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

[Drake]

I will use a lot of copper to save 1%.  6% is significant.

For an off grid system, the angle is a major issue.

At 12:35 PM 2/21/2011, you wrote:
>Jim,
>Obviously, your latitude will make a big 
>difference. The further north you go the wider 
>the summer to winter sun angle. Also, I'd want 
>to know if that data was taken using just I/V 
>curves or through a controller which had MPPT 
>capabilities. In a real world situation with 
>MPPT, I'm guessing that matching the array tilt 
>to the sun angle would make more than a 6% difference at 40°+ latitudes.
>Besides, what's wrong with an extra 6%??
>Cheers, bob-O
>
>On Feb 19, 2011, at 8:03 PM, North Texas Renewable Energy Inc wrote:
>
>At least that's the conclusion of Gottfried Wilhelm Leibniz.
>"The largest difference of the [PV] plant yield 
>was less than 6% for tilt angles between 0° and 70°."
>This begs the question, where did the notion 
>that tilt to latitude is critical come from. 
>Surely NREL or someone else has tested this 
>concept before. Anyway if N-S angle energy 
>production loss is only 6% to +/-35° then E-W 
>should be too, right? But it's not.
>Here's why. If you measured irradiance at 
>10°-70° only at noon over 12 months, the air 
>mass would at its minimum during the entire test 
>and so irradiance deviation would be too. AM 
>would not be constant at +/- 35° E-W which has 
>been verified by NREL and others for a long 
>time, AM increases the further from solar noon the sun gets.
>But if the Earths tilt is 23.5 degrees and 
>Gottfried measured to 35 degrees, the difference 
>is 11.5 degrees at summer and winter solstice. 
>And if your array angle is +/- 11.5 deg from 
>true south, rule of thumb is that irradiance 
>losses are minimal. Maybe only 6% or so.
>This puts the significance of array tilt in a 
>whole new light. Pun intended...
>Of course there is a fee to download the entire 
>document but the abstract is here
><http://tinyurl.com/4zf2syk>http://tinyurl.com/4zf2syk
>http://www.scopus.com/record/display.url?eid=2-s2.0-78951495350&origin=inward&txGid=kX6CkwoH_w_VL01NbmaciIC%3a2
>
>
>Jim Duncan
>North Texas Renewable Energy
>
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Drake Chamberlin
Athens Electric
OH License 44810
CO license 3773
NABCEP Certified PV
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