measuring photovoltaic temperature

Discussion in 'The Projects Forum' started by mah, Jan 12, 2014.

  1. mah

    Thread Starter Active Member

    Mar 15, 2010
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    could i use lm35 to measure surface temperature of photovoltaic solar cell ? or should i use temperature sensor specially for that purpose ?
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Assuming the solar-cell gives out 5V minimum, yes you can use an LM35, it gives out 10mV/C, so all you would need is a dvm to measure the temp.
     
  3. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    Yes, you can. The usual LM35 package (TO-92) has one side that is flat, use that side to attach LM35 to the surface whose temperature you want to measure.

    While searching for temperature sensors for my own needs. I came to suggestion of using TMP36 instead of LM35. There are two advantages in using TMP36:
    1) LM35 needs two power supplies in order to read full range of temperatures.
    2) LM35 with just positive power supply only gets as low as +2 ºC. So if you ever need to know if you reached 0 ºC, you will never know.

    Here is tutorial on using LM35 and TMP36: http://learn.adafruit.com/tmp36-temperature-sensor
     
  4. mah

    Thread Starter Active Member

    Mar 15, 2010
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    i don't need negative temperature so lm35 (TO92) is enough. but i read in its datasheet that it is affected by air temperature so i need some body that tried it with photovoltaic to tell me about his experiment .

    thanks
     
  5. wayneh

    Expert

    Sep 9, 2010
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    The way to mitigate that is to insulate it from ambient conditions. For example place a foam pad behind it and its leads, so that it only "sees" the PV panel.

    Oh by the way, I was picturing the sensor on the BACK of the panel. I assume there is minimal ∆T from front to back of the PV panel. If you really need the surface temp of an active panel, I'd consider a non-contact IR gun.
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    The temp of a surface being measured is affected by the "air" too.. being in physical contact with the material should allow a fairly reasonable accuracy..
    What accuracy do you require?
     
  7. mah

    Thread Starter Active Member

    Mar 15, 2010
    276
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    I need ±1°C. I tried LM35 in the back of the module its dimension 120*50 cm
    but i got power equivalent to higher temperature by 15 °C than LM35 output, could that be possible
     
  8. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    I can't understand your question.
     
    wayneh likes this.
  9. mah

    Thread Starter Active Member

    Mar 15, 2010
    276
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    i got output power 90 watt and that is equivalent to 55 °c but th lm35 give output 0.40 V which means 40 °c could this be a loss in accuracy or there is another reason?
     
  10. wayneh

    Expert

    Sep 9, 2010
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    The reason is that your model of output power versus temperature is wrong for the current operating conditions. The panel may be getting old, or has dirt on it, or your illumination is less than specified, or many other reasons.
     
  11. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    ^^ +1
    temperature cannot be relied upon to accurately determine cell output.
     
  12. wayneh

    Expert

    Sep 9, 2010
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    To put it another way, it's the tail that does not wag the dog.

    Once PV performance at one temperature is known, your model may allow a decent estimate of performance at some other temperature, but it cannot be used in the reverse.
     
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