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On the design and monitoring of photovoltaic systems for rural homesWilliams, Nathaniel John January 2011 (has links)
It is estimated that 1.6 billion people today live without access to electricity. Most of these people live in remote rural areas in developing countries. One economic solution to this problem is the deployment of small domestic photovoltaic (PV) systems called solar home systems (SHS). In order to improve the performance and reduce the life cycle cost of these systems, accurate monitoring data of real SHSs is required. To this end, two SHSs typical of those found in the field were designed and installed, one in a rural area of the Eastern Cape of South Africa and the other in the laboratory. Monitoring systems were designed to record energy ows in the system and important environmental parameters. A novel technique was developed to correct for measurement errors occurring during the utilization of pulse width modulation charge control techniques. These errors were found to be as large as 47.6 percent. Simulations show that correction techniques produce measurement errors that are up to 20 times smaller than uncorrected values, depending upon the operating conditions. As a tool to aid in the analysis of monitoring data, a PV performance model was developed. The model, used to predict the maximum power point (MPP) power of a PV array, was able to predict MPP energy production to within 0.2 percent over the course of three days. Monitoring data from the laboratory system shows that the largest sources of energy loss are charge control, module under performance relative to manufacturer specifications and operation of the PV array away from MPP. These accounted for losses of approximately 18-27 percent, 15 percent and 8-11 percent of rated PV energy under standard test conditions, respectively. Energy consumed by loads on the systems was less than 50 percent of rated PV energy for both the remote and laboratory systems. Performance ratios (PR) for the laboratory system ranged from 0.38 to 0.49 for the three monitoring periods. The remote system produced a PR of 0.46. In both systems the PV arrays appear to have been oversized. This was due to overestimation of the energy requirements of the loads on the systems. In the laboratory system, the loads consisting of three compact fluorescent lamps and one incandescent lamp, were used to simulate a typical SHS load pro le and collectively consumed only 85 percent of their rated power. The 8 predicted load profile for the remote system proved to be signi cantly overestimated. The results of the monitoring project demonstrate the importance of acquiring an accurate estimation of the energy demand from loads on the system. Overestimations result in over-sized arrays and energy lost to charge control while under-sized systems risk damaging system batteries and load shedding. Significant under-performance of the PV module used in the laboratory system, underlines the importance of measuring module IV curves and verifying manufacturer specifications before system deployment. It was also found that signi cant PV array performance gains could be obtained by the use of maximum power point tracking charge controllers. Increased PV array performance leads to smaller arrays and reduced system cost.
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Design and performance analysis of hybrid photovoltaic-thermal grid connected system for residential application.Mutombo, Ntumba Marc-Alain. January 2012 (has links)
High output electrical energy is obtained from photovoltaic (PV) systems subject to high
irradiance. However, at high irradiance, the efficiency of PV systems drops due to increase of
the temperature of the systems. In order to improve the efficiency of photovoltaic systems, much
effort has been spent on developing hybrid photovoltaic thermal (PVT) systems using water as a
coolant to withdraw heat from solar modules.
This research is focused on the study of the behavior of hybrid PVT collectors using rectangular
channel profiles which provide a large surface for heat exchange between PV panels and thermal
collectors unlike the circular channel profile used in conventional PV systems. In hybrid PVT
systems, coolant water circulates in a closed circuit by means of the thermosyphon phenomenon
and the heat from this water is extracted from a storage tank and can be used in hot water
systems instead of an electric geyser.
Numerical models of water velocity in channels due to the thermosyphon phenomenon and the
temperature of solar modules was developed and a system was designed for modest Durban
household demand. A simulation was run for specific summer and winter days comparing a
conventional PV system and a hybrid PVT system. The results were very encouraging, and
demonstrated that the equipment is capable of extending the PVT application potential in the
domestic sector where more than 40% of electricity cost is heating water. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2012.
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