Saving water on concentrated solar power plants: The holistic approach of the WASCOP project

CSP plant are facing the new challenge of being water thrifty because of their desert, hot and arid usual location. Actually, the water consumption of a CSP plant can reach around 2500 m³/GWh. Solutions have to be found to face the constraint of a reducing water availability in the concerned areas. Regarding the different water use items (power block's cooling : 90% of the total water use, solar field cleaning, up to 5% and steam generation), the WASCOP project is aiming at proposing different kind of solution in a holistic approach that will support the reduction of the water used by the whole plant without affecting its profitability. Regarding cooling, dry cooling is turning to zero the water use but the plant efficiency and profitability is significantly affected due to capacity limitations under high ambience and additional utilities costs. The solutions proposed in WASCOP are turned to increase the efficiency of the cooling systems under high ambience, through the addition of heat storage for delayed heat exhaust, the addition of water spray for enthalpic air refreshment of dry cooling systems and their increased efficiency and the optimized management of hybrized cooling system (wet/dry). For the cleaning needs of the plant, WASCOP proposes to develop different cleaning strategies. Firstly, limitation of the dust settlement on the optical surfaces is done through dust barriers and antisoiling coatings (both for reflectors and absorber's glasses). Secondly detection of the soiling level, for adapted cleaning frequencies at different locations within the solar field, is proposed thanks to different kind of soiling sensors : at low cost for a wide distribution, or with a capacity to discriminate soiling to mirror permanent degradation, or for specifically absorbers glasses. Thirdly, innovative cleaning devices using very few water, are proposed such as an ultrasonic cleaner, removing settled dust with a thin water layer thanks to cavitation properties, and a heliostat cleaner using the optical surface condensed water, and the rotating properties of the heliostat to remove dust with an adapted rotating cleaning lip. All the solutions developed in WASCOP are supported by numerical modelling as to be able to propose them within a single toolbox, selecting the most adapted solutions, depending on the plant technologies (type of solar field : PTC, LFR or ST and type of current cooling : WCC,ACC, Hybridized…) and locations (DNI, soiling rate…). Current results show that the proposed solutions are able to reduce the water use significantly both for cooling and cleaning purposes without affecting the plant global efficiency. Additional works have whatever to be done to better quantify the associated water reduction of individual solution and their synergy potentials.