Insolation

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Insolation

Insolation is a measure of solar radiation energy received on a given surface area in a given time.

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Insolation is a measure of solar radiation energy received on a given surface area in a given time. It is commonly expressed as average irradiance

Irradiance

Irradiance, radiant emittance, and radiant exitance are radiometry terms for the power of electromagnetic radiation at a surface, per unit area....
in watts per square meter (W/m²) or kilowatt-hours per square meter per day (kW·h/(m²·day)) (or hours/day). In the case of photovoltaics

Photovoltaics

Photovoltaics is the field of technology and research related to the application of solar cells for energy by converting sunlight directly into electricity....
it is commonly measured as kWh/(kW_p·y) (kilowatt hours per year per kilowatt peak rating).

The given surface may be a planet, or a terrestrial object inside the atmosphere of a planet, or any object exposed to solar rays outside of an atmosphere, including spacecraft

Spacecraft

A spacecraft is a Craft or machine designed for spaceflight. On a sub-orbital spaceflight, a spacecraft enters outer space then returns to the Earth....
. Some of the solar radiation will be absorbed, causing radiant heating of the object, and the remainder will be reflected. The proportion of radiation reflected or absorbed depends on the object's reflectivity

Reflectivity

In photometry and heat transfer, reflectivity is the fraction of incident radiation Reflection by a surface. In general it must be treated as a directional property that is a function of the reflected direction, the incident direction, and the incident wavelength....
or albedo

Albedo

The albedo of an object is the extent to which it diffusely reflects light from the Sun. It is therefore a more specific form of the term reflectivity....
, respectively.

Projection effect

The insolation into a surface is largest when the surface directly faces the Sun. As the angle increases between the direction normal to the surface and the direction of the rays of sunlight, the insolation is reduced in proportion to the cosine of the angle. This is known in optics as Lambert's cosine law
Lambert's cosine law

Lambert's cosine law in optics says that the radiant intensity observed from a "Lambertian" surface is directly proportional to the cosine of the angle ? between the observer's line of sight and the surface normal....
. This 'projection effect' is the main reason why the polar region

Polar region

Earth polar regions are the areas of the globe surrounding the geographical pole also known as Geographical zone. The North Pole and South Pole being the centers, these regions are dominated by the polar ice caps, resting respectively on the Arctic Ocean and the continent of Antarctica....
s are much colder than equatorial regions on Earth. On an annual average the poles receive less insolation than does the equator, because at the poles the Earth's surface is angled away from the Sun.

Earth's insolation

Direct insolation

Direct insolation is the solar irradiance measured at a given location on Earth with a surface element perpendicular to the Sun's rays, excluding diffuse insolation ....
is the solar irradiance

Irradiance

Irradiance, radiant emittance, and radiant exitance are radiometry terms for the power of electromagnetic radiation at a surface, per unit area....
measured at a given location on Earth with a surface element perpendicular to the Sun's rays, excluding diffuse insolation

Diffuse insolation

Diffuse insolation is the solar radiation that is scattered or reflected by atmospheric components to the earth's surface.External links...
(the solar radiation that is scattered or reflected by atmospheric components in the sky). Direct insolation is equal to the solar constant minus the atmospheric losses due to absorption

Absorption (electromagnetic radiation)

In physics, absorption of electromagnetic radiation is the way by which the energy of a photon is taken up by matter, typically the electrons of an atom....
and scattering. While the solar constant varies with the Earth-Sun distance

Earth's orbit

In astronomy, The Earth's Orbit involves the Earth orbiting the Sun at an average distance of about 150 million kilometers every 365.242199 mean solar days ....
and solar cycle

Solar cycle

The solar cycle, or the solar magnetic activity cycle, is the main source of periodic solar variation driving variations in space weather....
s, the losses depend on the time of day (length of light's path through the atmosphere depending on the Solar elevation angle

Solar elevation angle

The solar elevation angle is the elevation angle of the sun. That is, the angle between the directionof the sun and the horizon. It can be calculated, to a good approximation, using the...
), cloud cover

Cloud cover

Cloud cover refers to the fraction of the sky obscured by clouds when observed from a particular location....
, moisture

Moisture

Moisture generally refers to the presence of water, often in trace amounts.The moisture content is often an important aspect of various Food including cheese and many dried goods such as tea where excess moisture can promote Bacteria, Bacterial decay, Mold, or Rot over time....
content, and other impurities.

Over the course of a year the average solar radiation arriving at the top of the Earth's atmosphere is roughly 1,366 watt

WATT

WATT is a radio station broadcasting a News radio-Talk radio-Sports radio format. Licensed to Cadillac, Michigan, it first began broadcasting in 1945....
s per square meter

Square metre

The square metre is the SI derived unit of area, with symbol m?. It is defined as the area of a square whose sides measure exactly one metre....
(see solar constant). The radiant power is distributed across the entire electromagnetic spectrum

Electromagnetic spectrum

The electromagnetic spectrum is the range of all possible electromagnetic radiation frequencies. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation from that particular object....
, although most of the power is in the visible light portion of the spectrum. The Sun's rays are attenuated

Attenuation

In physics, attenuation is the gradual loss in intensity of any kind of flux through a medium. For instance, sunlight is attenuated by dark glasses, and X-rays are attenuated by lead....
as they pass though the atmosphere

Atmosphere

An atmosphere is a layer of gases that may surround a material body of sufficient mass, by the gravity of the body, and are retained for a longer duration if gravity is high and the atmosphere's temperature is low....
, thus reducing the insolation at the Earth's surface to approximately 1,000 watts per square meter for a surface perpendicular to the Sun's rays at sea level on a clear day.

The actual figure varies with the Sun angle at different times of year, according to the distance the sunlight

Sunlight

Sunlight, in the broad sense, is the total spectroscopy of the electromagnetic radiation given off by the Sun. On Earth, sunlight is Filter ed through the Earth's atmosphere, and the solar radiation is obvious as daylight when the Sun is above the horizon....
travels through the air

AIR

Air is the part of Earth's atmosphere that humans breath and as such Air .Air may also refer to:...
, and depending on the extent of atmospheric haze and cloud cover. Ignoring clouds, the average insolation for the Earth is approximately 250 watts per square meter (6 (kW·h/m²)/day), taking into account the lower radiation intensity in early morning and evening, and its near-absence at night.

The insolation of the sun can also be expressed in Suns, where one Sun equals 1,000 W/m² at the point of arrival, with kWh/(m²·day) displayed as hours/day. This makes calculating the output of a Solar panel at a particular location a matter of multiplying the rating of the panel times the expected number of hours/day of sun (at 1,000 W/m²). One Sun is a unit of power flux

Flux

In the various subfields of physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks.*In the study of transport phenomena , flux is defined as the amount that flows through a unit area per unit time....
, not a standard value for actual insolation. Sometimes this unit is referred to as a Sol, not to be confused with a sol, meaning one solar day on, for example, a different planet, such as Mars.

Applications

In spacecraft

Spacecraft

A spacecraft is a Craft or machine designed for spaceflight. On a sub-orbital spaceflight, a spacecraft enters outer space then returns to the Earth....
design and planetology, it is the primary variable affecting equilibrium

Thermodynamic equilibrium

In thermodynamics, a thermodynamics#Thermodynamic system is said to be in thermodynamic equilibrium when it is in thermal equilibrium, mechanical equilibrium, and chemical equilibrium....
temperature

Temperature

In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater temperature....
and global climate.

In construction, insolation is an important consideration when designing a building for a particular climate. It is one of the most important climate variables for human comfort and building energy efficiency.

The projection effect can be used in architecture

Architecture

The term architecture can refer to a process, a profession or documentation.As a process, architecture is the activity of designing and construction buildings and other physical structures by a person or a computer, primarily to provide shelter....
to design buildings that are cool in summer and warm in winter, by providing large vertical windows on the equator-facing side of the building (the south face in the northern hemisphere

Northern Hemisphere

The Northern Hemisphere is the half of a planet that is north of the equator?the word sphere literally means 'half sphere'. It is also that half of the celestial sphere north of the celestial equator....
, or the north face in the southern hemisphere

Southern Hemisphere

The Southern Hemisphere is the half of a planet that is south of the equator?the word sphere literally means 'half ball'. It is also that half of the celestial sphere south of the celestial equator....
): this maximizes insolation in the winter months when the Sun is low in the sky, and minimizes it in the summer when the noonday Sun is high in the sky. (The Sun's north/south path

Analemma

In astronomy, an analemma is a curve representing the angular offset of a celestial body from its mean position on the celestial sphere as viewed from another celestial body ....
through the sky spans 47 degrees through the year).

Insolation figures are used as an input to worksheets to size solar power systems

Solar power

Solar energy is the radiant light and heat from the Sun that has been harnessed by humans since ancient history using a range of ever-evolving technologies....
for the location where they will be installed. The figures can be obtained from an insolation map or by city or region from insolation tables that were generated with historical data over the last 30-50 years. Photovoltaic panels are rated under standard conditions to determine the Wp rating (watts peak

Solar cell

A solar cell or photovoltaic cell is a device that converts sunlight directly into electricity by the photovoltaic effect. Sometimes the term solar cell is reserved for devices intended specifically to capture energy from sunlight, while the term photovoltaic cell is used when the source is unspecified....
), which can then be used with the insolation of a region to determine the expected output, along with other factors such as tilt, tracking and shading (which can be included to create the installed Wp rating). Insolation values range from 800 to 950 kWh/(kWp·y) in Norway

Norway

Norway , officially the Kingdom of Norway, is a constitutional monarchy in Northern Europe that occupies the western portion of the Scandinavian Peninsula....
to up to 2,900 in Australia

Australia

Australia, officially the Commonwealth of Australia, is a country in the southern hemisphere comprising the Australia of the world's smallest continent, the major island of Tasmania, and numerous list of islands of Australia in the Indian Ocean and Pacific Oceans....
.

In the fields of civil engineering

Civil engineering

Civil engineering is a Professional Engineer discipline that deals with the design, construction and maintenance of the physical and naturally built environment, including works such as bridges, roads, canals, dams and buildings....
and hydrology

Hydrology

Hydrology is the study of the movement, distribution, and quality of water throughout the Earth, and thus addresses both the hydrologic cycle and water resources....
, numerical models of snowmelt runoff use observations of insolation. This permits estimation of the rate at which water is released from a melting snowpack. Field measurement is accomplished using a pyranometer

Pyranometer

A pyranometer is a type of actinometer used to measure broadband solar irradiance on a planar surface and is a sensor that is designed to measure the solar radiation flux density from a field of view of 180 degrees....
.

Conversion factor (multiply top row by factor to obtain side column)
	W/m²	kW·h/(m²·day)	sun hours/day	kWh/(m²·y)	kWh/(kWp·y)
W/m²	1	41.66666	41.66666	0.1140796	0.1521061
kW·h/(m²·day)	0.024	1	1	0.0027379	0.0036505
sun hours/day	0.024	1	1	0.0027379	0.0036505
kWh/(m²·y)	8.765813	365.2422	365.2422	1	1.333333
kWh/(kWp·y)	6.574360	273.9316	273.9316	0.75	1

External links

including interannual variability

Insolation

Projection effect

Earth's insolation

Applications

See also

External links