Raising the Lifetime of Functional Materials for Concentrated Solar Power Technology

Project Information

RAISELIFE

Grant agreement ID: 686008

DOI

10.3030/686008

Project closed

EC signature date 18 March 2016

Start date 1 April 2016

End date 31 March 2020

Funded under

• INDUSTRIAL LEADERSHIP - Leadership in enabling and industrial technologies - Advanced materials

Total cost

€ 10 368 740,98

EU contribution

€ 9 291 722,75

Coordinated by

DEUTSCHES ZENTRUM FUR LUFT - UND RAUMFAHRT EV
Germany

Periodic Reporting for period 3 - RAISELIFE (Raising the Lifetime of Functional Materials for Concentrated Solar Power Technology)

Reporting period: 2019-04-01 to 2020-03-31

Summary of the context and overall objectives of the project

The RAISELIFE project was conducted from April 2016 until March 2020 and was funded within the H2020 program of the European Commission. The project aimed at developing novel materials with extended lifetime and performance for parabolic trough and solar tower CSP plants and thus reducing electricity generation costs. The project brought together a broad consortium formed of industry partners, SMEs and research institutes of the CSP and material science sector.
The following materials were investigated in RAISELIFE: 1) protective and anti-soiling coatings for glass reflectors, 2) thin-glass composite reflectors for heliostats, 3) high-temperature secondary reflectors, 4) absorber coatings for tubular solar tower receivers, 5) absorber coatings for non-evacuated line-focus collectors, 6) abrasion resistant anti-reflective coatings for glass envelope tubes, 7) corrosion resistant high-temperature metals and coatings for molten salt. Fig. 1 illustrates some of the material developments.
The testing activities involved outdoor exposure and accelerated testing in climate chambers and under concentrated solar radiation. Failure modes were examined and the developed materials were optimized in terms of lifetime. Performance and degradation models were derived and fed into a techno-economic analysis using system simulation tools. This had the aim to determine the economic benefit of the newly developed materials compared to the state of the art materials.

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

Among the highlights of the achievements of the RAISELIFE project the following points can be remarked:
• Qualification of a novel receiver coating developed by BSII, which will be employed in the commercial 100MWe DEWA solar tower project in Dubai. The developed lifetime model predicts that the solar absorptance of the BSII coating will remain above 95% for about 7 years on ferritic steel substrate T91 (for steam receivers) and about 15 years on nickel base alloy Inconel 617 (for molten salt receiver). The higher lifetime compared to the state of the art Pyromark coating leads to a LCEO reduction of about 1.1%.
• Validation of durability of solar cured receiver coatings, opening the possibility to cure the coating directly on the top of the tower. This reduces expensive panel dismantling and furnace curing, fossil fuels (gas burners) as well as down-time of the power plant.
• From an economic point of view the optimum recoating interval of T91 receivers has been determined to be eight years by means of system simulation tools.
• An automatic coating machine prototype has been built which achieves 4 times lower thickness variation than manual painting and thus reduces possible hot spots in the coating.
• The price of solar mirrors can be reduced down to 12€/m² by using low-cost 2-layer coating systems, which showed to be as durable as 3-layer systems, with degradation rates of 2% in solar reflectance at exposure sites of corrosivity C2 after 20 years of exposure according to the developed lifetime models. In C3 environments, the degradation is slightly higher compared to 3-layer systems (4% vs. 2%).
• Design and construction of a composite thin glass heliostat for wind loads >45m/s at low weight and possible cost reductions of 30%, lowering expected heliostat cost from 68€/m² to about 45€/m².
• Anti-soiling coatings for the front glass of mirrors have shown to be able to increase the reflector cleanliness up to 1.5pp.
• Development of a selective receiver coating for non-evacuated line focusing receiver tubes operating up to 400°C. Negligible degradation after 18 months of in-service testing and >15 months of furnace testing.
• Improvement of the abrasion resistance of an anti-reflective coating for evacuated line focusing receiver tubes. The coating was deposited in an industrial coating line on a commercial receiver tube and was validated during 12 months of in-service testing. The coating is ready for commercialization.
• Development of weldable protective coatings for ferritic steels in molten salt environment, with high cost reduction potential compared to nickel base alloys. Stability proven for 10,000h during static and dynamic tests at 580°C in solar salt. Weld joints were tested up to 1,000h performing better than non-coated materials.
• Improvement of the durability of a novel high-temperature secondary reflector, albeit stability at 400°C has not been fully demonstrated. The secondary reflector has potential to increase the electricity yield by 1.57 % in the RAISELIFE reference solar tower plant, given that it withstands the high heat load.
• Publication of catalogue of best practices containing several testing and analysis methods of materials employed for CSP technologies
• Organization of two workshops for CSP stakeholders with around 70 participants each to disseminate the results achieved in the project

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.
- Durability of absorber coatings for molten salt towers (up to 750°C skin temperature) is estimated to be doubled compared to state of the art Pyromark 2500 coating, while maintaing the same optical efficiency.
- 2x2 m² receiver panels for solar towers can be coated automatically. A homogeneous coating application was achieved: 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 have been increased to α=0.955; ε=0.078 (250°C) compared to the state of the art α=0.92; ε=0.13 (250°C), without any degradation at 400°C after more than one year of testing.
- No significant mass loss was detected on aluminide diffusion coated samples in contact with solar salt at 580°C for 10,000h, whereas for non-coated T91 and VM12 the material loss is 193µm at 580°C and 68µm.

As a result of the testing activity in RAISELIFE, BSII will employ the developed receiver coating in the largest single-site CSP project in the world, the 700MW molten salt tower awarded by Dubai Electricity and Water Authority. The tower will be constructed in 2020, it will have the world’s tallest solar tower, measuring 260 metres, and the LCEO will be 7.3 $Ct/kWh. The work related to improvement of line focussing absorbers will help to trigger the solar process heat market with its huge potential (0.9 million GWht/year corresponding to more than 400'000 European jobs).

As one of RAISELIFE’s primary goals, we projected that commercial implementation of the subject technologies could account for as much as 2.5-3 Euro-cent LCOE reduction per kWh of electricity produced for solar tower technology between 2015 and 2020. Back in 2015 when this goal was set, the typical LCOE of CSP systems was around 20 Euro-cents/kWhe. Thus we aimed at reducing the LCOE by 12.5 - 15%. In the past years, the LCEO of CSP systems dropped significantly to 8.9 Euro-cents/kWhe. On top of this reduction, it was shown within RAISELIFE that an additional LCOE reduction of 0.9 Euro-cents/kWhe is possible using the novel material developments. This corresponds to relative LCOE reduction of 9.8%, thus almost achieving the initially set goal.

Overview on materials tested in RAISELIFE