Solar radiation, often dubbed the solar resource or just sunlight, is a general term for the electromagnetic radiation emitted through the sun. Solar radiation deserve to be captured and turned into useful forms that, such together heat and electricity, using a variety of technologies. However, the technological feasibility and also economical operation of these technologies at a details location depends on the available solar resource.

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Basic Principles

Every location on earth receives sunlight at least component of the year. The quantity of solar radiation the reaches any one point out on the Earth"s surface ar varies follow to:

Geographic locationTime of daySeasonLocal landscapeLocal weather.

Because the earth is round, the sunlight strikes the surface ar at different angles, ranging from 0° (just above the horizon) to 90° (directly overhead). When the sun"s rays are vertical, the Earth"s surface gets every the possible. The an ext slanted the sun"s beam are, the longer they travel through the atmosphere, becoming much more scattered and diffuse. Due to the fact that the earth is round, the frigid polar areas never gain a high sun, and also because the the tilted axis of rotation, these locations receive no sun at every during component of the year.

The planet revolves roughly the sunlight in one elliptical orbit and also is closer come the sun during part of the year. When the sun is nearer the Earth, the Earth"s surface receives a little much more solar The planet is nearer the sun when it is summer in the southern hemisphere and winter in the north hemisphere. However, the existence of large oceans moderates the name is summers and colder winters one would intend to check out in the southern hemisphere together a result of this difference.

The 23.5° tilt in the Earth"s axis of rotation is a more far-reaching factor in determining the quantity of sunshine striking the planet at a specific location. Tilting outcomes in longer days in the northern hemisphere from the feather (vernal) equinox to the autumn (autumnal) equinox and also longer work in the southern hemisphere during the other 6 months. Days and nights room both exactly 12 hrs long ~ above the equinoxes, i beg your pardon occur annually on or approximately March 23 and also September 22.

Countries such as the joined States, which lie in the center latitudes, receive an ext solar in the summer no only since days space longer, but likewise because the sun is practically overhead. The sun"s rays are far an ext slanted throughout the shorter days the the winter months. Cities such together Denver, Colorado, (near 40° latitude) receive practically three times an ext solar in June than they execute in December.

The rotation of the planet is also responsible for hourly variations in sunlight. In the beforehand morning and late afternoon, the sun is low in the sky. Its beam travel more through the environment than in ~ noon, as soon as the sunlight is at its highest possible point. On a clean day, the best amount of solar reaches a solar collector roughly solar noon.

Diffuse and Direct Solar Radiation

As sunlight passes through the atmosphere, some of it is absorbed, scattered, and reflected by:

Air moleculesWater vaporCloudsDustPollutantsForest firesVolcanoes.

This is called diffuse solar radiation. The solar radiation the reaches the Earth"s surface ar without being diffused is called direct beam solar radiation. The amount of the diffuse and also direct solar radiation is called global solar radiation. Atmospheric conditions can reduce direct beam radiation by 10% top top clear, dried days and also by 100% during thick, cloudy days.


Scientists measure up the quantity of sunlight falling on specific locations at various times of the year. Lock then calculation the lot of sunlight falling on areas at the same latitude with comparable climates. Dimensions of solar are frequently expressed as full radiation on a horizontal surface,or as total radiation on a surface ar tracking the sun.

Radiation data for solar electric (photovoltaic) systems are frequently represented together kilowatt-hours every square meter (kWh/m2). Straight estimates that solar may likewise be to express as watt per square meter (W/m2).

Radiation data because that solar water heating and space heating systems space usually stood for in brother thermal systems per square foot (Btu/ft2).


The solar source across the United claims is ample because that photovoltaic (PV) systems due to the fact that they use both direct and scattered sunlight. Other technologies might be more limited. However, the amount of power produced by any type of solar an innovation at a certain site relies on how much the the sun"s get it. Thus, solar technologies role most properly in the southwestern unified States, i m sorry receives the biggest amount the solar

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Solar source Maps

View solar resource maps for both PV and also concentrating solar-thermal power.

Additional Information

Learn more about just how solar works and also the solar office"s photovoltaics and concentrating solar-thermal power programs.