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Background and Introduction to Thermal Energy Storage
Thermal energy is produced through the movement of particles within a system or object, it can also be referred to as kinetic energy.
Over the last 100 years or so, the energy storage sector has evolved and adapted to the changing needs and developments in technology. Generally, energy storage refers to the storage of electricity, but thermal storage is another kind of energy storage that is equally important.
Thermal storage - the storage of cold or heat - is used to achieve load shifting on the electrical grid, to enhance the energy efficiency of HVAC equipment, and to behave as auxiliary cold storage for shipping containers that are refrigerated.
Energy storage systems provide a host of technological approaches to help manage power supply. These measures will go a long way in creating a more flexible energy infrastructure and provide huge cost savings to consumers and utilities, alike.
Energy storage technologies can be categorized into six types:
- Thermal – Traps heat and cold to produce energy on demand
- Solid state batteries – Electrochemical storage solutions that include sophisticated capacitors and batteries
- Flow batteries - Energy is directly stored in the electrolyte solution
- Flywheels – Mechanical devices that harness rotational energy to provide instant electricity
- Pumped hydro power - Creates large-scale reservoirs of energy with water
- Compressed air energy storage – Uses compressed air to produce a powerful energy reserve
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Thermal batteries are considered a reliable source of specific energy. They are non-rechargeable, single use batteries that can be stored for a long time without any need for maintenance.
These batteries can be used at any time and only require several tenths of a second before they are ready for activation.
Thermal batteries can work even under unfavorable mechanical or climatic environments. The intrinsic proprieties of these high-temperature galvanic primary cells, also known as reserve batteries, allow them to withstand rigorous mechanical stresses of acceleration, vibration, shock, and spin.
It is possible to optimize the design of these batteries for capacity or power. Thermal batteries are safe, rugged and reliable, and have a prolonged inactive shelf life of up to 20 years.
There are two types of thermal batteries - primary lithium batteries and customized, multipurpose thermal batteries.
Primary lithium batteries are fully inert before activation and are the only power sources to consistently operate in adverse environments. They are maintenance-free and possess a long storage-life.
Customized, multipurpose thermal batteries provide several output voltages from a single battery and instantly supply electrical power.
The key characteristics of thermal batteries are as follows:
- Power output ranges from a few watts to several kilowatts
- Typical chemistry is lithium iron disulfide. The electrolyte is generally an eutectic mixture of potassium chlorides and lithium
- They comprise a metallic salt electrolyte, which is non-conducting when solid at ambient temperature but turns into an excellent ionic conductor when molten
- When thermal batteries are activated by a pyrotechnic charge, they supply a high burst of power for a short period
The key application areas of thermal batteries are given below:
- Thermal batteries have intrinsic qualities that make them an ideal solution for smart munitions and artillery shells. They are ideal due to their sturdiness to withstand harsh environments and storage conditions.
- Thermal batteries used in the emergency power system (EPS) in a new supersonic trainer aircraft has proven to be a more cost-effective solution and requires less maintenance than standard systems based on methanol/oxygen or hydrazine. These batteries are also used for ejector seat applications.
- Thermal batteries are used in thermal hybrid vehicles to use heat storage of surplus exhaust heat from an internal combustion engine.
- The thermal atomic battery is ideal for use in situations that require prolonged operation without battery recharging or replacement. Such situations include unmanned scientific facilities, pacemaker and spacecraft, to mention a few.
- Lithium oxyhalide batteries are used in power munitions and missiles that need batteries with a high level of energy on demand and a long shelf life.
- When used in households, thermal batteries provide cooling and heating options with site-derived, renewable energy. These batteries reduce the dependency of homes on imported energy and fossil fuels, and also stabilize heating costs.
- An increased amount of thermal energy is generated during operation, where each system may generate 200 W-250 W of heat. Cooling systems present in the data centers help to dissipate the heat produced by the computer systems, improving performance and reliability.
Ceramic Battery Technology
Several types of battery technologies are available in the market. Among these, Johnson Thermo-Electrochemical Convertor (JTEC) is considered a premium battery technology.
Dr. Lonnie Johnson, CEO and Founder of Johnson R&D, invented the Johnson Thermo-Electrochemical Convertor (JTEC). Johnson holds more than 100 patents and his technologies have been rated as world-class by media such as TIME, Popular Mechanics and CNN.
The JTEC is a sophisticated heat engine that has the potential to change heat into electricity with double the efficiency of the exiting techniques. The JTEC is considered to be superior in its environmental responsibility as it uses waste heat at industrial processes or solar farms.
The JTEC is an all solid-state device operating on the Ericsson cycle, which provides the maximum theoretical efficiency available from a converter working between two temperatures. This thermo-electrochemical convertor uses the fluid pressure’s electro-chemical potential that is applied across a proton conductive membrane (PCM).
A membrane electrode assembly (MEA) is developed with the membrane and a pair of electrodes. Two MEA stacks are used by the JTEC - one stack is attached to a low temperature heat sink and the other is coupled to a high temperature heat source.
The engine of the JTEC is scalable and has a wide range of applications ranging from Micro Electro Mechanical Systems (MEMS) to power for large-scale applications such as fixed power plants. The technology is ideal for use in spacecraft, air vehicles, land vehicles, and field generators.
The JTEC uses heat from fuel combustion, solar, low grade industrial waste heat or waste heat obtained from other power generation systems such as nuclear power plants, combustion turbines, internal combustion engines, and fuel cells. The JTEC’s heat pump feature allows it to be used as a drop-in replacement for currently available HVAC equipment in industrial, commercial, or residential settings.
JBT’s ceramic batteries are solid-state batteries that provide the following benefits:
- Rechargeable, flexible, and compact enough to be medically implanted
- Designed to improve energy density, safety, and robustness through the development of low-cost processing technology and innovative materials
- Possess up to three times the energy of lithium-ion batteries in the same weight and size
- Relatively safer than that of lithium-ion batteries as they use ceramic electrolytes and not gel or liquid electrolytes
- Suitable for adverse environments and have been shown to work beyond 150°C
- Possess high energy density-footprint efficiency and do not explode or catch fire
- Can tolerate lower and higher voltages than most traditional batteries
- Designed to reduce self-discharge than standard lithium-ion batteries
A JBT solid-state lithium-metal chemistry has been tested in very severe environments, undergoing drilling, boiling water, and other stress testing. In no circumstance did the battery catch fire or explode, unlike current battery technologies available on the market.
JBT has made thin film batteries of various shapes, sizes, and configurations.
In addition to the JTEC technology, other battery technologies include Sunamp heat batteries and AllCell’s PCC™ material.
Thermal Energy Storage
Heat batteries from Sunamp include SunampStack, SunampCube, and SunampPV. SunampStack is a cost-saving heat storage device that optimizes the operation of renewable heat sources.
SunampCube collects waste heat for re-use, and is ideal for commercial scale and large community heat storage. This device ensures consistent generation and deals with grid constraints.
SunampPV is capable of storing surplus electricity from a Solar PV array as heat. It also has the potential to deliver fast-flowing hot water on-demand.
AllCell offer innovative battery solutions that provide several benefits over other lithium-ion batteries. These solutions are used in a wide range of energy storage applications, such as off-grid solar storage, solar lighting, electric vehicle charging, and frequency regulation.
AllCell’s PCC™ thermal management technology is an energy storage medium that absorbs and distributes heat, providing compact and lightweight battery packs with industry-leading safety and extended cycle-life. The PCC™ has double the gravimetric energy density of lead acid batteries and is much more cost-effective than most lithium-ion batteries.
Research and Development
A graphene battery has been developed that has the potential to convert ambient heat into electric current. This invention increases the prospect of green, clean batteries powered by ambient heat, and represents a significant progress in the research of self-powered technology.
Wonder material graphene is sustainable and eco-friendly, and holds unlimited possibilities for various applications, including an alternative source of energy storage.
In 2014, American firm Angstron Materials launched a number of graphene products that include a series of graphene-enhanced anode materials for lithium-ion batteries. Called “NANO GCA”, the battery materials are designed to provide a high capacity anode and support many charge/discharge cycles by integrating silicon with conductive and mechanically reinforcing graphene.
In the same year, US-based Vorbeck Materials announced a lightweight flexible power source called the Vor-Power strap, which can be joined to a bag strap to allow a mobile charging station through USB and micro USB ports. Believed to be the world’s first graphene-enhanced battery, the Vor-Power strap is lightweight and provides 7,200 mAh power.
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Advancements are also being made in graphene batteries for electric vehicles, such as graphene-enhanced Li-ion batteries. Tesla had proposed the development of a new battery technology that could nearly double the capacity of its Model S electric car.
In September 2014, UK-based OXIS Energy and Perpetuus partnered to co-develop graphene-based electrodes for lithium-sulfur batteries, which will provide better energy density and allow electric cars to drive a longer distance on a just a single battery charge.
In another interesting venture, US-based company, Graphene 3D Labs announced plans to print 3D graphene batteries. Such graphene-based batteries could exceed commercially available batteries.
Spanish company Graphenano claims that it will soon introduce graphene polymer cells, which are significantly lighter and safer than lithium-ion equivalents. According to a study performed in 2015, graphene doubles the energy density of lithium-ion batteries.
Swinburne University researchers have developed a new graphene-based energy-storage technology that could soon replace the batteries used in phones, cars, etc.