Principles of CSP performance assessment

The performance of a concentrated solar power component of Systems describes ist capacity to accomplish ist design purpose in concentrating and(or converting solar irradiance to useful energy. Generally, this can be quantified by ist Efficiency relating the useful Output of the System or component to the nergy Input or effort. In Addition, for some Standard components, key performance indicators such as specific heat loss for parabolic trough Receivers and Focus Deviation for mirrors have been established in the past decade. The assessment of the performance of a component or System is necessarily based on the measurement of ist operational characteristics, typically involving the Evaluation of energy balances of the System itsefl and/or its heat Transfer fluid (HTF) under specific well-known operating conditions. The Information on prevailing or resulting conditions can be obtained using appropriate measurement Equipment. The key measurement challenges in concentrating solar power applications are presented by high temperature and pressure, concentrated solar Radiation, as well as Special HTF´s such as thermal oil or molten salts

Calibration Procedures for Rotating Shadowband Irradiometers

Concentrated Solar Power (CSP) projects require accurate assessment and monitoring of the available direct beam resource. To this end, ground measurements on site are inexpendable. Pyrheliometers with thermopile sensors as specified in [ISO 9060] are the standard instruments for field measurements of direct beam irradiance. During long-term deployment however, their comparatively high accuracy can only be maintained if the window through which the direct beam enters the instrument is cleaned frequently [Geuder and Quaschning, 2006]. In the case of long-term solar resource assessments on site this can pose a problem in terms of logistics and maintenance costs. This is particularly relevant, if the measuring site is in a remote location. Rotating Shadowband Irradiometers (RSI) on the other hand have a lower accuracy to start with due to systematic errors of its photodiode sensor. However, they are less affected by soiling [Geuder and Quaschning, 2006] and provide higher accuracy in long-term measuring campaigns at sites where cleaning is not possible on a daily basis. Furthermore, they are comparatively inexpensive and do not require as much additional equipment i.e. a tracking system. A solar panel is sufficient for power supply. The systematic errors of the sensor used in RSIs are caused by cosine and temperature effects and its spectral non-uniform responsivity. A number of correction functions can be employed to reduce these errors significantly. Additionally, a thorough calibration of the sensor with application of the correction functions can further improve the quality of measurements. The calibration procedures of thermopile pyranometers and pyrheliometers are well documented in standards such as [ISO 9059], [ISO 9846] and [ISO 9847]. Because these standards are not applicable to RSIs due to their inherent characteristics specific calibration procedures for this type of instrument were developed. This work shall discuss the differences between calibration procedures for thermopile irradiometers and RSI and aspects which can be transferred from the existing standards to RSI calibration. Some of the existing calibration methods have been successfully employed for a number of years. However, a thorough assessment of the necessary calibration duration with multiple measurements from several instruments has not been carried out before this project. Therefore, besides the comparison of calibration methods this work examines to which extend the RSI calibration results fluctuate in dependence on the duration of the calibration measuring period and furthermore provide a basis on which to choose the most suitable duration

Wolken-Transmissionsgrad-Zuweisung für ein räumlich hochaufgelöstes Echtzeit DNI Karten-Kurzzeitprognose-System

Kurzzeitprognosen der Solarstrahlung für die nächsten 15 Minuten bergen ein großes Potenzial zur Betriebsoptimierung von solarthermischen Kraftwerken, PV-Systemen als auch des Netzbetriebs. Kameragestützte Prognosesysteme erfuhren in den letzten Jahren einen signifikanten Entwicklungsschub, begünstigt durch die Verfügbarkeit von günstigen hochauflösenden Kameras, der Fortschritte bei den verfügbaren Speicher- und Rechenkapazitäten und dem stetigen Wachstum des solaren Anteils im weltweiten Energiemix. Das Potenzial für räumlich aufgelöste Kurzzeitprognosen der Globalstrahlung wurde u.a. in [1] untersucht. [2] und [3] beschreiben Methoden für Direktstrahlungsprognosen, welche bis zu vier unabhängige 2D Wolkenschichten berücksichtigen. In [4] werden zwei Kameras mit Fischaugenobjektiven für eine detaillierte 3D Wolken-Photogrammmetrie eingesetzt. Im Rahmen dieser Arbeit wurde ein Echtzeit- kurzzeitprognose-System für räumlich hochaufgelöste (5mx5m) DNI Karten basierend auf zwei bis vier Standard Überwachungskameras (Mobotix Q24 oder Q25) entwickelt [5]. Im vorgestellten System wird jede sichtbare Wolke als individuelles 3D Objekt in einem virtuellen Raum modelliert. Jedem Wolkenobjekt im Raum werden die Attribute Höhe, Position, Dicke und Transmissionsgrad zugewiesen. Ein individueller Bewegungsvektor wird für jedes Wolkenobjekt ermittelt. Mittels dieses Systems können Kurzzeitprognosen der Direktstrahlung (DNI) auch bei komplexen mehrschichtigen Wolkenzugsbedingungen erstellt werden

Nowcasting of DNI maps for the solar field based on voxel carving and individual 3D cloud objects from all sky images

International audienc

Impact of DNI nowcasting on annual revenues of CSP plants for a time of delivery based feed in tariff

The impact of a combined nowcast for direct normal irradiation on revenues of two different concentrating solar power plant technologies under a time-of delivery-tariff is investigated. The nowcasts merge several satellite and NWP based nowcasts together with a smart persistence approach in order to generate a best-of nowcast for all now- and forecast time horizons up to 9 hours and in a 15 min temporal resolution. The applied tariff scheme is similar to that used in South Africa for some of the CSP plants erected in that country with considerably increased remuneration during the evening hours with maximum energy demand. The study investigates the impact both with respect to the annual energy yield and the economic annual revenues of CSP plants. The results for the combined nowcast are compared with results using ECMWF IFS based DNI forecasts which are commercially available for plant operators as well as with a persistence approach and the ideal forecast derived from ground-based observations

Management and Exploitation of Solar Resource Knowledge

Knowledge of the solar energy resource is essential for the planning and operation of solar energy systems. In past years there has been substantial European and national funding to develop information systems on solar radiation data, leading to the situations that several data bases exist in parallel, developed by different approaches, various spatial and temporal coverages and resolutions including those exploiting satellite data. The user of these products may end up with different results for the same requested sites. To better guide the users, a benchmarking exercise is under preparation. A set of reference data has been collected and benchmarking measures and rules have been defined. The results of the benchmarking and the feedback from stakeholders will be integrated into a guide of best practices in the application of solar resource knowledge. Access to data has been quite fragmented. Each service has its own way of access to the data and delivery format. A new broker portal based on the experience of the project Soda aims to unify and ease the access to distributed data sources and applications providing solar resource information