With a growing population and energy demand in the world, there is a pressing need for research to create secure and accessible energy options with greatly reduced emissions of greenhouse gases.
International Energy Agency in Science for Today’s Energy Challenges (2006)
Context of the project
Energy challenges
Faced with growing energy demand and climate change, our societies have turned to the development of technologies based on renewable energy sources for the past 20 years.
Solar energy
Among these renewable sources, the solar energy received on Earth can provide more than 1400 times the energy consumed annually.
Thus photovoltaic (PV) power plants are for instance deployed on a large scale worldwide. PV however directly converts the solar flux into electricity that is fed into the grid without storage.
Concentrated Solar Power (CSP): the “other” solar energy
In all thermal power plants, a thermodynamic cycle is used to produce electricity from steam, via a steam turbine. Steam is first generated by heating water through: combustion of gas, biomass, coal, etc., or nuclear fission.
In concentrated solar power plants, steam is generated by concentrating the solar radiation with mirrors on a solar absorber (tube or plate). This absorber is run by a heat transfer fluid (HTF: mineral oils, molten salts, etc.). It converts solar radiation into heat, transferred to the HTF and exchanged with water to produce steam.
Compared to other renewable energies, the main advantages of CSP technologies are that:
they produce heat first;
this heat can easily be stored on a large scale, thus compensating for solar resource intermittence, even overnight, providing continuous heat and electricity production;
it can also directly be used for industrial processes (Solar Heat for Industrial Processes, or SHIP).
Current and future deployment of CSP
In 2019, almost 10 GW of CSP plants are already installed or planned worldwide. Forecasts predict that up to 1600 GW could be installed by 2050 [source: ESTELA].
CSP projects around the world (June 2019) [source: solarpaces.org] Deployment scenarios for Solar Thermal Electricity production capacity [source: ESTELA]
CSP technologies have a great potential for supplying heat and solar thermal electricity in the near future.
Drivers for cost reduction in STE […]
Improved absorber coating
Improved durability
ESTELA Solar Thermal Electricity Global Outlook 2016
Challenges
Towards higher temperatures
In (solar) thermal power plants, the efficiency of the thermodynamic cycle increases with temperature (Carnot). Thus the future of CSP tends towards higher temperature technologies, with a necessity to develop suitable materials.
Optical efficiency
In CSP technologies, the solar absorber needs to convert efficiently the concentrated solar radiation into heat to be transferred to the HTF. To do so, it should present spectral selectivity:
high absorption in the solar spectrum (0.28 – 2.5 µm)
low infrared emissivity to limit radiative thermal losses (e.g. 1 – 30 µm at 500°C)
Ideal solar spectral selectivity
Absorber paints are sometimes used but only fulfill the first requirement. Solar selective absorber coatings (SSACs) have also been developed and are commercially available. They only work for vacuum-protected solar absorbers. Active R&D is at play for air-stable high temperature SSACs.
Durability
The coated absorbers are submitted to extreme conditions of use during several tens of years of operation: concentrated solar irradiation, high temperatures (400 – 1000°C), cyclic and quick thermal loads, contact with corrosive agents (oxygen, water vapor, pollutants), etc.
This implies complexly correlated thermally-induced and thermomechanical aging phenomena, such as oxidation and corrosion, atomic diffusion, cracking, fatigue, creep, etc.
These phenomena are usually detrimental to the optical properties and efficiency of the materials, and must be studied to provide more efficient and durable solutions. Few and non-standardized aging tests have however been carried out, especially in air.
Project objectives
Materials
New high temperature and high performance nanostructured solar selective absorber coatings will be developed in the project, for CSP conversion into heat and electricity. A wide range of compositions and 2D (multinanolayers) / 3D (inclusions at the nanoscale) architectures will be explored.
Fabrication processes
Modular high density plasma deposition techniques, i.e, PECVD and/or PVD, will be developed for the fabrication of these coatings. They will allow the deposition of complex coatings on 3D parts, with high deposition rates and high transfer potential to industry. They also satisfy the REACH European directives.
IDEFIX reactor (PROMES Perpignan)
Thermal stability and durability
A particular attention will be brought on the evolution of their microstructure and thermo-optical properties with thermal and solar-induced aging, to ensure their long-term efficiency in representative conditions of use.
Solar Accelerated Aging Facility (PROMES Odeillo)
Final objective
Lifting the barrier to the transition from conventional thin films to innovative nanocomposite solutions, developed by efficient and versatile plasmas adapted to industrial transfer, should enable a leap towards high performance for CSP.
Project members
The project consortium is composed of 4 French research laboratories and 1 industrial partner, recognized in the fields of nanostructured coatings deposition and characterization, low pressure plasmas and CSP applications.
