Thermal Response Test for Underground Thermal Energy Storages (Annex 21)

Thermal Response Test (TRT) is a measurement method to determine the heat transfer properties of a borehole heat exchanger and its surrounding ground in order to predict the thermal performance of a ground-source energy system. The two most vital parameters are the effective thermal conductivity of the ground and thermal resistance within the borehole. These measurement results are important for proper BTES design but also for commissioning and failure analysis. This method has significantly supported the rapid spreading of BTES systems and the introduction of this technology in “new” countries.

The overall objectives of Annex 21 are to compile TRT experiences worldwide in order to identify problems, carry out further research and development, disseminate gained knowledge, and promote the technology. Based on the overview, a TRT state of the art, new developments and further work are studied.

Official members of Annex 21 are currently: Canada, Finland, Germany, Japan, Korea, Sweden, Norway, Turkey and Spain. Further, the following countries participate as observers: Argentina, Austria, Belgium, China, Italy, Switzerland, The Netherlands and USA. Seven experts meetings were held so far. The Annex will expire in summer 2011.

Information on the outcome of the Annex 21 experts meetings can be found at

If you have related topics, publications, applications or projects which could be included in the work of this Annex, please contact Manfred Reuß

Applying Energy Storage in Ultra-low Energy Buildings (Annex 23)

Sustainable buildings will need to be energy efficient well beyond current levels of energy use. They will need to take advantage of renewable and waste energy to approach ultra-low energy buildings1. Such buildings will need to apply thermal and electrical energy storage techniques customized for smaller loads, more dis-tributed electrical sources and community based thermal sources. Lower exergy heating and cooling sources will be more common. This will require that energy storage be intimately integrated into sustainable building design. Many past appli-cations simply responded to conventional heating and cooling loads. Recent re-sults from low energy demonstrations, distributed generation trials and results from other Annexes and IAs such as Annex 37 of the ECBCS IA, Low Exergy Sys-tems for Heating and Cooling need to be evaluated. Although the ECES IA has treated energy storage in the earth, in groundwater, with and without heat pumps and storing waste and naturally occurring energy sources, it is still not clear how these can best be integrated into ultra-low energy buildings capable of being rep-licated generally in a variety of climates and technical capabilities.

Energy storage has often been applied in standard buildings that happened to be available. The objective was to demonstrate that the energy storage techniques could be successfully applied rather than to optimize the building performance. Indeed the design of the building and the design of the energy storage were often not coordinated and energy storage simply supplied the building demand what-ever it might be.

Responsible for this proposal of a new Annex is Fariborz Haghighat .

Annex 23 Subtask A-B Final Report is available here

Draft Final Report of Annex 23 is available - here - 13 MB
If you want to read the complete proposal click - here - 93 kB .

Surplus Heat Management using Advanced TES for CO2 mitigation (Annex 25)

The world’s total energy supply is 136500 TWh/year whereas the energy use is approximately 94000 TWh/year (IEA Key Statistics, 2008). By inspecting these figures, one can see that close to 1/3 of the world’s energy supply is “wasted” in energy conversion. In reality, the number is even larger, perhaps as much as 50%, since for example the tank-to-wheel efficiency of engine driven transportation is only 20%, and boiler efficiencies seldom are above 90%. From a sustainability perspective, increasing the efficiency in many energy conversion processes is crucial. As the demand for energy increases in all sectors, and all over the world, waste heat management will be a cost-effective way of securing the supply of energy and power while mitigating the emissions of CO2. Such management is most effectively done in cases where the waste heat flow are large, like industrial processes, or in cases where the value of increases waste heat utilization is large, like in the vehicles and transporting goods sector. Recent advances in compact thermal energy storage has encouraged this initiative to explore solutions where waste heat management can be enhanced, facilitated and even enabled by integrating thermal energy storage technology.
The general objective of this Annex is to identify and demonstrate cost-effective strategies for waste heat management using advanced TES. New knowledge will be generated with regards to:

  1. The potential for advanced TES to minimize process waste heat through better process integration, enabling the use of waste heat for internal heating demands or cooling demands (via heat driven cooling).
  2. The potential for advanced TES to cost-effectively increase waste heat driven power generation in industrial applications.
  3. The potential for advanced TES to enable external use of heat from industrial-scale processes through effective thermal energy distribution.
  4. The potential for advanced TES to increase the utilization of waste heat in vehicles like on-board cooling and minimization of cold-start.
  5. The potential for advanced TES to increase the use of waste cooling (e.g., the large cooling potential associated with LNG regasification) and free cooling for comfort cooling applications.

Thus, a sub-goal of this proposed annex is to really dig into the waste heat utilization issue from a very broad perspective, and show the great potential for using advanced TES towards reaching a resource efficient energy system where waste heat (and cold) is minimized. This has a good potential for attracting a large number of participants from a variety of disciplines and levels of R&D (basic research to commercial systems).

If you are interested in this new Annex activity, please contact Luisa Cabeza .
The Annex homepage can be found here.

Electric Energy Storage: Future Energy Storage Demand (Annex 26)

The future of electricity network involves a massive penetration of unpredictable renewable energies. For insuring network stability as well as for maximizing the energy efficiency of such networks, storage is a key issue. Up to now, the integration of renewable energies did not take into account the demand side and was performed in a “fit and forget” way. The optimum evolution in an economic perspective is in the future to have an integration that is respecting the needs. One solution – beneath demand side management and grid extension – is the use of energy storages. The main purpose of adding energy storage systems in the electricity grid is to collect and store overproduced, unused energy and be able to reuse it during times when it is actually needed. Essentially the system will balance the disparity between energy supply and energy demand. Worldwide between 2% and 7% of the installed power plants are backed up by energy storage systems (99% pumped hydro systems). The future demand of energy storage devices is actually unknown. Only the main influence factors on this demand are known.
The overall objective of this task is to develop a method or approach to calculate the regional energy balancing demand and to derive regional storage demand rasterizing the area and taking into account that there are competitive technical solutions. This objective can be subdivided into ten specific objectives:

  • To rasterize the whole area to typical small self-similar elements,
  • to identify and characterize typical fluctuating energy demand for different elements which stands for different regions and grid situations (e.g. intermeshing),
  • to identify and characterize typical fluctuating energy production (wind, PV) for different elements which stand for different regions and renewable energy potential (e.g. wind velocity),
  • to identify and characterize typical conventional energy production (gas turbine, nuclear power plant) for different elements which stand for different regions and conventional energy production,
  • to reduce different grid structures to a fistful typical systems and to simulate their inner intermeshing and their exterior connectivity (transport, import, export),
  • to derive balancing demand for each typical region,
  • to derive energy storage demand as a share of the total balancing demand, taken into account that the most successful economic solution will be realized,
  • to develop a method or model to transfer these results to other countries and regions,
  • to assess the technical and economical impact of energy storages on the performance of the energy system, and
  • to disseminate the knowledge and experience acquired in this task.

A secondary objective of this task is to create an active and effective research network in which researchers and industry working in the field of electric energy storage can collaborate.

If you are interested in this new Annex activity, please contact Christian Doetsch .

If you want to read more about the planned activities, please click - here - 266 kB .

Integration of Renewable Energies by Distributed Energy Storage Systems (Annex 28)

Operating agent:

Dr. Andreas Hauer
Bavarian Center for Applied Energy Research, ZAE Bayern

Dr. Christian Doetsch,
Fraunhofer Institute UMSICHT

Start: January 2014
End: December 2016

The Implementing Agreement “Energy Conservation through Energy Storage” (ECES) approved at the Executive Committee Meeting in 2-3 December 2013 in Ljubljana, Slovenia, the new Annex on the “Integration of Renewable Energies by distributed Energy Storage Systems”. This Annex should focus on the overall storage properties and their impact on the integration of renewable energy rather than the specific challenges of each energy storage technology. Collaboration with other Implementing Agreements (IA) within the IEA Technology Network and other institutions active in the field of distributed energy storage is crucial for this Annex.
The contribution of renewable energy to overall global energy production is expected to grow worldwide. Most renewable energy sources, like wind, PV, and solar-thermal are fluctuating resources. Significant storage capacity is needed to smooth out these fluctuations for reliable future energy systems. At the moment the focus is on large, central energy storage technologies like pumped hydro or the conversion of surplus electricity into fuels such as hydrogen or methane. The potential for small, distributed energy storage technologies remains mostly unexplored.
The overall goal of Annex 28 is to foster the role of DES and to better evaluate the potential storage capacities for the integration of renewables at an economical competitive level. To reach this goal, distributed energy storage technologies and their properties will be examined, storage properties requirements depending on the different renewable energy sources will be reviewed and possible control and operation strategies for DES and technologies by smart grids will be studied. Finally the potential of DES systems for the integration of renewable energies based on the actual final energy demand shall be quantified and guidelines for choosing the most suitable DES technology for the actual application will be developed. Best practice and success stories examples will be given.
The scope of this Annex includes all energy storage technologies suitable on the consumer side. Three main fields of application – households, trade and commerce and industry – will be investigated.
The kick-off workshop and experts meeting will take place in Munich. Germany on April 9-11 2014.
If you are interested in more information, please contact Andreas Hauer

Material Research and Development for Improved TES Systems (Annex 29)

Operating agent:

Dr. Andreas Hauer
Bavarian Center for Applied Energy Research, ZAE Bayern

Start: January 2013
End: December 2015

At the Executive Committee Meeting in Auckland, New Zealand, November 2012, this Annex was approved. The objective of this joint Task with the IEA Solar Heating & Cooling Implementing Agreement is to continue the activities started in Annex 24 “Compact Thermal Energy Storage: Material Development for System Integration”.
From the experience of the experts in the first period of the Task, it was concluded that one strong point elaborated is the interaction between the materials experts and the application experts, and the facilitation of this interaction by the division of the work into two subtasks: materials and applications.
The experiences of Annex 24 lead to a structure of the new Annex 29, with three materials working groups, one subtask for applications and one working group on economical evaluation of thermal energy storage (TES) systems.
The economical evaluation will be performed by a bottom-up approach (while in Annex 24 a top-down approach was used). A questionnaire was sent out to predict the expected cost of each storage system, including material and other components. Within the material oriented working groups, novel storage materials – phase change materials or working pairs for thermo-chemical reactions – will be developed, tested and characterized. Finally they should be described by multi-scale simulation models in order to predict their performance under the operation conditions given by the application subtask. This subtask is responsible to define reference conditions for relevant application field for TES.
Next Experts Meeting and Workshop will be held in Lyon, France, on April 28-30 2014. More information can be found at