AS rS

ASE r SE

Earth

Earth

Figure 2.2 The Radiant Power through the Surface of a Sphere with Radius rSE is the Same as through the Surface of the Sun

This determines the extraterrestrial irradiance experienced at Earth's orbital distance from the sun. However, the distance between the sun and Earth is not constant throughout the year. It varies between 1.47 • 108 km and 1.52 • 108 km. This causes a variation in the irradiance, Ee, of between 1325 W/m2 and 1420 W/m2. The average value, called the solar constant, E0, is:

This value can be measured outside the Earth's atmosphere on a surface perpendicular to the solar radiation. The symbol I0 is also used for the solar constant.

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Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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