Direct irradiance on tilted surfaces

The horizontal surface in Figure 2.14 with the area Ahor receives the same radiant power as a smaller area As which is normal (perpendicular) to the incoming sunlight.

With

^dir,hor Edir,hor Ahor ^dir,s Edir,s As and

Figure 2.14 Irradiance on a Horizontal Area Ahor and an Area As Perpendicular to the Sunlight

it follows that:

dir,s

dir,hor

It becomes apparent that the direct normal or beam irradiance Edirs on a surface perpendicular to the path of the light is higher than the direct irradiance Edihor on a horizontal surface; this fact is taken into account when planning solar energy systems. Inclining the surface of the system increases the energy yield, especially at high latitudes with low solar height angles.

With ft-u from (2.24), the direct irradiance on a tilted surface is Edi dir,s

Edir,tilt cos Stilt

The direct irradiation of a tilted surface can be calculated directly from the direct irradiation on the horizontal surface:

cos Stilt sin /s

However, for low sun heights, small variations of the horizontal irradiance can cause unrealistically high irradiances on tilted surfaces. Therefore, it should always be checked that the calculated direct irradiance on a tilted plane is below a maximum threshold.

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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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