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Procedure (continued):
8. Expose the solar module to sunlight or an indoor light. The meter should indicate a current. Depending on the size of the module, the current may be a few hundred mA or more in direct sunlight. A smaller module like the one shown below may produce up to 50 mA in bright sunlight.
 Click to view enlarged version.
Congratulations! You have successfully made a solar radiometer. If the multimeter indicates no current or too much current when the solar module is exposed to light, follow the steps below to find and resolve the problem:
Solar Module Provides Too Much Current?
Larger solar modules may produce more current in bright sunlight than the multimeter can display. This is the case if the meter needle of an analog multimeter swings all the way to the right or if the display of a digital multimeter rises to "1" and goes no higher. Should this occur, you can try these fixes:
1. Be sure the multimeter selector switch is set to the highest milliampere setting. This may be 200 mA (or 200 m) for a digital multimeter and 500 mA (or 500 m) for an analog multimeter.
2. Your multimeter should have an input connection socket for measuring high current (up to 10 amperes). This input socket will usually be marked "10A DC" or "+10 A" (+ 10 amperes). If you are using a solar module that delivers too much current to read with the multimeter's milliampere settings, move the module's positive lead (red or white) to the multimeter's high current input socket.
3. Try covering part of the solar module with black paper or black tape. You can experiment with how much needs to be covered by exposing the solar module to bright sunlight outdoors.
Solar Module Provides No Current?
1. If the multimeter does not indicate a current, make sure the meter has a fresh battery. Be sure that the multimeter is set to the proper position. Also, make sure that the exposed wire leads of the solar module are not pushed too far into their respective sockets. The exposed wire of each lead must be in contact with the inside of the metal socket wall. If too much cotton is removed from the ends of the swabs, the swabs will not fit snugly into the sockets, and the solar module wires will not stay in contact with the inside of the sockets.
2. If the multimeter still does not indicate a current when the solar module is exposed to light, remove the two wires from the module and insert the two test leads into the multimeter. The black test lead should be plugged into the socket marked "Common, "Com," or "- Com." The red lead should be plugged into the socket marked "V ? mA." While the solar module is exposed to bright light, touch the black probe to the black (or gray) lead from the solar panel and the red probe to the red (or white) lead. The multimeter should indicate a current. If so, the solar module is properly working. Try reattaching the solar module leads to the multimeter using the cotton swabs.
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Project Ideas:
You can use your solar radiometer to learn much about sunlight. Before beginning, be sure to protect yourself by wearing sunglasses and a hat.
Caution: Always wear sunglasses and a hat while measuring sunlight. Never look at the sun under any circumstances!
Here are some projects you can try:
1. Measure Outdoor Sunlight.
You can use your solar radiometer to measure sunlight at regular intervals during a day or at noon from day to day. Each measurement should be made from the same location, and you should hold the multimeter and its solar module in the same orientation during each measurement. For best results, you should stand facing south (north if you live in the southern hemisphere). You can point the solar module directly at the sun, but it's best to point it straight up for each measurement. Or you can do both. Whatever method you choose, use the same method for each measurement. Record the date, time, solar current and sky condition during each measurement.
Here is a set of solar measurements made at or near solar noon during a string of 10 days from a field called Geronimo Creek Observatory in South Texas using a solar radiometer similar in principle to the one described here:
|
| DATE |
TIME |
SOLAR CURRENT (mA) |
SKY CONDITION (SUN EXPOSURE, CLOUDS, HAZE, ETC.) |
| 26-Jul-08 |
12:45:56 |
15.23 |
NEARLY CLEAR, thick Sahara dust, sky milky blue, 1/10 small cumulus. |
| 27-Jul-08 |
12:43:24 | 15.14 |
MOSTLY CLEAR. Less dust, sky light blue, cirrus to south. |
| 28-Jul-08 | 12:46:57 |
15.60 |
NEARLY CLEAR with cirrus swaths to north and south. Sky light blue. |
| 29-Jul-08 | 01:05:17 | 15.63 |
Sun very open,1/2 cirrus, sky light blue. | | 30-Jul-08 |
12:28:37 |
18.04 |
Sun open, 1/2 cumulus, sky light blue. |
| 31-Jul-08 |
12:28:15 |
16.60 |
Sun open, haze, sky light blue, 1/3 cumulus and cirrus. |
| 1-Aug-08 |
01:07:41 |
16.42 | Sun open, sky light blue, 1/3 cumulus. |
| 2-Aug-08 | 12:51:27 |
16.90 |
Sun open, sky medium blue, 1/3 cumulus. |
| 3-Aug-08 |
12:47:10 |
15.13 |
TOTAL CLEAR, cirrus far north and east, sky light blue, hazy, HOT! |
| 4-Aug-08 |
12:53:56 |
16.23 |
Sun open, sky light blue, 1/4 cumulus. |
These measurements were made with the solar sensor facing straight up. The data in the solar current column are multiplied by 10 to make them compatible with a typical solar module. The solar currents listed in the table are much more meaningful when viewed as a graph like this.
 Click to view enlarged version.
Project: Measure sunlight at noon for a week or more and make a graph of your results. (Remember that noon is an hour late when Daylight Saving Time is in effect.) Measure sunlight every half hour over the course of a day and make a graph of your results. Use a solar noon calculator to assist you.
Note that the graph above shows less solar current, hence, less sunshine the first four days and on August 3. Why? For clues, look at the last column in the data table above under SKY CONDITION and then move to the next project . . .
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Click to view enlarged version.
