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Supplies Needed:
Note: You can find many sources for supplies at retail stores and by searching the web.
1. Solar Cell Module (with wire leads). A solar cell module is one or more solar cells installed inside a protective plastic case or covering. Any solar cell module with wire leads should work, but smaller ones are best. (This project was prepared with a 3-volt, 50 milliampere module measuring 2.5 cm (1 inch) x 4.4 cm (1.75 inches).) Avoid using modules without wire leads, for they require that wires be soldered to the module. Select the least expensive module you can find that has wire leads and is enclosed in a protective, plastic housing.
2. Digital or Analog Multimeter. Inexpensive analog and digital multimeters are available from hobby shops, large retail stores, scientific supply companies, and other sources. Very inexpensive digital multimeters are available online and from scientific supply companies. Important: Select a multimeter that has removable probes.
3. Cotton swab.
4. Single- or double-sided tape or self-adhesive Velcro (TM) hook and loop fastening strips for attaching solar module to the multimeter.
5. Pencil or pen and notebook or, alternatively, a clip board with a spreadsheet arranged like this:
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TIME |
SOLAR CURRENT (mA) |
SKY CONDITION (SUN EXPOSURE, CLOUDS, HAZE, ( ETC.) |
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Procedure:
Follow these steps to make a solar radiometer by connecting the solar cell module to the multimeter:
1. Twist and remove most (but not all) of the cotton from both ends of a cotton swab.
2. Cut the swab into two equal lengths.
3. If the test leads (wire probes) are plugged into the multimeter's input sockets, remove them. Note that each probe has a plug at one end and an exposed metal probe at the other.
4. Use tape or Velcro (TM) hook and loop fastening strips to attach the solar module to the top of the multimeter as shown below. Velcro is best for permanent attachment. For temporary use, duct tape is best. Tear a 5-cm (2-inch) length of tape from a 5-cm (2-inch) wide roll of duct tape. Roll and overlap the tape into a cylinder with the sticky side facing outward. Press the tape against the back of the solar module and then press the module onto the top end of the multimeter.
 Click to view enlarged version.
5. The multimeter will have two or more sockets for the test leads. One socket will be marked "Common, "Com," or "- Com." This is the "common" or "ground" socket to the multimeter. Insert the exposed wire section of the black (or gray) negative (-) wire from the solar panel into this socket so that the metal wire is near the metal inside the socket. While holding the wire in place, insert the cotton end of one of the two swabs into the socket to hold the wire in place. The swab should fit snugly inside the socket. If it is too loose, prepare a second set of swabs by removing less cotton.
 Click to view enlarged version.
6. Another socket on the multimeter will be marked "V ? mA" or similar. This socket is for using the multimeter to measure volts (V), resistance in ohms (?) and current in milliamperes (mA). You want to measure the current in milliamperes produced by the solar module. Insert the red (or white) positive (+) wire from the solar module into this socket so that the metal wire is near the metal inside the socket. While holding the wire in place, insert the cotton end of the second swab into the socket to hold the wire in place.
7. Inspect the multiple-position switch on the multimeter. Look for a set of numbers that indicate current in amps (A) or milliamperes (mA). Rotate the switch until it points to the highest mA setting. This is typically "200 mA" for a digital multimeter and 500 mA for an analog multimeter. (The photo on the next page shows the multimeter set to 200 mA.) Do not use a voltage setting. The voltage from the solar module will rapidly increase with light and then level off. The current from the solar module will increase uniformly (linearly) with light until it saturates (reaches a peak).
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