Every second the Sun converts 700 million tons of Hydrogen into Helium, reaching temperatures above 15 million degrees.
In this process of nuclear fusion, an energy of 4×1023 kJ is generated every second… more than the energy consumed by mankind from its origin to the present day. However, as long as we do not build a Dyson sphere – and it does not seem that this will happen in the short term – only a small fraction of this energy will reach the Earth.
The energy received from the Sun varies each day, among other factors due to the elliptical orbit of the Earth, although by convention we say that about 1.400 W/m2 reach the atmosphere: this is the solar constant.
However, in the atmosphere there are a series of absorptions and reflections -such as UVC in ozone- that cause only about half of this amount to reach the earth’s surface.
In the graph we can see the spectrum of the radiation reaching the outer atmosphere (yellow) and the Earth’s surface (red), compared to that of the black body at 5.250C.
We see in the graph above that most of the energy we receive from the Sun is in the 300 to 1.300 nm area of the electromagnetic spectrum, which is doubly interesting:
. The visible range is between 400 and 800nm
. The working range of the photovoltaic technology is between 400 and 1.200 nm.
In other words, the energy we receive from the sun has great potential for saving energy through natural lighting systems and producing electricity with photovoltaic systems.
In fact, in recent decades, mankind has developed and reduced the cost of technologies that make it possible to transform 20% of the energy received from the sun into electricity.
Taking into account that a building in our country receives energy from the Sun of about 2.000 kWh/m2 per year and that its consumption is around 200 kWh/m2… we wonder if we are not doing something wrong: the implementation of a good daylighting system could reduce the energy needs of a building by about 20 kWh/m2, savings that could reach more than 100 kWh/m2 if combined with a photovoltaic system.
Author
Director Artesolar Daylighting
Physicist and Electronic Engineer. WELL AP.
Professionally involved in energy efficiency, sustainability and wellness in buildings, with 20 years of experience in photovoltaics, daylighting and BESS.
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