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Final Report Summary - RESTRUCTURE (Redox Materials-based Structured Reactors/Heat Exchangers for Thermo-Chemical Heat Storage Systems in Concentrated Solar Power Plants)

Executive Summary:
RESTRUCTURE was a 51-month project, partially funded by the EC under the FP7 programme, aiming at the exploitation of the heat effects of reversible chemical reduction-oxidation (redox) reactions for the storage and on-demand controlled release of solar heat. The new concept introduced by RESTRUCTURE is, instead of using packed or fluidized beds of the redox material as the heat storage medium, to employ monolithic structures, made entirely or partially from the redox active materials. The project involved 6 partners from 5 EU countries. The partnership included 2 Research Centers, 3 large industries and 1 SME.
The project studies started with screening of candidate redox compositions via both theoretical and experimental studies and identification of the most promising ones to be further considered on the basis of specific key performance indicators. The qualified compositions were shaped to small-scale structured reactors/heat exchangers, also taking into account preliminary reactor modeling studies which were subsequently refined with experimental findings of the evaluation and characterization of those in-project prepared structured bodies. A key-achievement around the mid-term of the project related to the proof-of-concept experimental validation of the core idea of RESTRUCTURE, as briefly described above. This finding provided confidence for the continuation of project activities, which involved scaled-up production of honeycomb-shaped cobalt oxide based structures. Despite the challenges identified, the relevant activities were successfully concluded and the structures were employed for the construction of a pilot reactor/heat exchanger, allowing thermochemical storage (TCS) of solar heat on the basis of the two step cobalt/cobaltous oxide reversible redox cycle.
The detailed design of the reactor was achieved via the aforementioned detailed numerical model. The pilot and all its required peripherals for detailed monitoring and control of its operation were installed at the research platform of Solar Tower Juelich (STJ) in Germany. The system was successfully operated and the main findings of relevant experimental campaigns can be summarized as follows: a) Successful proof-of-concept validation of RESTRUCTURE technology at scaled-up and nearly realistic operating conditions; b) Energy density values in the range of 135-205 kWh/m3 vs. 71 kWh/m3 of the existing sensible heat storage system at STJ. Substantial further increase can be achieved, if certain improvements (defined in the attached document) are implemented in the future; c) The system showed sufficient robustness and operational flexibility on the basis of 28 redox cycles performed in total. Further longer-term studies are required in the future to elaborate on such very important aspects.
The results obtained from the pilot system operation were used to validate/refine the numerical reactor model, which was subsequently used for the design of a scaled-up (i.e. commercially-relevant size) reactor. The project concluded with the detailed techno-economic evaluation of the technology introduced by RESTRUCTURE and more specifically by considering the scaled-up redox TCS reactor derived from the numerical studies integrated into a 70.5 MWe air-operated Solar Tower CSP plant. Calculated LCOE values were found to be within the range of acceptable costs defined by IEA and the US DoE/Sunshot initiative for conventional and renewable power production and storage technologies respectively. Moreover, obvious environmental benefits (in terms of CO2 emission savings) via utilization of the RESTRUCTURE technology were quantified.
As an overall conclusion, RESTRUCTURE introduced and successfully validated a conceptually simple approach for incorporation of redox TCS in future high temperature air-operated CSP plants, by advancing the relevant technology from a TRL 3 to TRL 4-5. This constituted the first step towards further development for the introduction of a novel and 100% renewable technology into the CSP sector.
Project Context and Objectives:
The RESTRUCTURE project was a 51-month undertaking, partially funded by the EC under the FP7 programme, aiming at the exploitation of the heat effects of reversible chemical reduction-oxidation (redox) reactions for the storage and on-demand controlled release of solar heat. The new concept introduced by RESTRUCTURE is, instead of using packed or fluidized beds of the redox material as the heat storage medium, to employ monolithic structures, made entirely or partially from the redox active materials. The project’s main scientific/technical objectives were:
- The development of suitable redox systems with thermochemical heat storage (THS) and release capability quantified via fast reduction and re-oxidation kinetics, prolonged lifetime as well as constant activity and cyclability.
- The design of new structured honeycomb/foam reactors/heat exchangers with enhanced transport, thermal and heat recovery properties, also incorporating a high amount of redox material per volume.
- The shaping of the redox powders above to heat storage structures with sufficient thermomechanical properties.
- The demonstration of the structured reactor/heat exchangers for cyclic heat storage/release operation, within the operating temperature range of future high temperature solar tower plant designs.
- The manufacture of a pilot-scale structured reactor/heat exchanger, its coupling to an existing solar tower facility (Solar Tower Jülich/STJ research platform) and the on-site validation of the technology by demonstrating heat storage/release capability during on-sun and off-sun operation respectively, reaching energy storage density levels of at least 400 kJ/kg and storage capability for seven days.
- Identification of investment and operational cost of a 70.5 MWe commercial plant incorporating the particular THS system and comparison to the EU targets of: (a) Thermal Energy Storage Cost of 18 €/kWhe, (b) a levelized electricity cost of 0.10 €/kWh and (c) a storage efficiency higher than 90%.
- Presentation of a suitable strategy for the introduction of the technology into the market within a reasonable period of 5-10 years after the end of the project.

Project Results:
Detailed informaiton on the achievements/results of the project per workpackage (WP) is provided in the attached document.
Potential Impact:
The final outcome of the project, despite the non-trivial challenges identified in its duration, is assessed as very positive. The main benefits from the successful implementation of RESTRUCTURE can be summarized as follows:
-The proof-of-concept validation of this novel THS concept under relevant conditions has set the basis for the subsequent more thorough investigation and development of the technology towards enhancing CSP penetration in the market. The technology, provided that certain challenges already identified by RESTRUCTURE will be overcome, can significantly contribute to the implementation of compact, simple and high energy density storage systems that will facilitate the main advantages of CSP cf. other renewable technologies: a) the ability to operate at high temperatures, thereby being capable of achieving higher efficiencies and b) the ability to significantly mitigate or even eliminate issues related to intermittent energy production via employing high energy density storage systems.
-Based on the above point, RESTRUCTURE has set the basis for further development of a technology that has a fair potential to contribute to the penetration of 100% environmentally friendly energy production processes (i.e. CSP), with obvious benefits in terms of CO2 emissions savings and additional jobs creation.
-The activities of RESTRUCTURE have brought up a new momentum and a new development direction to the companies involved. The project helped to diversify and to broaden the companies’ portfolio of skills and interests. It supported Abengoa Solar’s trend of moving into solar process heat and solar chemistry, helped widening LiqTech’s expertise of forming ceramic structures out of reactive materials applicable in many fields, and supported Molycorp in identifying potential applications of their materials in the field of solar power production and solar chemistry.
-The successful completion of RESTRUCTURE has brought Europe to a leading position with respect to the development of novel redox thermochemical storage concepts and also demonstrated a clear mid-term horizon commercialization potential. RESTRUCTURE brought the technology from a technology readiness level of 3 (i.e. experimental proof of concept) before its initiation to 4-5 (i.e. technology validated in relevant environment). The project partners will intensify their efforts towards continuation of RESTRUCTURE work via future follow-up developmental projects, so that this strategic innovation advantage will be maintained and the technology will reach pre-commercialization during the next 5-10 years.

Additional information is provided in the attached document.
List of Websites:

Contact person: Dr. George Karagiannakis
Researcher at the Aerosol & Particle Technology Laboratory/Chemical Process & Energy Resources Institute/Centre for Research & Technology Hellas (APTL/CPERI/CERTH)
6th km Charilaou-Thermi road, PO Box: 60361, 57001
Thermi-Thessaloniki, Greece
Tel: +30 2310498198

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Record Number: 189195 / Last updated on: 2016-09-15