Solar Cells - An Intro and Overview

To understand the field of solar energy, one must begin with solar cells (otherwise known as photovoltaic cells.) Basically, these are devices that convert light directly into electricity. The photovoltaics market is generally invested in the manufacture of cells made of wafer-like pieces of silicon. Typically, many individual cells are assembled together in frames, forming a solar array. There are currently three types of solar cell commonly available for practical residential and personal use.

The cheapest and least efficient type of solar cell is known as amorphous silicon. This is a form of silicon that can be applied to a material (usually glass) in a thin film. It is therefore much cheaper to manufacture. A strong disadvantage of this material is that it lacks the well-ordered crystalline pattern of other forms of silicon, and features a large drop-off in conversion efficiency.

The highest efficiency comes from monocrystalline silicon cells, constructed of single crystals cut from large cylindrical ingots, resulting in circular wafer-like cells. This rounded shape comes with one disadvantage: multiple cells can't be framed snugly together, resulting in some wasted space. This raises some contention as to whether or not, when framed together in a larger arrays, these cells produce notably more electricity than the polycrystalline cell variety. Panels made with monocrystalline cells also come with a higher price tag.

Based on sales, the most common type of photovoltaic cell is polycrystalline. These are made from multiple silicon crystals and cut into square wafers to be mounted together in an array. They are cheaper and easier to manufacture than monocrystalline cells, but slightly less efficient.

Solar power is one of the fastest growing fields in energy production, and new developments are being made all the time. R&D labs around the world are developing cells boasting higher conversion rates. Panels are being developed made from cheaper forms of silicon, and a process has even been developed to recycle or "re-purpose" suitable material from scrapped semiconductor wafers. The AIST, a Japanese research facility, has been able to develop transparent panels that convert UV light into electricity while allowing visible light to pass through. Such a material could one day be used to replace windows. Bottom line, solar energy is a massive field, and the small, unassuming solar cell has the potential to carry the world into a cleaner and easier future.

Edmund E. Taylor has researched and writes on a number of topics including solar energy, the green movement, renewable resources and recycling. His background is in teaching and higher education. For more of Edmund's articles on green energy, please visit PV Power, a supplier of residential and commercial solar power information.

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.

Deevan Solar Panel Hot Water Heating.

Concentrated Solar Power California.