Michael Röttger

Large-scale and long-term CPV power plant field results

The purpose of this paper is twofold: Firstly, we define three performance metrics to evaluate Concentrator Photovoltaic (CPV) power plants, namely performance ratio, performance index and availability. Secondly, we apply these metrics to analyze more than six years of field data from two-long running, small power plants, and some weeks of field data from one large-scale power plant, all based on Soitec’s CPV technology. We find that all three plants deliver more energy than expected and identify two points for improving the energy modeling of large-scale plants with central inverters.

Recent progress in concentrator photovoltaics

In this paper, a review of the recent progress in concentrator photovoltaics (CPV) is given. In the first part, an introduction to CPV includes the concepts of solar concentration and the specific advantages of CPV. Then, the various optical designs are presented and discussed. In the second part, the recent success in bringing this technology to market ready products is described. Exemplarily, the FLATCON® CPV technology is described in detail and data of the field performance are presented. The design of the FLATCON CPV module is based on Fresnel lenses and III-V multijunction solar cells (MJC). With these modules Concentrix installed a demo tracker and two power plants in Spain in 2008. Field data of these systems with a maximum AC efficiency of 23% are presented and discussed in detail. In 2009, the first systems were installed with the module CX-75 which is produced on the fully automated production line of Concentrix in Freiburg. This module has a DC efficiency of 27% flashed. The field data which are presented demonstrate an outstanding AC system efficiency of 25%.

How predictable is DNI? An evaluation of day ahead DNI forecasts from four different providers

Forecast DNI values in hourly resolution for one day ahead are evaluated by a comparison with pyrheliometer ground measurements. Three months of such day ahead forecasts from four different providers for a site close to Questa, NM, USA are analyzed firstly by calculating the RMSE and the mean bias error. Secondly, cumulative distributions of the DNI forecast errors are calculated as they better suit the context of a utilitys use of the forecast.

Field performance of Concentrix CPV systems

Concentrix modules are based on III-V triple junction cells, a Fresnel lens array with a relatively small single lens aperture of 5 square inch, and a cover and bottom plate made out of glass. The first installations were conducted in 2008 in Europe, later installations followed in the US, in East Asia, in the Arabian Peninsula, and in Africa. This paper gives an overview of the performance of Soitec´s CPV systems with special focus on reliability, the different climatic conditions and their impact on the system performance. The seasonal distribution of the direct normal irradiation at the mentioned locations was found to be very different which enabled us to perform studies on the system performance depending on irradiation and ambient temperature. The first generation modules which were installed in 2008 had an average efficiency of 25%, resulting in a peak solar-to-grid system efficiency of 23% and an average AC system energy efficiency of > 20%. The system peak efficiencies of the second and third module generations reach maximum values of > 25% and average AC system efficiencies of > 22%. A detailed analysis of the reliability and the performance of the different system generations is presented.

Field performance of FLATCON® power plants and demo systems

In this paper, a short introduction in design considerations of FLATCON® CPV module and field data of the system technology over up to two years are presented as well as field experiences with the operation of the systems. FLATCON® modules are based on III–V triple junction cells, a Fresnel lens array, and a glass cover and bottom plate. In 2008, Concentrix installed a single tracker system and two power plants in Spain. A system solar‐to‐grid AC energy efficiency of 21% over the whole period of two years with maximum system AC power efficiency values of 23% for a single tracker system are shown. Similar systems installed in 2009 and equipped with the current FLATCON® module CX‐75 achieved system AC power efficiencies of 25%. The effects on power plant performance of spectral variations of the solar irradiation, soiling and also dew formation in wintertime are discussed.

On-Sun Performance of FLATCON® CPV Systems

Concentrating photovoltaic (CPV) systems based on III-V semiconductors entered the photovoltaic market recently. Concentrix Solar deploys the FLATCON® CPV module technology originally developed at the Fraunhofer Institute for Solar Energy Systems ISE. This paper gives a short introduction in design considerations of FLATCON CPV module and provides detailed field data of the system technology over up to two years are presented as well as field experiences with the operation of the systems. FLATCON modules are based on III-V triple junction cells, a Fresnel lens array, and a glass cover and bottom plate. In 2008, Concentrix installed a single tracker system and two power plants in Spain. A system solar-to-grid AC energy efficiency of 21% over the whole period of two years with maximum system AC power efficiency values of 23% for a single tracker system are shown. Similar systems installed in 2009 and equipped with the current FLATCON module CX-75 achieved system AC power efficiencies of 25%. The effects of spectral variations of the solar irradiation on power plant performance are discussed.