Characterizations and Performance of a Solid-State Inverter and its Applications in Photovoltaics B.A. Ezekoye, Ph.D. * and V.N. Ugha, M.Sc. * Department of Physics and Astronomy, University of Nigeria, Nsukka. E-mail: bezekoye@yahoo.com ABSTRACT We designed, constructed, and characterized a solid-state inverter, one of the most expensive devices in a standard PV system, using locally made materials in Nigeria. The device is used to convert the DC generated by solar cells to AC for optimum utilization, and was designed with following specifications: waveform- square wave: rated output power- 50W, maximum power intake- 55W, frequency- 50Hz, input voltage- 18 – 22V, output voltage- 220 – 240V, maximum current intake- 4A. The characterization of the locally made inverter was carried out and the results show that the efficiency of this inverter varied with the solar intensity, which is in agreement with theory. The output square wave of the inverter has low power consumption, maximum utilization of available power, is economical, and is free from high frequency oscillations that may come from a nearby wave- generating- source. (Keywords: photovoltaic, solar, direct current, alternating current, electronics) INTRODUCTION A photovoltaic (PV) array, regardless of its size and sophistication, can generate only direct current (DC) electricity. Fortunately, there are many applications for which DC is perfectly suitable. More fortunately, DC electricity can be converted to alternating current (AC) with relative ease and efficiency through the use of a device called an inverter. It is the inverter that makes the PV technology compatible with the type of equipment and appliances encountered in the average homes. There are two possible input sources of PV electricity in a house: the array itself and in a stand-alone system (the battery bank). If the load demand is for AC, an inverter must occupy a position in the system between the batteries and the load. Inverters are nothing new; they have been around as long as there has been need for converting DC electricity to AC. The early rotary type of inverter had internal moving parts. The DC electrical source powered a DC motor connected to an AC alternator, which produced AC electricity for the load. Rotary inverters are still manufactured, largely for use in marine aircraft electrical systems, where a clean AC signal is desired and efficiency is not critical. Virtually all the inverters used with alternative power systems are transistorized, solid state devices. Solid-state inverters are preferred for their higher efficiency, ease of maintenance, and infrequency of repair. Important output specifications to consider when searching for DC to AC inverters include maximum voltage, maximum steady state current, maximum power, and frequency range. Output waveform choices include pure sine wave, square wave, stepped wave, and triangular wave. Pure sine wave is the best waveform, as it is the shape of an ideal AC electrical signal from a wall outlet. The highest quality inverters produce a true sine wave output, which requires fairly expensive components in the inverter. True sine wave outputs are normally found only in higher-end models. A square wave is a ‘flattened-out’ version of a sine wave. Instead of the voltage smoothly increasing from the negative maximum to the positive maximum and back again, it shifts suddenly from negative to positive, stays there for a half cycle, and then jumps to full negative and stays there for half a cycle, then repeats. A stepped wave is a quasi-square wave or sine wave. They are typically inexpensive power inverters that mimic a sine wave using a stepped The Pacific Journal of Science and Technology –4– http://www.akamaiuniversity.us/PJST.htm Volume 8. Number 1. May 2007 (Spring)