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 "watt·hour/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)

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

[JohnS]

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/m² 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.

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

[JohnS]

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.

and what about an average value:

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

Thank you very much

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

Thanking you in advance for kind support

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

Thanking you in advance for kind support

[JohnS]

Originally Posted by Unregistered

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)

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