Tobias Gerstmaier

Validation of the PVSyst Performance Model for the Concentrix CPV Technology

The accuracy of the two‐stage PVSyst model for the Concentrix CPV Technology is determined by comparing modeled to measured values. For both stages, i) the module model and ii) the power plant model, the underlying approaches are explained and methods for obtaining the model parameters are presented. The performance of both models is quantified using 19 months of outdoor measurements for the module model and 9 months of measurements at four different sites for the power plant model. Results are presented by giving statistical quantities for the model accuracy.

Software Modeling of FLATCON© CPV Systems

This paper describes an approach of making the FLATCON® CPV technology compatible with standard photovoltaic simulation software like PVSYST and INSEL in order to facilitate yield estimations for potential power plant sites. Due to the use of triple‐junction cells, the FLATCON® CPV module efficiency is more sensitive to changes in the solar spectrum than the efficiency of an average single‐junction flat plate module. Besides that, the concentrating optics show a temperature dependency. These effects result in a non‐linear component in the short circuit dependency on the direct normal irradiance. By means of introducing a “Utilization Factor”, deduced from both measured data and theoretical considerations, these CPV peculiarities can be considered in standard software tools and transferred to other locations without the need of overly complex measurements or algorithms.

Concentrix Solar's progress in developing highly efficient modules

This paper presents the new module generation (CX‐75‐III), which was developed in an all‐embracing cost optimization. The single primary lens was refined for optical efficiency and its size increased to 5.7×5.7 cm2, thus dramatically reducing the part count. Thermal simulations were used in order to dimension the heat spreader and ensure the reliability due to a low cell temperature. Furthermore, recent developments for cost optimization and high module efficiencies are presented. Results on prototype modules with a new heat spreader design, a new primary lens and also with refractive secondary optical elements are shown. The use of reflective secondaries has lead to an STC efficiency of 30.6%. Furthermore, different anti‐reflection coatings have been examined in order to assess their impact on performance and reliability.

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.

From a 32 m2 system with 90 CPV modules to a 105 m2 system with 12 CPV modules - Soitec's new CPV system CX-S530

In 2008, Soitec started to launch a 32m2 CPV system which included 90 modules per tracker. In order to realize the fast installation of multi-MW power plants the CPV module CX-M500 with an aperture area of 7,84 m2 was developed together with the new tracker CX-T030 which is optimized for carrying 12 of the new modules. This paper gives an overview over the evolution of this CPV system. The module is based on components of the field proven earlier Concentrix module generations. The tracker is a classical pylon type with two AC motor powered slewing ring drives. A new control device was developed which uses the power-optimized sun tracking algorithm. The major development steps and their results are presented.

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%.

Spectrally resolved DNI measurements: Results of a field comparison of spectroradiometers, component cells and the SOLIS satellite model

One remote sensing and two in-situ methods for quantifying the spectral distribution of the direct normal irradiance and its impact on multi-junction solar cells are compared for three different sites in Southern Europe, on the Arabian Peninsula and in the South West of the USA. For each method, the uncertainty is assessed. The spectral parameter Z is used to quantify the differences between the methods.

Concentrating photovoltaic systems

Abstract The first section of this chapter introduces the principles of concentrating photovoltaic (CPV) technology. Since there is a huge diversity in system designs, the most common principles are outlined and examples for CPV systems are presented. The second section discusses the most important impacts on the performance of CPV systems. In contrast to standard photovoltaic (PV), the influence of the cell temperature on the output power is much less important. On the other hand, multijunction solar cells are used in high-concentration systems and therefore daily and seasonal changes in the spectrum have a stronger impact on the energy output compared to flat-plate PV. However, it is discussed that these effects must be seriously considered for the instantaneous power output but over a full year of energy production there is an averaging effect and the most dominant influence remains the irradiance. Sections 10.3 and 10.4 deal with the evaluation of CPV technology. Here, standards are an essential prerequisite. International Electrotechnical Commission standards for CPV technology are currently under development and drafts are already published. The sections give insight into the standards and detailed information about the benefits of these standards and provide examples of how to use them. Further, recent results of module, system and power station evaluation, applying these standards for the first time, are presented.

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.