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GLASUNTES Report Summary

Project ID: 656753
Funded under: H2020-EU.1.3.2.

Periodic Reporting for period 1 - GLASUNTES (Innovative high temperature thermal energy storage concept for CSP plants exceeding 50% efficiency)

Reporting period: 2016-05-01 to 2018-04-30

Summary of the context and overall objectives of the project

Energy provision is a big challenge for our Society, being the present production/consumption paradigm not sustainable. To change current trends, a large increase in the share of Renewable Energy Sources (RESs) is crucial.
The evolution towards a society not based on fossil fuels has become a matter of the greatest interest, and solar energy has the potential of providing 27% of global electricity in 2050 – above all others RESs – of which around 11% from Concentrated Solar Power (CSP).

CSP systems have the distinctive ability of providing dispatchable power: State-of-the-Art (SoA) CSP plants featuring Thermal Energy Storage (TES) run overnight or with cloudy sky, providing renewable base–load generation and ancillary services aiding the penetration of intermittent sources such as wind and solar PV. Still, deployment lags behind expectations and technology breakthroughs are needed in order to significantly reduce costs.
Most notably, TES options working at temperatures exceeding 700 C still need to be developed.

GLASUNTES aims at bridging this gap by achieving three main objectives, i.e., to prove the feasibility and assess the potential of

1. an innovative CSP concept whereby (i) the receiver is co-located with the TES vessel, and (ii) the solar radiation is directly absorbed by the liquid storage medium;
2. the adoption of common glass-forming compounds as novel TES materials. These are nontoxic and inexpensive (mainly sand), and the related know-how is already available from the glass manufacturing field;
3. the CSP systems resulting from the integration between receiver–TES and recently proposed high-performance power conversion units based on supercritical CO2 thermodynamic cycles.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

During the first part of the project, an innovative experimental setup was designed which allowed to test the key process of direct absorption of concentrated sunlight into molten glass.
The setup was designed and constructed at ETH Zurich, and tested at the ETH High Flux Solar Simulator (HFSS) with radiative input as high as 1200 suns (or 1.2 MW/m2).
The ad-hoc designed system to measure the temperature field within the glass melt operated as expected and glass temperatures as high as 1300 C were measured. Different types and colors of common container glass samples were tested.
A numerical model of the system was also developed, which couples the ETH in-house Monte Carlo ray tracing software with the CFD solver Ansys Fluent. This numerical tool was validated against the measured glass temperatures.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The pioneering experiments conducted in the first part of the project demonstrated that molten glass can be used as a stable direct absorber of concentrated solar radiation at temperatures as high as 1300 C, without any particular containment issue. This results meets and exceeds the project target of 1000 ℃.
Avoiding the presence of heat transfer surfaces (e.g., tubes) removes the limitations of maximum temperatures and heat fluxes hampering the performance of current solar receivers.
The achieved temperatures would allow for the coupling of the proposed receiver-TES system with all the most promising thermo-electric conversion technologies (e.g., supercritical CO2 systems and gas turbines), getting closer to the high-efficiency CSP systems envisaged by all the international development roadmaps for this technology.

The work will now focus on the design of a scale-up model of the receiver-TES system, made possible by the software tool validated in the first part of the work. New glass compositions will be considered.
Another activity, already started, deals with the modeling at system level. In this case, the detailed design model is reduced to be included in a modeling framework including the solar-harvesting system (i.e., the heliostats fields and the beam-down optics) and the power conversion unit, in this case a supercritical CO2 power plant.

Further experimental activity will be devoted to prove the feasibility of efficiently withdrawing the thermal power stored in the system. However, the realization of this phase is dependent on the available funds.

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