NOTICIAS

Today we interview Cristina Prieto, associate professor at the University of Seville, Spain. She has been R&D manager at Abengoa, where she has been dedicated to the development of thermal energy storage solutions for solar thermal applications. She has led more than 20 international R&D projects related to thermal storage, with more than 50 papers in citation index journals and 13 patents. She obtained her PhD researching molten salt storage solutions and has participated in the European Commission's SET-Integrated plan for renewable technologies and regularly acts as an external evaluator for European Research Programs. Hello Cristina, thank you very much for talking with us. After so many years as R&D director in a private company, what motivated you to move to university? Are you still involved in research? After more than 20 years working in the private sector, I saw the chance to give back to society the lessons learned during this period in the development of new renewable technologies. From my point of view, we all must contribute to the new generations of engineers so they can take over in this area that is so necessary in this situation of global warming we are living. In the university, it is expected from us to maintain our research lines. I am currently investigating ways to improve the technology of thermal energy storage. I am fully supporting the role this technology can achieve in the dispatchability of the concentrated solar power industry and for hybridizing other renewable technologies. In fact, I am feeling very proud since a few months ago the European Commission has granted us the Horizon Europe project HYBRIDplus, where we are specifically developing this type of storage. Tell us a little more about HYBRIDplus, what is it about? HYBRIDplus aims to demonstrate an electrified thermal energy storage (TES) concept for concentrated solar power plants based on phase change materials (PCM). Instead of storing the heat in the conventional two molten salt tanks, we use this so-called phase change materials, that store the energy as latent heat with higher energy density than sensible systems. The PCMs is a technology that is well known at the academia, but that presents some handicaps that difficult its integration in the industry, being one of them the low thermal coefficient of the PCM. What we do in the project, is to integrate metal wools in the PCM so the heat transfer coefficient is highly enhanced while at the same time we use this metal as an electric heater to hybridize the TES, allowing us to store excess electricity from a PV plant for example. In the end, we are building a bridge for the PCM technology to jump to the big leagues. And how does this new storage improve the current CSP plants? As you know, I came from an industrial background, and I still have a very practical mindset when talking about research. Nowadays everybody understands the necessity of decarbonization and dispatchability, but the main issue is still the cost. The CSP industry is required to attain these objectives, but it cannot compete with the low cost of PV and wind. What we are doing here is to introduce the highly efficient supercritical CO₂ cycle in the CSP plant, which will help making it more competitive, but to do so, we need to increase the temperature of the heat transfer fluid, which directly impact the storage unit. The hybrid concept we are developing in the project, uses the traditional molten salts only as HTF, not as storage material, and thus we can reach up to 600 ºC in the salts without degradation -that is a residence time related phenomenon- and store the energy efficiently in the PCM. This PCM is also designed in a cascade configuration, taking advantage of the phase change energy of different materials to maximize the heat transfer. In parallel, since we have electrified our storage tank, we can use low-cost excess electricity from intermittent renewable sources that could pose a challenge to the grid for charging our storage, and then discharge when required. The HYBRIDplus plant can then increase the competitiveness of CSP plants by increasing the power cycle efficiency and by using low-cost electricity from non-dispatchable sources, and to do so, it is essential to develop this new storage concept. And everything is done at the University of Seville? The University of Seville is the coordinator of the project, and we are building the pilot plant in our laboratories, but we are a full consortium of 7 partners developing the concept. We have two other universities, KTH Royal Institute of Technology from Sweden and University of Lleida also from Spain, in charge of the technoeconomic models and environmental assessment the first and of the thermophysical characterization and compatibility analysis the latter. We also have 4 SMEs with us, each of them with an important expertise and point of view in the project. The German company SEICO is providing all his extended knowledge in electric heaters, the Spanish engineering Build to Zero helps with the engineering and provides its point of view as possible end user, the also German Deutsches Metallfaserwerk (STAX) is an expert in the fabrication of metal wools with years of experience and, last but not least, we have the French R2M solution for helping with the communication and exploitation activities. Aside from this project, are you involved in any other investigation related to CSP? The University has given me the opportunity to continue developing the thermal energy storage technology, that has always been the basis of my research. Actually, I am very focused on the dispatchability of high-penetration renewable energy systems, and on the decarbonization of process heat. Aside from HYBRIDplus, I am coordinating a national project for the development of an electrified modular TES for process heat applications, and I am participating also in the TopCSP project, from the MSCA grant, which studies the dynamic behaviour of the solar salts and its degradation due to high temperatures on the boundary layer during heat transfer. “I really hope that these innovations help to increase the relevance of the CSP technology, so much required as the most dispatchable renewable technology”.