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Numerical and experimental analysis of a novel thermal energy storage for a small-scale concentrated solar power plant

Periodic Reporting for period 1 - Small-scale CSP (Numerical and experimental analysis of a novel thermal energy storage for a small-scale concentrated solar power plant)

Reporting period: 2018-06-01 to 2020-05-31

The biggest challenge for renewable energy sources is to match the demand with the supply. By using thermal energy storage for concentrated solar power plants, the stability, reliability, and capacity factor of the plants are improved. Currently used concentrated solar power technologies (parabolic trough collector, solar power tower, linear Fresnel reflector) use heavy and very expensive glass mirrors and receivers. Apart from that, conventional thermal storages are also expensive as these are based on molten salts, which are expensive and their handling requires special materials. As a result, conventional concentrated solar power technologies are only suitable for large-scale installations in regions with high annual direct normal irradiance.

This project addresses the development of a cost-effective concentrated solar energy driven cogeneration system with thermal energy storage. To this end, the project addresses the investigation of a novel micro-structured polymer foil-based concentrated solar power system and investigations of a novel packed-bed rock thermal energy storage system. The micro-structured polymer foil-based concentrated solar power system has the advantages of a low installation cost and a low operation and maintenance cost. The thermal energy storage is based on a packed-bed rock with heat storage charging and discharging using evaporation and condensation of heat transfer fluid.

The results indicate that the micro-structured polymer foil-based concentrated solar power plant with packed-bed rock thermal energy storage is a promising alternative for cogeneration/multi-generation plants. The project contributes to the development of a cost-efficient renewable energy systems, reducing the dependence on fossil fuels and reducing the carbon dioxide emissions of the heat and power generation sector, thus helping to attain socio-economic and environmental targets in the context of the EU 2020 vision.
The work performed during the project includes:

• Development of a project plan, and project coordination and management.
• Development of a data management plan.
• Detailed review on concentrated solar power (CSP) driven multi-generation systems, including the technical and economical viabilities, and issues related to the system design and integration with different systems.
• Techno-economic analyses of a parabolic trough collector based plant and a foil-based CSP plant including a conventional two-tank thermal energy storage (TES) and an organic Rankine cycle (ORC) power system.
• Techno-economic analysis and optimization of micro-structured polymer foil-based CSP plant with ORC power system and multi-effect distillation system for fresh water generation.
• Comparative analysis of a foil-based CSP driven system with two-tank indirect (using different heat transfer fluids for the solar field and the TES), two-tank direct (using the same heat transfer fluid for the solar field and the TES) and packed-bed rock thermal energy storage. Apart from that, operating strategies were also identified for such plants.
• Experimental investigations of a packed-bed rock (granite stone) TES with heat storage charging using the evaporation of heat transfer fluid at industrial partner’s (Heliac ApS, Denmark) facility developed for this novel TES proof of concept.
• Analysis of a packed-bed rock TES with heat storage charging and discharging using evaporation and condensation of heat transfer fluid.
• Training activities on simulation tools already available at DTU Mechanical Engineering, description of the working principle of the foil-based CSP system provided by industrial partner Heliac ApS, Denmark, preparation of data management plan, patent process overview and pitch preparation.
• Presentation of project results at international conferences.
• Supervision of post-graduate students.
• Outreach activities through: (i) participation in the event/workshop organized by the Marie Curie Alumni Association; (ii) project open day; and (iii) seminars.
• Presentation of project results at department events/meetings and at meetings with the industrial partners.

The results suggest that the micro-structured polymer foil-based CSP plant can reduce the levelized cost of electricity by up to about 40 % compared to the small to medium scale plants with the conventional and the most widely used parabolic trough collector technology. Based on the techno-economic analysis, cyclopentane is a preferred ORC power system working fluid and the packed-bed rock thermal energy storage is a preferred storage option for the foil-based solar collector powered cogeneration plant. It is preferable to use an enthalpy based approach, compared to the conventional temperature based approach, for modelling the phase change of the heat transfer fluid for the proposed thermal energy storage. Experimental investigations during the proof of concept for the proposed TES suggest that the use of vacuum in the system allows low loss of energy quality (the difference between input and output temperature), as the boiling point varies gradually with the storage temperature.

The outcomes and results have so far been disseminated in 2 peer-reviewed conference publications in proceedings and 1 book chapter, which are all available as an open-source. In addition, 3 papers will be published shortly in peer-reviewed top international journals targeting researchers in the field of renewable energy. The project activities have been disseminated by social media (e.g. Linkedin, ResearchGate) and the project website. The work was done in close collaboration with the industrial partners and that has resulted in an effective transfer of the results to industries.
The progress of the project beyond the state of the art include the following: 1) the first analysis of a micro-structured polymer foil-based CSP system, 2) models for the analysis and optimization of foil-based CSP driven co-generation systems, 3) experimental investigations of a proof of concept for a packed bed rock thermal energy storage system with heat storage charging using the evaporation of the heat transfer fluid, and 4) modelling and analysis of different thermal energy storage system and ORC power system working fluid options for the foil-based CSP plant.

The cost-effective micro-structured polymer foil-based solar collectors are easy to produce and just a single machine can produce about 100 GWth equivalent solar collectors, which is more than the globally installed CSP capacity today. Therefore, a high cost-reduction potential exists with this solar collector technology. A thermal energy storage system based on packed-bed rock uses inexpensive material to store energy. The successful commercialization of the foil-based CSP plant with packed-bed rock thermal energy storage will help to attain socio-economic and environmental targets. Furthermore, developing expert knowledge in this field will lead the way for future commercialisation, stimulating investment, creating new jobs, and businesses within the energy sector. The wide use of the investigated technology has the potential to assist the 2015 Paris Agreement on climate change by reducing greenhouse gases emission from the electricity, district heating, industrial process heat and/or freshwater production sectors.