🔋Energy Storage Technologies Unit 9 – Thermal Energy Storage: Types and Methods

What's Thermal Energy Storage?

• Thermal energy storage (TES) involves capturing and storing thermal energy for later use
• Enables the storage of heat or cold to be utilized at a different time than when it was generated
• Decouples the supply and demand of thermal energy, allowing for more efficient and flexible energy systems
• Can be achieved through various methods such as sensible heat storage, latent heat storage, and thermochemical storage
• Plays a crucial role in reducing energy consumption, improving energy efficiency, and integrating renewable energy sources
• Helps to balance energy supply and demand by storing excess thermal energy during off-peak periods and releasing it during peak demand
• Offers the potential to reduce greenhouse gas emissions by minimizing the reliance on fossil fuels for heating and cooling applications

Why It Matters

• TES is essential for the efficient utilization of renewable energy sources (solar thermal, geothermal)
• Helps to reduce the mismatch between energy supply and demand, improving the overall efficiency of energy systems
• Enables the integration of intermittent renewable energy sources by storing excess energy for later use
• Contributes to the reduction of peak energy demand, leading to cost savings and reduced strain on energy infrastructure
• Facilitates the implementation of district heating and cooling systems, improving energy efficiency in urban areas
• Supports the decarbonization of the heating and cooling sectors by reducing the reliance on fossil fuels
• Enhances energy security by providing a reliable and dispatchable source of thermal energy

Types of Thermal Energy Storage

• Sensible heat storage
  • Utilizes the heat capacity of a storage medium to store thermal energy
  • Involves heating or cooling a material without changing its phase
  • Common storage media include water, rock, concrete, and molten salts
• Latent heat storage
  • Exploits the phase change of a material to store thermal energy
  • Utilizes the latent heat absorbed or released during phase transitions (solid-liquid, liquid-gas)
  • Phase change materials (PCMs) such as paraffin wax, salt hydrates, and fatty acids are commonly used
• Thermochemical storage
  • Relies on reversible chemical reactions to store and release thermal energy
  • Utilizes the energy absorbed or released during chemical reactions
  • Offers high energy storage densities and long-term storage capabilities
  • Examples include metal hydrides, carbonates, and hydroxides

Key Methods and Technologies

• Sensible heat storage systems
  • Water tanks and aquifers for low-temperature applications
  • Rock beds and concrete for high-temperature applications
  • Molten salt storage for concentrated solar power plants
• Latent heat storage systems
  • Encapsulated PCMs for building applications (walls, ceilings, floors)
  • Shell-and-tube heat exchangers with PCMs for industrial processes
  • PCM-enhanced heat sinks for electronic cooling
• Thermochemical storage systems
  • Adsorption and absorption systems using zeolites, silica gel, or salt hydrates
  • Chemical heat pumps utilizing metal hydrides or ammonia-based reactions
  • Calcium looping processes for high-temperature applications
• Hybrid storage systems
  • Combining sensible and latent heat storage for improved performance
  • Integration of thermochemical storage with sensible or latent heat storage

Materials Used in TES

• Sensible heat storage materials
  • Water: Widely used for low-temperature applications due to its high specific heat capacity
  • Rock and concrete: Suitable for high-temperature applications due to their thermal stability
  • Molten salts: Utilized in concentrated solar power plants for their high heat capacity and thermal stability
• Latent heat storage materials (PCMs)
  • Organic PCMs: Paraffin wax, fatty acids, and polyethylene glycol
  • Inorganic PCMs: Salt hydrates, metallic alloys, and eutectic mixtures
  • Encapsulation materials: Polymers, metals, and ceramics for containing PCMs
• Thermochemical storage materials
  • Adsorbents: Zeolites, silica gel, and activated carbon
  • Salt hydrates: Calcium chloride, magnesium chloride, and lithium bromide
  • Metal hydrides: Magnesium hydride, sodium alanate, and lithium hydride
• Heat transfer fluids
  • Water, glycol solutions, and thermal oils for low-temperature applications
  • Molten salts, liquid metals, and supercritical fluids for high-temperature applications

Applications and Case Studies

• Building heating and cooling
  • Passive solar design with thermal mass (concrete, brick) for energy storage
  • PCM-enhanced building envelopes (walls, ceilings) for thermal regulation
  • Seasonal thermal energy storage (STES) for district heating and cooling
• Industrial processes
  • Waste heat recovery and storage for later use in industrial processes
  • High-temperature TES for solar thermal power generation (molten salt storage)
  • TES for process heat in food processing, textile, and chemical industries
• Renewable energy integration
  • Concentrating solar power (CSP) plants with molten salt storage for dispatchable electricity generation
  • Geothermal energy storage using aquifers or rock beds
  • Integration of TES with wind or solar photovoltaic systems for energy management
• Transportation
  • TES for thermal management in electric vehicles (battery cooling, cabin heating)
  • Thermal energy recovery and storage in internal combustion engines
  • Latent heat storage for refrigerated transport and cold chain logistics

Efficiency and Performance Factors

• Storage capacity: Amount of thermal energy that can be stored in the system
  • Depends on the storage medium, system design, and operating conditions
  • Higher storage capacity allows for longer discharge durations and increased flexibility
• Charge and discharge rates: Speed at which thermal energy can be stored and released
  • Influenced by the heat transfer characteristics of the storage medium and system design
  • Higher charge and discharge rates enable faster response times and improved system dynamics
• Heat transfer efficiency: Effectiveness of heat transfer between the storage medium and the heat transfer fluid
  • Depends on the thermal properties of the materials, surface area, and flow conditions
  • Higher heat transfer efficiency reduces thermal losses and improves overall system performance
• Thermal losses: Undesired heat transfer from the storage system to the surroundings
  • Influenced by the insulation quality, surface area, and temperature difference
  • Minimizing thermal losses is crucial for maintaining the stored energy over time
• Cycling stability: Ability of the storage system to maintain its performance over repeated charge-discharge cycles
  • Affected by material degradation, corrosion, and thermal stresses
  • High cycling stability ensures long-term reliability and reduces maintenance requirements
• Cost-effectiveness: Economic viability of the TES system considering capital costs, operating costs, and energy savings
  • Depends on factors such as material costs, system complexity, and energy prices
  • Optimizing cost-effectiveness is essential for the widespread adoption of TES technologies

Future Developments and Challenges

• Advanced materials research
  • Development of novel PCMs with higher energy storage densities and improved thermal properties
  • Exploration of nanomaterials and composite materials for enhanced heat transfer and stability
  • Investigation of thermochemical storage materials with higher energy densities and reversibility
• System integration and optimization
  • Integration of TES with renewable energy sources and existing energy infrastructure
  • Optimization of system design and control strategies for improved efficiency and flexibility
  • Development of advanced heat exchanger designs and heat transfer enhancement techniques
• Thermal management and control
  • Advancements in thermal insulation materials and techniques to minimize heat losses
  • Development of intelligent control systems for optimal charging and discharging of TES systems
  • Integration of predictive models and real-time monitoring for improved system performance
• Techno-economic analysis and policy support
  • Comprehensive assessment of the economic feasibility and environmental benefits of TES systems
  • Development of supportive policies and incentives to encourage the adoption of TES technologies
  • Identification of potential market opportunities and business models for TES applications
• Standardization and certification
  • Establishment of standardized testing and performance evaluation methods for TES systems
  • Development of certification schemes to ensure the quality and reliability of TES products
  • Collaboration among industry stakeholders to promote interoperability and compatibility of TES components