Photovoltaics (PV)
Why PV matters to Local Governments
Solar PV cells are ideal for urban applications because they can easily utilize the empty space of urban rooftops, requiring no additional land. With no moving parts, this technology is easily maintained and has minimal costs once installed. It is also modular and scalable, allowing for matching the size and power to individual needs, available space, and electricity demand curves. In the developing world, PV has the increased advantage of being ideal for off-grid applications.
The Technology
Sunlight is converted directly into electricity in a solar photovoltaic cell. This conversion occurs (in the common crystalline silicon cell) when solar radiation hits two identical electrodes in a conducting solution, forcing the electrons into a negative charge, and generating a current when the electrons (which have been kept apart by impurities in the silicon) flow through a wire connecting the negative and positive ends of the cell. This current is captured in DC form (like batteries), where it goes through an inverter (if one is not storing it) to alter the current to AC, which is the same current found in the grid and that is used in our homes and businesses.
It is the PV cell that produces the electricity, groups of cells are called modules, and groups of modules are called an array. The number of KW and MW in a solar PV system depend on the PV cell technology and the number of cells and modules strung together. PV systems are used in off-grid, stand-alone systems or are connected to the grid.
Collecting the Solar Resource
PV arrays are normally facing south, where the suns rays are the strongest, and often angled to best capture the most sunlight. In the temperate zone, this angle will change with the seasons, to face the sun's location in the sky. PV arrays can be either fixed or mounted on tracks. With a fixed system a seasonal adjustment of the modules is needed to capture the best solar angle. With a PV system on tracks, the system will adjust itself to the best angle daily and seasonally. Tracking systems enhance the efficiency of a PV system while they increase the overall cost of the system. Solar PV has the advantage of being able to produce electricity when it is most needed, during the day allowing electricity produced from solar technologies to qualify for sale in peak markets. Energy storage (see relevant section at left) could allow for the management of solar facilities with other renewable systems, and enhance the overall electrical system uptake of RE technologies.
There are a number of different forms of solar pv, that follow slightly different reaction paths, including crystalline silicon (described above), poly-crystalline silicon, concentrating solar power, and thin film technologies.
The cost of PV cells are dramatically coming down due to large influxes of research and through the experience gained worldwide in production and installation. With increases of efficiency in pv cells, more solar radiation can be converted into electricity per cell, and consequently less cells are needed to produce a given amount of energy. These efficiency increases reduce cost, and improved efficiency is an ongoing trend.
