Can Energy Be Created And Stored?
Energy is the ability to do work or produce heat. It comes in many different forms that can be converted from one to another, such as kinetic energy, potential energy, thermal energy, chemical energy, nuclear energy, electrical energy, and more. Energy can be transferred between objects or transformed into different types, but it cannot be created or destroyed according to the law of conservation of energy.
Potential energy is stored energy based on an object’s position or arrangement. For example, a book held above the ground has potential energy that can be released as kinetic energy if it falls. Similarly, chemical bonds contain potential energy that can be released as heat during chemical reactions.
Kinetic energy is energy associated with motion. Any moving object contains kinetic energy proportional to its mass and velocity squared. Kinetic energy can be transferred between objects during collisions or other interactions. Other forms of energy, like potential energy, can be converted to kinetic energy when released.
Forms of Energy
Energy exists in various forms that can be categorized into main types. The most common forms of energy include:
Mechanical Energy
Mechanical energy refers to energy stored in objects by virtue of their position or shape. Examples include the potential energy of a rock held high up, or the elastic energy stored in a compressed spring.
Thermal Energy
Thermal energy arises from the random motion of particles that make up matter. The faster the particles move, the more thermal energy they possess, as characterized by temperature.
Chemical Energy
Chemical energy is stored in the bonds between atoms and molecules. Chemical reactions like combustion convert this potential energy into thermal energy and kinetic energy.
Nuclear Energy
Nuclear energy originates from forces between particles in the atomic nucleus. Nuclear fission and fusion reactions release enormous amounts of nuclear energy.
Electrical Energy
Electrical energy results from the motion of charged particles like electrons. Batteries and generators use chemical or mechanical energy to create electricity.
Electromagnetic Energy
Electromagnetic energy consists of oscillating electric and magnetic fields, including visible light, radio waves, and X-rays. It can propagate through space and interact with matter.
Energy Transformations
Energy can change from one form to another. For example, chemical energy in gasoline can be transformed into thermal energy and kinetic energy when combusting the gasoline in a car engine. The thermal energy heats the engine and surrounding air while the kinetic energy propels the pistons to move the car. Some common energy transformations include:
- Chemical energy in food transforming to thermal energy and kinetic energy in the body
- Electrical energy in power lines transforming to light and thermal energy in a lightbulb
- Nuclear energy in uranium transforming to thermal energy to spin turbines for generating electricity
- Solar energy transforming into electrical energy in photovoltaic cells
- Mechanical energy of wind transforming into electrical energy in wind turbines
Energy transformations allow us to harness energy sources like fossil fuels, nuclear, wind, and solar to generate useful forms of energy like electricity. Understanding energy transformations is key to utilizing different energy sources.
Creating Energy
While energy can be transformed from one form to another, the total amount of energy in a closed system always remains constant. This principle is known as the law of conservation of energy. In other words, energy cannot be created from nothing or destroyed into nothing.
For example, a generator doesn’t actually create electrical energy. Instead, it converts mechanical energy from the motion of turbines into electrical energy. The mechanical energy that powers the turbine originally came from another source like the chemical energy in burning fuel, potential energy from falling water, or kinetic energy from wind.
So in essence, energy is simply transferred or transformed. This is why the law of conservation of energy states that the total amount of energy in a closed system remains the same. While energy can change forms, it cannot be created out of nothing or destroyed into nothing.
Storing Energy
Energy storage involves converting energy from forms that are difficult to store to more conveniently or economically storable forms. The most common ways to store energy include:
- Chemical energy storage – converting electrical energy into chemical energy that can be stored in batteries.
- Mechanical energy storage – using mechanical devices like compressed air energy storage (CAES) and flywheels to store energy.
- Thermal energy storage – using materials and technologies like molten salt and ice storage to store thermal energy.
- Electrochemical energy storage – storing electrical energy in the form of chemical energy via reversible chemical reactions, like in rechargeable batteries.
- Electrical energy storage – storing energy in electric fields or magnetic fields, like in capacitors and superconducting magnetic energy storage (SMES).
Energy storage provides a buffer between energy generation and energy use. It allows excess energy produced to be captured for later use when energy generation exceeds demand. Stored energy can also be used to meet spikes in demand and improve the reliability and resiliency of energy systems.
Chemical Energy Storage
Chemical energy storage relies on chemical reactions to store and release energy on demand. The two main technologies for chemical storage are batteries and fuel cells.
Batteries store chemical energy and convert it to electrical energy through redox reactions. The most common battery chemistries are lead-acid, nickel-cadmium (NiCd), nickel-metal hydride (NiMH), and lithium-ion (Li-ion). Lead-acid batteries are inexpensive but have lower energy density. NiCd and NiMH offer improved energy density but contain toxic metals. Li-ion batteries have high energy density and no toxic metals, making them ideal for consumer electronics and electric vehicles.
Fuel cells convert the chemical energy in a fuel, often hydrogen, directly into electricity through an electrochemical reaction. Since the chemical energy is stored externally, fuel cells can offer higher energy capacity than batteries. Common fuel cell types include proton exchange membrane fuel cells (PEMFC), solid oxide fuel cells (SOFC), and molten carbonate fuel cells (MCFC). PEMFCs operate at low temperatures, making them suitable for vehicles and consumer electronics. SOFCs and MCFCs operate at high temperatures and are better suited for stationary power generation.
Continued research aims to improve the energy density, durability, charging rates, and safety of batteries. New fuel cell designs also seek to increase efficiency and reduce costs. Chemical energy storage will remain critical for energy portability and on-demand power delivery.
Mechanical Energy Storage
Mechanical energy storage involves converting electrical energy into a mechanical form that can be stored and converted back into electricity when needed. Some common methods of mechanical energy storage include:
- Flywheels – Kinetic energy is stored in the form of rotational energy in a spinning flywheel. When electricity is needed, the flywheel’s rotational energy is converted into electricity by attaching a generator.
- Compressed air energy storage (CAES) – Energy is stored by compressing air in an airtight underground cavern or container. The pressurized air can be released to turn a turbine and generate electricity.
- Pumped hydroelectric storage – Water is pumped uphill into a reservoir during off-peak hours when electricity demand is low. The stored potential energy can then be released to flow downhill and turn hydroelectric turbines when electricity is needed.
Mechanical storage has the advantages of being able to respond quickly to meet sudden spikes in electricity demand. It also offers a storage medium that can hold large amounts of energy. The main limitations are geographic constraints, as suitable sites are needed for pumped hydro or compressed air storage.
Thermal Energy Storage
Thermal energy storage (TES) involves the storage of heat or cold for later use in applications like heating, cooling, and industrial processes. There are three main categories of TES technologies: sensible heat storage, latent heat storage, and thermochemical storage.
Sensible heat storage is the simplest form of TES. It involves heating or cooling a liquid or solid storage medium. Water is commonly used as a sensible heat storage material in tanks or pits. Heat is absorbed as the temperature rises, and heat is released as the temperature falls. The amount of heat stored depends on the specific heat capacity of the material, its temperature change, and its mass. Sensible heat storage is low cost but requires large volumes of material to store substantial amounts of energy.
Latent heat storage involves phase change materials (PCMs) that melt or solidify at a desired temperature, absorbing or releasing large amounts of heat energy. Common PCMs include water, salts, paraffin waxes, and fatty acids. Latent heat storage can achieve much higher energy storage densities than sensible heat systems. The phase change occurs at an almost constant temperature, allowing the capture of thermal energy at the melting point and release at the freezing point.
Thermochemical energy storage utilizes reversible chemical reactions that absorb and release heat. A thermochemical material like metal hydrides, organic compounds, or salts is subjected to a chemical reaction with water or another working fluid to charge the system, storing the thermal energy. The chemical reaction can later be reversed to discharge heat and return the thermochemical material to its original state. Thermochemical storage offers very high energy storage densities but remains an emerging and costly technology.
Applications
Energy storage has become an integral part of many systems and processes in the modern world. Here are some examples of how stored energy is utilized in practice:
Batteries: Devices like smartphones, laptops, electric vehicles and more are powered by batteries that store chemical energy and release it on demand. Lithium-ion batteries are the most common type used in portable electronics today.
Fuel Cells: These electrochemical cells convert the chemical energy stored in fuels like hydrogen into electrical energy. Fuel cells are used to power everything from vehicles to commercial buildings.
Flywheels: These mechanical devices store rotational kinetic energy and deliver short bursts of power when needed. Flywheels provide backup power for systems like satellites and the International Space Station.
Pumped Hydro Storage: A form of large-scale energy storage where water is pumped uphill into reservoirs during off-peak hours and released to generate hydroelectricity when demand is high.
Compressed Air Energy Storage (CAES): Air is compressed and stored under pressure in underground caverns/tanks. The high-pressure air can be released to drive turbines and generate electricity when required.
Thermal Storage: Methods like molten salt storage and ice storage allow thermal energy to be stored for heating/cooling purposes. Used in concentrated solar power plants and HVAC systems.
Future Outlook
As the world transitions to renewable energy sources like solar and wind power, the ability to efficiently store energy becomes increasingly important. Since these sources are intermittent, energy storage is needed to provide consistent power supply and grid stability. Advances in storage technology are critical to enable higher renewable energy penetration.
Several promising storage technologies are emerging to meet growing needs. Flow batteries offer utility-scale storage capacity for the grid. Solid-state batteries provide improved safety and stability over lithium-ion. Thermal storage solutions like molten salt can retain heat to balance generation and demand. Hydrogen production via electrolysis enables long-term storage for transportation applications.
However, significant challenges remain. Most technologies are too expensive for widespread adoption. Performance and longevity need improvement. Integrating massive storage capacity into the existing grid is complex. New market mechanisms and policy incentives are required to spur deployment. Safety issues need to be thoroughly addressed.
With increased investment and research, energy storage can be enhanced to fully support renewable energy. Much work remains to develop optimized, affordable systems. But advancing storage technology is an essential step to building a sustainable energy future.
