Photovoltaic Cell: Converting Light to Electricity Outcomes: 1. Understand that a photovoltaic cell produces DC voltage when light shines on its surface. 2. Understand that the electrical voltage produced by a photovoltaic cell depends in part on the intensity of the light shining on it: greater intensity = greater voltage. 1 P a g e
3. Understand that the electrical voltage produced by a photovoltaic cell is proportional to the surface area of the cell s active surface. Materials: A photovoltaic cell A lamp A multimeter that can measure current and voltage Setup: 1. Set up the lamp in a place where it will shine with full brightness onto the surface where the PV cell will be placed. A typical 100 W lamp shining onto the surface from a distance or a foot should work fine. 2. Set up the multimeter with its probes connected to the PV cell s electrical terminals. Jumper wires with alligator clips may be necessary to connect to the probe ends. 3. Refer to the setup page for the multimeter at the end of this sheet to see how the probe plugs and dial need to be configured to make the different measurements (current and voltage) you will be doing. What To Do: 1. Measure the surface area of the photovoltaic cell, in square centimeters. Surface area = length x width, assuming the cell is rectangular. 2. Connect the multimeter probes to the PV cell s electrical terminals and set it to measure voltage. 3. Place the PV cell under the lamp and move it around until you find the position where it generates a maximum voltage. Record that voltage. 4. Without changing the position of the lamp or PV cell, switch the multimeter over to measure electrical current and record the value. 5. Calculate the power, in Watts, produced by the PV cell, with current in Amps and voltage in Volts: Power = Current x Voltage Questions: 1. What happens to the voltage generated by the PV cell when you change the angle of the cell s face with respect to the lamp? At what angle does the cell generate maximum voltage? 2. How many of these PV cells would you need to power a 100 W incandescent light bulb? 2 P a g e
3. How many would you need to power a 20 W CFL bulb? 4. How many Watts would a full square meter (10,000 square centimeters) of this type of photovoltaic cell produce? (Hint: First calculate Watts per square centimeter by dividing the maximum power generated by the cell s surface area, in square centimeters, that you calculated, then multiply that result by 10,000 cm.) Further Experimentation: Repeat the experiment, but using full sunlight instead of a lamp. To achieve the maximum voltage and current (and thus power) from the Sun, you ll need to aim the PV cell s active surface at the Sun as directly as possible. Once you find the right position for the cell, make sure you don t change it between readings of voltage and current. Once you have calculated the power that a full square meter of this PV cell would generate, you can calculate the efficiency of the cell at converting sunlight to electricity. The approximate intensity of full sunlight (in a clear sky) at the Earth s surface is about 1000 W per square meter. So, if you divide the power that 1 square meter of PV cell generates by 1000, and multiply that result by 100 to a percentage, the result is the efficiency of the cell. For example, if the maximum power of 1 square meter of PV cell surface is 70 Watts, then the efficiency of the cell is: Efficiency = (70 / 1000) x 100 = 7% 3 P a g e
Photovoltaic Cell Worksheet PV Cell Dimensions: Length cm Width cm Surface Area (if a rectangle) = Length x Width: cm 2 Lamp Experiment: Maximum Voltage Volts Maximum Current Amps Maximum Power = Volts x Amps: Watts How many cells needed to power a 100 W incandescent bulb: How many cells needed to power a 10 W CFL bulb: Power per cm 2 = Maximum Power / Surface Area: W/cm 2 Power per m 2 = (Power per cm 2 ) x (10,000): Sun Experiment (optional): Maximum Voltage Volts Maximum Current Amps Maximum Power = Volts x Amps: Watts Power per cm 2 = Maximum Power / Surface Area: W/cm 2 Power per m 2 = (Power per cm 2 ) x (10,000): Watts Efficiency of PV Cell = (Power per m 2 / 1000) x 100: % 4 P a g e
RED probe in VΩmA BLACK probe in COM DIAL to DCA, 20m RED probe in VΩmA BLACK probe in COM DIAL to DCV, 20 RED probe in 10ADC BLACK probe in COM DIAL to 10A This will measure electric current up to a maximum of 20 milliamps DC. This will measure electric voltage up to a maximum of 20 Volts DC This will measure electric voltage up to a maximum of 10 Amps DC. 5 P a g e