[RE-wrenches] Array tilt angle doesn't matter?

Tue Feb 22 19:30:45 PST 2011

OK.  I understand fully the declination, heck I live below the tropic of Cancer so get to experience the Lahaina Noon phenomenon.  I also understand sun angle above the horizon but that’s not what the original comment was about.  It was about the *difference* between winter and summer sun angles relative to a high latitude point on the globe and my argument is that it is the same everywhere, i.e. 47 degrees difference between the low N/S point of the sun at noon versus the high N/S point at noon.  That doesn’t change.  At one latitude the sun may “bottom out” at 12 degrees above the horizon and at another it may bottom out at 40 degrees above the horizon but the difference between that the top point at each latitude is still 47 degrees.

From: Darryl Thayer 
Sent: Tuesday, February 22, 2011 5:19 PM
To: RE-wrenches 
Subject: Re: [RE-wrenches] Array tilt angle doesn't matter?

At noon LST the sun is latitude angle from Zenith, the solar declination is 23.5 degrees and the sun on the solstices is above and below the equinox position by the declination.  Everywhere on earth, however the day length varies and the sunset angle varies depending upon latitude.    

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From: Tom Elliot <tom at wagonmaker.com>
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Sent: Tue, February 22, 2011 8:16:54 PM
Subject: Re: [RE-wrenches] Array tilt angle doesn't matter?

Hmmm, I guess there could be a factor that enters into it due to the curvature of the earth but the difference between the tropics of Cancer and Capricorn, the extent of relative solar movement, is 47 degrees and that’s not about to change.

From: Dave Palumbo 
Sent: Tuesday, February 22, 2011 3:51 PM
To: 'RE-wrenches' 
Subject: Re: [RE-wrenches] Array tilt angle doesn't matter?

Tom,

This is coming from old memory, so I give this with a grain of salt, but I believe the noontime sun angle at my latitude (44.5) is about 78 degrees on June 21st and about 22 degrees on December 21st. That’s a difference of 56 degrees.

David Palumbo

Independent Power LLC 

462 Solar Way Drive

Hyde Park, VT 05655

www.independentpowerllc.com 

NABCEP Certified PV Installer

Vermont Solar Partner

23 Years Experience, (802) 888-7194 

From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Tom Elliot
Sent: Tuesday, February 22, 2011 7:46 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Array tilt angle doesn't matter?

“The further north you go the wider the summer to winter sun angle.”

Bob-O.  Explain this one to me please.  The difference between winter solstice and summer solstice sun angle is 47 degrees, everywhere on the planet, even in Hawaii.  I suspect that in higher latitudes a lower sun angle means more atmosphere to affect insolation but the planet, last time I checked, is tilted the same everywhere.

Tom

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