Convert W/m2 to mJ/m2 ?
ANikolaev
Any one help convert W/m2 to mJ/m2 for solar radiation?
Alex
Gene Nygaard
ANikolaev <Aleksandr...@ksu.ru> wrote:
>Any one help convert W/m2 to mJ/m2 for solar radiation?
>Alex
Multiply by the time in seconds to get joules per square metre, then
multiply by 1000. (Why do you want millijoules per square metre? It
would seem to me that you'd be more likely to want to express the
result in megajoules per square metre, unless your're dealing with
time periods of nanoseconds or something like that.)
A watt is one joule per second.
Gene Nygaard
EBurger
Alex Nikolaev wrote:
>Any one help convert W/m2 to mJ/m2 for solar radiation?
If by "mJ" you mean millijoules, there's a problem in that Watts are
Joules per second, measuring power (energy/time) and Joules measure energy
itself. You could multiply W times the duration of the solar radiation in
seconds to get J, then by 1000 to get mJ.
My apologies if "mJ" means something else besides millijoules :-).
Tom Ehrensperger
Joseph Bartlo
EBurger <ebu...@aol.com> wrote in article
<19970411032...@ladder01.news.aol.com>...
Not everyone is aware of all our conventions, especially if from
elsewhere (?). I think Alex meant Megajoules (typically used
for solar radiation because they produce comfortable base 10
numerical values). If so, he should be aware that milli refers
to 1000 parts of 1 (eg, 1 g = 1000 mg), and Mega means
millions (1000000 J = 1 MJ).
A 'Watt' (W) is a 'Joule' (J) per second (sec). Thus,
1 W = 1 J/sec
No power & energy conversion is possible, as you state, but
E = Int(t1,t2) P dt , Int representing integral from t1 to t2
Average solar energy fluxes during sufficiently small periods
(e.g. 20 minutes) are sufficient to estimate daily solar energy
amount using sums during the periods. E.g., suppose global
solar energy flux averages centered at shown times are :
10:10 500 W/m^2
10:30 530 W/m^2
10:50 270 W/m^2
Time period is 20 min = 1200 sec then total solar energy
amount during the hour is
E = (500)(1200) + (530)(1200) + (270)(1200) =
1560000 J = 1.56 MJ/m^2
Such can be done for an entire day, solar energy amount for
clear summer days being near 30 MJ/m^2 (a nice, comfy
number) :)
Joseph
Gene Nygaard
"Joseph Bartlo" <jba...@ptd.net> wrote:
>Not everyone is aware of all our conventions, especially if from
>elsewhere (?). I think Alex meant Megajoules (typically used
>for solar radiation because they produce comfortable base 10
>numerical values). If so, he should be aware that milli refers
>to 1000 parts of 1 (eg, 1 g = 1000 mg), and Mega means
>millions (1000000 J = 1 MJ).
The symbols for milli- and mega- are the same worldwide. It is
usually only the Americans who haven't figured them out yet.
>A 'Watt' (W) is a 'Joule' (J) per second (sec). Thus,
Of course, just because the symbols for units named after people start
with an uppercase letter, that doesn't mean the words for the symbols
should be capitalized. It is watts and joules. Nor is the prefix
mega- capitalized, though its symbol is.
> 1 W = 1 J/sec
The correct symbol for seconds is s, not sec.
>No power & energy conversion is possible, as you state, but
> E = Int(t1,t2) P dt , Int representing integral from t1 to t2
>
>Average solar energy fluxes during sufficiently small periods
>(e.g. 20 minutes) are sufficient to estimate daily solar energy
>amount using sums during the periods. E.g., suppose global
>solar energy flux averages centered at shown times are :
> 10:10 500 W/m^2
> 10:30 530 W/m^2
> 10:50 270 W/m^2
>Time period is 20 min = 1200 sec then total solar energy
>amount during the hour is
> E = (500)(1200) + (530)(1200) + (270)(1200) =
> 1560000 J = 1.56 MJ/m^2
>Such can be done for an entire day, solar energy amount for
>clear summer days being near 30 MJ/m^2 (a nice, comfy
>number) :)
Thus the actual unit is not MJ/m² but MJ/(m²·d) here, or MJ/(m²·h) in
your previous example. Carelessness in expressing these units makes
them hard to understand.
Gene
Bernd Kuemmel
Yes, but what is a factor of 10^9 among friends!
>Not everyone is aware of all our conventions, especially if from
>elsewhere (?). I think Alex meant Megajoules (typically used
>for solar radiation because they produce comfortable base 10
>numerical values). If so, he should be aware that milli refers
>to 1000 parts of 1 (eg, 1 g = 1000 mg), and Mega means
>millions (1000000 J = 1 MJ).
Regards
Bernd
dubeypr...@gmail.com
iputp...@gmail.com
> EBurger <ebu...@aol.com> wrote in article
> <19970411032...@ladder01.news.aol.com>...
> > Alex Nikolaev wrote:
> >
> > >Any one help convert W/m2 to mJ/m2 for solar radiation?
> >
> > If by "mJ" you mean millijoules, there's a problem in that Watts are
> > Joules per second, measuring power (energy/time) and Joules measure energy
> > itself. You could multiply W times the duration of the solar radiation in
> > seconds to get J, then by 1000 to get mJ.
> >
> > My apologies if "mJ" means something else besides millijoules :-).
>
> elsewhere (?). I think Alex meant Megajoules (typically used
> for solar radiation because they produce comfortable base 10
> numerical values). If so, he should be aware that milli refers
> to 1000 parts of 1 (eg, 1 g = 1000 mg), and Mega means
> millions (1000000 J = 1 MJ).
>
>
>
>
> E = Int(t1,t2) P dt , Int representing integral from t1 to t2
>
> Average solar energy fluxes during sufficiently small periods
> (e.g. 20 minutes) are sufficient to estimate daily solar energy
> amount using sums during the periods. E.g., suppose global
> solar energy flux averages centered at shown times are :
>
> 10:10 500 W/m^2
> 10:30 530 W/m^2
> 10:50 270 W/m^2
>
> Time period is 20 min = 1200 sec then total solar energy
> amount during the hour is
>
> E = (500)(1200) + (530)(1200) + (270)(1200) =
> 1560000 J = 1.56 MJ/m^2
>
> Such can be done for an entire day, solar energy amount for
> clear summer days being near 30 MJ/m^2 (a nice, comfy
> number) :)
>
>
Okay..that is make sense