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Flexible automated manufacturing of RST Facets: High Performance Solar Reflectors for CSP industry

Periodic Reporting for period 1 - AUTO-RST (Flexible automated manufacturing of RST Facets: High Performance Solar Reflectors for CSP industry)

Reporting period: 2019-10-01 to 2020-09-30

The performance/cost ratio of the available solar energy systems in the market is still not good enough. There are multiple improvement possibilities in CSP central tower energy generation. Today’s great challenge of the sector is to achieve a more efficient use of this technology.
TEWER has been addressing this problem by improving the RST facet,the reflective element used in heliostat-field concentration technologies
The most common commercial facet solutions are stamped and sandwich facets.Their typical reflectance is about 92-93%, and they are strongly influenced by wind induced vibrations, they are structurally weak, and the different thermal coefficient of the components causes a strong degradation of the optical quality with temperature variations, causing an average optical quality worse than 2 mrad. As for sandwich-type facets, they are multi-layered structures made up of the superposition of several layers (a metal structure, a polymer layer and a mirror) forming a sandwich. The main problems with this kind of facets are: the degradation of optical quality in operating conditions, loss of performance due to aging of the materials, insufficient mechanical performance for large-sized facets and they massive damage when blocking the concentrated light from another heliostat. They have an average optical quality of around 1.5 mrad, an average reflectance of 93-94% and maximum sizes of 4.5sqm.
In order to fill theses gaps, AUTO-RST project will remarkably enhance the optical quality to values lower than 0.6 mrad for any operational conditions and will be able to produce the first facets of up to 7sqm. This will allow to reduce the solar field investment by 15% (around 23M€ out of 156M€), disrupting the existing tower thermosolar market.
RST is a unique breakthrough, a sandwich-type, high performance facet, with a robust behaviour under changing conditions and a disruptive design and manufacturing process. The RST facet has an optical quality never seen before, and its unique characteristics have already been tested in relevant environments stimulating the interest in many potential clients. The great challenge and the high-risk of this project, is to be able to design a flexible automated manufacturing process, with a high-degree of customization, which allows to produce onsite thousands of these ground-braking facets, at twice the size of any currently available: 1) keeping the innovative features and high-optical quality 2) at record fast manufacturing times and 3) with high flexibility and low cost, all with one single customizable machine.
CSP is one of the most promising and sustainable renewable energy according to International Energy Agency (IEA. IEA’s roadmap projections to 2050 say that with appropriate support, CSP could provide 11.3 % of global electricity and up to 4% of the electricity generated in Europe.
An initial phase was dedicated to defining the product as well as the process. A profound revision from the point of view of both the process as well as the product was made in order to make the most of those learnings when making the decisions that have eventually defined the fabrication process
There has been a profound exploration of the different aspects comprising the process and product definition. From the process perspective, the already used alternatives have been revisited and the potential new ones re-evaluated, therefore examining in detail the different types of polyurethane injection systems, the different approaches to apply the design curvature to the solar reflectors and the spectrum of process parameters that need to be controlled during the process in order to get replicability in the process, key for the successful project execution. Different options linked to the measurement possibilities to be used for quality validation have been explored and compared aiming to find the best applicable system
A deep market exploration has been carried out aiming to integrate in the product design the characteristics that make the most of the existing supply chain avoiding features that would introduce limitations on this front. A profound exploration of the glass and mirror fabrication industries have been done. Progress has been done with the polyurethane supplier of choice to validate that the formulation complies with the aggressive cycle time targeted for the process.
AutoRST pilot line has been designed and specified, including the core injection press as well all auxiliary station that enable the process flow. Additionally, product specifications the validation processes have been defined to be used during the fabrication runs
Apart from the actual pilot line a very detailed costing exercise has been performed not only from the perspective of the product but to the whole execution of an on-site fabrication project. Great level of detail has been applied to this evaluation since it will be a the core of the value proposition.
In parallel to this activity an in-depth evaluation of the market has been done not only looking at the potential application of the RST facet to heliostats in solar tower plants but to other potential application that have been gaining momentum over the last year and that might have a significant impact in the near future.
The novel value proposition of AUTO-RST stands on the following characteristics
High optical quality (up to 53% increase)
Ground-breaking design which drastically minimizes the variance of its physical characteristics and performance in working conditions
High reflectance (increase of 1-2%)
High stiffness and adaptability to different heliostat solutions
Solar mirror fully supported by the foam which absorbs energy impacts and reduces the risk of breaking during hailstorms

Progress beyond the SoA in automated manufacturing process:
Innovative design and manufacturing process which allows to produce big facets of up to 7 sqm, with spherical curvature and slope error better than 0.6 mrad with a cost lower than 25 €/sqm
Scalable design with nominal sizes of 2.5 3.5 4.5 and 7 m2
Unique onsite manufacturing process that allows the variation of the design curvature for different positions of the heliostat at the solar field matching customer needs, without cost increase due to additional tooling

Technological expected results:
New generation of final RST’s representative series with implementation and certification of the improvements and technological upgrades, made in the flexible automated pre-series production representative process and validated on real operational environment, available to the professional market from 2021 (TRL6-7 to TRL9).
Scale-up the flexible automated manufacturing process for the RST facet: Management of the foam components, injection, movements, tempering process, maturation process and optical quality control process (TRL7 to TRL9)
Demonstrate the capacity to produce RST facets with consistent performance and sizes up to 7 sqm (TRL7 to TRL9)
Reduce the production cycle time from 2 hours per facet down to 15 minutes, approximately (TRL7 to TRL9)
Reduce the manufacturing cost to achieve the target cost of 25 €/m2 (TRL7 to TRL9)

Commercial and business expected results
Sales: in 2022/2023 TEWER needs to sell at least 700.000m2
Engagement of at least 5 clients and a network of value-adding partners in each major CSP market areas by 2022.
Enter the Chinese, LATAM and MENA markes
RST facet integrated in a real heliostat