Solar cells are in fact large area semiconductor diodes. Due to photovoltaic effect energy of light (energy of photons) converts into electrical current. The term “photovoltaic” comes from the Greek φῶς (phōs) meaning “light”, and from “Volt”, the unit of electro-motive force, the volt, which in turn comes from the last name of the Italian physicist Alessandro Volta, inventor of the battery (electrochemical cell). The term “photo-voltaic” has been in use in English since 1849.
Solar cells produce electricity in three steps;
- Photons in light hit the solar cells and are absorbed by semiconducting materials, such as silicon.
- Electrons (negatively charged) are knocked loose from their atoms, causing an electric potential difference. Current starts flowing through the material to cancel the potential and this electricity is captured. Due to the special composition of solar cells, the electrons are only allowed to move in a single direction.
- An array of solar cells converts solar energy into a usable amount of direct current (DC) electricity.
In this lab, we discovered the relationship between a light source and solar cell. In two different experiments, we measured the voltage output of the solar cell. In the first experiment, using a flashlight and solar cell connected to the NXT in order to measure the voltage output, we placed the light source in different distances and measured the voltage output of the solar cell. It was noticeable that the further the light source the lesser the voltage output. In the second experiment, the distance of the light source was kept constant and we changed the light color using colored filters. Therefore, the voltage output varies because of changing the color of the light leads to changing in the energy of the photons according to the following formula:
E= hc/λ
Where E is the energy of the photon, h is Planck constant (6,626·10-34Js), λ is the wavelength, and c is the speed of light.
Experiment (1)
The main point of this experiment is to determine the relationship between the solar cell and the light source in terms of the distance. Basically, if the light source is placed far from the solar cell, the light intensity becomes smaller resulting in smaller voltage output.
Therefore, we can conclude that the voltage output is inversely proportional to the distance of the light source.
Experiment (2):
For this experiment, we had to figure out the relationship between the wavelength of light and its energy of the photons. As stated before by the equation, the energy of the photon (E) is inversely proportional to the wavelength. Therefore, light consisting of high energy photons (such as “blue” light) has a short wavelength. Light consisting of low energy photons (such as “red” light) has a long wavelength.
References
http://www.pvresources.com/introduction/solarcells.aspx
http://en.wikipedia.org/wiki/Solar_cell
http://www.pveducation.org/pvcdrom/properties-of-sunlight/energy-of-photon