Thermal energy storage solutions (TES)
Thermal energy storage is one of the most promising and versatile technologies for addressing the challenges of the transition towards a sustainable energy system. As the world shifts towards the use of renewable energies such as solar and wind, ensuring a stable and efficient power grid becomes crucial. In this article, we will explore the benefits of thermal storage, its applications in the power grid, its relevance in the energy transition, and how it compares to other storage solutions.
What is Thermal Energy Storage?
Thermal energy storage involves capturing heat or cold, storing it, and releasing it when needed. This type of storage is used for both electricity generation and to meet industrial or domestic thermal needs.
Through specialized materials, such as phase change materials, thermal storage enables the retention of large amounts of energy over extended periods, improving system efficiency and contributing to sustainable energy.
Benefits of Thermal Storage for the Power Grid
Thermal energy storage offers practical and sustainable solutions to enhance the performance and stability of the power grid, especially in a system increasingly dependent on renewable energies. Among its main benefits are:
– Balance Between Supply and Demand
It allows storing excess energy produced by renewable sources, such as solar or wind, during periods of low demand and releasing it during peak hours. This helps maintain a constant and reliable energy supply.
– Reduction in Fossil Fuel Use
By providing an alternative energy source during high-demand periods, thermal storage minimizes the need to activate backup plants powered by fossil fuels, thereby reducing pollutant emissions.
– Greater Integration of Renewable Energies
It facilitates the large-scale adoption of clean energies by addressing intermittency issues and ensuring that energy is available even when there’s no sun or wind.
– Optimization of Electrical Infrastructure
It reduces pressure on the power grid by managing consumption peaks and preventing overloads, which decreases the need for additional infrastructure investments.
– Lower Energy Costs
By stabilizing electricity prices and reducing dependence on costly energy sources during high-demand periods, thermal storage benefits both operators and end consumers.
Benefits of Thermal Storage for Industry
Thermal energy storage not only plays a crucial role in grid stabilization but also provides significant benefits in the industrial sector, where energy consumption is intensive and continuous.
– Reduction of Operational Costs
Industries can store thermal energy during low-cost energy hours (e.g., when there’s an excess of renewable energy) and use it later, reducing energy bills and improving operational profitability
– Energy Efficiency
Thermal storage allows the recovery and reuse of residual heat generated by industrial processes that would otherwise be wasted. This not only reduces overall energy consumption but also enhances operational sustainability.
– Decarbonization of Industrial Processes
By integrating thermal storage with renewable energies, industries can reduce their dependency on fossil fuels, especially in sectors requiring high temperatures, such as steelmaking, chemical, and ceramic industries. This contributes to lowering their carbon footprint.
– Operational Continuity
In industries with critical processes requiring a constant heat supply, thermal storage ensures operational continuity by supplying thermal energy during power outages or interruptions in the main energy supply.
– Flexibility in Production
Thermal energy storage allows industries to adjust their thermal production according to market demands without relying exclusively on renewable energy generation hours. This provides greater control and flexibility.
Types of Thermal Energy Storage (TES)
Sensible Storage
This method stores heat using materials such as water or molten salts, where the temperature change indicates the amount of energy stored. It is commonly used in solar thermal plants.
Example: Hot water in heating systems
In buildings and homes, water is used as a thermal storage medium for heating systems and domestic hot water.Example: Molten salt tanks in solar thermal plants
In plants such as Solana (USA), Noor III (Morocco), or Cerro Dominador (Chile), molten salts are used to store heat and generate electricity even after sunset.
Latent Storage
This method uses phase change materials (PCM) that absorb or release heat when changing state (solid to liquid or vice versa). It is highly efficient and space-saving compared to sensible storage.
Example: PCM in energy-efficient buildings
Some sustainable buildings incorporate phase change materials in walls or ceilings to regulate indoor temperature, absorbing heat during the day and releasing it at night.Example: Storage in refrigeration systems
In the food industry, PCM is used to maintain low temperatures in containers or transport systems without requiring constant energy input.
Thermochemical Storage
This storage relies on reversible chemical reactions to store or release heat. It offers high energy density and is ideal for long-term storage.
Example: Calcium hydroxide in thermal storage
In research projects, materials like calcium hydroxide are used for long-term heat storage through chemical reactions, with potential for industrial applications.Example: Ammonia absorption in climate control systems
Some experimental solutions use ammonia in thermochemical processes to store thermal energy for refrigeration and air conditioning applications.
Comparison Between Types of Thermal Energy Storage
The following table compares the main types of thermal energy storage:
Criterion | Sensible Storage | Latent Storage (PCM) | Thermochemical Storage |
Operating Principle | Stores energy by changing the temperature of a material. | Stores energy through phase changes (solid-liquid, liquid-gas, etc.). | Uses reversible chemical reactions to store energy. |
Common Materials | Water, rocks, concrete, molten salts. | Phase change materials such as paraffin, eutectic salts. | Metal oxides, carbonates, ammonia, among other compounds. |
Energy Density | Low to medium. Depends on the material’s specific heat. | Medium to high, depending on the PCM used. | High, superior to the other methods. |
Constant Temperature | Temperature changes during energy charging and discharging. | Energy is stored at a constant temperature during phase change. | Temperature depends on the chemical reaction used. |
Storage Duration | Ideal for short- and medium-term storage. | Efficient for short- and medium-term applications. | Can store energy for long periods without significant losses. |
Implementation Cost | Relatively low, especially with materials like water or rock. | Moderate; PCMs can be more expensive. | High due to complexity and specific materials required. |
Efficiency | Medium, limited by heat losses. | High, due to the ability to store energy at a constant temperature. | Medium to high, depending on the chemical reaction used. |
Common Applications | Heating, cooling, CSP plants (with molten salts). | Climate control, compact thermal batteries, industrial processes. | Long-term renewable energy storage projects, industrial processes. |
Key Advantages | Simplicity and low cost. Widely available materials. | High energy density per unit volume and efficiency. | Long-term storage capacity and high energy density. |
Disadvantages | Requires large volumes to store significant amounts of energy. | High initial cost and PCM degradation after several cycles. | High technical complexity and high implementation cost. |
Conclusion:
Sensible Storage: Ideal for cost-effective, large-scale solutions using materials like water or rocks.
Latent Storage (PCM): Perfect for applications where space is limited and thermal efficiency is a priority.
Thermochemical Storage: The best option for long-term, high-density thermal energy storage, although with greater technical complexity and cost.
Importance in the Energy Transition
The energy transition aims to replace fossil fuels with renewable energy sources such as solar, wind, and hydraulic power. However, one of the greatest challenges in achieving this goal is the lack of energy storage in the electrical grid.
Renewable sources are intermittent: the sun doesn’t always shine, the wind doesn’t constantly blow, and energy demands don’t always align with peak generation periods. Without efficient storage systems, the electrical grid faces significant imbalances, especially during demand peaks. In such situations, fossil fuel backup plants are often activated, increasing greenhouse gas emissions and hindering progress toward a sustainable energy model.
Thermal energy storage emerges as an ideal solution to address these grid imbalances. During peak renewable production, such as hours of high solar radiation or strong winds, excess energy can be converted into heat and stored in thermal systems, like molten salt tanks or phase-change materials. This stored heat can later be released—either to generate electricity or to meet specific thermal demands—when renewable sources are unavailable, such as at night or on cloudy days.
This approach not only ensures greater grid stability but also reduces the need to activate fossil fuel-based backup plants, which are often highly polluting and costly. Instead of wasting surplus renewable energy or depending on unsustainable sources, thermal storage serves as a bridge, ensuring that clean energy is available at any time of day.
Furthermore, thermal storage offers flexible applications, ranging from solar renewable energy to industrial processes and building climate control, making it a versatile tool for advancing sustainable energy.
Comparing Thermal Storage with Other Energy Storage Systems
Below are the main differences, advantages, and disadvantages of thermal storage systems, lithium-ion batteries, hydraulic storage, and hydrogen storage. This table highlights key features for assessing their performance and specific applications.
Criterion | Thermal Storage | Lithium-Ion Batteries | Pumped Hydroelectric Storage | Hydrogen Storage |
Operating Principle | Stores energy as heat (sensible heat, latent heat, or thermochemical reaction), usable directly or converted into electricity. | Converts electricity into chemical energy through electrochemical reactions in lithium-ion cells. | Pumps water to an elevated reservoir using excess energy, releasing it to generate electricity. | Converts electricity into hydrogen via electrolysis, which is stored and reconverted into electricity or heat. |
Versatility | High: allows storing and using heat or converting it into electricity as needed. | Low: specific storage for electricity. | Medium: designed exclusively for electricity but very effective. | High: hydrogen energy can be used in industry, transportation, and power generation. |
Energy Density | Variable, depending on the system (high in PCM and thermochemical; medium in sensible heat like salts). | High, especially in compact applications like electronics or vehicles. | Low, limited by the physical capacity of water and pumping height. | High, but depends on the storage method (compression, liquefaction). |
Scalability | High, especially in large industrial projects and solar plants. | Medium: suitable for domestic or grid-scale applications with technological limitations. | High, for large power grids with suitable terrain. | High, but initial infrastructure costs are significant. |
Initial Cost | High, but competitive in large-scale projects due to scalability. | Moderate, but proportional to system size, with decreasing prices. | Very high, requires complex geographical infrastructure. | High, due to the need for electrolyzers, tanks, and compressors. |
Operating Cost | Low to medium, with minimal maintenance in systems like salts or PCM. | Medium, influenced by chemical degradation of batteries. | Low, but includes regular maintenance of turbines and hydraulic systems. | High, due to efficiency losses and hydrogen handling. |
Efficiency | Variable (40–90%), depending on the type: PCM and thermochemical have higher efficiency than sensible heat. | High (90–95%) in charge-discharge cycles, ideal for fast-response systems. | Medium-high (70–85%), affected by mechanical and pumping losses. | Low (30–40%) considering the full cycle. |
Storage Duration | High: days to weeks or months depending on the system and type of energy. | Short to medium term: ideal for hours or days of storage. | Medium term, focused on balancing hourly generation and demand. | High: from weeks to months, with minimal significant losses. |
Conversion Flexibility | High: compatible with direct heat, electricity, and hybrid processes. | Low: electrical only. | Low: optimized exclusively for electricity. | High: hydrogen allows electrical, thermal, and industrial applications. |
Environmental Impact | Low, especially with recyclable materials like PCM or salts. | Medium: lithium extraction and battery disposal have ecological impacts. | High: requires large amounts of water and affects local ecosystems. | Variable: can be low if hydrogen is green, but high if leaks occur. |
Key Advantages | Usage flexibility, scalability, cost-effectiveness in large projects, decarbonization potential for industries. | High efficiency, fast response, ideal for small-scale and distributed storage. | Large capacity for grid stabilization. | Versatility in applications, potential for seasonal storage. |
Disadvantages | Lower efficiency in electricity conversion (in sensible heat systems). | Degradation with repeated cycles, still expensive in large systems. | Dependence on specific geography, high initial costs. | Low overall efficiency, high costs, and developing technology. |
Conclusion
Thermal Storage: Offers high versatility and scalability, making it ideal for industrial applications, decarbonization processes, and large-scale projects such as CSP plants and hybrid cogeneration. Its ability to work with both heat and electricity is a key differentiator.
Lithium-Ion Batteries: The most suitable option for domestic or small-scale applications, where efficiency and speed are crucial. Although costs have decreased, their environmental impact requires attention.
Hydraulic Storage: A robust solution for large-scale grid stabilization, although limited by the need for specific geography and high initial investment.
Hydrogen: Promising for seasonal storage and industrial applications, although its low efficiency and high initial cost require technological improvements for broader adoption.
The Most Used Thermal Storage: Molten Salts
The most developed thermal energy storage today is molten salt tank storage. The use of molten salts in thermal storage, common in solar thermal plants, allows heat to be stored on a large scale to generate electricity even without sunlight. This technology is key to integrating renewable energies into the grid. Learn more about its operation and benefits in our dedicated article.
Thermal Storage Engineering Projects at RPow
RPow leads innovation in thermal energy storage, developing advanced solutions that drive the transition toward a more sustainable and efficient energy system. Below are three of its standout projects:
Integration of Thermal Storage with Renewable Energies
This project helps maximize the efficiency and stability of renewable sources, such as solar and wind, through thermal storage systems designed to supply energy during low-generation periods. More details here:TES for Cogeneration Plant – RPOW – Renewable power onwards
Thermal Solutions for Industry
An innovative approach that integrates thermal energy storage into industrial processes, improving sustainability, recovering residual heat, and reducing the carbon footprint of operations. Learn more about this project: TES for Oil and Gas – RPOW – Renewable power onwards
Thermochemical and Latent Heat Storage Technology
For the construction of a Thermal Energy Storage Pilot Plant, RPow is developing advanced storage systems based on both molten salts and latent heat and thermochemical reactions (specifically adsorption reactions). Discover this project here: EPC of Thermal Storage Pilot Plant at CIIAE Facilities – RPOW – Renewable power onwards
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