The Effect of Varying Light Intensity on the Power Output of a Solar Cell

The Effect of Varying Light Intensity on the Power Output of a Solar Cell
planning Theoretical Background. Photovoltaic (solar) cells are cells that generate an electromotive force (emf) and therefore provide a current without a battery. The cell consists of a junction between two different materials, often p-type silicon and n-type silicon and light of certain wavelengths is able to ionise the atoms in the silicon. The junction allows the ionised electrons to spontaneously drift from one material to the other. This causes an overall positive charge to build up in the material losing electrons and a negative charge in the material gaining electrons. The electromagnetic radiation (light) gives the electrons enough kinetic energy to move freely and a current within the circuit is produced
Diagram to show the photovoltaic effect in a solar cell The Photoelectric Effect What effects power output of a cell? The amount of power available from a photovoltaic device will depend on:
The type of material
The area/size of the material
The intensity of the sunlight
The wavelength of the sunlight
The age/efficiency of the PV cell
The heat/temperature of the solar cell
The effect of light intensity on the power output of a cell : A single crystal silicon cell cannot (currently) convert more than 25% of the solar energy into electricity, and a cell of 100cm2 will produce approx 1.5 watts at 0.5 volts DC and 3 amps under full summer sunlight. The power output of the cell is almost directly proportional to the intensity of the sunlight, i.e. if you half the sunlight intensity, the power will also be halved. Solar cell IV curve The voltage of a PV cell does not depend the size of the cell, nor does it vary much with changing light intensity, whereas the current output is almost directly proportional to the light intensity and size of the cell. Using the information I have gathered and explained above, I would expect to see certain general trends when looking at the results of my experiments: 1) The power output should increase proportionally as the intensity of the light increases. 2) The voltage of the cell should remain fairly constant with the variation of the light intensity. 3) The current output should increase as the light intensity increases. As I want to test the effect on power output of a solar cell dependant on the light intensity, I will have to consider the following variables in this experiment: ============== 1) I will use the same size cell in each of the experiments. ============ 2) The light bulb will be placed at a distance of 2cm away from the cell and be face on to the bulb. 3) The wires will be the same length and type. 4) The experiment will take place in a room with a constant light source so that this will not cause any variation in results. 5) The factor that will be changing is the brightness of the light bulb; varying the voltage so as to increase and decrease the light intensity as required will change this. I will vary the voltage of a light bulb placed at a specific distance from a solar cell and measure the voltage and current produced. I will then calculate the power output using the equation: ============== P = IV Experiment equipment ==== 12-volt light bulb Variable power supply pack 4 wires Ammeter Voltmeter Solar cell Diagram to show physical arrangement of apparatus. Diagram 1. Diagram 2. ===== Method == 1) Set up the two circuits as in diagrams 1 and 2 above. 2) Place solar cell directly face on to the bulb at a distance of 2cm and so the bulb and solar cell are level. 3) Starting at 2 volts measure the voltage and current produced by the solar cell. 4) Gradually increase the voltage of the light bulb so that measurements can be taken at intervals of 1 volt to determine the effect of the light intensity on the power output. 5) Using the equation P = IV and the measurements taken, calculate the power output of the solar cells at each given voltage. 6) Repeat the experiment until you have 3 sets of results of similar values to ensure the results are accurate. observing and recording Results Table to show current and voltage of a circuit involving a solar cell to show the effects of varying light intensity. Experiment 1 Experiment 2 Experiment 3 Voltage of bulb Amps Voltage Amps Voltage Amps Voltage 2v 0.00A 56.4mv 0.00A 56.7mv 0.00A 56.2mv 3v 0.00A 118.8mv 0.00A 119.6mv 0.00A 119.2mv 4v 0.00A 0.200v 0.00A 0.199v 0.00A 0.199v 5v 0.00A 0.248v 0.00A 0.247v 0.00A 0.247v 6v 0.01A 0.285v 0.01A 0.284v 0.01A 0.283v 7v 0.01A 0.312v 0.02A 0.311v 0.02A 0.311v 8v 0.02A 0.340v 0.02A 0.339v 0.02A 0.338v 9v 0.03A 0.363v 0.03A 0.360v 0.03A 0.360v 10v 0.06A 0.400v 0.06A 0.414v 0.07A 0.414v 11v 0.07A 0.413v 0.07A 0.414v 0.07A 0.414v 12v 0.10A 0.439v 0.10A 0.438v 0.10A 0.437v The table below shows average values of current and voltage and total power output of the solar cell. Average Results Power output Voltage of bulb Amps Voltage P=IV Watts 2v 0.00A 56.43mv 0.00w 3v 0.00A 119.2mv 0.00w 4v 0.00A 0.119v 0.00w 5v 0.00A 0.247v 0.00w 6v 0.01A 0.284v 2.85X10^-3w 7v 0.016A 0.311v 4.98X10^-3w 8v 0.02A 0.339v 6.78X10^-3w 9v 0.03A 0.361v 1.08X10^-2w 10v 0.063A 0.409v 2.39X10^-2w 11v 0.074A 0.414v 3.06X10^-2w 12v 0.10A 0.438v 4.38X10^-2w interpreting and evaluating Analysis Looking at the average results where the light bulb was between 6 and 12volts I noticed: 1) The voltage has remained fairly constant with the increase of light intensity with only a change of 0.041volts overall. 2) The current has increased overall by 0.09amps. 3) The power output increased proportionally as the light intensity increased, when the light intensity was doubled from 6 ? 12V the power output nearly doubled from 2.85 X10^-3w to 4.38 X10^-3w The results that have arisen from the experiment conducted above are in keeping with the results that are known quantative values for the current, voltage and power outputs of photo voltaic cells. I knew that the power output of a cell is almost directly proportional to the intensity of the light and my results, as shown in (3) above prove this. The voltage of the cell was expected to remain fairly constant with the change in light intensity and looking at my results and from (1) above I can say that this is correct. The current output from the solar cell increased as the light intensity increased, by a total of 9amps, this again was expected to happen. The results that I collated in the tables above are all fairly constant although in the table of average results the current increases more during the transition from 9-10volts and 11-12volts. On both occasions the current increases by 0.03amps where as for all the other results the increase is only approx 0.01amps. It is important to note that this increase could be caused by an experimental error such as a change in the light of the room that the experiment was being conducted in, causing an inaccuracy in the results collected. Evaluation -???- The experiment conducted above was accurate with reliable results. To further improve on these results should I conduct this experiment again I would ensure that the room used would have a constant light intensity i.e. a dark room. In addition to this I would also measure the current and voltage of the solar cell with a more sensitive/accurate meter; the multi meter used could only detect amps emitting from the solar cell when the light bulb was set at 6 Volts or above therefore limiting the scope of the results obtained in this experiment. References -???- Salters Horners advanced physics. Nelkon & Parker advanced level physics Murdoch education.

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