Investigation of Solar cells
Introduction
Solar cells, also known as photovoltaic cells, rely on the photoelectric effect to convert the solar radiation into electric energy. Photoelectric effect refers to the tendency of materials to emit electrons when light is shown on them. The electrons dislodged from the surface of an object as a result of light being shown on the surface of such materials are referred to as photoelectrons. Not all materials exhibit the ability to emit electrons when placed along the path of light. Most with the ability to emit electrons are metals.
Silicon is a key ingredient of a solar cell. Being a semiconductor, silicon’s ability to conduct electricity lies between that of a metal and that of an electric insulator. In silicon, this property is influenced by the fact that silicon has impurities in its structure. Sunlight comprises of particles called photons. When sunlight is shown onto the surface of a solar cell, the photons transfer their energy to the free electrons found in the silicon structure. Thus, the free electrons get knocked off the atoms. This phenomenon embodies the manner in which the white ball knocks a colored ball and transfers its kinetic energy to the colored ball in the game of pool. The freeing of the electrons, however, does not constitute the entire process of converting the sunlight energy into electrical energy. Rather, the freed electrons must be harnessed to create an electric current. This process can be accomplished by creating an electrical imbalance within the cell. The imbalance makes it possible for the current to flow.
The manner in which the structure of silicon is arranged makes it possible for the electrical imbalance to be created. The structure of silicon is such that there are two types of silicon atoms (n-type and p-type) in a tightly bound structure. The n-type atoms have spare electrons while p-type has no spare electrons. Within a solar panel, the two types of silicon atoms are placed side by side. Due to this arrangement, the spare electrons in the n-type atoms jump into the gaps in the p-type silicon atoms. This makes the n-type silicon gain a positive charge while the p-type atoms acquire a negative charge. Consequently, an electric field is created across the across the cell. Silicon, being a semiconductor, maintains this electric imbalance, hence enabling electric current to flow. As the photons from the sun continue to strike the electrons off the silicon atoms, they are driven according to the electrical imbalance. The constant electric current maintained within the solar cell enables it to be used to drive various machines and appliances.
The output of a solar panel is influenced by many factors such as sunlight intensity, temperature, orientation, and color of the panel among other factors. An increase in the sunlight intensity incident on the surface of a solar panel leads to an increase in the output of the panel. In this case, intensity increase results in increased number of free electrons being dislodged from the silicon material within the solar panel. Consequently, a high potential difference is created, hence resulting in high current flow. Sunlight intensity is influenced by such factors as cloud cover and shade. An increase in temperature leads to an increase in electrical conductivity of silicon in the solar panel. The higher the electrical conductivity of the silicon is, the lower the magnitude of electric field within the solar panel becomes. An explanation for this phenomenon is that as the semiconductor, silicon, becomes more electrically conductive, the charges in the material become more balanced too. The size of each cell in the solar panel does not affect the voltage output of the panel. Rather, it affects the current output. However, the area of a solar panel exposed to sunlight might influence the voltage output since as the surface area exposed to light increases, the number of free electrons dislodged increases too. In this experiment, the effect of the area of a solar panel exposed to light on the voltage output of the panel was investigated. In this case, the diameter of the area (the same as the diameter of the hole in each cardboard) exposed to sunlight formed the independent variable while the voltage output of the panel was taken as the dependent variable.
The voltage output of a solar panel depends on the area of the panel exposed to sunlight. The following prediction was made in this experiment:
If a smaller area of the solar panel is exposed to sunlight, there would be a decrease in the voltage output and vice versa because the greater the exposure to sunlight the panel is, the higher the number of freed electrons becomes, and the higher the electrical imbalance in the cells become.
Therefore, if the area exposed to sunlight is doubled, the voltage output of the solar panel will also double.
Method
The following materials were used in the experiment:
Solar cell
Lamp
8 pieces of black Cardboards with circular holes at the centers that have the following diameters: 0.85cm, 1.85 cm, 2.85cm, 3.85cm,, 4.85cm, 5.85cm, 6.85cm, and 7.85cm.
Multimeter Probes
Multimeter
Clamp and stand
The experiment was conducted at night in a room. A wide sheet of paper was placed on a table. The solar panel was then placed on the paper. The lamp was then clamped vertically above the solar panel. Next, the panel was connected to the multimeter using the multimeter probes. Next, a piece of cardboard was placed on the panel. All the lights in the room were then turned off except the light from the lamp. With the lamp turned on, the multimeter reading was recorded. The measuring of the voltage output process was repeated using different cardboards. Three trials were conducted and the average values recorded.
The average voltage output readings with their corresponding cardboard diameter are shown in the table below:
Evaluation
The graph showing the relationship between the output voltage and the diameter of the cardboard (cm)
The cardboard was used to regulate the surface area of the solar panel exposed to light. Each cardboard had a circular hole at the center through which light from the lamp passed to the solar panel. The lamp was placed approximately 40cm above the solar panel. The position of the lamp was maintained for every cardboard to make sure that any variation in light intensity is eliminated. The proximity of the lamp from the panel influences the intensity of light that can illuminate the surface of the solar panel. The experiment was carried out at night, and all the lights were turned off to ensure that the only light that illuminates the surface of the solar panel comes from the lamp. Black cardboard was used to ensure that light from the lamp does not pass to the panel. The digital multimeter was preferred because the visual indication of reading changes is better than that of an analog multimeter since the analog multimeter exhibits damping torque. Therefore, using an analog multimeter was could have resulted in more errors. Some anomalies were noted in the multimeter readings. Such readings were excluded from the calculation of the average values of the output voltage. This experiment is reproducible since the three trials conducted for every cardboard produced values that are reliable.
Reviews
The graph of output voltage against the diameter of the cardboard hole shows that an increase in the diameter results in an increase in the output voltage of the panel since it has a positive gradient. The area of the holes of the cardboard is the same as the area the panel is exposed to. Therefore, the results show that an increase in the surface of the solar panel the solar panel is exposed to leads to an increase in the voltage output of the panel and vice versa. Therefore, my prediction is accepted.
