Energy from the Sun

The Earth receives 174 petawatts (PW) of solar radiation at the upper atmosphere. While traveling through the atmosphere, 6% of the incoming solar radiation (insolation) is reflected and 16% is absorbed. Average atmospheric conditions (clouds, dust, pollutants) further reduce insolation by 20% through reflection and 3% through absorption. The absorption of solar energy by atmospheric convection (sensible heat transport) and by the evaporation and condensation of water vapor (latent heat transport) drive the winds and the water cycle.[4]
Atmospheric conditions not only reduce the quantity of insolation reaching the Earth's surface but also affect the quality of insolation by diffusing approximately 20% of the incoming light and altering its spectrum.[5] After passing through the Earth's atmosphere approximately half the insolation is in the visible electromagnetic spectrum with the other half mostly in the infrared spectrum, and a small part of ultraviolet radiation.[6] Upon reaching the surface, insolation is absorbed by the oceans, earth and plants. The energy captured in the oceans drives the thermohaline cycle. As such, solar energy is ultimately responsible for temperature driven ocean currents such as the thermohaline cycle and wind driven currents such as the Gulf Stream. The energy absorbed by the earth in conjunction with that recycled by the Greenhouse effect warms the surface to an average temperature of approximately 14°C.[7] The solar energy captured by plants and other phototrophs is converted to chemical energy via photosynthesis. All the food we eat, wood we build with and fossil fuels we use are products of photosynthesis.[8]
The flows and stores of solar energy are vast in comparison to human energy needs.
The total solar energy available to the earth is approximately 3850 zettajoules (ZJ) per year.[9]
Oceans absorb approximately 285 ZJ of solar energy per year.
Winds can theoretically supply 6 ZJ of energy per year.[10]
Biomass captures approximately 1.8 ZJ of solar energy per year.[11][9]
Worldwide energy consumption was 0.471 ZJ in 2004.[12]
The map on the right (top) shows how solar radiation at the top of the earth's atmosphere varies with latitude. The bottom map shows annual average ground level insolation. For example, in North America the average insolation at ground level over an entire year (including nights and periods of cloudy weather) lies between 125 and 375 W/m² (3 to 9 kWh/m²/day).[13] At present, photovoltaic panels typically convert about 15% of incident sunlight into electricity; therefore, a solar panel in the contiguous United States on average delivers 19 to 56 W/m² or 0.45 - 1.35 kWh/m²/day.[14]

Solar power

Solar energy (also knows as solar radiation or insolation) is energy from the sun. This energy, in the form of heat and light, supports all life on Earth, drives the Earth's climate and weather and is predominately responsible for the class of resources collectively known as renewable energy.

Solar energy also broadly describes technologies that utilize sunlight. The applications are diverse and date back millennia. The Greeks, Native Americans and Chinese warmed their buildings by orienting them toward the sun. In Europe, farmers used elaborate field orientation and thermal mass to increase crop yields during the Little Ice Age. Modern solar technologies continue to harness the sun to provide water heating, daylighting and even flight.[1][2]

Solar power generally describes technologies that convert sunlight into electricity and in some cases thermal or mechanical power. In 1866, the French engineer Auguste Mouchout successfully powered a steam engine with sunlight. This is the first known example of a solar powered mechanical device. Over the next 50 years inventors such as John Ericsson, Charles Tellier and Frank Shuman developed solar powered devices for irrigation, refrigeration and locomotion. The progeny of these early developments are concentrating solar power plants.[2]

The modern age of solar power arrived in 1954 when researchers at Bell Laboratories developed a photovoltaic cell capable of effectively converting light into electricity. This breakthrough marked a fundamental change in how power is generated. Since then solar cells efficiencies have improved from 6% to 15% with experimental cells reaching efficiencies over 40%. Prices on the other hand have fallen from $300 per watt to less than $3 per watt.[3]

The utilization of solar energy and solar power spans from traditional technologies that provide food, heat and light to electricity which is uniquely modern. The diversity of form and long history of solar energy are manifest in a wide variety of applications.