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FLUWS — Flexible Upcycled Waste Material based Sensible Thermal Energy Storage for CSP

FLUWS aims to develop and validate a more flexible, reliable, environmentally friendly and cost-effective thermal energy storage (TES) system futureproofed for next generation concentrating solar power (CSP) plants operating at higher temperatures and hybridized with PV, which are recognized as the two main paths for reaching cost-efficiency of CSP in the near future. Specifically, FLUWS validates up to TRL 5 a novel TES concept that ensures elevated thermal efficiency with minimum environmental impact thanks to on the one hand the upcycling of waste and residual materials from the ceramic industry and the use of air as heat transfer fluid, and on the other thanks to building on previous consortium know-how in the development of new cost-effective radial packed-bed TES and materials for high temperature applications. The new FLUWS TES will enable more flexible and modular CSP systems as it will have embedded electric heaters driven by renewable electricity and will be designed for easier integration with compact gas Brayton cycles (i.e. supercritical CO2 and air-driven), thus facilitating the provision of additional services from CSP to the grid and widening the applications of CSP as a competitive technology for combined heat and power in the industrial sector.


Today, CSP is not on track towards achieving the IEA Net Zero Emission scenario’s targets. In the last years a capacity addition of below 1 GW for a total installed capacity of about 7 GW has been attained, highlighting a wide and concerning gap between the 64 GW installed CSP capacity projected in the 2030 IEA target and the reality of market deployment. Global and EU CSP markets need a new boost, being more grid flexible and profitable without the need of feed-in tariffs. To that end, much more effort is needed to develop novel and highly efficient solutions, maximizing CSP flexibility and storage capabilities, reducing the costs and overcoming some intrinsic technological barriers. The integration of TES is a key feature of CSP plants. The TES grants the possibility to provide firm and flexible electrical production capacity to utilities and grid operators while also enabling effective management of a greater share of variable energy from other renewable sources. In particular, while the CSP market in EU has been almost stagnant since 2013, PV continued to expand rapidly leading also to drastic cost reductions. This large penetration of PV into the grids is dramatically requiring a backup to support the grid stability and its ability to provide peak power periods outside of central sunny hours of the day. A smart hybridization of PV and CSP plants, in which excess PV production can be transformed into thermal energy and stored by the CSP plant, appears to be more attractive and cost-effective, with new-generation CSP plants capable to be more grid flexible and independent from subsidies. However, advances are needed in the understanding of optimal hybridization strategies, also including control and dynamic aspects, to widen the services provided by hybrid CSP-PV plants in the energy sectors whilst maximizing their profitability and massively contributing to a reduction of the overall greenhouse gas emissions.

FLUWS fully and systematically addresses the identified challenges. FLUWS will develop and validate, at TRL 5, a novel flexible and cost-effective thermal energy storage for concentrating solar power plants hybridized with PV plants.

Aim and objectives

The main objective of FLUWS is to develop, model, prototype, and validate at TRL 5 an innovative, flexible and scalable thermal energy storage for CSP applications. To achieve that the project will:

  • Develop, prototype and validate an innovative, flexible, and scalable packed bed TES with an energy capacity of 50 kWh.

  • Perform a comprehensive material characterization at high temperature of the waste material streams as received and of the final TES material produced by upcycling of the waste.

  • Develop optimal TES material bricks ensuring maximized thermal performance and elevated mechanical resistance and manufacture of at least 2 m3 of the TES material bricks by means of an improved cost-effective and efficient production process.

  • Develop, prototype and validate an innovative, efficient and reliable integrated energy system based on high temperature heat pump for industrial flexible heat provision.

  • Maximizing the flexibility and dispatchability of CSP plants including FLUWS solutions in the future energy system landscape and minimize the impact of the FLUWS solutions by maximizing their circularity by design and leading to more socially/stakeholders accepted CSP systems.

  • Promote FLUWS solutions across EU and non–EU and facilitate market uptake and path to TRL9 and commercialization.

Project partners

Funding is provided by Horizon Europe (CINEA) - Grant Agreement No 101147257.

Timeframe: June 2024 – May 2027


Konstantinos Apostolopoulos Kalkavouras
Konstantinos Apostolopoulos Kalkavouras doctoral student Profile
Ana Sanchez Sanz
Ana Sanchez Sanz doctoral student Profile
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