Meteorological information is essential for the design, the operation and the qualification of CSP plants and their components. The department “Qualification” determines the meteorological parameters that are relevant for CSP and analyzes their effect on the design and performance of this technology. The activities are carried out mainly at the Meteorological Station for Solar Technologies (METAS) at the Plataforma Solar de Almería (PSA) which is operated in close collaboration with CIEMAT.
The most obvious parameter that is required is the direct normal irradiance (DNI). Its accurate measurement is one of the key topics. The accuracy of the DNI measurement is crucial for the uncertainty of the overall efficiency measurement of a CSP collector.
To reduce the uncertainty of DNI measurements to a minimum, sophisticated sensor calibration is required.
In addition to this, CSP project developers require accurate information on the solar resource of a specific site. DLR works on standards and guidelines for solar resource assessment to increase the quality of meteorological data sets for project development. This work is carried out in the framework of the IEA Solar Heating and Cooling Task 46 “Solar Resource Assessment and Forecasting“ and SolarPACES.
As solar resource assessment often involves measurements at remote sites, DLR investigates robust and less maintenance intense instruments as Rotating Shadowband Irradiometers. Their accuracy is investigated and their calibration is performed and developed further.
Besides DNI, also other meteorological parameters that are relevant for CSP are investigated. Dynamic wind loads on collector structures and receivers have an impact on the efficiency of CSP systems. For this reason, DLR offers e.g. wind measurements with high temporal resolution.
The department’s research topics also include advanced measurands for solar resource assessment and CSP qualification. Especially for the operation of CSP plants under harsh desert conditions, new parameters have to be investigated.
Therefore many of the following activities are performed hand in hand with the enerMENA project at several sites in the Middle East and North Africa additionally to their original installation at PSA. Hence, DLR gains a practical insight into meteorological conditions in the region and the challenges faced by project development in these countries.
One of these advanced measurands is the circumsolar radiation. Circumsolar radiation is in large part included in common DNI measurements, but only partially intercepted by the receivers of focusing collectors. Therefore, it has to be considered in solar resource assessments. DLR developed and applies measurement techniques to determine the circumsolar radiation and investigates the effect on CSP.
DLR also investigates the soiling level of CSP plant components. Dust deposition e.g. on the concentrators significantly reduces the reflectivity and thus the efficiency of CSP plants. The TraCS system allows the routine measurement of soiling levels of mirrors.
Another new parameter for resource assessment which is investigated is the atmospheric extinction in concentrating plants. Measurement approaches for this topic are developed and applied.
Aerosols play a key role for the three examples mentioned (sunshape, soiling and extinction). Thus the department “Qualification” routinely performs measurements with an AERONET sun photometer, LIDAR systems and dust samplers. The analysis of aerosols in the lower atmosphere also creates synergy with the department’s durability studies.
| | The sunshape measurement system consisting of Visidyne’s SAM (left) and a CIMEL sunphotometer (right) at the Plataforma Solar de Almería. The sunphotometer is part of the AERONET.
Furthermore, the dynamic effects of clouds on the solar resource are investigated. Their influence on the circumsolar radiation and the spatial and temporal variation of DNI is crucial for CSP. Various all sky imagers are complemented with LIDAR systems for these studies.
CESA-1 tower at PSA in standby position for a hazy and a clear atmosphere.
Two all sky images taken by the same camera 1 minute after each other at the Plataforma Solar de Almería.