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WASCOP: Soiling Prediction Model, Tests of Mirror Coatings and Innovative Cleaning Methods for Solar Mirrors

Eleven research institutes and industry partners from seven European countries and from Morocco involved in the project WASCOP have set an ambitious goal: they want to reduce water consumption by more than 70%, using appropriate methods, not compromising the system efficiency.

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Mirror samples with different dust repellent coatings and meteorological measurement instruments for the development of the soiling model in Moroccan arid region. Bild: DLR

In research, politics and industry the issue of water conservation is a key challenge in order to promote the acceptance and further implementation of CSP technology.Solar thermal power plants need water mainly for cooling purposes in the turbine cycle and for mirror cleaning. For both applications, the project partners from research and industry will develop and test innovative measures to reduce water consumption within the next four years. The Institute of Solar Research is involved with three research groups in the project WASCOP.

Site selection is crucial

Dr. Stefan Wilbert’s DLR research team based at the Plataforma Solar de Almería in Spain is working on a model to improve the understanding of the meteorological causes of soling and the mechanisms of particle adhesion.

The model is a first step towards a space resolved prediction of soiling rates. This can reduce the requirements for cleaning and thus the water consumption inof a concentrating solar thermal power plant already in the planning phase. The results of this task can further be used by the project partners to develop strategies against soiling during plant operation, for example by adapting the nocturnal parking positions of the collectors.

The accumulation of dust, dirt and sand on the mirrors of the collectors reduces their reflectivity and thus the yield of the power plant. Therefore, cleaning vehicles regularly clean the solar mirrors and absorber tubes using brushes and high-pressure water. A solar thermal power plant with 50 megawatts electric output and a thermal storage capacity of seven and a half hours full load operation can have a mirror surface area of approximately 500,000 square meters. Roughly 180 cubic meters of demineralized water are required daily for the cleaning of a solar field of such size.

Protective coatings and innovative cleaning methods for low water consumption

Special coatings on the solar reflectors can reduce the adhesion of dirt and particles to the mirror surface. In laboratory tests and outdoor exposure campaigns at the Plataforma Solar de Almería and several desert locations, Dr. Florian Sutter’s DLR research group investigates the efficiency and durability of different anti-soiling coatings. These shall maintain its dirt-repelling and reflective properties in harsh desert climates as long as possible.

An innovative, water saving method for mirror cleaning makes use of the dew water that condenses on the mirror surfaces mainly during in the morning hours. The Stuttgart-based DLR solar researcher Andreas Pfahl is developing a cleaning lip system that moves along the mirror with the help of gravity.

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Heliostat mirror cleaning system using dew water and a gravity driven lip. Images: DLR

Reduced water consumption with dry cooling

In a CSP plant, water is heated by solar-generated heat and converted into steam that drives a turbine to generate electricity. This vapor is then cooled with water or air to condense back into water that can be used again to generate steam. A CSP plant with conventional water cooling uses about 90% of its total water consumption to dissipate the condensation heat from the turbine cycle and 10 % for the cleaning of the solar field.

The use of dry cooling with air instead of water has been shown to reduce water consumption by up to 90 %. However, dry cooling systems reduce the overall system efficiency as they require electrical power to run the large fans of the cooling unit. A goal of the project WASCOP is to significantly increase the efficiency of dry and hybrid cooling technologies.

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Representatives of the project partners at the kick-off meeting held in Brussels on 12/13 January. Picture: CEA/Bourdon

Further participating organisations in projekt WASCOP- Water Saving for Concentrated Solar Power:

Commissariat à l’Énergie Atomique et aux Énergies Alternatives, Frankreich
Centro de Investigaciones Energéticas, Medioambiental Technologicas – CIEMAT, Spanien
Cranfield University, Großbritannien
Fundacion Tekniker, Spanien
Moroccan Agency For Solar Energy SA, Marokko
Rioglass Solar S.A., Spanien
Archimede Solar Energy S.r.l., Italien
OMT Solutions B.V., Niederlande
Hamon d´Hondt, Frankreich
AMIRES s.r.o., Tschechien

source:http://www.dlr.de/

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