|» CENTRAL RECEIVER FACILITIES: CESA-1 & CRS
The PSA has two exceptional facilities for the testing and validation of central receiver technology components and applications. The CRS and CESA-1 enable projects to be undertaken and technologies validated in the hundreds-of-kilowatt range. They are outdoor laboratories specially conditioned for scaling and qualifying systems prior to commercial demonstration.
The CESA-I project, was promoted by the Spanish Ministry of Industry and Energy and inaugurated in May 1983 to demonstrate the feasibility of central receiver solar plants and enable the development of the necessary technology. At present, the CESA-1 does not produce electricity, but is a very flexible facility operated for testing subsystems and components such as heliostats, solar receivers, thermal storage, solarized gas turbines, control systems and concentrated high flux solar radiation measurement instrumentation. It is also used for other applications that require high photon concentrations on relatively large surfaces, such as in chemical or high-temperature processes, surface treatment of materials or astrophysics experiments.
Direct solar radiation is collected by the facility's 330 x 250-m south-facing field of 300 39.6-m2 heliostats distributed in 16 rows. The heliostats have a nominal mean 90% reflectivity, the solar tracking error on each axis is 1.2 mrad and the reflected beam image quality is 3 mrad. The CESA-1 facility has the most extensive experience in glass-metal heliostats in the world, with first generation units manufactured by SENER and CASA as well as second generation units with reflective facets by ASINEL and third generation facets and prototypes developed by CIEMAT and SOLUCAR. In spite of its over 20 years of age, the heliostat field is in good working condition due to a strategic program of continual mirror-facet replacement and drive mechanism maintenance and replacement. To the north of the field are two additional areas used as test platforms for new heliostat prototypes, one located 380 m from the tower and the other 500 away from it. The maximum thermal power delivered by the field onto the receiver aperture is 7 MW at a typical design irradiance of 950 W/m2, achieving a peak flux of 3.3 MW/m2. 99% of the power is focused on a 4 m-diameter circle and 90% in a 2.8 m circle.
View of the CESA-I tower reflected in an heliostat.
The 80-m-high concrete tower, which has a 100‑ton load capacity, has three test levels:
The tower is complete with a 5-ton-capacity crane at the top and a freight elevator that can handle up to 1000-kg loads. Finally, for those tests that require electricity production, the facility has a 1.2‑MW two-stage turbine in a Rankin cycle designed to operate with 520ºC 100‑bar superheated steam.
- A cavity adapted for use as a solar furnace for materials testing at 45 m, which has been used very successfully in reproducing the heat ramp on space shuttles during their reentry into the atmosphere in test pieces of the ceramic shield and also for surface treatment of steels and other metal compounds.
- A cavity with a calorimetry test bed for pressurized volumetric receivers at 60 m.
- A multipurpose test facility for new receiver concepts at 75 m.
- A volumetric air receiver test facility at the top of the tower at 80 m.
|» 2.7 MWt SSPS-CRS FACILITY
The SSPS-CRS plant was inaugurated as part of the International Energy Agency’s SSPS project (Small Solar Power Systems) in September 1981. Originally conceived to demonstrate continuous electricity generation, it used a receiver cooled by liquid sodium that also acted as the thermal storage medium.
At the present time, as with the CESA-I plant, it is a test facility devoted mainly to testing small solar receivers in the 200 to 350-kWth capacity range.
The heliostat field is made up of 91 39.3-m2 first generation units manufactured by Martin-Marietta. A second field north of it has 20 52-m2 and 65-m2 second-generation supporting heliostats manufactured by MBB and Asinel.
The original CRS heliostat field was improved several years ago with the conversion of all of its heliostats into completely autonomous units powered by photovoltaic energy, with centralized control communicated by radio by a concept developed and patented by PSA researchers. This first autonomous heliostat field, which does not require the use of channels or cabling, was made possible by financial assistance from the Ministry of Science and Technology’s PROFIT program.
A CRS field heliostat reflecting the tower
The nominal average reflectivity of the field is 87%, the solar tracking error is 1.2 mrad per axis and the optical reflected beam quality is 3 mrad. Under typical conditions of 950 W/m2, total field capacity is 2.7 MWth and peak flux is 2.5 MW/m2. 99% of the power is collected in a 2.5-m-diameter circumference and 90% in a 1.8-m circumference.
The 43-m-high metal tower has two test platforms. The first is a two-level open area at 32 and 26 m prepared for testing new receivers for thermochemical applications.
The second test platform is at the top of the tower at 43 m, and houses an enclosed room with crane and calorimetric test bed for the evaluation of small atmospheric-pressure volumetric receivers, and solar reactors for hydrogen production. The tower infrastructure is completed with a 600-kg-capacity crane and a 1000-kg-capacity rack elevator.
The facility’s calorimetric test bed consists of an air-recirculation circuit with axial fan and 40-kW electric heater to control the air-return temperature as well as instrumentation to measure the temperature, pressure and flow rate. Absorber outlet air is cooled by a water-cooled heat exchanger used for indirect thermal balance. The calorimetric bench has been successfully employed since 1986 with logical improvements and updating, for the evaluation of all kinds of metal and ceramic volumetric absorbers.
Aerial View of the CRS Facility
Two PROHERMES II (Programmable Heliostat and Receiver Measuring System II) measurement systems are used to characterize the concentrated solar radiation flux map on both towers. For this, the concentrated incident solar beam is intercepted by a Lambertian target, located on a plane parallel and immediately in front of the receiver aperture, at which moment a high-resolution CCD camera records the image. After its exhaustive treatment, the total power can be integrated, and the rest of the magnitudes of interest, such as peak flux or statistical energy distribution parameters on the receiver can be calculated.