A solar cell or photovoltaic cell is a device that changes light energy into electricity. Photovoltaics are best known as a method for making electricity by using solar cells to change energy from the sun into a flow of electrons. The was first noticed by Alexandre-Edmond Becquerel in 1839. Practically all photovoltaic devices are some type of photodiode.
Solar cells can be used to power tools or to recharge a storage battery. The first actual request of photovoltaics was to power orbiting satellites and other spacecrafts, but today the most photovoltaic modules are used for grid connected power creation. In this case a tool called an inverter is required to convert the direct current to alternating current. Cells require protection from the environment and are usually packaged tightly behind a glass sheet. When more power is required than a single cell can give off, cells are electrically connected together to form photovoltaic modules, or solar panels. A single module is enough to power an emergency telephone, but for a house or a power station the modules must be arranged in multiples as arrays.
Solar cell
Solar cells have many applications. They have long been used in situations where electrical power from the grid is unavailable, such as in remote area power systems, Earth-orbiting satellites and space probes, consumer systems, e.g. handheld calculators or wrist watches, remote radiotelephones and water pumping applications. More recently, they are starting to be used in assemblies of solar modules connected to the electricity grid through an inverter, often in combination with net metering.
Solar cells are regarded as one of the key technologies towards a sustainable energy supply.
The first generation photovoltaic consists of a large-area, single layer p-n junction diode, which is capable of generating usable electrical energy from light sources with the wavelengths of sunlight. These cells are typically made using a silicon wafer. First generation photovoltaic cells (also known as silicon wafer-based solar cells) are the dominant technology in the commercial production of solar cells, accounting for more than 86% of the solar cell market.
The second generation of photovoltaic materials is based on the use of thin-film deposits of semiconductors. These devices were initially designed to be high-efficiency, multiple junction photovoltaic cells. Later, the advantage of using a thin-film of material was noted, reducing the mass of material required for cell design. This contributed to a prediction of greatly reduced costs for thin film solar cells. Currently (2007) there are different technologies/semiconductor materials under investigation or in mass production, such as amorphous silicon, poly-crystalline silicon, micro-crystalline silicon, cadmium telluride, copper indium selenide/sulfide. Typically, the efficiencies of thin-film solar cells are lower compared with silicon (wafer-based) solar cells, but manufacturing costs are also lower, so that a lower price in terms of $/watt of electrical output can be achieved. Another advantage of the reduced mass is that less support is needed when placing panels on rooftops and it allows fitting panels on light materials or flexible materials, even textiles. This allows for portable roll-up solar panels, which can fit in a backpack and be used to power cell phones or laptops in remote areas.
Third generation photovoltaics are very different from the other two, broadly defined as semiconductor devices which do not rely on a traditional p-n junction to separate photogenerated charge carriers. These new devices include photoelectrochemical cells, Polymer solar cells, and nanocrystal solar cells.
Companies working on third generation photovoltaics include "Xsunx, Konarka Technologies, Inc.", "Nanosolar" and "Nanosys". Research is also being done in this area by the USA's "National Renewable Energy Laboratory" (http://www.nrel.gov/).
Alternating current
An alternating current (AC) is an electric current of which magnitude and direction vary, unlike direct current, whose direction remains constant. This means that the direction of current flowing in a circuit is constantly being reversed back and forth. This is done with any type of AC voltage source.
The usual waveform of an AC power circuit is a sine wave, because this leads to the most efficient transmission of energy. However, in certain applications different waveforms are used, such as triangular or square waves. Inexpensive power inverters produce a square wave with a pause between the change in direction.
When one speaks of alternating current one mostly refers to the form in which electricity is delivered to businesses and residences. The AC comes from a power plant. The direction of the electricity switches back 60 times every second (or 50 times in some parts of the world). This happens so fast that a light bulb does not stop glowing.
Both audio and radio signals carried on electrical wire are also examples of alternating current. In these applications, an important goal is often the recovery of information encoded (or modulated) onto the AC signal.
Nikola Tesla experimented with electrical resonance and studied various lighting systems. He invented an induction motor, new types of generators and transformers, and a system of alternating current power transmission.
William Stanley, Jr. designed one of the first practical devices to transfer AC power efficiently between isolated circuits. Using pairs of coils wound on a common iron core, his design, called an induction coil, was an early precursor of the modern transformer. The system used today was devised in the late nineteenth century, largely by Nikola Tesla. Contributions were also made by George Westinghouse, Lucien Gaulard, John Dixon Gibbs,Wilhelm Siemens and Oliver Shallenger. AC systems overcame the limitations of the direct current system used by Thomas Edison to distribute electricity efficiently over long distances.
The Mill Creek hydroelectric plant was built near Redlands, California in 1893. Designed by Almirian Decker, it used 10,000 volt three-phase electric power which eventually became the standard method for power stations throughout the world.
AC power is cheaper and easier to make electronic devices. The power switches for AC power are also less expensive to make. It is less expensive than DC because you can increase and decrease the current very easily. AC can use high voltages with smaller current to reduce losses when you send power. AC reduces the heating in the wires. DC power could be sent, but it would lose a lot of energy and you would have to put more work in it to send it great distances. AC transformers are installed everywhere, including atop utility poles and underground. Alternating current works by switching the current many times back and forth constantly while it goes back to the source it came from.
Direct current
Direct current (DC or ""continuous current"") is the flow of electricity in a single direction, from the positive to the negative terminals (potential, poles).
The direct current always flow in the same direction, distinguishing it from the alternating current (AC). Direct current used to be called "Galvanic current".
Batteries are some of the main sources of direct current (DC), but many other sources also exist such as bridge rectifiers in power supply, solar panels, etc.
Typically, the current goes through a conductor and other things that can carry DC. DC is also sent through a vacuum as in electron beams or ion beams.
The first commercial electric power transmission was developed by Thomas Edison in the late nineteenth century using direct current. Today nearly all electric power distribution uses alternating current because of the advantages with transformers and transmission. High-voltage direct current is often used for transporting electricity to places far away.