Research

Aim

In the TOPCSP project, we establish the overall research objective of improving the design of the different systems of a CSP plant to increase its cost-competitiveness, reliability, environmental profile, and operational safety. The research programme of this project is organised into three work packages:

  1. Cost reduction and improved reliability of commercial CSP plants.
  2. Next generation of CSP plants working with alternative fluids.
  3. New scientific approaches and computational tools to generate disruptive innovation in CSP technologies.

These WPs will contribute to the overall research objective by:
  • improving molten salt-based technology which has the lowest costs and higher capacity factors and the direct steam generation plants that are suitable at a lower scale (WP1),
  • developing a high-temperature liquid receiver and the sCO2 power block of the next generation of CSP plants and proposing new systems to contribute to enhancing the flexibility of CSP plants using molten salt reservoirs and solar fuels (WP2), and
  • developing computational tools (WP3) to improve the analysis and design of the systems considered in WPs 1-2.

The network will train 10 doctoral candidates (DCs) with the solid technical and scientific knowledge and transferable skills needed to contribute either from the academic or the industrial sector to the development of innovative technologies and so that they will be capable of solving the challenges that currently face the solar thermal power industry.
CSP research requires outstanding human resources covering a wide range of competences, as well as complex and large infrastructures. Both aspects need cooperation between different EU countries and the joint efforts of R&D centres and industry, to avoid misalignments of key targets and to reach the most effective cost reduction.

Projects

The TOPCSP doctoral network offers 10 PhD places funded by the Horizon-MSCA DN-2021 call of the European Union

The 10 TOPCSP projects

DC1 – Task 1.1: Universal flux density measurement system for large-scale external and cavity receivers with high-performance image processing

Development and deployment of a universal flux density measurement system for large-scale external and cavity receivers with high-performance image processing.

Project objectives

Currently there are no commercially available measurement systems to determine the flux distribution on large-scale receivers, apart from punctual measurements obtained by flux gauge radiometers. Continuous measurement of the flux density distribution would facilitate efficient receiver operation and heliostat for control to avoid exceeding the maximum allowed heat flux and to preserve receiver integrity. In addition, the heat flux measured is needed to quantify the efficiencies of the receiver and heliostat field.

 
DC1, hosted by DLR, will conduct research on a way to cover both external and cavity receivers in flux density measurements. The task involves several challenges. It is to be investigated whether several elements of known measurement techniques can be combined into a novel method which meets the objective. Several camera-based flux density measurement techniques require communication with the heliostat field control system to incorporate heliostat field status information into the measurement or to perform defined heliostat focus shifts. A high level of automation of the measurement is targeted. It is conceivable that tools from the artificial intelligence field could pave the way for significantly increasing the performance of image processing and reducing the measurement effort. These techniques have recently been applied to heliostat calibration obtaining impressive results. In the end, an optimised flux density measuring technique should be available which can be easily applied to different receiver types on industrial scale.

Secondments:

  • at Synhelion: fulfilment of the the industrial requirements placed on flux density measuring system.
  • at the Cyprus Institute: testing of the measuring system at the PROTEAS Field Facility.

DC2 – Task 1.2: Turbulent two-phase flows in direct steam generation solar receiver

Numerical simulation of the turbulent two-phase flow of direct steam generation solar receivers and validation the results with experiments. Construction of the experimental data base.
The results of the simulations of a direct steam generation receiver providing the amount of steam produced and the thermomechanical stress imposed on the tube material.

Project objectives

One of the concentrated solar technologies currently being developed consists of direct steam generation (DSG) in the solar receiver. This eliminates the need for a HTF, reduces the number of heat exchangers and potentially increases the efficiency of the plant. The steam produced can either drive a turbine to generate electricity or be directly used by an industrial process or a heating network. DSG in the receiver of parabolic trough collectors is proven technology although numerical studies are limited due to the lack of knowledge about the thermo-physical process of two-phase flow boiling in the horizontal and inclined DSG receivers and current numerical modelling and experimental correlations are limited to specific case studies. Reliable prediction of the two-phase flow regime in the receiver is of critical importance for two reasons: (i) predicting the amount of steam produced and, thus, plant production, and (ii) predicting the thermomechanical stresses imposed on the tube materials.


DC2, hosted by CNRS, will set up numerical simulations to model the flow in the DSG plant, and the thermal conduction in the walls of the receiver. In addition, the researcher will set up a small-scale experiment, without solar irradiation, to reproduce the physics of boiling flows in a DSG receiver. The experimental data will be compared with the computational results to validate the modelling approach.

Secondments:

  • at Virtualmech: calculation of mechanical stress and deformation of the receiver tubes
  • at DLR: system level simulation of an optimised DSG plant integrating the results of the numerical simulations of the receiver.

DC3 – Task 1.3: Improved steam cycle layouts to improve flexibility and reduce cost of the CSP plants power block

Development of modified steam cycle layouts to improve flexibility and reduce the cost the power block of CSP plants.

Project objectives

The transient operation of a thermal power plant is limited by the thermally induced stress in critical components (such as steam turbines, pipes, heat exchangers) during start up, shut down and load change. Such limitations are a significant drawback with respect to the annual full load hours and to lifetime of components. With the aim of achieving higher turbine inlet temperatures, such thermally induced stress becomes much more important. Modified steam supply and the application of preheating/warm keeping technologies for critical components can greatly shorten the start-up times and increase the transient load gradients. Furthermore, studies indicate that modifications in the cycle layout of thermal power plants currently optimised for thermal efficiency can contribute to a design that leads to lower installation and operation costs. The developments made for conventional plants can also be adopted to improve operation flexibility and to reduce the costs of the Rankine cycle used in CSP plants.


DC3, hosted by RWTH, will analyse technologies and cycle layouts that were initially developed to increase the operational flexibility of conventional fossil fuel-fired power plants. Based on a comprehensive techno-economic assessment, the DC will identify the technologies and cycle layouts that are most promising regarding a future application in CSP plants. In the next step, the researcher will develop a simulation model of a Rankine cycle that corresponds to a state-of-the-art CSP power plant working with conventional nitrate molten salt. This model will be used as a reference for the following detailed assessment of the previously identified technologies and cycle layouts. For this detailed assessment, the DC will integrate the various technologies and layouts into the developed simulation model.

Secondments:

  • at UNIBS: comprehensive assessment of the considered technologies and layouts on the operation of the CSP plant using steady-state and transient simulations
  • at VM: correlation of the obtained simulation results with economic parameters to quantify the corresponding cost reduction potential for CSP plants.

DC4 – Task 2.1: New liquid HTFs for the next generation of CSP plant

Thermomechanical study of central solar receivers working with high temperature heat transfer fluids (HTS) using state-of-the-art numerical models and experiments performed in singular facilities.

Project objectives

Thermal energy conversion into electricity in current CSP plants is based on conventional steam cycle technology because the maximum temperature of the HTF is 565 °C. As a result, the power section has limited efficiency (approximately 40%) and suffers from high condensing temperatures and high capital costs. Innovative HTFs (advanced molten salts and liquid metals) that have been proposed as heat transfer and/or storage media must withstand temperatures up to 750 °C, have limited corrosion and be safe and environmentally friendly. In this way, the Rankine cycle could be substituted by a sCO2 cycle, which has a higher efficiency at moderate maximum temperatures and high compactness, simplicity, and flexibility. Many aspects need further research before higher temperature fluid technology can be industrially implemented, such as the high corrosion rates of chloride salts, the high melting temperature of carbonate molten salt, the determination of heat transfer coefficients, the start-up process when the fluid circulates in the receiver and the design of a heat exchanger to transfer the heat to the fluid circulating in the power block.

DC4 hosted at UC3M

DC4, hosted at UC3M, will compare different HTFs in terms of thermodynamic properties, heat transfer and heat storage characteristics and material compatibility with respect to state-of-the-art solar salts. The DC will perform experiments at the molten salt loop facility exposing the receiver pipe at different heat fluxes using an induction heater. The results on tube and fluid temperatures, tube deformation and corrosion will be obtained to determine the operational limits of the receiver. In parallel the DC will conduct numerical simulation that will be validated using the experimental results.

Secondments:

  • at CNRS: CFD simulation of the tube to develop heat transfer correlations for the high temperature molten salt flow in the receiver tube.
  • at Acerinox: the corrosion of innovative alloys exposed to molten salt will be studied at and the DC will be trained in the mechanical testing of steel tubes that can provide data on the mechanical properties needed in the simulation of the mechanical behaviour of the receiver.

DC5 – Task 2.2: Supercritical CO2 cycles for the next generation of CSP plants

Development of a sCO2 power cycle model that works with modified working fluids (CO” with additives in a limited quantity) with a higher efficiency and lower cost compared with a state-of-the-art solar tower technology.

Project objectives

Many ongoing research projects are based on sCO2 technology in CSP plants. However, relatively high ambient temperatures remain the Achilles heel of sCO2 power cycles as the efficiency of these systems drops dramatically when the ambient temperature is close to or higher than the critical temperature of sCO2 (31 °C). An optimal fluid should have the characteristics of sCO2, except for the critical temperature, which should be above 60 °C to take advantage of the high performance of a Rankine condensing cycle. Preliminary studies carried out by UNIBS on TiCl4-CO2 and N2O4-CO2 blends show that they can achieve power block conversion efficiencies as high as 50% at 700 °C maximum temperature, and with power block capital costs below 700 $/kW, thus outperforming state-of-the-art sCO2 cycles.

 
DC5, hosted by UNIBS, will investigate novel modified working fluids made of CO2 and additional elements in limited quantity so that condensation is enabled at temperatures as high as 60 °C while still withstanding the required peak cycle temperatures. A power cycle model will be developed to determine the thermal to power conversion efficiency supported by both theoretical and experimental. In this manner, the most promising next generation power cycle configurations for CSP applications will be identified.

Secondments:

  • at RWTH: study of the performance of a solar plant with a supercritical cycle working with the CO2 mixture.
  • at Brembana&Rolle: designs of salt-to-sCO2 heat exchangers

DC6 – Task 2.3: Design, sizing, and analysis of molten salt heating systems as energy reservoirs

To design and model a molten salt heating system to be used as a thermal reservoir and to test the thermal resistance in contact with the circulating molten salt.

The final design and numerical model of the novel molten salt heating system and experimental data on the behaviour of the resistance in contact with molten salt.

Project objectives

Intermittent renewable sources such as PV and wind can generate instabilities in the grid due to their poor manageability. To solve this issue, energy storage systems are seen as a possible solution to increase the share of renewable energy and reach the target values. In this line, as energy reservoirs, molten salt storage systems have been proposed as suitable candidates, with proven efficiency in the CSP market. To adapt this system as thermal batteries, the validation of new key components such as the electric heater shell and tube heat exchangers for direct charge from electricity is needed.

 
DC6, hosted by USE will work on: (i) developing specific design guidelines and sizing based on the needs of storage and the connected equipment, (ii) determining the heat transfer between the electric resistances and molten salts, and proposing new correlations for the convective film coefficient and (iii) analysing the wear process of both the electric resistance and the heater material due to the interaction with the molten salts at high temperature. Numerical simulations and system level simulation of the molten salt energy reservoir integrated in a CSP plant will be performed to determine the size of the system and the inlet and outlet conditions needed in the electric heater shell and tube heat exchanger.

Secondments:

  • at UC3M: experimental work in the lab-scale molten salt loop to study the heat transfer between the molten salt circulating at high velocity and the surface of the electric elements.
  • at Solarlite: analysis of critical parts of the heat exchanger using FEM simulations.

DC7 – Task 2.4: Concentrated solar system for solar fuels production

Optimisation and techno-economic performance analysis of thermomechanical cycles for H2 production to be integrated in a point-focus CSP system.

Project objectives

Novel receivers coupled with a point focus system will be able to achieve high concentration ratios and temperatures (>1000 °C). Thermal storage at these temperatures presents serious technical disadvantages but high concentration ratios can be efficiently used to provide heat for CO and H2 production from renewable carbonaceous feedstock. In the long term, direct production of fuels from CO2 and H2O is foreseen. Solar fuels, such as H2, allow solar energy to be chemically stored. This energy can then be further processed into mechanical work by turbines or internal combustion engines or be used to generate electricity in fuel cells. Thermochemical cycles based on, e.g., sulphur and cerium are being investigated. Photo-thermochemical cycles, in which the high temperature reduction is replaced by a photo-chemical step at ambient temperature, are at an early stage of investigation.

 
In this task, DC7, hosted by POLIMI, will consider the most promising thermochemical and photo-thermochemical cycles for H2 production, and will evaluate their integration in point-focus CSP systems. The system concentration ratio, flux distribution and operating temperature will be optimised to identify the best operating conditions given by the trade-off between optical efficiency and reactor yield. Besides, results in terms of solar-to-fuel conversion efficiency under design conditions, yearly H2 yield, and preliminary economic assessment will be provided.

Secondments:

  • at CyI: generative design approach to optimize the receiver-reactor design.
  • at Synhelion: experiments related to the chemistry of solar syngas production from biogenic feedstocks such as biogas/bio-methane or biomass.

DC8: Generative designs of solar tower receivers

Development of an open-source computational framework to automatically generate receiver designs fulfilling multiple objectives.

Project objectives

Multi-objective optimisation methods employing generative design to determine and optimise selected receiver geometries have been explored in the past. However, more geometries need to be investigated and additional parameters, e.g. peak temperature, should be included to ensure that the designs are technically feasible.

The goal of this activity is, for a given heliostat field configuration, to develop computationally efficient generative design approaches to achieve the multi-objective optimisation of the receiver design for selected receiver types. DC8, hosted by CyI, will develop a computational framework to automatically generate receiver designs, evaluate them against the multiple objectives to be achieved, and learn from the evaluations to improve the designs (e.g. the receiver thermal behaviour) until a satisfactory design is obtained. This activity will explore the utilisation of state-of-the-art artificial intelligence tools and techniques such as generative adversarial networks, while exploring reinforcement learning algorithms for iteratively optimising generative design. Once developed, the generative design computational framework will be applied to the design of a 130-kWth molten salt cavity receiver prototype specifically optimised for the heliostat field and tower at the Cyprus Institute’s PROTEAS testing facility.

Secondments:

  • at POLIMI: heliostat field configuration that should be considered in the optimisation of the solar receiver.
  • at JCR: application of the software developed to the design and definition of the receiver of an industrial-scale CSP plant.

DC9: Coupled optimisation of solar field and receiver/cavity geometry and thermal/hydraulic design

Development of software framework to solve the coupled optimisation/design of solar field and receiver/cavity geometry based on cost, performance (optical, thermal and mechanical), and durability.

Project objectives

Two of the most expensive parts of a CRS (central receiver system) are the solar field and the receiver on top of the tower. In addition, 40% of the energy losses in the system are associated with the heliostat field, while another 40% can be attributed to the receiver. The state of the art of CRSs has advanced in the optimisation of the solar field, and the thermal-hydraulic design optimisation of the receiver. However, both tasks are performed independently of each other. CFD and finite element analysis (FEA) models are often used to analyse the receiver’s thermal-hydraulic behaviour. However, due to their complexity, it is difficult to integrate these models into, for example, generative designs or AI-based models. Any optimisation or improvement process would benefit from a coupled formulation of the problem. To that end, mathematical reduced-order models (ROMs), techniques will be explored for the fast simulation of turbulent flows with energy transfer as the basis for the simulation of receivers in tower configurations, including heat losses due to turbulent convection to the ambient environment.


DC9, hosted by VM, will develop full CFD-FEA as well as reduced order models to design receivers at the optimisation level (reduced order) or final design full-order systems. Reduced order models of the thermal-hydraulic behaviour of receivers will be coupled with models of the solar field raytracing. This will allow optimised solar fields to be designed and receivers with a lower capital expense (CAPEX) and better performance and durability.

DC9 hosted by VM

Secondments:

  • at CyI: integration of the reduced-order models into artificial intelligence tools to design the coupled solar field receiver.
  • at DLR: techno-economic optimisation of the CSP plant.

DC10 – Task 3.3: Full economic and environmental analysis of CSP plants

Life cycle Analysis and economic analysis of a state-of-the-art CSP plants and comparison of the results with other renewable energy generation technologies.

Project objectives

In technologies such as solar and wind, it has been implicitly assumed that once their LCOEs are lower than those of conventional plants, their deployment should be competitive and economically efficient. However, the overall environmental impact of these different solutions cannot be easily compared and should be considered in investors’ decisions. Life cycle assessments (LCAs) of CSP plants have been published before, with most of them concerning parabolic trough CSP plants. Analyses of tower power plants have also been presented. 

However, impact categories, such as metal depletion, human toxicity or natural land transformation were not included in those studies, despite their significant environmental impact in the LCA of the materials employed in molten salt CSP plants. Hence, there is an urgent need to obtain an accurate life cycle inventory of the CSP worldwide. Currently, there are no LCA data including the operation or dismantling phases. In theory, CSP plants were supplied with sufficient material to give the plant a 25- to 30-year useful lifetime.

DC10 hosted by JCR

However, several operational problems are reducing this expected lifetime. Corrosion, low cycle fatigue and transient thermal stresses should be considered to avoid equipment damage and their effects should be considered in LCA studies. In addition, a roadmap on how to dismantle these plants with the lowest environmental impacts has become essential to truly include CSP technology under the requirements of a circular economy.

DC10, hosted by JCR, will develop a LCA of different configurations of CSP plants with energy storage. The LCA will include not only the most relevant impact categories such as global warming, water, and land use, but also mineral resources, human toxicity, cumulative energy demand, particulate matter formation, etc. This analysis will be compared with the LCA results of parabolic trough CSP plants and their hybridisation with renewable fuels, PV power stations and wind farms. An economic analysis will be conducted following new approaches, such as life cycle cost analysis, which considers the full socioeconomic and environmental impact of each technology.

Secondments:

  • at UC3M: LCA model of CSP plants.
  • at USE: LCA related to the storage system.

Publications

Here you will find the publications of the different TOPCSP projects