Watch POLYPHEM final results video!

As POLYPHEM ended in August 2022, we have published a new video to present the impacts, challenges, and success of the project. The takes were made by all partners all over Europe, from the Thémis Solar Tower, in Targasonne (France) where the experiments were proceeded, to Germany, Denmark, and Spain!

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Video transcript

POLYPHEM is a Horizon 2020 project funded under the Energy programme. Coordinated by CNRS and implemented by 9 partners from 4 EU member countries.

[Alain Ferriere, Coordinator, CNRS-PROMES] The objective of POLYPHEM is to improve the flexibility and performance of CSP plant at small scale to meet the requirements of local variable demand of energy. Aside from being the Coordinator of the POLYPHEM project, CNRS was in charge of the construction of the thermal process, including the instrumentation, and of the operation of the prototype plant. CNRS also contributed to the design of the solar receiver through the assessment of properties of materials at high temperature using the solar furnace. In addition to that, CNRS carried out the testing at laboratory scale of the thermocline thermal storage system in a specific test facility called Microsol. The most challenging for CNRS has been the continuous need for adapting the engineering to address all the technical issues raised along the execution of the project. In the end, we could complete the construction of a part of the concept and we are now ready for testing.

[Sébastien Chomette, CEA] For POLYPHEM Project, CEA designed a tailor–made Air solar receiver able to resist to high temperature, oxidation, and mechanical constraints. As a result, Nickel-based Alloy 600 and Alloy 230 were benchmarked as the best materials for the inner and outer tubes of the receiver. Mocks-up were manufactured by hot isostatic pressure process. The alloy is interfaced with copper using diffusion bonding junctions. Welding was the most challenging in the construction phase. Covid-19 situation forced us to source the tubes from new suppliers. Unexpected leakage occurred, and despite our best efforts, we could not repair the receiver and deliver it on site. For the needs of the testing of the thermal process in the project, the source of heat is substituted by a combustor.

[Margarita Rodriguez Garcia, CIEMAT-PSA] In POLYPHEM project, Ciemat in conjunction with other partners, has explored the innovative approach of using concrete as a main material for the thermal storage system. The goal was to decrease the cost of systems of large storage capacities by removing the limitations in tank sizes that metallic walls impose, using a cheap but highly efficient storage material and configuration. As a result, a thermocline tank with concrete bricks as structured filler, concrete walls and concrete foundations, was successfully designed, erected, and tested.

[Juan Manuel Carruncho Rodado, ARRAELA] At Arraela we have developed a new formulation of concrete whose characteristics for Thermal Energy Storage at high temperatures (it can work up to 600ºC without deterioration) make it a unique and ideal material for storing thermal energy.

[Esther Rojas Bravo, CIEMAT-PSA] Simulation models to foresee the thermohydraulic behaviour have been improved and successfully adapted for POLYPHEM! The biggest challenges have been on the material side to develop an appropriate concrete mixture for thermal energy storage while being compatible with the heat transfer fluid, on the erection side to find out an adequate procedure not very time consuming to allocate the filler in the tank, and on the modelling side to adapt the current approaches to the specific features of POLYPHEM. To face all these challenges, the close collaboration between partners has played a critical role.

[Nicholas Chandler, Franhofer ISE] Fraunhofer ISE main contribution to the project has been through development of virtual models of the components and of the whole plant. We created, together with other partners, both static and dynamic simulation models with the ambitious goal of having a verified digital twin of the technology towards the end of the project. The virtual models have been deployed in different tasks: from supporting the design of the plant and defining the layout to the evaluation of the technology, benchmarking, and optimization, but also life cycle analysis and we verified most of them! I think that through virtual models implemented in our in-house tools, RayTrace3D and ColSimCSP, which helped the consortium understand the impact of various parameters better and faster, we were able to save a lot of time and effort within the project. Our main challenge was to collect data about the various subcomponents and to integrate them into specific models to generate a consistent and unique model of plant.

[Andreas Pöppinghaus, KAEFER] In 2010 KAEFER has created a dedicated renewable energies department. The goal was to contribute to the technical development of green power generation. KAEFER initiated the Polyphem project with the aim to address decentralized power generation from solar source with increased efficiency. Special emphasis was put on ruggedness of the design and ease of maintenance. This to stimulate local independence, economic growth and creation of high-quality jobs.

[Daniel Ipse, KAEFER] In order to eliminate the steam cycle, KAEFER utilized a micro heavy duty gas turbine as central part of the plant. The heat input for the gas turbine is to be delivered from a high concentrating solar receiver. The exhaust heat of the turbine is utilized in an organic rankine cycle to produce electricity, again. With the thermal oil energy storage, the operation of the ORC can be extended into hours of lack of sunshine. With the special catalytic combustion chamber contributed by KAEFER, the plant can even produce electricity and heat completely independent from solar irradiation. In 2021 the micro heavy duty gas turbine together with the catalytic combustor executed successfully trial operation at KAEFER`s facility in Bremen.

[Richard Aumann, ORCAN Energy] We from Orcan Energy are Experts in converting heat of any source into electricity by organic Rankine cycle machine. As no additional fuel has to be burnt for the module to run, the electricity is CO2 free. Another renewable heat source is heat from solar radiation – and this brings us to the Polyphem project! We take the residual heat from the solar driven gas turbine to produce additional electricity and to optimize the efficiency. Within the Polyphem project we have been evaluating how we can operate our process at higher evaporation temperature compared to state of the art. We knew that we will gain better efficiency by that. The challenge was to ensure a reliable operation at a higher evaporation temperature as well – and we have been successful with this in the Polyphem project.

[Jens Jorgen Falsig, AALBORG CSP] The Aalborg CSP scope in the POLYPHEM project was to design and supply a high efficient air/oil heat exchanger utilizing the waste energy in the exhaust from the Micro turbine for delivering hot thermal oil to be utilized in either the ORC or stored in the Thermal Energy Storage. The aim was to lower the back pressure on the air side of the heat exchanger, and by that minimizing the performance drop of the micro turbine. Later in the project, when the air receiver failed in manufacturing, Aalborg CSP agreed to design and supply a hot air generator with a diesel burner, to substitute the micro turbine exhaust in order to be able to test the bottom cycle on the site in Themis as originally scheduled.

[Alain Ferriere, Coordinator, CNRS-PROMES] Despite a major technical issue on the solar receiver, we succeeded having many specific results. The main achievements are the selection of alloys and concrete materials, the design, modelling and construction of new components, and the assessment of performance with simulation or testing. Finally, the project could bring the technology from TRL3 to TRL4 or TRL5!

[Andreas Pöppinghaus, KAEFER] The deployment of the technology is considered. Due to the simplicity, large parts of the plant can be produced and erected in the target country as local content. Also, maintenance can be done locally by trained personnel. So large parts of rural areas without proper energy infrastructure can gain power independence without harming the environment by transporting diesel over long distances. This project was very challenging for all of us, even more in the international context of Covid. Although all the objectives could not be reached, it was successful in many aspects. The collaboration between the partners was necessary to address all the technical issues and to propose and develop appropriate solutions.

[Alain Ferriere, CNRS-PROMES] We are convinced that the outcomes of the POLYPHEM project will allow in the short term:  to reinforce the competitiveness of this new low-carbon energy technology,  to favour its integration in the medium term in the worldwide energy mix  and to contribute to the mitigation of climate change.

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