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

[Peter Parrish]

Interesting abstract.

One thing that struck me was the lack of measured data on power production
(if that indeed is the object of this study). I guess one can infer the Pmp
from "the short circuit current (Isc ), the open circuit voltage (Uoc ) and
the cell temperature (T) of each cell". I also wonder how often the data
points were recorded. With the general availability of micro-inverters,
their use would have been a better choice.

In the final analysis, if the data is sound, the result may only apply to
Hannover (high latitude and low-insolation) and similar sites.

How orientation-dependent is indirect radiation?

It would be great if we could read the whole article...

- Peter 


 
Peter T. Parrish, Ph.D., President
California Solar Engineering, Inc.
820 Cynthia Ave., Los Angeles, CA 90065
CA Lic. 854779, NABCEP Cert. 031806-26
peter.parrish at calsolareng.com  
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885

 
________________________________________
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of North Texas
Renewable Energy Inc
Sent: Saturday, February 19, 2011 8:04 PM
To: RE Wrenches
Subject: [RE-wrenches] Array tilt angle doesn't matter?

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