Theoretical Question

quique

Does this statement seem correct:

When the azimuth angle is 0 degrees, which means true south, the sun will be at its highest angle of elevation for that particular day.

This is taken out of some course material I am reading. Its translated from english and I have found errors before, so I need to know if this is erroneous or if Im not really understanding the concepts.

I understand azimuth is the HORIZONTAL angle between south and true south. Sun elevation is the VERTICAL angle from horizon to the suns position in the sky. But Im not clear as to why when azimuth is 0 (a horizontal measure of angle), it should mean the suns elevation is highest (vertical measure of angle)?

ELEVATION
The sun starts the day with elevation 0 deg, and rises to whatever it can (90 deg in the summer and perhaps 20 in the winter depending on location) during the day and goes back to to when it sets in the west. So basically Altitude during the day goes from 0 - 90 - 0.

AZIMUTH
I thought Azimuth was a fixed value during the day, based on the location and time of year. But according to the statement, azimuth changes during the day much in the same way (because it is related to?) the sun elevation angle?

solarix

Re: Theoretical Question

The way I take this is that the highest angle of sun elevation occurs when the sun is at an azimuth angle of 0 degrees. And azimuth angle is relative to the observer not the horizontal angle of the sun.

quique

Re: Theoretical Question

So the azimuth angle does change during the day? Its not a fixed value during the day for a given day of the year? Am I getting confused with magnetic declination?

Rybren

Re: Theoretical Question

My interpretation (for the little that it's worth) is that the sun is at its highest elevation angle when it is due south (True and NOT Magnetic) of your location. This should be referred to as 180 degrees True and not 0 Degrees, which would be North)

Declination is the angle between Magnetic and True. This angle changes over time.

Cariboocoot

Re: Theoretical Question

The world is round. In both directions.

Rybren

Re: Theoretical Question

Cariboocoot wrote: »

The world is round. In both directions.

More or less

quique

Re: Theoretical Question

Yes its just that I have 3 terms Im trying to put into perspective here:

Sun Elevation: This I understand. Its use is given by the fact that in the in the winter time, the south is not high up in the sky above our heads at 90 deg as it is in the summer. Therefore, we must adjust for the elevation because we want the sun rays to hit the face of the pv array as perpendicularly as possible.

Magnetic declination: This I also understand. Its use is given by the fact that depending on your geographical location, true north or south varies. In the US example, west of the mississippi, declination is east of north, so we must adjust for it.


But Azimuth im still a bit confused. I think its because azimuth is the concept which is used to explain magnetic declination, so Im trying to find another use for it. But I guess its use is given by magnetic declination, correct?

Cariboocoot

Re: Theoretical Question

Azimuth is the degrees difference (+ or -) from a reference point (solar South) to an observed body (the sun in this case).

Elevation or more accurately angle of elevation (sometimes called altitude although that is erroneous) is the same, but on the plain perpendicular to azimuth and referencing vertical zero (level).

Azimuth may be used to explain magnetic declination although it shouldn't be as declination explains it: the degrees difference (+ or -) between true South and magnetic South (which as you know varies from place to place).

So magnetic declination is used to get the correct reference point to determine azimuth angle of the sun from.

Now stop making me think up definitions and explanations; it's like an archeological expedition trying to find that stuff in my Swiss-cheesed memory!

quique

Re: Theoretical Question

Thanks...thats a bit better. Im just trying to understand how to properly orient a solar panel array so Im reading through all this material. I decided to look up videos instead which might be easier to follow.

Cariboocoot

Re: Theoretical Question

quique wrote: »

Thanks...thats a bit better. Im just trying to understand how to properly orient a solar panel array so Im reading through all this material. I decided to look up videos instead which might be easier to follow.

Oh dear. You've now entered the Solar Zone.

The old standard of aiming panels directly solar South has fallen by the wayside, as sometimes it is advantageous to aim them a bit more easterly or a bit more westerly depending on the particular site location and usage pattern.

Of course they can be mounted on a tracker which will follow the azimuth angle through the day (and elevation angle through the year if it is dual axis). Or considering how cheap panels are these days you can install multiple arrays aimed in different directions and achieve "stationary tracking".

Actually knowing the precise optimum panel angle is not much of a concern these days, as due to the drop in panel costs we are no longer needing to squeeze every last Watt hour out of the day.

quique

Re: Theoretical Question

Yeah it may not be so relevant but the course Im taking will surely think it is. So Im trying to understand it.

So I guess where I was confused as to what azimuth calculations apply to. But Im getting a clearer picture now, thanks.

quique

Re: Theoretical Question

So the process would be:

stand up on a roof
Use the compass to find south
Adjust magnetic south using magnetic declination to find true south
Using true south determine the azimuth angle of the sun

Cariboocoot

Re: Theoretical Question

quique wrote: »

So the process would be:

stand up on a roof
Use the compass to find south
Adjust magnetic south using magnetic declination to find true south
Using true south determine the azimuth angle of the sun

Well, it's probably safer to do it standing on the ground (the azimuth will be the same) but yes that's basically it.

Keep in mind that as far as placing a fixed array is concerned it's irrelevant as the azimuth angle of the sun changes through the day but the panels' angle doesn't. When the panels are aligned at true solar South, that's it. What the sun does it does, and the array output will vary accordingly. Yearly elevation has more bearing, as at some latitudes it can have a significant affect to change it through the year.

This may help you understand the situation: http://www.macslab.com/optsolar.html
Or it may confuse you more.

ggunn

Re: Theoretical Question

quique wrote: »

Does this statement seem correct:

When the azimuth angle is 0 degrees, which means true south, the sun will be at its highest angle of elevation for that particular day.

This is taken out of some course material I am reading. Its translated from english and I have found errors before, so I need to know if this is erroneous or if Im not really understanding the concepts.

I understand azimuth is the HORIZONTAL angle between south and true south. Sun elevation is the VERTICAL angle from horizon to the suns position in the sky. But Im not clear as to why when azimuth is 0 (a horizontal measure of angle), it should mean the suns elevation is highest (vertical measure of angle)?

ELEVATION
The sun starts the day with elevation 0 deg, and rises to whatever it can (90 deg in the summer and perhaps 20 in the winter depending on location) during the day and goes back to to when it sets in the west. So basically Altitude during the day goes from 0 - 90 - 0.

AZIMUTH
I thought Azimuth was a fixed value during the day, based on the location and time of year. But according to the statement, azimuth changes during the day much in the same way (because it is related to?) the sun elevation angle?

It means the apparent azimuth angle of the sun, which is zero degrees at solar noon at wherever you are. At that time the sun will be at its highest apparent elevation for that day, and at that time on the summer solstice it will be the highest it ever gets. No matter where you are on the planet, the difference between the maximum elevation at solar noon on the summer solstice and on the winter solstice is 47 degrees, which is twice the tilt angle between the axis of the earth and a line normal to the plane of the ecliptic. On the equinoxes the sun's elevation angle at solar noon is equal to the latitude of the point of observation.

NorthGuy

Re: Theoretical Question

ggunn wrote: »

... at that time on the summer solstice it will be the highest it ever gets. No matter where you are on the planet ...

That's not true if you're between tropics. For example, on equator, it'll be highest at equinox.

Cariboocoot

Re: Theoretical Question

Seasons are reversed between Northern and Southern hemispheres. Thought I should mention that because we too often think it's the same everywhere.

The closer to the Equator (from either side) the less it matters.

northerner

Re: Theoretical Question

You can simply use a calculator to determine the suns angle and thus determine the optimum solar array angle(s).

http://www.esrl.noaa.gov/gmd/grad/solcalc/azel.html

bmet

Re: Theoretical Question

quique wrote: »

Thanks...thats a bit better. Im just trying to understand how to properly orient a solar panel array so Im reading through all this material. I decided to look up videos instead which might be easier to follow.

Use the references given to find the time for Solar Noon at your location. THEN, 10 minutes before Solar Noon, hold a Pringles can, upright, onto the surface of your panel. Orient the panel until no shadow is cast from the Pringles can. Take note of the angle and direction. Repeat for all your other panels.

quique

Re: Theoretical Question

Cool! I like this azimuth and navigation stuff...i think from now on ill start to tell people where im going in navigational/azimuth terms

niel

Re: Theoretical Question

quique wrote: »

Cool! I like this azimuth and navigation stuff...i think from now on ill start to tell people where im going in navigational/azimuth terms

i think you may confuse them just as you were confused with it. ok, i see, that's the plan.8)