Andreas Witzig

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High PV utilization ratios in buildings, i.e. the consumption of most of the PV energy within the building premises, can reduce the energy losses in distribution networks, and mitigate overvoltages and transformer overloadings. For this reason, some countries have adopted, or are discussing, regulatory instruments to motivate local utilization of PV energy.(More)
The computation of optical modes inside axisymmetric cavity resonators with a general spatial permittivity profile is a formidable computational task. In order to avoid spurious modes the vector Helmholtz equations are discretised by a mixed finite element approach. We formulate the method for first and second order Nédélec edge and Lagrange nodal elements.(More)
The computation of optical modes inside axisymmetric cavity resonators with a general spatial permittivity profile is a formidable computational task. In order to avoid spurious modes the vector Helmholtz equations are discretised by a mixed finite element approach. We formulate the method for first and second order Nédélec edge and Lagrange nodal elements.(More)
Self-sufficiency of systems with photovoltaic (PV) energy production gets more and more important. Demand side management with the use of heat pump and thermal energy storage has proven to be an efficient and effective means for increasing the PV self-consumption ratio [1, 2]. Accurate prediction of the self-consumption and the resulting self-sufficiency(More)
Dedicated to my wife Rosa, and my children Alex and Sarah ii Acknowledgments The work documented in this thesis is the result of a common effort, after all there is no use for an ultra-stable super-efficient optical setup without anything to measure. I would like to start by thanking my thesis advisor Prof. Andrea Fiore for the countless hours spent on(More)
The performance of today's commercial vertical cavity surface emitting lasers (VCSELs), results from designs that include the sensitive interplay of thermal, electrical and optical effects. Simulation with a predictive character needs to capture these aspects quantitatively, and the underlying equations have to be solved in multiple dimensions in space. In(More)
Optical modes of microcavities are determined by solving Maxwell's vectorial wave equation subject to an open boundary taking radiation, diffraction effects, optical gain and absorption into account. Using a continuation scheme the optical problem is solved together with the electro-thermal device equations in a self-consistent fashion. The model is(More)
The analysis of filter devices based on eigenmodes provides a facile and fast means to simulate the reflection and transmission function and shows good agreement with the measurements. The computing time is proportional to the number of eigenmodes, and the analysis yields an analytical expression for the transfer functions. The method can be easily applied(More)
Penetration of the waveguide mode into the substrate has some effects in Nitride-based semiconductor lasers grown on Silicon Carbide while it is usually not a problem in Arsenide-based devices. We observe oscillations in the red part of the measured gain spectrum of an (Al,In)GaN semiconductor lasers. These have been attributed to the presence of a standing(More)
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