Hobbies And Interests
Materials Needed
Measuring a solar cell requires a few items, including a lamp with a light bulb of 100 watts or more, a solar cell, and at least one handheld multimeter that registers current and voltage -- two is better, as you can measure current and voltage at the same time. To measure current, you̵7;ll need a 1/2-watt, 10-ohm resistor you can obtain at any electronics hobby outlet. For a more thorough investigation, have a variable autotransformer handy to change the brightness of the light, and graph paper to chart the solar cell̵7;s response to light. If you have Excel or similar software, you can make the graph on a computer instead of by hand. A handheld calculator helps in multiplying voltage and current figures.
Required Lighting
Place a bright lamp about 2 feet from the solar cell. If the lamp is further away, its light will be dimmer than you need, and if it̵7;s closer, it may heat up the solar cell and reduce the cell̵7;s output. If you want to graph several power measurements, use an incandescent lamp. Otherwise, a light emitting diode or fluorescent lamp will work as long as it has the equivalent brightness of a 100-watt bulb. The light should be pointed directly at the surface of the cell, rather than at an angle.
Measuring Voltage
To determine the solar cell̵7;s power, you measure two quantities with the multimeter -- current and voltage -- then calculate the power in a later step. To measure the voltage, turn the light on and connect the solar cell̵7;s red and black wires to the corresponding positive and negative terminals of the meter. Turn the meter on and set it to measure direct current volts. The meter should indicate a number somewhere from 0.5 to 10 volts, depending on the cell. If the meter displays a negative number, you have the cell connected backwards. This does not hurt the cell or the meter, it simply gives you a negative number instead of a positive one. Write down the voltage reading.
Measuring Current
Disconnect the meter and solar cell and set the meter to read direct current, or DC, in the range of a few hundred milliamps. Connect the solar cell̵7;s red wire to one leg of the resistor and connect the other leg to the positive probe of the meter. Connect the meter̵7;s negative probe to the solar cell̵7;s black wire. Read the DC value on the meter̵7;s display and write it down. The number should be positive. If it isn't, the meter is connected in reverse.
Calculating Power
You use units of watts when measuring electrical power output. A watt is the power developed when one of current flows with one volt of potential. To calculate power, multiply the solar cell̵7;s volts times amps. For example, if your voltage measurement was 0.5 volts and the current output was 10 milliamps, then multiply 0.5 by 10 milliamps for 5 milliwatts of output.
Graphing
By varying the brightness of the lamp, you can make a curve of the solar cell̵7;s power output. Do this exercise in a dimly-lit room. Plug the autotransformer into a household outlet and plug the lamp into the transformer̵7;s socket. Turn the autotransformer knob to about 30 volts, or just as the lamp begins to light with a dull-red glow. Take current and voltage readings following the instructions above. Increase the autotransformer setting by 10 volts and repeat the measurement. Keep increasing until the knob is set to 120 volts and take the final readings. As you do, note the knob setting and current and voltage readings. Multiply each reading of current and voltage to obtain a corresponding power amount. On a graph, label the Y-axis ̶0;Power̶1; and the X-axis ̶0;Lamp Voltage.̶1; Mark the points using the data you obtained. You may notice that the solar cell̵7;s output increases to a point, then flattens out. This means you have reached the cell̵7;s maximum output and it doesn̵7;t make any more power.