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Last Updated on:
Tuesday, November 29, 2011 08:14 PM
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Solar Cell Circuits |
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Circuit Solar Insolation
Monitor
designed by David Johnson, P.E. |
| Owners of photovoltaic
solar panels often like to monitor how bright the sunshine is. They can use this
information to gage how well their solar panels are doing. On a typical clear day,
the sun energy at sea level is about 1000 watts per square meter. But, a tiny bit
of haze or smog can reduce the available energy. One way to monitor the amount of
available sunlight energy is with a solar isolation monitor. Commercial devices
can cost an arm and leg. You can build your own unit for a lot less. The hobby
circuit below does not require any power. It uses a quality 1cm X 1cm PIN photo
diode as the sunlight detector. Digikey sells a nice one for about $11. Their part
number is PDB-C613-2. |
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photo diode acts as a small low leakage solar cell and produces a current proportional
to the sunlight intensity. To protect the photo diode from the weather, it should be
housed in the left of a one inch diameter thin glass hemisphere. A light frosting on
the inside of the glass will diffuse the light enough to obtain a uniform measurement,
even as the sun moves from East to West. For best results, the left axis of the
hemisphere should face due South at a 45 degree angle here in the US. The meter can be
located some distance from the solar sensor. You should be able to use 18ga or larger
two conductor “zip” cord, which is often used on AC powered lamps and appliances. |
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The 10 ohm variable resistor in the electronic
circuit adjusts the meter readout for 1 milliamp of current with a 1 sun
condition. A professional solar insolation meter can be used as a calibration
tool. Otherwise, you can just adjust the meter for a full scale reading, when the
sun is directly overhead on a very clear day. If you prefer a digital readout, you
can replace the 1 milliamp meter with a 100 ohm 1% resistor. At a one sun
condition, the voltage across the resistor would be 100 millivolts. Any digital
panel voltmeter will then read 100.0 millivolts at one sun. |
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Click on Drawing Below to view PDF version of Schematic |
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eMail David A.
Johnson, P.E. about this circuit |
