Among the many techniques for obtaining heat and electricity, solar thermal collectors, photovoltaic (PV) technology and PV/thermal (PV/T) technology have a very important place. The PV/T collectors enable the simultaneous conversion of solar radiation into thermal and electrical energy in a single device, with better space utilization and cost efficiency during construction. Specially designed PV/T collectors can replace the outer walls or roof covers and can be widely used in private houses, flat complexes, hospitals, schools, tourist and other objects for water heating and electrical energy generation. Due to their great application potential, hybrid collectors have been the subject of very intensive scientific research and technical development for many years. In this review article, the focus is on the research, development and application of the PV/T water systems in the last 10 years. The main task of researchers and manufacturers is to increase the efficiency of PV modules and thermal absorbers, using new materials and design types as well as their proper integration into the PV/T collector. It is also necessary to reduce the cost of these systems and make them more competitive in the market. In addition, the importance of PV/T systems is in providing energy in clean and environmentally friendly ways.
This paper discusses the application of flat panel reflectors in conjunction with photovoltaic cell used to power wireless sensor node. The aim of the reflectors is to increase the indoor ambient light energy harvesting efficiency, especially under low illumination levels (<200 lx). The benefit of the reflectors usage is in the reduction of the node cold boot time and increase of the data transmission frequency. In addition, the physical placement and orientation of nodes in a wireless sensor network is less dependent on the illumination conditions. This paper presents a simple theoretical model suitable for the calculation of the optimal inclination angle for the reflectors. Experimental data show that the cold boot time can be reduced up to 30% and data transmission frequency increased almost twice by using two reflectors of the same size as the photovoltaic cell. The reflectors are produced in the conventional printed circuit board technology, so they can be incorporated into the node design with negligible costs.Index Terms-Flat panel reflectors, photovoltaic, energy harvesting, wireless sensor node.
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