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The Basics & The Gaps - Thermal Energy Storage

The Basics & The Gaps is the Future Cleantech Architects flagship series of factsheets and animations which aims to summarise the key facts and figures on some of the most challenging issues and technological innovations needed to reach net-zero.

Thermal Energy Storage and the heat sector

The heat sector plays a crucial role in the global economy and the energy transition: it accounts for 50% of global final energy use and over 25% of global greenhouse gas emissions. How can we decarbonize the heat sector? What role can Thermal Energy Storage play in reaching our net-zero goals? Read our Factsheet below! 

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[1] Heat consumption is responsible for over 25% of global emissions 

Total global GHG emissions, around 55 Gt CO2eq: Our World in Data (2023), “Greenhouse gas emissions” and UN environment program (2022), “Emissions Gap Report 2022” (page 6, table 2.1). 

Share of global GHG emissions from heat as final energy use: 14 Gt CO2: IEA (2022), “Renewables 2022” (chapter 3, “Renewable heat”, page 108). 

Heat-related CO2 emissions split between industry and buildings: IEA (2021), “Renewables 2021” (chapter 3, “Renewable heat”, page 114). 

 

[2] Heat accounts for 50% of global final energy use, but only 25% of the heat is currently renewable 

Global annual energy use is on the order of 420 EJ ≈ 120,000 TWh: IEA (2021), ”Key World Energy Statistics”. 

Heat accounts for roughly 50% of global final energy consumption, while electricity and transport account for approximately (20%) and (30%). Furthermore, about 25% of heat comes from renewable sources (combining modern renewable heat and traditional biomass use: IEA (2021), “Renewables 2021” (chapter 3, “Renewable heat”, page 114). 

 

[3] Heat is needed over a wide range of temperatures, but most of it is used at low and medium temperatures 

The share of total heat demand (including domestic & industrial settings) at different temperature levels was compiled using data from LDES Council (2022), “Net-zero heat. Long Duration Energy Storage to accelerate energy system decarbonization” (exhibits 3 and 5, pages 20-21). 

The diagram shows that nearly 80% of heat is used below 500ºC, and about 60% of heat is used below 100ºC. At these temperatures, low-carbon heat sources (such as heat pumps, solar thermal and geothermal) are particularly abundant and cost-effective, as are currently commercial TES technologies. Furthermore, data from a recent study by Thiel and Stark (see “To decarbonize industry, we must decarbonize heat”, Figure 2, page 534) shows a close correlation between heat usage and CO2 emissions over different temperature ranges, meaning that decarbonizing low- and medium-temperature heat would also imply eliminating the majority of the sector’s emissions. 

 

[4] The things we need heat for, and the clean heat sources we can use 

Data on temperature ranges for several low-carbon heat sources and applications was compiled and adapted from COLUMBIA CGEP (2019), “Low-carbon heat solutions for heavy industry: sources, options, and costs today” (Table 1, page 11, and Figure 1, page 33), together with FCA’s internal knowledge and analysis. 

 

[5] How thermal energy storage (TES) can help us decarbonize heat 

The diagram was created by simplifying and adapting a diagram from EERA (2022), “Industrial Thermal Energy Storage. Supporting the transition to decarbonize industry” (Figures 3 and 4, pages 11-12), together with FCA’s internal knowledge and analysis. 

 

[6] The thermal energy storage (TES) technologies that we have. How long they last, and what they can be used for. 

The diagram was created by compiling and adapting data from EERA (2022), “Industrial Thermal Energy Storage. Supporting the transition to decarbonize industry” (Tables 1 and 3, pages 14 and 24), together with FCA’s internal knowledge and analysis, in conversation with academic experts and innovators. 

 

[7] Our recommendations 

Policy recommendations have been collected and adapted from the following sources, together with FCA’s own recommendations based on interactions with innovators and policymakers: IRENA (2020), “Innovation Outlook: Thermal Energy Storage”, EERA (2022), “Industrial Thermal Energy Storage. Supporting the transition to decarbonize industry”, LDES Council (2022), “Net-zero heat. Long Duration Energy Storage to accelerate energy system decarbonization”, EASE (2023), “Thermal Energy Storage”, Energy Storage Coalition (2023), “Breaking Barriers: Enabling Energy Storage through Effective Policy Design”. 

 

Summary list of sources: 

Condensed list as included in factsheet: OurWorldInData(2023), UNEP (2022), IEA (2021), IEA (2022), CGEP (2019), LDES Council (2022), EERA (2022), IRENA (2020), EASE (2023), ESC (2023). 

Highlights

The Heat Sector in Focus: Essential Applications and Clean Heat Sources

Heat consumption spans a wide range of temperatures, processes, and services, including in domestic and industrial settings. At low temperatures, large quantities of heat are needed to heat up buildings and hot water. At higher temperatures, heat is used for different industrial processes, from processing pulp and paper, and the manufacturing of chemicals to the manufacturing of cement, glass, and metals, with some processes requiring heat up to 2000ºC and above.

While most heat is currently generated by burning fossil fuels, several alternative low-carbon heat sources are at our disposal. Some of the low-carbon sources that can supply heat on demand are limited by several factors: such as geography (geothermal energy); political and social acceptance (nuclear energy); limited supply (biomass); and high cost, low efficiency, and lack of infrastructure (hydrogen).

On the other hand, solar thermal energy is a low-carbon source that is highly scalable within the global solar belt. While solar radiation is inherently dependent on the day/night cycle and weather variations, the integration with thermal storage makes solar thermal energy a flexible source able to supply heat around the clock.

However, the most universal and scalable low-carbon heat source is electrification, which consumes green electricity (e.g. from wind and solar photovoltaic plants) and turns it to heat via devices such as heat pumps (for heat up to 200ºC) and electric resistors (for industrial applications up to
almost 2000ºC). While heat pumps and resistors can inherently deliver heat on demand, the addition of thermal storage allows these devices to consume electricity at the most optimal times: when supply from solar and wind is high, and when the cost and the emissions are low. This provides the power grid with additional flexibility and stability and helps integrate larger shares of renewable energy.

The heat sector plays a crucial role in the global economy and the energy transition: it accounts for 50% of global final energy use and over 25% of global greenhouse gas emissions.

However, we are a long way away from decarbonizing heat: currently, only 25% of global heat production is derived from renewable sources, and about half of that comes from traditional biomass usage in buildings.

The sheer size of the heat sector (including both industrial and domestic settings) and its emissions are often overlooked. Furthermore, the crucial role that thermal energy storage technologies can play in decarbonizing heat while providing extra flexibility to the whole energy system is also neglected. This can result in loss of critical funding.

To decarbonize heat as quickly as possible, we need to recognize the magnitude of the heat sector, prioritize its decarbonization within policy frameworks, and secure the necessary investment to scale up the deployment of energy efficiency measures and thermal energy storage technologies.

Thermal Energy Storage is more advanced than you think

While some Thermal Energy Storage technologies require further support for RD&D, many others are mature and ready to deploy. 

Thermal Energy Storage is an efficient and cost-effective tool ready to support the growth in renewables. There is a multitude of TES technologies and materials, covering a wide range of temperatures, storage durations, and applications, in different stages of readiness. 

Some of the most mature TES technologies include: 

✅ Medium and high-temperature “sensible heat” storage tanks, containing liquid or solid thermal materials, that supply industrial heat. 

In particular, thermal storage for steam generation at temperatures up to 500ºC is a mature and cost-effective technology that can store and supply heat for several hours or even days. For instance, the concentrated solar power (CSP) industry has deployed molten salt technology globally, exceeding 20 GWh of thermal storage installed by 2020, and is on track to double that by 2026. 

✅ Low-temperature stores, that store and supply heat for several weeks or even months. 

These include underground stores typically used to heat a single building or a small group of buildings, and large hot-water “pit reservoirs” used for district heating (with hot water up to 80-90ºC). These technologies have been successfully deployed for several decades, especially in northern European countries such as Denmark. 

On the other hand, TES technologies that can store heat both at high temperatures and for very long durations, such as chemical heat storage, are still in early stages of development and require further support for research, development, and demonstration

Thermal Energy Storage (TES) can play a vital role in decarbonizing the heat sector

The size of the heat sector and its large impact on climate (over 25% of global greenhouse gas emissions) are often underestimated. Similarly, the important role that TES technologies can play in decarbonizing the sector tends to go unnoticed.

Thermal Energy Storage captures different intermittent energy sources in the form of heat, which is then available on demand for different applications (including in buildings and industrial settings). TES can be coupled with several low-carbon heat sources, such as wind and solar electricity that has been turned to heat (or “direct electrification”), solar thermal, and geothermal energy. It can also help reuse waste heat from industrial processes.

TES also facilitates renewable integration, mitigating curtailment, and expanding the availability of heat during periods of low renewable supply. By decoupling supply and demand, it favors the consumption of cleaner, low-cost electricity, increasing energy flexibility, energy efficiency, and energy security.

Multiple TES technologies are available, covering a wide range of temperatures, storage durations, and applications. While some of these technologies still require further support for RD&D, many others are ready to deploy and support the growth in renewable energies.

Learn more about Energy Storage

Our Long Duration Energy Storage Factsheet
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