Showing papers by "Yahia Baghzouz published in 2015"

Basic Photovoltaic Theory

Abstract: Electric power generation by means of photovoltaics (PVs) has seen an explosive growth worldwide over the past decade. This growth is driven in part by a global concern about climate change, the adoption of renewable portfolio standards, government rebates and tax incentives, and reduction in PV system cost. This article presents the basic theory on how a silicon-based PV cell converts sunlight into electricity. Silicon material and sunlight properties are reviewed with emphasis on the amount of energy that is needed to free valence electrons (i.e., bandgap) and energy content of sunlight throughout the solar spectrum. The need to add impurities to form n-type and p-type materials, for the purpose of separating the free electrons from the holes left behind, is clearly addressed. The electrical characteristics of a p–n junction solar cell are described in terms of drift and diffusion currents and the strength of the electric field that appears across the depletion region. Owing to their similarities, the equivalent circuit model of the cell when exposed to sunlight is derived from that of a p–n junction diode. The impact of changes in the numerous variables that appear in the circuit model, on the cell current–voltage (I–V) curve and power conversion efficiency, are reviewed, along with the building blocks that make up a solar PV module. Keywords: solar spectrum; semiconductor materials; doping; diode circuit model; cell efficiency

Evaluation of the impact of partial shading on the performance of a grid-tied photovoltaic system

Abstract: Partial shading on a solar photovoltaic (PV) array is known to have a significant impact on its energy yield. This paper presents experimental measurements on a 2 kW grid-tied PV array under different shading profiles that are caused by structures of various shapes at different times of the year. A simulation method that provides an accurate description of shadow movement of the simpler structure on the array surface at different times of the day is presented. While the shade geometry can be accurately predicted, lack of knowledge about the relative amount of sunlight received by the most shaded cell in each group of cells in shunt with bypass diodes limits the simulation tool from determining the impact on the I-V and P-V curves of the array.

On determinig the control techniques embedded in a commercial single-phase grid-tied PV inverter

Abstract: Grid-tied photovoltaic inverter manufacturers rarely reveal the type of power electronic circuit topology and the type of technique used to track maximum power, control of power injected into the grid, and method used to avoid islanding operation. In this paper, an attempt is made to gain such information on a commercial 2.5 kW inverter by measuring the voltage and current waveforms under normal operation and during utility outages, analyzing such waveforms, and replicating these through computer simulations. The experience gained from such an academic exercise is found to be very valuable to students.

Experimental test on temperature rise of conductors in roof-mounted conduits

Abstract: Conductors for most buildings in the United States are sized using the National Electrical Code (NEC). The 2014 NEC now requires that a value be added to the ambient temperature used to determine the ampacity of conductors installed on rooftops. This paper reports the results of a related experimental test (on both energized and non-energized cables) that is conducted on a rooftop of a building located in the desert southwest during the hottest period of the year. The recorded temperature rise of the conductors tested is compared to the temperature adders specified in the Code. The maximum recorded temperature of the energized conductors is also compared to the rated temperature of the conductor insulation.