Calculating the power output of the photovoltaic cell:
Power (W) = Current (A) x Voltage (V)
To measure the power output, plot a graph of voltage against 1/current and measure the gradient of the best fit line.
I used my preliminary results to draw a graph and to measure the power output.
Equation of graph:
y = 0.001x - 1.7657
Gradient = Power Output = 0.001W
Calculating the power input of the photovoltaic cell:
To measure the power input, measure the irradiance (in Watts/m2) of the bulb with an irradiance meter. This measurement must be taken at the same fixed distance away from the bulb as the solar cell.
Irradiance (watts/m2) = ……………
Then measure the dimensions of the solar cell in order to calculate the area of the solar cell.
The power input of the solar cell can then be calculated as follows:
Power (W) = Irradiance (Wm-2) x Area (m2)
Calculating the efficiency of solar cell:
Efficiency = (Power output / Power Input) x 100
Solar Panel:
Below are diagrams to show how the experiment will be set up to measure the rate of heating of water by the bulb:
Procedure:
Set up the equipments as shown above. The copper tube has to be completely filled with cold water before the bung is inserted into the tube. Place the copper tube underneath the 150W bulb, but on an insulating wood surface so that heat can not be lost by conduction. Turn off all lights, and ensure the room is in complete darkness, so that the only incident light will come from the 150W bulb when it is turned on. Measure and record the initial temperature of the water. Turn on the 150W bulb and record the temperature of the water 30 minutes after the bulb is turned on. Turn off the bulb and leave the experiment to cool for a few minutes. Then carefully remove the bung from the copper tube and empty the tube into a measuring cylinder. Measure and record the volume of water that was heated. Repeat this experiment two more times, ensuring that the ‘solar panel’ cools completely before refilling with cold water.
Results:
The bulb was at a height of ………. m above the solar cell.
Average Change in Temperature (°C) = …………°C
Average Volume of water heated (cm3) = ………… cm3
Calculating the power output of the solar panel:
ΔQ = mcΔθ
Where:- ΔQ = Energy output (J)
m = Mass of water (g) = Volume of water (cm3)
c = Specific heat capacity of water (4.184 J g–1 K–1)
Δθ = Change in Temperature (K)
However this value will not be very accurate as the water inside the tube may not be warmed uniformly. Since the temperature sensor is at the end of the tube, the water at the sensor may be colder than in the middle of the tube. If a motor was inserted into the system so that the water was circulated, like in a real solar panel, then the water would be heated uniformly and the measured temperature would be more accurate.
Power (W) = ΔQ (J) / Δt (s)
where Δt = 30 minutes = 1800 s
Calculating the power input of the solar panel
To measure the power input, measure the irradiance (in Watts/m2) of the bulb with an irradiance meter. This measurement must be taken at the same fixed distance away from the bulb as the solar panel.
Irradiance (watts/m2) = ……………
Then measure the dimensions of the solar panel in order to calculate the area of the solar panel.
The power input of the solar panel can then be calculated as follows:
Power (W) = Irradiance (Wm-2) x Area (m2)
Calculating the efficiency of solar panel:
Efficiency = (Power output / Power Input) x 100
Safety Precautions:
The 150W bulb will become very hot during experiments and so care must be taken. If the bulb has to be removed, make sure it is turned off and has cooled down before touching it.
During the solar panel experiment, take care when handling the black copper pipes as they may become very hot during the experiment. Leave the ‘solar panel’ to cool for a few minutes after the bulb is turned off before touching it. Take care when emptying the copper tube into the measuring cylinder as the water inside may be very hot. Also, care must be taken as the 150W bulb is connected to the mains and water is being used in this experiment. Carelessness could lead to electrocution.
Factors to be taken into account when comparing the two methods:
The input energy has to be identical if the experiments are being compared. Therefore, the bulb must be placed at the same fixed height above both experiments. The experiments must be conducted in complete darkness so that the only incident light during both experiments comes from the 150W bulb.
In the solar cell experiment not all incident light energy will be converted to electrical energy as some light may be reflected off the surface of the solar cell. In the solar panel experiment, some thermal energy from the water may be lost by conduction and radiation to the surroundings.
Bibliography:
Wikipedia - Solar Cell
Intensity
Irradiance
Irradiance meter
