How Thermal Energy Storage Can Transform the Future of Energy

Thermal energy storage (TES) is a technology that allows the transfer and storage of heat or cold energy for later use. TES can help improve energy efficiency, reduce greenhouse gas emissions, and integrate renewable energy sources into the power grid. TES can also provide flexibility and reliability for energy supply and demand management, as well as reduce the cost of electricity and heating/cooling services.

TES has a wide range of applications in different sectors, such as:

• Power plants: TES can store excess electricity from wind and solar farms as heat, and release it when needed to generate power. TES can also enhance the performance and stability of conventional thermal power plants by providing peak shaving, load shifting, and frequency regulation.
• Industrial processes: TES can recover and reuse waste heat from industrial processes, such as steel, cement, and chemical production, to reduce fuel consumption and emissions. TES can also provide process heat or cooling at different temperature levels for various industrial applications.
• Buildings: TES can store heat or cold from solar collectors, heat pumps, or chillers, and use it to provide space heating or cooling, domestic hot water, or ice melting. TES can also reduce the peak demand and energy cost of buildings by shifting the operation of heating/cooling systems to off-peak hours.
• Transportation: TES can store thermal energy from vehicle engines or brakes, and use it to improve the fuel efficiency and emission reduction of vehicles. TES can also provide thermal comfort for passengers by regulating the cabin temperature.

In this blog post, we will explore the different types of TES systems, the current and emerging TES technologies, and some case studies of successful TES projects around the world. We will also discuss the potential and challenges of TES for achieving a sustainable and low-carbon energy system.

Types of TES systems

TES systems can be classified into three categories based on the state of the storage material: sensible, latent, and thermochemical.

• Sensible TES systems store thermal energy by changing the temperature of a solid or liquid material, such as water, rocks, sand, or oil. The amount of thermal energy stored depends on the mass, specific heat, and temperature difference of the material. Sensible TES systems are simple, reliable, and low-cost, but they require large volumes and high insulation to prevent heat losses.
• Latent TES systems store thermal energy by changing the phase of a material, such as ice, wax, or salt hydrates. The amount of thermal energy stored depends on the mass and latent heat of the material. Latent TES systems can store large amounts of thermal energy at a constant temperature, but they have challenges such as low conductivity, phase separation, and supercooling.
• Thermochemical TES systems store thermal energy by breaking or forming chemical bonds between a material and a reactant, such as metal hydrides, sorbents, or fuels. The amount of thermal energy stored depends on the mass and enthalpy of the reaction. Thermochemical TES systems can store very large amounts of thermal energy for long periods of time, but they have challenges such as slow kinetics, reversibility, and stability.

The table below summarizes the main characteristics, advantages, and disadvantages of each category of TES systems:

Current and emerging TES technologies

In this section, we will highlight some of the most widely used and promising TES technologies that belong to each category of TES systems. We will also evaluate their potential and challenges for large-scale and long-term storage applications.

Sensible TES technologies

Some of the most common sensible TES technologies are:

• Water tanks: Water tanks are the simplest and most widely used sensible TES technology. They can store heat or cold in water using electric heaters, heat pumps, or chillers. Water tanks can provide short-term storage for domestic hot water, space heating/cooling, or ice storage. Water tanks have a low cost, high reliability, and easy maintenance, but they require large volumes and high insulation to prevent heat losses.
• Molten salt: Molten salt is a sensible TES technology that uses a mixture of sodium and potassium nitrate salts as the storage medium. Molten salt can store heat at high temperatures (up to 600°C) and high pressures (up to 100 bar). Molten salt is mainly used for concentrating solar power (CSP) plants, where it can store the solar thermal energy during the day and release it at night or during cloudy periods to generate electricity. Molten salt has a high energy density, high thermal stability, and long lifetime, but it has challenges such as corrosion, freezing, and toxicity.
• Rocks: Rocks are a sensible TES technology that uses crushed rocks or pebbles as the storage medium. Rocks can store heat at medium temperatures (up to 300°C) and low pressures (up to 10 bar). Rocks can be used for large-scale and long-term storage applications, such as district heating/cooling, industrial waste heat recovery, or seasonal storage. Rocks have a low cost, high availability, and environmental friendliness, but they have challenges such as low conductivity, high volume, and dust formation.

Some of the emerging sensible TES technologies are:

• Concrete: Concrete is a sensible TES technology that uses concrete blocks or modules as the storage medium. Concrete can store heat at high temperatures (up to 500°C) and low pressures (up to 10 bar). Concrete can be used for large-scale and long-term storage applications, such as CSP plants, power-to-heat systems, or seasonal storage. Concrete has a high energy density, high durability, and easy integration with existing structures, but it has challenges such as cracking, moisture absorption, and thermal expansion.
• Phase change slurry: Phase change slurry is a sensible TES technology that uses a liquid carrier fluid with dispersed microencapsulated phase change materials (MPCMs) as the storage medium. Phase change slurry can store heat or cold at low to medium temperatures (up to 100°C) and atmospheric pressure. Phase change slurry can be used for short-term storage applications, such as building heating/cooling, domestic hot water, or thermal management of electronic devices. Phase change slurry has a high energy density, high conductivity, and easy transportability, but it has challenges such as stability, viscosity, and cost.

Latent TES technologies

Some of the most common latent TES technologies are:

• Ice: Ice is a latent TES technology that uses water as the storage medium. Ice can store cold energy at 0°C and atmospheric pressure. Ice can be used for short-term storage applications, such as building cooling, ice skating rinks, or food preservation. Ice has a high energy density, low cost, and easy availability, but it has challenges such as low conductivity, large volume change, and freezing damage.
• Wax: Wax is a latent TES technology that uses organic compounds such as paraffin or fatty acids as the storage medium. Wax can store heat at low to medium temperatures (up to 100°C) and atmospheric pressure. Wax can be used for short-term storage applications, such as building heating, domestic hot water, or thermal management of electronic devices. Wax has a high energy density, high compatibility, and easy encapsulation, but it has challenges such as low conductivity, flammability, and ageing.
• Salt hydrates: Salt hydrates are a latent TES technology that uses inorganic salts such as sodium sulfate or magnesium chloride as the storage medium. Salt hydrates can store heat at medium to high temperatures (up to 200°C) and atmospheric pressure. Salt hydrates can be used for medium-term storage applications, such as industrial process heat, district heating, or solar thermal systems. Salt hydrates have a high energy density, low cost, and high stability, but they have challenges such as phase separation, supercooling, and corrosion.

Some of the emerging latent TES technologies are:

• Metallic alloys: Metallic alloys are a latent TES technology that uses metal-based materials such as aluminium-silicon or magnesium-zinc as the storage medium. Metallic alloys can store heat at high temperatures (up to 700°C) and high pressures (up to 100 bar). Metallic alloys can be used for large-scale and long-term storage applications, such as CSP plants, power-to-heat systems, or seasonal storage. Metallic alloys have a very high energy density, high conductivity, and long lifetime, but they have challenges such as high cost, low availability, and toxicity.
• Shape memory alloys: Shape memory alloys are a latent TES technology that uses materials such as nickel-titanium or copper-aluminium-nickel as the storage medium. Shape memory alloys can store mechanical energy by changing their shape when heated or cooled. Shape memory alloys can be used for novel storage applications, such as smart windows, self-healing structures, or wearable devices. Shape memory alloys have a high energy density, high efficiency, and multifunctionality, but they have challenges such as hysteresis, fatigue, and complexity.

Thermochemical TES technologies

Some of the most common thermochemical TES technologies are:

• Metal hydrides: Metal hydrides are a thermochemical TES technology that uses metal-based materials such as magnesium, iron, or nickel as the storage medium. Metal hydrides can store heat by absorbing hydrogen gas and releasing it when heated. Metal hydrides can store heat at high temperatures (up to 600°C) and high pressures (up to 200 bar). Metal hydrides can be used for large-scale and long-term storage applications, such as CSP plants, power-to-gas systems, or hydrogen production. Metal hydrides have a very high energy density, high reversibility, and high safety, but they have challenges such as high cost, low availability, and low kinetics.
• Sorption: Sorption is a thermochemical TES technology that uses materials such as zeolites, silica gel, or activated carbon as the storage medium. Sorption can store heat by adsorbing or absorbing water vapor and releasing it when heated. Sorption can store heat at low to medium temperatures (up to 200°C) and low pressures (up to 10 bar). Sorption can be used for medium-term storage applications, such as building heating/cooling, district heating/cooling, or solar thermal systems. Sorption has a high energy density, low cost, and low environmental impact, but it has challenges such as low conductivity, moisture sensitivity, and cycling degradation.

Some of the emerging thermochemical TES technologies are:

• Solid-state batteries: Solid-state batteries are a thermochemical TES technology that uses materials such as lithium metal or lithium-ion as the storage medium. Solid-state batteries can store electrical energy by converting it into chemical energy and vice versa. Solid-state batteries can store heat at low to medium temperatures (up to 100°C) and atmospheric pressure. Solid-state batteries can be used for novel storage applications, such as electric vehicles, smart grids, or wearable devices. Solid-state batteries have a high energy density, high efficiency, and long lifetime, but they have challenges such as high cost, low availability, and safety issues.
• Fuel cells: Fuel cells are a thermochemical TES technology that uses materials such as hydrogen or methanol as the storage medium. Fuel cells can store electrical energy by converting it into chemical energy and vice versa. Fuel cells can store heat at low to medium temperatures (up to 200°C) and atmospheric pressure. Fuel cells can be used for novel storage applications, such as electric vehicles, smart grids, or portable power sources. Fuel cells have a high energy density, high efficiency, and low emissions, but they have challenges such as high cost, low availability, and durability issues.

Case studies of TES projects

In this section, we will present some examples of successful TES projects around the world, and analyse their technical, economic, and environmental aspects. We will also identify the key factors and best practices for implementing TES solutions in different contexts.

PepsiCo’s crisp production in the Netherlands

In collaboration with Eneco and Kraftblock, PepsiCo is revolutionizing its crisp production at their Broek op Langedijk site in the Netherlands by using innovative renewable energy technology. The initiative employs Kraftblock’s cutting-edge thermal battery technology, which incorporates an innovative material capable of storing heat up to 1,300˚C. This stored heat, derived from hot air heated by wind energy, can be utilized for up to 14 days.

During off-peak periods and night time, PepsiCo accesses economical renewable electricity from North Sea wind farms and converts it into hot air. This hot air heats Kraftblock’s iron ‘nuggets’ to 800˚C within ‘super’ insulated storage units. Simultaneously, PepsiCo employs direct electrification, powering two of its electric thermal oil boilers.

Once the heat is transferred from the hot air to these insulated storage units, it is stored and then used to heat thermal oil during peak periods when energy costs are high. The use of a hot air to thermal oil heat exchanger supplies energy to PepsiCo’s production processes, allowing the company to switch off its electric thermal oil boilers, thus enhancing energy efficiency.

Key factors for this initiative’s success include:

• The use of Kraftblock’s state-of-the-art thermal battery technology for energy storage.
• Sourcing cheaper renewable electricity during off-peak periods.
• Harnessing stored heat during peak periods through the deployment of a hot air to thermal oil heat exchanger.
• Adding insulation to the storage units, thereby maintaining high temperatures for an extended period.

This novel collaboration aligns with PepsiCo’s broader sustainability commitments, which include a 40% reduction in greenhouse gas emissions by 2030, and achieving net-zero emissions by 2040. The company continues to source innovative solutions like Kraftblock’s technology to boost their sustainability agenda, now steered by the newly assigned chief sustainability officer for Europe, Archana Jagannathan.

Gemasolar CSP plant in Spain

The Gemasolar CSP plant is a 19.9 MW power plant that uses molten salt as the sensible TES medium. The plant consists of a solar field with 2,650 heliostats that concentrate the sunlight onto a central tower receiver, where the molten salt is heated up to 565°C. The molten salt then flows to a storage tank, where it can store up to 1,010 MWh of thermal energy. The molten salt can then be used to generate steam and drive a turbine to produce electricity. The plant can operate for up to 15 hours without sunlight, and has an annual capacity factor of 75%.

The Gemasolar CSP plant is the first commercial-scale CSP plant with molten salt storage in the world. The plant has been operating since 2011, and has achieved several records, such as producing electricity for 36 consecutive days in 2013. The plant has also reduced its CO2 emissions by about 30,000 tons per year. The plant has a capital cost of about €230 million, and a levelized cost of electricity (LCOE) of about €0.27 per kWh.

The key factors for the success of the Gemasolar CSP plant are:

• The use of molten salt as the TES medium, allows high-temperature storage, high-energy density, and long-term storage.
• The use of a tower receiver, allows higher concentration ratios, higher efficiency, and lower land use than parabolic troughs or dishes.
• The use of a dry cooling system reduces water consumption by about 90% compared to wet cooling systems.
• The use of a hybrid operation mode, which allows the integration of natural gas as a backup fuel to ensure grid stability and reliability.

Drake Landing Solar Community in Canada

The Drake Landing Solar Community (DLSC) is a residential community that uses borehole thermal energy storage (BTES) as the sensible TES medium. The community consists of 52 single-family homes that are connected to a district heating system. The system consists of a solar field with 800 flat-plate collectors that collect solar thermal energy during the summer months. The solar thermal energy is then transferred to an underground BTES system, where it is stored in an array of 144 boreholes that are 35 m deep and cover an area of 35 m by 35 m.

The BTES system can store up to 34 MWh of thermal energy. During the winter months, the BTES system supplies heat to the homes through a heat exchanger and a heat pump. The system can meet up to 97% of the space heating demand of the homes.

The DLSC is the first large-scale BTES system in North America. The system has been operating since 2007, and has achieved several milestones, such as reaching a solar fraction of 100% in 2012. The system has also reduced its CO2 emissions by about 5 tons per home per year. The system has a capital cost of about CAD$8 million, and a payback period of about 25 years.

The key factors for the success of the DLSC are:

• The use of BTES as the TES medium, allows low-temperature storage, low heat losses, and seasonal storage.
• The use of flat-plate collectors, which are simple, reliable, and low-cost compared to evacuated tube collectors or concentrating collectors.
• The use of a district heating system reduces the installation and maintenance costs and increases the efficiency and reliability compared to individual heating systems.
• The use of an integrated design approach, which involves the collaboration of different stakeholders, such as homeowners, developers, engineers, and utilities.

IceBank system in the United States

The IceBank system is a latent TES technology that uses water as the storage medium. The system consists of modular tanks that contain water and an internal heat exchanger. The tanks are connected to a chiller that cools the water and freezes it into ice during off-peak hours. The ice then melts and cools the water during peak hours. The chilled water can then be used for building cooling or air conditioning. The system can store up to 1.8 MWh of cooling energy per tank.

The IceBank system is one of the most widely used latent TES technologies in the world. The system has been installed in more than 4,000 buildings in over 60 countries, such as the Bank of America Tower in New York, the Staples Center in Los Angeles, and the Marina Bay Sands in Singapore. The system has also reduced its peak demand by up to 40%, and its energy cost by up to 20%. The system has a capital cost of about $150 per kWh, and a payback period of about 3 to 5 years.

The key factors for the success of the IceBank system are:

• The use of water as the TES medium, allows high-energy density, low cost, and easy availability.
• The use of modular tanks, allows flexibility, scalability, and easy installation and maintenance.
• The use of a partial storage strategy allows the optimization of the chiller size, the storage capacity, and the operating schedule.
• The use of a thermal energy service model, allows the customers to pay only for the cooling service, not for the equipment or maintenance.

FAQ – Frequently Asked Questions

How can thermal energy storage transform the future of energy?

Thermal energy storage (TES) can transform the future of energy by enabling more efficient and flexible use of renewable energy sources, reducing greenhouse gas emissions, and lowering energy costs. TES can store excess heat or cold from solar, wind, or other sources when they are abundant, and release it when they are scarce or expensive. TES can also help balance the supply and demand of electricity, reduce peak loads, and improve grid stability.

What are the benefits of thermal energy storage?

Some of the benefits of TES are:

• It can increase the share of renewable energy in the energy mix and reduce dependence on fossil fuels.
• It can lower energy bills for consumers and businesses by shifting demand to off-peak periods when electricity is cheaper.
• It can improve the performance and reliability of heating and cooling systems, enhance thermal comfort, and reduce maintenance costs.
• It can reduce CO2 emissions and other pollutants by avoiding the use of inefficient or dirty power plants.

What are the types of thermal energy storage?

There are three main types of TES:

• Sensible heat storage: This involves storing heat or cold in a medium such as water, air, soil, or rocks. The temperature of the medium changes as it absorbs or releases heat.
• Latent heat storage: This involves storing heat or cold in a material that undergoes a phase change, such as water turning into ice or salt hydrates melting. The temperature of the material remains constant as it absorbs or releases heat.
• Thermochemical storage: This involves storing heat or cold in a material that undergoes a reversible chemical reaction, such as metal hydrides or sorption materials. The temperature and pressure of the material change as it absorbs or releases heat.

What are the applications of thermal energy storage?

TES can be used for various applications, such as:

• Building heating and cooling: TES can store heat or cold from solar collectors, heat pumps, chillers, or other sources, and use it to provide space heating, cooling, or hot water for buildings.
• District heating and cooling: TES can store heat or cold from centralized plants that use waste heat, biomass, geothermal, or other sources, and distribute it to multiple buildings through a network of pipes.
• Industrial processes: TES can store heat or cold from industrial processes that have variable or intermittent demand, such as food processing, chemical production, or metal smelting, and use it to improve efficiency and reduce waste.
• Power generation: TES can store heat from concentrated solar power plants, nuclear reactors, or other sources, and use it to generate electricity when needed.

How can thermal energy storage be integrated with smart grids?

Thermal energy storage can be integrated with smart grids to provide demand response, frequency regulation, voltage control, and other ancillary services. TES systems can communicate with smart meters, sensors, and controllers to adjust their charging and discharging patterns according to the grid conditions, price signals, and user preferences. TES systems can also participate in energy markets and trade electricity or heat with other prosumers or aggregators.

What are the future prospects of thermal energy storage?

Thermal energy storage has a great potential to grow and expand in the future, as the demand for clean and reliable energy increases. TES can benefit from the development of new materials, technologies, and applications, as well as the improvement of existing ones. TES can also benefit from the integration of different types of TES systems, such as hybrid TES, cascaded TES, or coupled TES. TES can also benefit from the collaboration of different stakeholders, such as researchers, policymakers, industry players, and consumers.

Conclusion

In this blog post, we have explored the concept, benefits, and applications of thermal energy storage (TES). We have also discussed the different types of TES systems, the current and emerging TES technologies, and some case studies of successful TES projects around the world.

We have learned that TES is a technology that can store heat or cold energy for later use. TES can help improve energy efficiency, reduce greenhouse gas emissions, and integrate renewable energy sources into the power grid. TES can also provide flexibility and reliability for energy supply and demand management, as well as reduce the cost of electricity and heating/cooling services.

We have also learned that TES systems can be classified into three categories based on the state of the storage material: sensible, latent, and thermochemical. Each category has its own characteristics, advantages, and disadvantages. We have also learned that there are many TES technologies that belong to each category, such as water tanks, molten salt, rocks, ice, wax, salt hydrates, metal hydrides, sorption, solid-state batteries, and fuel cells. Each technology has its own potential and challenges for large-scale and long-term storage applications.

Finally, we have learned that there are many examples of successful TES projects around the world, such as the Gemasolar CSP plant in Spain, the Drake Landing Solar Community in Canada, and the IceBank system in the United States. Each project has its own technical, economic, and environmental aspects. We have also learned that there are some key factors and best practices for implementing TES solutions in different contexts, such as the use of appropriate TES medium, receiver, cooling system, operation mode, design approach, and service model.

We hope that this blog post has given you a comprehensive overview of TES and its importance and relevance for achieving a sustainable and low-carbon energy system. We also hope that this blog post has inspired you to learn more about TES and its technologies. If you have any questions or comments, please feel free to contact us or leave a comment below.