Martin Neubauer

New module design with 4-junction solar cells for high efficiencies

CPV systems using 3-junction solar cells have proven good performance and reliability. As the performance of 3-junction cells is saturating [1], the logical next step is the introduction of 4-junction (4-J) solar cells into CPV modules. The current world record for cell efficiency under concentrated light of 46.0% was achieved using a wafer bonded Soitec 4-J cell (SmartCell™) [1-4]. This paper discusses a new module design, optimized for harvesting the full potential provided by this high cell efficiency. Prototype modules have been built in order to explore the design space. A module efficiency of 38.9% under concentrator standard test conditions has been achieved.

Fresnel Lens Concentrator with Improved Thermal Behavior

Recent investigations of silicone‐on‐glass (SoG) Fresnel lens concentrator optics have shown a dependence of the optical efficiency and module performance on lens temperature. It was shown that the temperature dependence is dominated by a reduction of the refractive index with increasing temperature and a deformation of the lens structure due to thermal expansion of the lens material. We succeeded in modeling these effects on a computer by simulating thermal deformations of the lens structure using the finite element method (FEM) and analyzing the resulting deformed structure using ray tracing simulations. In former work, we were able to demonstrate a very good match to high precision optical measurements of Fresnel lenses at varying temperatures. The detailed insight we gained through our measurements and computer simulations was used to develop and manufacture a lens with improved optical performance at the temperature interval which is relevant for operation within a concentrator photovoltaic module. F...

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.

CPV module with Fresnel lens primary optics and homogenizing secondary optics

In this work CPV modules based on Fresnel lenses and using refractive secondary optical elements (SOEs) are investigated. Pure silicone as well as glass SOEs glued on top of the solar cells are explored in prototype modules. They are differently manufactured in respect to how the secondary optics was assembled. For example, units with secondary silicone optics directly casted to solar cells are manufactured. For a design of glued glass optics and Fresnel lenses, the optical design is analyzed experimentally. Moreover, the long term stability has been intensively tested by accelerated aging tests and outdoor experiments. Here, the focus was on the used silicone material and the adhesion of the silicone to the glass interface.