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The price of electricity provides an excellent opportunity to apply a stand-alone Residential Photovoltaic System which combines two or more sources of generation. Due to the increasing impact of Renewable Portfolio Standard (RPS) on the electricity market, energy generation using renewable resources such as solar, wind, biomass, and geothermal is becoming more common and has created challenges to solar power delivery systems design, operation and maintenance. In remote areas where there is no access to power grids, residences rely upon expensive diesel generators.
Photovoltaic (PV) systems utilize solar panels to directly convert solar energy into electrical energy. These panels consist of many PV solar cells which are semiconductor devices that convert incident solar energy into dc current. The most attractive features of PV panels are the nonexistence of moving parts for some designs, slow degradation of the sealed solar cells, modular flexibility (from a few W to MW), and the simplicity of use and maintenance. In addition, solar energy is clean and renewable as well as being an inexhaustible source with great reliability.
Currently there are a number of technologies available for Residential Photovoltaic System cells with various ranges of efficiency and cost. National Renewable Energy Laboratory, Golden, Colorado (NREL) has published the average commercial module efficiencies. According to this source, commercial silicon efficiencies are between 14-18% as shown in Figure 1 . The key issues that are considered in the design are discussed below: The solar power intensity falling on a square meter (m2) of area is called “solar insolation” and is measured in W/m2. Outside the earth’s atmosphere the solar insolation is about 1.37kW/m2 and on the surface of the earth the insolation is usually assumed to be around 1.0kW/m2 which is the called “1-sun” or peak sun hour (PSH). The amount of average insolation at a particular site is also used to determine the panel and battery sizes.
Due to the tilted axis of the earth, the apparent path of the sun through the sky depends on the day of the year, the latitude and longitude of the observer, and the solar declination. In order to produce maximum energy a PV panel should face the sunlight at a 90° angle. To achieve that, a fixed collector should be pointed directly south and tilted at the angle of the local latitude positioning the collector parallel to the earth’s axis.
|Conceptual Design and Cost Estimated for a Stand- Alone Residential Photovoltaic System|