reversible electrochemical reactions. BES systems can be classified into different types based on the chemistry and materials used, such as lead-acid, lithium-ion, nickel-cadmium, sodium-sulphur, sodium ion, metal air, and solid-state batteries.

FBES systems use liquid electrolytes that are stored in external tanks and pumped through a cell stack to produce electricity. FBES systems can be classified into different types based on the active species and redox reactions, such as vanadium redox battery (VRB), polysulfide bromide battery (PSB), and zinc‐bromine (ZnBr) battery.

Paper battery is a thin and flexible device that combines the properties of a conventional battery and a supercapacitor. It uses carbon nanotubes and cellulose as electrodes and electrolyte, respectively, and can be printed, folded, cut, or stacked to achieve different shapes and capacities.

Flexible battery is a bendable and stretchable device that can be integrated with wearable electronics, medical implants, and smart textiles. It uses various materials and structures to achieve mechanical flexibility and durability, such as polymer electrolytes, nanowires, microbatteries, and origami designs.

3.4 Chemical Storage

Chemical Energy Storage (CES) systems are essential for the extended storage of chemical energy, utilising the inherent potential energy in the chemical bonds of materials. This stored energy is subsequently released through chemical reactions, playing a pivotal role in both electricity generation and transportation. Commonly used chemical fuels include coal, gasoline, diesel, natural gas, and hydrogen.

3.4.1 Hydrogen Energy Storage System

Hydrogen, lauded for its cleanliness and zero-emission attributes, stands out as an ideal energy carrier. Its production involves electrolysis or photocatalytic water splitting driven by sunlight. The hydrogen energy system comprises three main elements: a hydrogen generation unit (electrolyzer), a storage system, and an energy conversion unit (fuel cell). During excess power periods, hydrogen is produced through electrolysis and stored. Later, it is converted back into electricity during peak demand using fuel cells.

Fuel cells, integral to hydrogen energy systems, facilitate the conversion of stored chemical energy in hydrogen back into electrical energy. Fuel cells operate through a process where hydrogen and oxygen react electrochemically to produce electricity, with the only byproducts being water and heat. The four main components of a fuel cell include an anode, a cathode, an electrolyte, and an external circuit. During the electrochemical reaction, hydrogen is oxidized at the anode, producing protons and electrons. The protons flow through the electrolyte to the cathode, where they combine with oxygen and electrons to form water. This flow of electrons through an external circuit generates a current, ultimately producing electricity. Various types of fuel cells, such as proton exchange membrane fuel cells (PEMFC), alkaline fuel cells (AFC), phosphoric acid fuel cells (PAFC), molten carbonate fuel cells (MCFC), solid oxide fuel cells (SOFC), and direct methanol fuel cells (DMFC), exhibit distinct characteristics and applications, contributing to the versatility of fuel cell technology.

3.4.2 Synthetic Natural Gas (SNG):

Synthetic natural gas (SNG) production emerges as an alternative energy production method by converting coal or biomass into a clean energy source. Various thermal gasification processes are employed to produce SNG from coal and dry biomass. SNG can be stored in tanks, underground caverns, or integrated directly into the gas grid. The Great Plains Synfuels Plant in the USA exemplifies successful SNG production from lignite coal since 1984.

3.4.3 Solar Fuels

Solar fuels represent an innovative approach to harnessing solar energy for later use. The three primary methods include natural photosynthesis, artificial photosynthesis, and thermochemical production. Natural photosynthesis, a process employed by plants and bacteria, converts solar energy into carbohydrates. Artificial photosynthesis mimics this process, capturing sunlight to convert water and carbon dioxide into fuels. Thermochemical methods involve utilising sunlight to induce high-temperature reactions, producing carbon monoxide or hydrogen.

In recent years, notable projects like the Energiepark Mainz in Germany and the Markham Energy Storage Facility in Canada underscore the global adoption of hydrogen energy storage on a larger scale to address energy supply and demand imbalances. CES systems, including fuel cells, play a pivotal role in the transition towards sustainable and clean energy solutions, with ongoing research focusing on improving efficiency and overcoming challenges in storage and utilisation.

3.4.4 Electrical Storage

Electrical storage is characterised by the storage of energy in the form of electrical potential, facilitated by devices like batteries, supercapacitors, and flywheels. Lead-acid batteries find widespread application, particularly in uninterruptible power supply systems. Lithium-ion batteries, recognized for their high energy density, dominate the landscape of portable electronics and electric vehicles. Flow batteries, exemplified by the Vanadium Redox Battery (VRB), offer scalable, long-duration energy storage solutions. This diverse array of electrical storage technologies demonstrates the adaptability of electrical potential for various applications.

  1. Conclusion

In summary, the evolution of energy storage systems, marked by centuries of technological advancements, underscores their crucial role in addressing the complex challenges of global energy demand and climate change. From the foundational developments of fuel cells and lead-acid batteries to the contemporary diversity of thermal, mechanical, electrochemical, chemical, and electrical storage technologies, the trajectory of innovation reflects a dynamic response to the need for sustainable energy solutions. As the world commits to ambitious climate goals, the recent strides in hydrogen energy storage, synthetic natural gas production, solar fuels, and advanced battery systems exemplify a collective effort to diversify and optimize the energy storage landscape. These systems not only contribute to grid stability but also offer versatile solutions across industries, emphasizing the pivotal role of energy storage in shaping a cleaner and more sustainable energy future.

Author : Er. Dipti Paudel

Assistant Manager at Nepal Oil Corporation

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