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

North Texas Renewable Energy Inc ntrei at 1scom.net
Sat Feb 19 20:03:54 PST 2011


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://www.scopus.com/record/display.url?eid=2-s2.0-78951495350&origin=inwar
d&txGid=kX6CkwoH_w_VL01NbmaciIC%3a2


Jim Duncan
North Texas Renewable Energy

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