Announcement

Announcement Module
Collapse
No announcement yet.

Solar Radiation Conversion (mJ/m to W/m)

Page Title Module
Move Remove Collapse
X
Conversation Detail Module
Collapse
  • Filter
  • Time
  • Show
Clear All
new posts

  • Solar Radiation Conversion (mJ/m to W/m)

    Solar Radiation Conversion (mJ/m to W/m)
    by Andy_N on 05/26/05 at 11:05:28

    I'd like to convert solar radiation from MJ/m2 to W/m2. Any ideas?

    Thanks

    Re: Solar Radiation Conversion (mJ/m to W/m)
    by Robert Fogt on 05/26/05 at 20:06:34

    Not really. Megajoules is energy and Watts is power so there is no direct conversion between them.

    What about "megajoule/square meter" to "watthour/square meter"?

    A Watt is equal to one joule of energy per second. A human climbing a flight of stairs is doing work at the rate of about 200 watts. An automobile engine produces mechanical energy at a rate of 25,000 watts (approximately 30 horsepower)

  • #2
    Re: Solar Radiation Conversion (mJ/m to W/m)

    I also have the same problem. I would like to convert from W/m2 to MJ/m2. Could someone please advise??

    Comment


    • #3
      Re: Solar Radiation Conversion (mJ/m to W/m)

      Originally posted by Unregistered
      I also have the same problem. I would like to convert from W/m2 to MJ/m2. Could someone please advise??
      Normally the W/m available changes throughout the day as the sun's angle varies. The total energy (per day)available is the integral of P(t)*dt from sunrise to sunset.

      You HAVE to know the variation throughout the day, there is no good way to get there from peak watts at high noon.

      However, if you know latitude of the place, declination of the sun and assume zero cloud cover, zero blockage by buildings, trees, etc, you can calculate an idealized number. (It will depend on whether you have a tracking solar array (differs for 1-axis and 2-axis tracking) or fixed orientation). Most solar power texts cover the approximation.

      Comment


      • #4
        Re: Solar Radiation Conversion (mJ/m to W/m)

        you need to divide by time. A watt is a joule per second. Divide J/m2 by seconds operating - you get W/m2

        Comment


        • #5
          Re: Solar Radiation Conversion (mJ/m to W/m)

          Originally posted by Unregistered
          you need to divide by time. A watt is a joule per second. Divide J/m2 by seconds operating - you get W/m2
          Only if "average watts" are satisfactory OR power is known to be constant during the measurement period.

          Comment


          • #6
            Re: Solar Radiation Conversion (mJ/m to W/m)

            and what about an average value:

            I need to convert mJ/m2/day to W/m2/day ?

            Thank you very much

            Comment


            • #7
              Re: Solar Radiation Conversion (mJ/m to W/m)

              I wanna to convert mJ/sqm/day to W/sqm/m2

              Thanking you in advance for kind support

              Comment


              • #8
                Re: Solar Radiation Conversion (mJ/m to W/m)

                I wanna to convert mJ/sqm/day to W/sqm/m2

                Thanking you in advance for kind support

                Comment


                • #9
                  Re: Solar Radiation Conversion (mJ/m to W/m)

                  Originally posted by Unregistered View Post
                  I wanna to convert mJ/sqm/day to W/sqm/m2

                  Thanking you in advance for kind support
                  I suspect you mean megajoules (MJ) not millijoules (mJ), as millijoules per day wouldn't be enought to bother with.

                  If average watts (for the day) is acceptable, multiply by 10^ to get joules, then divide by 86400 s/day to get average watts.

                  If you need instantaneous watts, plot the accumulation of joules throughout the day, fit an approximating function and take the derivative (or invest in an instrument that will read watts directly)

                  Comment


                  • #10
                    Re: Solar Radiation Conversion (mJ/m to W/m)

                    What about converting microEinsteins converting MJ/m2? Could you work with Langleys as an intermediate step to take care of time?

                    Comment


                    • #11
                      Re: Solar Radiation Conversion (mJ/m to W/m)

                      Originally posted by Unregistered View Post
                      What about converting microEinsteins converting MJ/m2? Could you work with Langleys as an intermediate step to take care of time?
                      An einstein of photons is just a mole of photons, regardless of frequency or wavelength. However, it is often restricted to photosynthetically active radiation (PAR), from 400 - 700 nm. Photons of different wavelengths or frequencies have different energies. Unless you know the frequencies distribution, you can not not convert to energy. I suppose you can assume the middle of the above interval, 550 nm, and hope for the best, but 27.3% errors are possible.

                      Comment


                      • #12
                        Re: Solar Radiation Conversion (mJ/m to W/m)

                        Divide the values by 3.6 to convert from units of megajoules per square metre (MJ/m2) to kilowatt-hours per square metre (kWh/m2).

                        Comment


                        • #13
                          Re: Solar Radiation Conversion (mJ/m to W/m)

                          Hi,

                          I have collected solar radiation data throughout the day (every hour) in KJ/m2. I would like to convert these values to w/m2.

                          Any ideas on the conversion to use?

                          Regards

                          James

                          Comment


                          • #14
                            Re: Solar Radiation Conversion (mJ/m to W/m)

                            Originally posted by Unregistered View Post
                            Hi,

                            I have collected solar radiation data throughout the day (every hour) in KJ/m2. I would like to convert these values to w/m2.

                            Any ideas on the conversion to use?

                            Regards

                            James
                            A watt is a joule per second. There are 3600 s or 3.6 ks in 1 hr. Assuming the energy collected is over the full one hour period, divide by 3.6 ks to get W/m

                            If you collect 2700 kJ/m over 1 hr, this is
                            2700 kJ/m x1/3.6 ks = 750 W/m

                            Comment


                            • #15
                              Re: Solar Radiation Conversion (mJ/m to W/m)

                              1 mm/day = 2.45 MJ m-/day
                              1 Wm- = 0.0864 MJ m-/day

                              Comment

                              Previously entered content was automatically saved. Restore or Discard.
                              Auto-Saved
                              x
                              Insert: Thumbnail Small Medium Large Fullsize Remove  
                              x
                              x

                              Please enter the six letters or digits that appear in the image below.

                              Registration Image Refresh Image
                              Working...
                              X