Select your language: EN JP

The role of thermal energy storage in decarbonization

Jessica Hernandez, Analyst
December 27, 2021

Thermal energy storage (TES) can play a key role in industrial and power sector decarbonization. While storing thermal energy stretches back to the beginning of the Industrial Revolution, interest in larger-scale, high-temperature TES is relatively new — as industrial players are increasingly focused on the difficult task of decarbonizing production processes. The development of this technology has historically been tied to the concentrated solar power (CSP) sector. Yet, the simplicity of storing heat in comparison to storing electrical energy leads to many systems and technologies for storing thermal energy.

Fundamentally, heat can be stored as latent heat, sensible heat, or thermochemically.

  • For sensible heat storage, thermal energy is stored or released by heating or cooling a storage medium. Benefits include the ability to use very inexpensive materials (e.g., water, mineral oil, rocks, concrete, steel). However, at higher stored temperatures, material stability (both storage medium and balance of plant components) can be a challenge. Another hurdle is heat losses depending on the level of insulation of the storage container. This technology is the most advanced, as it is the simplest form of energy storage. Innovation is still ongoing, often around system integration and improving thermal conductivity, especially for systems using solid storage materials.

  • For latent heat storage, thermal energy causes a phase change of a storage material without a large change in temperature. Benefits include storing energy in a relatively small temperature range and at generally higher energy density compared with sensible heat storage. However, stability and lifetime of the phase change materials (PCM) remain challenges, along with heat losses depending on the level of insulation of the storage container. The technology is less mature than sensible heat storage, and innovation activity is focused on developing stable and long-lasting PCM across a wider range of temperatures.

  • For thermochemical storage, thermal energy drives a chemical reaction, and energy is stored in stable chemical bonds. Benefits include high energy density and the potential for much-longer-term energy storage. The product of the thermally driven chemical reaction can even be stored at ambient temperature. However, this technology poses many challenges, including material stability, energy loses, and more complex system design. The technology is earlier stage, either still in laboratory stage or being developed in a handful of pilot projects.

In general, the required temperature of the stored thermal energy determines what TES technologies are applicable. The figure below illustrates temperature ranges for various sensible and latent heat storage materials. This is just a sampling of materials; many potential storage materials are not included in this figure. Importantly, the figure does not include thermochemical storage materials or rock- or ceramic-based materials, which generally store medium to high temperatures (~300 °C to over 1,000 °C). For thermochemical systems, the specific materials (and the forward and reverse heat of reaction) determine the storage and delivery temperatures.

Graph showing the applicable temperature in degrees Celsius for different thermal energy storage materials

While each type of technology and application comes with specific challenges, some key factors to consider when assessing TES offerings are:

  • Thermal material complexity. This is one of the more straightforward factors, as it is crucial for TES systems to keep a low $/kWh design and use both a form factor and choice of material that don't present lifetime or cost concerns. In general, the cost of the material must come before attempts at making the system more efficient.

  • The footprint of storage. For example, water and mineral oil are inexpensive for low- or medium-heat storage but need insulated tanks — which require a large footprint. Additionally, water is limited to temperatures below 100 °C without more expensive system components to handle higher pressures. A benefit of latent and especially thermochemical TES is the potential for a smaller footprint compared with sensible TES.

  • The corrosiveness of the storage medium. For example, molten salts — which are often used in the CSP industry and can store higher temperatures while offering the thermal transfer advantages of liquids compared with solids — can be corrosive. This can raise overall costs by requiring more specialized storage tanks and increasing opex.

  • Temperature. Hotter isn’t always better. Higher temperatures generally give better round-trip efficiency when integrated into power generation cycles but, depending on the form of the thermal material, can complicate designs and make them expensive. Moreover, 600 °C is an important benchmark, as steel begins to lose structural integrity at higher temperatures.

  • Industry application. Overall, the application will determine the trade-offs for TES systems. Using the CSP example again, developers often accept the added complexity of molten salts because they allow for higher storage temperatures and thus higher heat-to-electricity efficiencies. With multiple distinct approaches to storing heat, players are differentiating mostly by the application each is targeting.

Key takeaways

TES can be an important pathway to industrial decarbonization given its high scalability, long service time, and low upfront cost compared with electrochemical energy storage systems. Furthermore, TES systems can increase industrial energy efficiency by storing waste heat for use in other processes. For this, system integration will be key, as it’s critical to consider how TES systems integrate into different industrial processes. Focusing on heat is a smart move as decarbonization efforts accelerate. Heat is an area that has been largely overlooked, while most companies have focused first on other decarbonization areas like electrification and renewable-power production. Offerings that can make heat dispatchable will unlock increased flexibility and potential additional revenue streams. In the future, it is likely to be more efficient and economically viable to deploy TES with a sector-coupling strategy, providing primarily industrial process heat while supporting the power generation sector. Companies should not neglect heat in decarbonization efforts and should think about heat storage as part of their future overall energy systems.

Why Hydrogen and Why Now?

Why Hydrogen and Why Now?

Read More
The Evolving Energy Story eBook

The Evolving Energy Story eBook

Read More
Over $5 Billion in Investments Focused on the Home Energy Management System

Over $5 Billion in Investments Focused on the Home Energy Management System

Read More
More Energy Resources
Schedule Your Demo