Solar Technology and Photovoltaic Cells

Concentrating photovoltaic’s (CPV) uses lenses and mirrors to focus the sun’s energy. This technology includes both a low-concentration approach, which increases the sun’s magnification by between 2 and 100 times, and a high concentration approach, which can increase the magnification by hundreds of suns when the PV efficiency exceeds 40%. CPV uses less photovoltaic material and increases performance, hopefully enough to offset any additional costs.

Concentrating Photovoltaics and Thermal (CPVT) is another technology; this produces both electricity and thermal heat in the same module. Thermal energy itself is a benefit from the sun, and other plants have a design of a solar power tower in which the mirrors focus sunlight on a heat receiver at the top that collects the heat and transfers it to piping inside the tower where is it circulated and used to make electricity. The design minimizes the field of piping to the vertical tower height to a few hundred meters and can reach temperatures in excess of 1000 degrees.While currently there are very few commercially operating tower installations, based on announcements, this technology may grow rapidly.

The Solar Two tower in California is an example of this technology and has the capability to produce 10 megawatts of power. Because of its success, Solar Tres is being built in Spain; this will be three times larger than the Solar Two plant and have a capacity of 17 megawatts. As it is, Solar Two’s tower has been removed in 2009 to make way for a larger solar project. Another solar thermal technology is the parabolic trough. The SEGS plants in California utilize this technology and have a capacity of 33 megawatts each. Nevada Solar One is another very large CSP project with a capacity of 64 megawatts, using Flabeg AG troughs made in Germany.

When we look into photovoltaic cell technology and the materials used, throughout the world crystalline silicon has been used as the light-absorbing semiconductor in most solar cells, even though it is a relatively poor absorber of light and requires a considerable thickness of material. Nevertheless, it has proved convenient because it yields stable solar cells with good efficiencies. There are two types of crystalline silicon are used in the industry. The first is mono crystalline, produced by slicing wafers from a high-purity single crystal. The second is multi crystalline silicon, made by sawing a cast block of silicon first into bars and then wafers. Most efficient production cells use mono crystalline c-Si with laser grooved, buried grid contacts for maximum light absorption and current collection. The main trend in crystalline silicon cell manufacture is toward multicrystalline technology. And for both mono- and multicrystalline Si, a semiconductor homo junction is formed by diffusing phosphorus into the top surface of the boron doped (p-type) Si wafer. Screen-printed contacts are applied to the front and rear of the cell, with the front contact pattern specially designed to allow maximum light exposure of the Si material with minimum electrical (resistive) losses in the cell. Crystalline silicon cell technology forms about 90% of solar cell demand. The balance comes from thin film technologies. Approximately 45% of the cost of a silicon cell solar module is driven by the cost of the silicon wafer, a further 35% is driven by the materials required to assemble the solar module.