Series: Powering Change

Powering Change: Low-grade waste heat recovery is a key priority for EU energy transition

Blog #2   –   Valorising low-grade waste heat is a key priority for EU’s energy transition from a fossil-fuel based production and consumption system towards a sustainably produced energy supply. In this article, Srilekha Ravvarapu (Senior Innovation Consultant – Green & Sustainable Innovations), discusses the key barriers and current state-of-the-art in low-grade waste heat recovery.

Low-grade waste heat and its significance in the EU

Waste heat, a by-product of thermal and mechanical industrial processes and human activity, presents a significant opportunity for valorisation. The EU generates approximately 10.8 Exajoules (EJ) of waste heat every year from power generation and industrial sectors (Fig 1)(1). Bloomberg estimates that capturing this waste heat and reusing it could save €67 billion for EU consumers(2).

Heat Recovery

While most industries successfully recover high- and medium-grade waste heat, valorising low-grade waste heat remains extremely challenging technologically, economically, and not common in practice. The main limitation is that the technological solutions to recovering the low-grade waste heat are still in their infancy, restricted only to ventilation or hot water systems and are therefore often still cost-ineffective.  In essence, low-grade waste heat is an overlooked energy resource, and its recovery can prove to be an incredible strategy that can help the EU achieve its climate neutrality goals by 2050(3).


What are heat grades?

The heat grades convey the ability to successfully harness waste heat. Waste heat from industries and buildings can be high grade (>400°C), medium grade (100°C–400°C) or low-grade (<100°C).  


Of the total waste heat generated, 2.7 EJ (25%) belong to the low-grade, and additionally, around 1.2 EJ/year of low temperature heat is available from urban sources such as the data centres, metro stations, waste water treatment plants and service sector buildings(1). This unexploited low-grade heat holds enormous potential to transform the heating sector of the EU and its successful recovery and utilisation can heat over 40% of the EU households. Indeed, the heating sector alone consumes almost half of the EU’s energy needs(4). As a policy boost, the incoming Energy Taxation Directive set to tax waste heat will provide an additional incentive to those who can valorise this low-grade waste heat.

While the opportunities to valorise low-grade waste heat are favourable, the nascent field is full of technological and logistical challenges.

Barriers to waste heat recovery and key factors to success:

Low-grade waste heat can be recovered to generate clean electricity or can be used for decarbonizing domestic or process heating. However, technical solutions are untested and standardized protocols for heat recovery and usage do not exist yet. Some key drawbacks are:

  • Efficiency: The heat transfer rate is low when recovering low-grade waste heat, hence large heat exchangers might be required to achieve optimum and efficient transfer. Also, the lower concentration of heat and a higher concentration of contaminants makes it more difficult for viable heat recovery, transfer and storage technologies to be developed.
  • Corrosion: When low-grade heat is in the form of water vapour it tends to cool down and mix with other particles, depositing corrosive solids onto the heat exchanger surfaces. The maintenance costs for cleaning and/or replacing can become highly expensive. The usage of advanced, non-corrosive materials for heat exchangers is thus an interesting area of research.
  • Long distance transportation: Another key challenge in valorising low temperature heat is associated with heat losses in transportation, especially if the waste sinks are at a certain distance to a waste heat source, reducing the cost effectiveness of the solution.

Technological breakthroughs and deep tech innovations enhancing the performance of low-grade heat recovery, which are also viable to be operated at a large scale, may build upon the existing, conventional modes of heat recovery from low-grade waste sources, listed below.

Current state-of-the-art technologies for heat recovery from low-grade sources

The state-of-the-art technologies for valorisation of low-grade waste heat have been at the experimentation level (TRL 4-5) so far, and commercial applications have been very limited. Some revolutionary research that has concluded in the recent past or remains ongoing includes:

Closed-loop Reverse ElectroDialysis (RED) to generate clean, renewable electricity from low-grade waste heat. Traditionally known as Liquid Dessicant Systems, RED adopts ionic exchange membranes to directly convert the potential of the salinity gradient into electricity. The RED stacks are coupled with thermally driven regeneration units in the so-called heat engine for converting low-grade waste heat into electricity.

Chemical adsorption consists of two types of working pairs for low-grade heat recovery: 1. Metal halides and ammonia and 2. Salt hydrates – water. When supplied to the adsorbent bed (salt hydrates for instance) low-grade waste heat breaks the binding force between the adsorbent and the adsorbate (refrigerant which is water vapour), charging takes place. Such adsorption-based heat batteries using a set of heat recovering, charging and discharging heat exchangers can valorise low-grade waste heat from industrial sites, and store and transport heat to distant sites for space or water heating.

Organic Ranking Cycle (ORC) is a thermal driven power cycle that is used for recovery of low-grade heat. While a conventional ranking cycle uses water as a fluid, the ORC uses a low boiling point fluid. The equipment typically comprises of a heat exchanger and pumps, and is CAPEX intensive. Also, if the heat exchanger’s performance is low, the working fluid does not evaporate completely, leaving liquid droplets in the turbine. This could lead to fouling, needing frequent maintenance which is also OPEX heavy.

Although the researchers have been focusing on the usage of conventional low-grade heat from industrial sites, valorising low-grade waste heat from urban sources remains a game-changing area of research. Although the innovation still needs to be scaled-up, its success would eliminate the long distance transportation barrier since such sources are locally situated, and the valorised heat could be supplied directly to urban areas of high heat demand; in areas of high urbanization or in off-grid areas where district heating infrastructure is lacking. Additionally, it will strengthen Europe’s position to be self-sufficient and resilient in case of geopolitical conflicts.

How we can support your heat recovery innovation?

If you are looking for funding for your technological innovations in heat recovery, our innovation consultants and energy experts at Catalyze can help. Energy is at the forefront of many of the EU’s funding programmes, and below is an overview. Contact us if you would like to further explore the funding landscape for energy:

  • (TRL 1-4) EIC Pathfinder(5) (Challenges: solar power harvesting space, responsible electronic, cooling, etc.) Funding rate: 100%.  Deadline: October 18, 2023. Expected deadlines in 2024: Open Call, March 2024; Challenges, October 2024.  (Learn more)
  • (TRL4-6) Eurostars(6). Funding rate varies per country, in general 40%-60%. Deadlines: 14 September 2023, 13 March 2024. If you are early in your technological roadmap and looking for international partners to organise collaborative R&D, Eureka Eurostars fits in well. We are proud to have helped the #1 ranked Eurostars proposal submitted by Cellcius from the Netherlands (see below for full article) that focused on advancing their breakthrough heat battery solution that aims to valorise low-grade waste heat from industrial sites for district heating. (Learn more)
  • (TRL 5-9) EIC Accelerator(7) Funding rate: 70%+equity investment. Deadline: 19 October 2023. Expected deadlines in 2024: January (Open only), March, June, October. If your technology is mature enough and needs further optimization or validation in a relevant environment, EIC Accelerator can be the target. The proposal can either be submitted under the open programme, or the Energy Storage challenge that might be more relevant. (Learn more)
  • (All stages) Horizon Europe(8) calls: your R&D focuses on specific objectives, and benefits from pan-Europe partnerships,  there are several opportunities available  under the Horizon Europe 2023-2024 work programme (learn more about Horizon Europe). For more information, please refer to the destination: ‘Efficient, sustainable, and inclusive energy use’, and the following relevant calls:
    • HORIZON-CL5-2023-D3-03-01 : Increasing the efficiency of innovative static energy conversion devices for electricity and heat/cold generation
    • HORIZON-CL5-2023-D3-01-09 : Waste heat reutilisation from data centres


Cellcius’ #1 ranked Eurostars project

Cellcius’ project, LOSS-FREE HEAT, ranked number 1 out of more than 400 applications Europe-wide. The project will deliver a groundbreaking heat distribution system that recovers unutilized low temperature industrial waste heat using salt and water, and transports it to distant end-users. Catalyze and Cellcius collaborated together to develop the top-of-class Eurostars proposal.

Read the full article here

Powering Change: Energy Transition series

Blog #1: Innovation Opportunities in the Energy Transition

Blog #2: Low-grade waste heat recovery is a key priority for EU energy transition

Blog #3: Sustainable Hydrogen

Blog #4: Critical Materials

Blog #5: Smart Grids





  1. Harnessing Waste Heat Could Save Europe €67 Billion. 
  2. An estimate of the ultralow waste heat available in the European Union.
  3. The role of low temperature wasteheat recovery in achieving 2050 goals: a policy positioning paper. 
  4. Heating and cooling
  5. EIC Pathfinder 2023 Overview – Download our EIC Guide. 
  6. Eureka Eurostars – Get funding – Funding Database. 
  7. EIC Accelerator – Writing the best proposal
  8. Horizon Europe – Prepare for the upcoming programme

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