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]
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]
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