The SAFR project aims to demonstrate the viability of using large scale energy storage to address key challenges of future electricity grids delivering renewable energy to homes and businesses.

SAFR is a project funded
by the European Union’s LIFE+ programme.
More information



A key priority of the EU is to reduce CO2 emissions and promote renewable energy sources. The related quantified goals are laid down in the EU “20-20-20” targets. To reach these targets, the actors along the electricity value chain need to overcome some technical and operational challenges. Energy storage is considered to play a critical role in this regard. However, the wider deployment of currently available technologies for long-term storage is limited due to geographic site requirements, development gaps and capital costs.

The transition towards a more sustainable European energy system poses a number of challenges for electricity grids, and new ways to facilitate an increased feed-in of volatile distributed renewable energy sources (DRES) are required.


The project Storage Application For Renewables (SAFR) aimed to enable a further expansion of the share of distributed renewable energy sources by developing an innovative and highly flexible thermoelectric energy storage system. This system operates as a flexible load (in order to avoid congestion) and as a generation unit (serving as a source of electricity in times of peak demand). The storage solution is highly flexible, location-independent and operates emission-free.

Overview of Results:

  • The energy storage system, based on a high-temperature thermal energy storage module, was designed and a full basic engineering was performed
  • A laboratory test system of approximately 1 MWh of capacity was designed
  • The laboratory test system was constructed at the TU Darmstadt
  • The  laboratory test system was operated over multiple charging and discharging cycles
  • The results were compared to computer simulations developed by the project engineers, successfully validating the storage technology

The SAFR project resulted in a validated design for a large capacity energy storage system to aid the integration of renewable energy in the electricity grids.


The SAFR Project ran from 1/6/2014 to 31/03/2017 with the support of the EU’s LIFE+ Programme.


The SAFR project is a collaboration between Trianel GmbH and Carbon-Clean Technologies GmbH.



SAFR is supported by the European Union’s LIFE programme. LIFE is the EU’s financial instrument supporting environmental, nature conservation and climate action projects throughout the EU. Since 1992, LIFE has co-financed some 4 171 projects, contributing approximately €3.4 billion euros to the protection of the environment and climate.


Summary of Technology

Energy storage concept

The SAFR project has developed a thermo-electric storage technology, which stores energy in the form of high-temperature heat. The energy storage system can store 500 MWh of energy, as much energy as three hundred European citizens use in one year.

The energy storage system is operated in two phases. It is charged by using electricity to heat air to extremely high temperatures. The air deposits its heat in a storage module, heating special temperature resistant ceramic material to temperatures over 1 000 °C. To discharge the system, cold air is pumped into the storage module. The air heats up, carrying the energy out of the storage module. This extremely hot air can then be used to drive highly efficient steam processes to regenerate the electricity. At the same time, the hot air can be used to generate hot water for district heating or for industrial processes.

The technology has been developed by Carbon-Clean Technologies GmbH, an innovative company based in Cologne, Germany.

Results of the SAFR project


Requirements Analysis

A model-based tool was developed to simulate how an energy storage system would operate under current conditions in the German electricity market. Two options were considered, a stand-alone storage system, and the integration of the storage system into the existing machinery of a conventional power plant. The simulations showed that the storage system should be able to store approximately 500 MWh of energy and be charged with 50 MW.

Process Engineering

The process engineering built on the specification, to design a technical system which could achieve the necessary storage capacities and efficiencies. Since a storage system is repeatedly charged and discharged, the process engineering considered a dynamic cycling process. Extensive state-of-the-art computer simulations were performed to optimise this dynamic cycle.

The process engineering determined the type of thermodynamic cycle needed, and specified process temperatures and pressures in order to achieve the highest possible storage density and efficiency in the system.

Engineering the Storage Module

CAD drawing of the storage system

The design of the storage module was performed, selecting materials and insulations which could withstand both the high temperatures and the repeated cycling of the system. The designs of the storage module were incorporated into a computer-aided-design (CAD) model of the entire storage system.

Engineering the Air Heater

To reach the high temperatures required for the storage system, a special air heater is required, which is not commercially available. This system was designed, and three prototypes have been tested in order to demonstrate its function and to improve the design.

Engineering the Power Generation System

The power generation system converts the stored high temperature heat back into electricity via an air and steam turbine cycle. Three concepts for this system were studied in detail through computer simulations, optimising the design of this system.

Engineering the Electrical Systems

A complex electrical system is required to achieve the high powers required for charging the storage system and to accurately control the multiple air heaters. Several concepts for the electrical systems were studied, and the best option was selected.

Laboratory testing of modules


In addition to designing the full-scale system, the SAFR project constructed a laboratory-scale demonstrator to prove that the system functions as our designs suggest. A 1 MWh storage module was designed and constructed. The 1 MWh of energy stored is almost as much energy as one person uses as electricity in a year.


The system was constructed at the Technical University of Darmstadt.

Test cycles

The system was operated, testing multiple charging and discharging cycles. A sensor suite monitored the temperature along the storage module and in the thermal insulation.


Extensive computer simulations were performed to compare the results of the practical tests to the designs for the full-scale system. The results of one of these tests is shown above. The experimental results (solid lines) for how the temperatures at different points along the module vary through multiple charging and discharging cycles fit extremely well with the results of our computer simulations, validating our model of how the storage system operates. This result allows us to be confident that the full-scale system will work according to our design.



The Layman’s Report is now available for download.




SAFR Project Layman's Report - English Version   SAFR Project Layman's Report - Deutsche Version


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For further Information, please contact:

Andreas Lemke
Trianel GmbH

Krefelder Straße 203
D-52070 Aachen

+49 (0) 9241 41320-997

Dr. Robert Pfab
Carbon-Clean Technologies GmbH

Im Zollhafen 24
D-50678 Cologne

+49 (0) 221 355 755 0 +49 (0) 221 355 755 90