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The sun's radiaton delivers energy in abundance. Yet, technologies to harness that energy have been costly. However, with costs coming down and attractive incentives in many countries, solar provides great opportunities for developers, investors and consumers.
Green Rhino Energy assists solar project developers and investors over the entire lifecycle. We provide advice on regulatory frameworks, revenue forecast, site potential, pricing and project due diligence.
The energy in solar irradiation comes in the form of electromagnetic waves of a wide spectrum. Longer wavelengths have less energy (for instance infrared) than shorter ones such as visible light or UV.
The spectrum can be depicted in a graph, the spectral distribution, which shows the relative weights of individual wavelengths plotted over all wavelenghts, measured in W / m (wavelength).
The diagram displays the spectrum of a sun ray just outside the entry into the earth’s atmosphere. The peak of the spectrum is within the visible spectrum, but there are still significant amounts of shorter and longer wavelengths present.
Intensity and Energy
For the purpose of solar power, the most significant measures are the intensity and energy delivered – one measure at a point in time, the other over a period of time.
At a point in time
Over a period of Time
As sunlight is smoothly distributed over whole areas, a mere figure for intensity is never sufficient without knowledge of the orientation of the surface in question. Typically, the orientation of a surface is described by the zenith angle, the angle between the sunbeam and the normal of the area. If the surface area is not perpendicular to the sunbeam (i.e. zenith angle is not zero), a larger area is required to catch the same flow as the cross section of the sunbeam.
If I0 denotes the intensity on a surface with the sun in its zenith, the intensity, I, on an area where the sun is observed under the zenith angle θ (see figure) the intensity is reduced to
Modelling Solar Irradiation
With planetary movements, processes in the atmosphere and other effects, solar radiation on earth is an intermittent source of energy.
On the earth’s surface the peak solar intensity hovers around 1 kW/m² on a horizontal surface at sea level with the sun in its apex on a clear day. In general, the value will depend on the position of the sun, the clearness of the sky and the geometry of the surface.
Due to the complex nature of some of the processes, no theoretical calculations for irradiance is entirely accurate. Nevertheless, these models are helpful in understanding the main drivers as well as: