Sunlight is the energy source that drives our planet. Each and every thing on this planet is a receptor of sunlight. Each species uses sunlight in its own way. Plants cannot move around in search for food and hence they rely on sunlight for cooking their own food. Without the UV rays in the sunlight, humans could suffer from a disease called rickets, because it is these rays that are necessary for human bodies to produce Vitamin D which in turn allows our bodies to absorb calcium. But there’s another way we can harness this energy. It’s by converting sunlight directly into electricity or by using its thermal energy to convert water into steam, which is indirectly converted into electricity.
On an average, earth receives 164 Watts per square meter for an entire day (24 hours). Multiply that with the surface area of the earth and it receives a whooping 84 Terawatts of Power. (Earth is called Terra in Latin, different from ‘tera’ watts.) Here’s a picture of the dynamics of solar radiation reaching our planet.
(Image: University of Oregon)
How do we collect sunlight?
We collect sunlight (solar energy) with solar panels. Solar panels are a collection or an array of photovoltaic modules. (photo = Greek phōs = “light” and “volt” = the unit of electro-motive force = last name of the Italian physicist Alessandro Volta) Photovoltaic modules are a collection of solar cells.
When particles of light aka quanta of light or photons hit these panels, they are absorbed by the semiconducting material of the panel. Example of a semiconducting material is silicon. A solar cell is made up of two types of semiconducting materials – p-type (more positive charges/holes) and n-type (more negative charges/electrons). They are sandwiched together to form a p-n junction and due to such a configuration, current flows only in one direction.
When I say photons hit this material, it means that the photons kick the electrons out of the n-type layer. The photons kick them out of their usual place and let them loose. The kicked electrons are all excited now and start moving into the p-type layer. But now they want to go back home, so they return back in a loop. This is what constitutes a flow.
In school, we’ve learnt that when electrons flow, we get electric current. This is due to difference in electric potential. Any system wants to go back to its stable state. Hence, to counteract this difference, the electrons move in a way to regain balance again (electrons get homesick).
The sandwich of p-type and n-type layers of semiconductor materials caused the electrons to flow in one direction. This kind of a flow of current is known as direct current (DC). But this is not what the appliances at our home use, do they? The appliances run on AC: alternating current. DC can be converted into AC with an inverter.
This is all for now. I’ll leave you with this song until I get back to you with the Part-II section of this blog post.
This blog post was first published at GreenHatters on February 14, 2014. Version edited for minor corrections. It’s a part of a series on solar power fundamentals.
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