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Photovoltaic devices convert light energy directly into electrical energy, and the primary objective of their use is the harvesting of light energy from the sun. The photovoltaic devices are silent when they operate and have no mechanical movement associated with their function. They operate under illumination and produce an electrical current that can be directly consumed or stored by chemical (batteries, hydrogen, etc.) or mechanical means (flywheels). The current conversion of power from sunlight into electrical power is not highly efficient; however, improvements are being made all the time. Aside from the very occasional solar eclipse, the sun is a reliable source of energy that the human race can depend on for the next five billion years.
The level of energy consumption by the humans on the planet in 2004 was approximately 15 terawatts (TW), with everything included. Most of this energy (87%) was derived from fossil-fuel sources. Continuous industrialization of developing countries, growth in human population, and a general increase in human welfare is projected to increase the demands for energy in the future by a large proportion. By the year 2050, the anticipated level of energy consumption by humans is 28â35 TW, which is a challenge we currently cannot meet with the sources of energy available. The global economy today is based on fossil fuel (coal, oil, and, gas) and, as a resource, is generally accepted to follow the Hubbert peak theory that, in brief, claims the rate of petroleum production follows a bell-shaped curve. The point at which the global demand for petroleum exceeds the rate of production is termed âpeak oil.â This point in time is when the global economy is predicted to collapse with more or less disastrous consequences. Depending on who you ask, peak-oil production may already have been reached or is imminent. The Hubbert peak theory is based on the fact that the resources are finite and that the rate of production to a rough approximation follows the rate of discovery with a time lag. For any resource, the rate of discovery is small to begin with followed by an increase to a certain maximum and then finally a decrease.
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