Ulf Blieske

Experimental studies on the development of a solar hybrid module with an aluminum microchannel evaporator

In recent years, the possibility to combine photovoltaics (PV) and solar thermal collectors into one hybrid module (PVT-module) has been increasingly investigated. PVT-modules produce thermal and electrical energy at the same time. As the efficiency of a photovoltaic module decreases with temperature, the temperature of the heat transfer media is often limited to about 30 °C and the PVT-module is combined with a heat pump, which increases the temperature on the “warm side”. This paper deals with a PVT-module, which combines a microchannel based evaporator of a CO2 (R744) heat pump with a PV panel (PVT-direct). The PVT-direct overall system is reduced to the refrigerant circuit due to the direct refrigerant expansion in the PVT-module. A conventional PVT heat pump system has an additional glycol-water circuit. Since a pump and an additional heat exchanger for the secondary cycle were omitted, the system has increased efficiency. Due to lower module temperatures, the increase of the photovoltaic efficiency is a further advantage of the PVT-direct-module. To prove the feasibility of the PVT-direct heat pump system, the Cologne Institute for Renewable Energy (CIRE) is developing and modeling a test facility for this purpose within the research project “PVT-direkt”. Furthermore, a functional PVT-direct-module with a microchannel based evaporator was designed and built. Much importance has been given to experimental studies under laboratory conditions in order to investigate (1) the adjustment of the functionality and layout of the PVT-direct-module for characterizing the joining of brazed joints in aluminum microchannel evaporators and (2) the influence of the backside aluminum plate of the PVT-direct-module regarding leakage currents and parasitic capacitances. The overall results obtained in these experimental studies are analyzed in this paper.

PV-systems for demonstration and training purposes in South America

This paper summarizes the climatic and national preconditions for photovoltaic energy production in Chile and Bolivia. Furthermore, design process, realization and monitoring of three different photovoltaic energy supply systems for professional schools in Chile and Bolivia are presented: Two 3-phase grid integrated systems and a 1-phase island system. The energy supply is part of an overall professional training concept under the leadership of Cristo Vive Bolivia and Cristo Vive Chile. Monitoring and calculations show that the energy demand of both schools can already be covered by moderate size PV systems on a monthly basis with performance ratios between 82% and 85%. The PV systems allow the shift from class-room education to project and problem based learning in the training program of young professionals in the field of renewable energy.

Good modules for bad weather

In this paper the different factors influencing the low light performance of solar cells and modules are analyzed and combined to simulate the low light performance of different solar module technologies. The parameters for the diverse technologies were extracted from module databases and the simulation was performed on the basis of high resolution weather data from a weather station in Lindenberg (Germany). The results show higher specific energy yields for all technologies compared to a standard c-Si module. A good performance under irradiances lower than 500W/m2 was observed for a-Si, CIS, CIGS and a textured c-Si module. For another low light definition (share of diffuse radiation > 50%) just the a-Si technology is giving a better performance compared to its total annual yield performance. The simulated c-Si module with a pyramidal textured front side encapsulation showed a high increase of energy yield for orientations deviating from the typical orientation, when compared to a standard c-Si module.