The sun is the source of almost all energy (except nuclear) used on Earth. Wind power, tidal energy, fossil fuels and hydroelectric plants all depend on the powerful engine that drives our solar system.

The sun generates approximately 3.8 x 10 23 kilowatts, an almost inconceivable flow of energy. However 99% of the sun's rays miss the Earth completely.

What remains for us is still however substantial as on a typical sunny day, each square meter of Earth, facing the sun, receives about one kilowatt of energy. A square plot of land 52-kilometer on each side receives solar energy equivalent to the total capacity of all US power plants.

Photovoltaics

Photovoltaic devices collect solar energy and convert it directly into electricity. Technologically, photovoltaic power systems are capable of providing power for any purpose, large or small, remote or urban. However, the cost of complete systems capable of producing reliable power 24 hours per day still is above that of utility power on a price per kilowatt basis.

The price of components for PV systems continues to drop, and the market has increased dramatically in recent years. PV power systems now compete in markets, which were previously the unchallenged domain of disposable batteries, diesel, gasoline, wind, and thermoelectric generators.

In some certain cases, a PV system can make more sense than the utility power grid.

Apart from falling prices, reliability, longevity, simplicity, low maintenance, silence and no pollution often make PV the best choice.

How It Works

The photovoltaic cell, commonly called a solar cell, is the basic unit of the PV power system. These cells convert light energy to electrical energy.

Presently virtually all-commercial solar cells are made from silicon.

A photovoltaic module is a group of solar cells electrically and mechanically connected and sealed in a weatherproof package. A module is the smallest photovoltaic unit that can feasibly be installed outdoors.

An array consists of the interconnected modules mounted on support structures.

Electrical Characteristics

The electrical output of a solar electric installation differs in some ways from other DC sources. The power and current produced by each cell is directly proportional to its illuminated area and the intensity of the sunlight striking the surface. Voltage, on the other hand, is relatively unaffected by cell area or illumination level.

The output of a current produced by a module increases in proportion to illumination.

When connected to a battery, voltage will be "clamped" to the battery's voltage and its current output will be determined by the point on the I-V curve where the voltage vector intersects.

Applications

PV power is at work all over the world today.