Changes

A more recent development in the use of direct sunlight is for the generation of electricity. Two different processes have been developed for this purpose: a thermal conversion process and a photovoltaic (PV) conversion process.

A more recent development in the use of direct sunlight is for the generation of electricity. Two different processes have been developed for this purpose: a thermal conversion process and a photovoltaic (PV) conversion process.

The solar thermal conversion process employs a large field of heliostats (two-axis movable mounted mirrors) that track the sun and reflect sunlight into a central receiver at the top of a solar tower. Water in the receiver is converted to steam that operates a turbine generator on the ground, producing electric power. The first experimental electric power plant using this technology (Solar One, near Barstow, California) was shut down in the late 1980s. A second, larger, and more advanced plant, Solar Two, started to operate in 1996 but was shut down in 1999 because of lack of funding. No other plants using this technology are now in operation. The economic viability of this electricity-generation process remains to be proven.

The solar thermal conversion process employs a large field of heliostats (two-axis movable mounted mirrors) that track the sun and reflect sunlight into a central receiver at the top of a solar tower. Water in the receiver is converted to steam that operates a turbine generator on the ground, producing electric power. The first experimental electric power plant using this technology ([http://wikipedia:The_Solar_Project| Solar One, near Barstow, California]) was shut down in the late 1980s. A second, larger, and more advanced plant, Solar Two, started to operate in 1996 but was shut down in 1999 because of lack of funding. As of 2005, no other plants using this technology are now in operation. The economic viability of this electricity-generation process remains to be proven.

The PV conversion process uses solar cells—solid-state semiconductor devices that convert sunlight directly into electricity, silently and without pollution. The PV process is the simplest, most dependable technology to harness the power of the sun. Solar cells or solar modules are easy to install and, as a result of their simplicity, require minimal maintenance.

The [http://science.howstuffworks.com/environmental/energy/solar-cell1.htm| PV conversion process] uses solar cells—solid-state semiconductor devices that convert sunlight directly into electricity, silently and without pollution. The PV process is the simplest, most dependable technology to harness the power of the sun. Solar cells or solar modules are easy to install and, as a result of their simplicity, require minimal maintenance.

Solar PV systems are successfully used today to generate electricity at a small scale in many countries and for many purposes. They are in particular demand where only modest amounts of power are required and in areas remote from electric power plants and without access to electricity grids: highway signs, rural water-pumping stations, remotely located communities and dwellings, space vehicles, and marine or air navigation beacons.

Solar PV systems are successfully used today to generate electricity at a small scale in many countries and for many purposes. They are in particular demand where only modest amounts of power are required and in areas remote from electric power plants and without access to electricity grids: highway signs, rural water-pumping stations, remotely located communities and dwellings, space vehicles, and marine or air navigation beacons.

In the last 35 years, the worldwide small-scale generation of electricity by PV devices has increased substantially, particularly in the last few years, from less than 5 MW/yr in the late 1970s to about 130 MW/yr in the late 1990s; but this is still a minute percentage of the total world generation of electricity.

In the last 35 years, the worldwide small-scale generation of electricity by PV devices has increased substantially, particularly in the last few years, from less than 5 milliwatts per year in the late 1970s to about 130 milliwatts per year in the late 1990s; but this is still a minute percentage of the total world generation of electricity.

Several economic, geographic, and technical barriers still need to be overcome for large-scale PV electricity generation to achieve significant penetration in the world electricity market.

Several economic, geographic, and technical barriers still need to be overcome for large-scale PV electricity generation to achieve significant penetration in the world electricity market.

A scheme suggested to overcome these geographic limitations is the placement of large arrays of solar cells in synchronous-orbit satellites 30,000–35,000 km above the Earth. The PV arrays would convert the high solar radiation to electricity, which in turn would be fed to a microwave generation system for transmission to Earth. The microwave transmissions would be collected by large receiving antenna systems and converted to alternating or direct current electricity. The possibility of placing one of these solar power satellites in orbit has received no serious consideration.

A scheme suggested to overcome these geographic limitations is the placement of large arrays of solar cells in synchronous-orbit satellites 30,000–35,000 km above the Earth. The PV arrays would convert the high solar radiation to electricity, which in turn would be fed to a microwave generation system for transmission to Earth. The microwave transmissions would be collected by large receiving antenna systems and converted to alternating or direct current electricity. The possibility of placing one of these solar power satellites in orbit has received no serious consideration.