Solar Irradiance

System

does anybody know what the solar irradiance is at the surface of the Earth, at a latitude of 30 degrees, and during the summer. The number i am currently working with is 1,000W/M^2, but that is the peak for solar irradiance in a day. I need a more accurate number for the entire day.

BB.

Re: Solar Irradiance

Assuming you are talking about the US (or a few selected places around the world)--the PV Watts website uses weather corrected solar irradiation numbers for its calculation (average by month, or even hour by hour, 365 days a year).

If you want to convert to other uses (setup for Grid Tied Solar)

-Bill

crewzer

Re: Solar Irradiance

The value is not constant for any given latitude due to environmental variables (i.e., weather, elevation, etc.).

Here are some U.S. examples at ~30 degrees N latitude to evaluate:

Austin, TX
New Orleans, LA
Jacksonville, FL

HTH,
Jim / crewzer

Windsun

Re: Solar Irradiance

http://www.gaisma.com/en/dir/us-country.html

From NOAA satellite data.

Dave Angelini

Re: Solar Irradiance

If the data is really important then the simple answer is you have to measure it.
Obtain the measurement instrument and log the data.

BB.

Re: Solar Irradiance

Windsun wrote: »

http://www.gaisma.com/en/dir/us-country.html

From NOAA satellite data.

Take this data with a grain of salt... At least for California, the data does not have near the resolution that it seems to claim.

For two cities (Pacifica, San Mateo) just 12 miles apart, it has the same solar Isolation listed... But one is on the coast and has 4 days of overcast and 2 days of sun during the summer--and the other has sun most days of the summer (marine layer effect and and local range of coastal hills that block the marine layer from coming inland).

Solar insolation can be dramatically affected by local weather patterns.

If you do not have accurate data for your area--logging the numbers for a year is a good start for large/expensive projects.

-Bill

Cariboocoot

Re: Solar Irradiance

If people think this doesn't have any bearing ...

I'm certain I get more irradiance at the cabin than in the Fraser Valley. There is an elevation difference of 2,700 feet. There is also far less pollution. The skies really are "bluer" in the Cariboo! (In the Valley they are sort of orange-brown much of the time. And people breath that stuff.)

But in order to test this accurately I'd need two systems exactly the same, and large enough so that any atmospheric differences would cause measurable results.

Windsun

Re: Solar Irradiance

Cariboocoot wrote: »

If people think this doesn't have any bearing ...

I'm certain I get more irradiance at the cabin than in the Fraser Valley. There is an elevation difference of 2,700 feet. There is also far less pollution. The skies really are "bluer" in the Cariboo! (In the Valley they are sort of orange-brown much of the time. And people breath that stuff.)

You get around 1% more per 1000 foot of altitude. If you consider the polution often present in low altitude cities, such as LA and Phoenix, the first 2000 to 4000 feet above that can actually make as much as 5% difference. Measurements taken about 10 years ago showed that insolation in Denver maxed out at around 1190, while San Diego at sea level was around 998 average best case.

But it is not really all that simple. The makeup of the light changes also, with light towards the UV end of the spectrum going up more.

Simultaneously taken measurements of solar irradiance with high resolution spectrometers at Garmisch-Partenkirchen, Germany (730 m a.s.l.) and Wank (1730 m a.s.l.), horizontally separated by 5 km, show a clear wavelength dependence of the altitude effect of the global irradiance: 9% per 1000 m at 370 nm increasing to 11% per 1000 m at 320 nm and 24% per 1000 m at 300 nm. The altitude effect of direct irradiance is considerably higher than that of global irradiance at all measured wavelenths.