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RAISELIFE Report Summary

Project ID: 686008
Funded under: H2020-EU.2.1.3.

Periodic Reporting for period 1 - RAISELIFE (Raising the Lifetime of Functional Materials for Concentrated Solar Power Technology)

Reporting period: 2016-04-01 to 2017-09-30

Summary of the context and overall objectives of the project

The European Renewable Energy Roadmap for 2020 establishes that 20% of final energy will be produced from renewable sources. With an increasing share of fluctuating wind and photovoltaic power generation, Concentrating Solar Power (CSP) technologies with thermal storage become more important due to the flexibility in dispatching power to the grid. In the Technology Roadmap published in 2014 by the International Energy Agency, the global electricity share of CSP systems is envisioned to reach 11% by 2050. The RAISELIFE project will enhance the lifetime and performance of key materials used in CSP technologies and will contribute to the compliance of these targets.
The following five key materials are investigated in RAISELIFE: 1) protective and anti-soiling coatings of primary reflectors, 2) high-reflective surfaces for heliostats, 3) high-temperature secondary reflectors, 4) receiver coatings for solar towers and line-focus collectors, 5) corrosion resistant high-temperature metals and coatings for steam and molten salts.
The project brings together a broad consortium formed of industry partners, SMEs and research institutes of the CSP and material science sector with the final goal of increasing durability and performance of materials and in consequence reducing electricity generation costs.

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

In the first 18 months of project implementation the following main achievements, grouped by key material, can be remarked:

1) Protective and anti-soiling coatings of primary reflectors:
- 8 types of silvered-glass mirrors of 2mm thickness with different protective paint systems have been manufactured
- 2 types of anti-soiling coated silvered-glass mirrors have been manufactured
- The samples are being weathered at 11 exposure sites, including desert, coastal and cold mountain climates
- Continuous cleanliness measurements of the anti-soiling coated samples are performed in Spain and Morocco

2) High-reflective surfaces for heliostats:
- Silvering and coating of 100µm and 200µm ultra-thin glass was performed
- Ultra-thin glass mirror samples of both thicknesses achieve around 96% reflectance
- Steel ball drop and puncture tests were performed and 200µm thickness was selected due to better mechanical properties
- Samples have been glued on a composite structure

3) High-temperature secondary reflectors:
- The temperature of the secondary reflector material was simulated for at different load cases (flux, wind, optical properties of the reflector)
- Operating conditions have been identified where the maximum reflector temperature is under 400°C
- First sample mirrors were manufactured
- Five accelerated aging tests were performed
- Analysis of degradation mechanism and coating optimization has started. Clear improvement in stability in damp-heat chamber was already seen

4) Receiver coatings for solar towers and line-focus collectors:
- 4 high solar absorptance coatings for solar towers have been produced on 3 different steel substrates (T91, VM12, T22) and 1 nickel base alloy (Inc617)
- Solar and environmental tests have been performed
- Coating optimization for extended lifetime and improved optical properties is ongoing
- A prototype of an automatic coating application machine was constructed
- Anti-reflective coatings for parabolic trough receivers with improved abrasion resistance have been produced and tested
- The optical properties of selective absorbers operating up to 400°C have been improved

5) Corrosion resistant high-temperature metals and coatings for steam and molten salts:
- Tests have been performed with T91 and VM12 and 5 coated samples in contact with solar salt at 560°C and 580°C for 1000h
- A cost-optimized molten salt mixture of 35wt.% NaNO3/65wt.% KNO3 has been selected for the next set of corrosion tests
- Tests with different salt impurity levels of 300, 500 and 700 ppm of Cl-/SO42- have been conducted for 1000h at 560°C. Salt impurities highly influence the corrosion rates of the materials
- A ceramic-based sensor has been adapted to monitor material corrosion rates in molten salt environments

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 main progress beyond the state of the art can be summarized as follows:
- 1.5 percentage points higher reflectance achieved with ultra-thin glass mirrors compared to state of the art 4mm silvered-glass mirror technology
- Secondary reflectors with reflectance of 92% are stable in damp-heat test for 2 months and 16 days at 400°C in the oven. State of the art was a stability of 1 month at 350°C in the oven
- The optical properties and lifetime of non-selective absorber coatings for solar tower application were improved: α=96%, ε=75% stable for 1000h at 750°C on Inc-617, 2000h at 650°C on VM12 and T91, 2000h at 570°C on T22, 100 dish cycles on VM12. Stability in environmental NSS, Condensation, Humidity Freeze and Damp Heat test was also proven. The state of the art was α=94%, ε=75% stable for 1700 h at 650°C
- For selective absorber coatings the progress is: α=95%; ε=22% stable for 2000 h at 600°C on T91, 100 dish cycles on VM12. Stable in environmental tests except failure after 480h in NSS test
- A homogeneous coating application was achieved with the prototype automatic coating machine: the thickness variation is less than 10µm compared to 30µm for manual painting
- Abrasion resistance of anti-reflective coatings for parabolic trough receivers was increased by factor 2.5 compared to the commercial coatings, without transmittance changes (0.972)
- Selective absorber properties for low temperature absorbers (400°C) have been increased to α=0.955; ε=0.05 (250°C) compared to the state of the art α=0.92; ε=0.13 (250°C)
- No significant mass loss was detected on aluminide diffusion coated samples in contact with solar salt at 560 and 580°C for 1000h, whereas for non-coated T91 and VM12 the material loss is 22µm at 580°C and 10µm at 560°C

As an example of the socio-economic impact of CSP, it is worth discussing the current construction of about 250 MW of CSP plants in Israel. The ""Ashalim"" project (name of the local town) has had a significant impact on the local economy. At Ashalim, BSII is building a 126 MW tower project while another group of companies is constructing a similar-sized parabolic trough project. Together, the CSP plants will provide about 2% of Israel's peak electricity capacity when brought on-line in 2018. Since Israel relies almost entirely on fossil fuel, this is a big step forward. Meanwhile, employment over the three years of construction has brought over 3000 jobs to an area with higher unemployment than the national average, and of course the various supporting industries from technical supply to security or catering have flourished during this time. Many of the previously unemployed workers were recruited from minority populations with lower socioeconomic conditions and educational backgrounds.
Soltigua focuses on small scale CSP for power generation and for solar process heat. The first application is particularly useful for remote communities such as small islands, rural villages or mining sites. The second application has the potential to create enormous fuel savings, provided the technology becomes sufficiently cost effective. A survey recently realized by Soltigua’s partner IRESEN for a 1 MWel small scale CSP plant in Benguerir (Morocco) has shown that small scale CSP is welcome by local communities.

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