Solving Water Issues for CSP Plants
Concentrated Solar Power (CSP) plants depend on high Direct Normal Irradiance (DNI) for power production and thus are located in rather arid regions. For wet cooling (~3,5 m³/MWhel), mirror cleaning (~0,3 m³/MWhel) and steam cycle (~0,5 m³/MWhel) CSP plants consume water, which is a scarce resource at many potential CSP locations.
The overall purpose of the SOLWARIS project is to upscale, implement and demonstrate cost-effective technologies and strategies that bring about a significant reduction of water consumption in CSP plants while maintaining high energetic performance of electrical power production. The approach proposed in SOLWARIS tackles all segments of water consumption in a CSP plant by setting ambitious water saving goals:
The project heads for a total reduction of water consumption by:
Within the SOLWARIS project several water saving technologies and strategies for CSP plants are developed and investigated. On top, they will be integrated and tested at the commercial parabolic trough power plant “La Africana” in Cordoba, Spain.
Conventional thermal power plants (and also most existing CSP plants) are cooled with wet cooling towers, which account for up to 90 % of CSP water consumption. In regions where water is scarce, air cooled condensers (ACC) are used instead of wet cooling towers. ACCs have almost no water consumption. In return the efficiency of a power plant with ACC is lower than the efficiency of a power plant with wet cooling tower. While the efficiency of wet cooling towers depends on the wet bulb temperature, the efficiency of ACCs depends on ambient air temperature, which can be rather high in locations of high DNI. Cooling with increased efficiency due to thermal cold storage (cTES) is investigated within the SOLWARIS project. The concept is based on a water basin that is cooled down during the night and is used to cool the power plant condenser during the day.
Several technologies investigated within the SOLWARIS project aim at reducing the water consumption for collector cleaning. Coatings for the mirrors and receivers are developed to reduce the soiling rate of the components; also fences are tested to protect the solar field from dust. Both technologies will reduce the soiling rate and thus the cleaning water consumption. 30 mirrors at “La Africana” will be equipped with newly developed soiling sensors, which will provide the operator with real time information on the local distribution of soiling and therefore enable demand oriented cleaning on a temporal and spatial scale. Also a soiling forecasting product will be developed to assist in the optimization of the cleaning schedule for the next three days in advance. With this information, cleaning activity can be ceased before an upcoming heavy soiling or rain event in order to save water and cleaning costs. Furthermore, an ultrasonic cleaning technology is developed, which will clean the mirrors with a fraction of the water consumption of state of the art cleaning technologies.
One additional idea to save water is to recover and reuse water. A Multi Effect Evaporation (MEE) water recovery plant will be integrated at “La Africana” within the project. It may recover the water dumped at the steam cycle blow down or wet cooling blow down or the concentrate rejected by the reversed osmosis water treatment plant, which demineralizes raw water for the CSP plant. MEE needs thermal energy, which most economically could be the otherwise dumped thermal energy of the solar field. More constantly it could be provided by an auxiliary oil heater, the thermal storage or the turbine, which would all reduce the efficiency.
The Institute of Solar Research of DLR is mainly engaged in two subtasks:
The department of qualification develops a soiling map and a soiling forecasting system in collaboration with BSC. An existing dust forecast system is extended to a dedicated soiling rate forecast product for CSP plants that will be brought to TRL7 and is an essentially new input for optimizing existing plant control and selecting future plant locations by integrating the soiling rate map derived from a reanalysis of historic dust model data with the novel soiling module.
The department of line focus systems develops an Operation and Maintenance (O&M) optimizer. The dispatch optimizer, currently reaching TRL 5 in the H2020 project PreFlexMS, is extended to an operation optimizer with special focus on all water-related issues. It will support the decision making of plant operators and make full use of all water-saving technologies, while increasing profit. The final O&M optimizer tool will be integrated into TSK’s FoSyS plant operation system and will serve the “La Africana” plant for optimal scheduling as TRL 7 implementation.