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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