I sometimes play with various tilt angles in PV Watts for different
locations too. The weather conditions at different times of year vary
from location to location so I don't think there is a one size fits all
solution here.
Also, I don't think this article or PV Watts takes into account snow
shed, which dictates steeper angles in winter.
R. Ray Walters
Chief Technical Officer, RemoteSolar.com
BS Mech Engineering, 1988
Former NABCEP Certified, 2004-2016
Licensed Master ELectrician, Colorado
303 505-8760
On 2/27/17 12:10 PM, Sindelar Solar wrote:
Wrenches,
One of my clients sent me this article on seasonal array tilt angles:
http://www.solarpaneltilt.com/#2season
It challenges some of the long-held numbers, although not
substantially, and I found it worth a review.
I have long advocated adjustment twice a year, staying at latitude
tilt for nine months and latitude +15 for winter, presuming that for
most homes a latitude tilt will be adequate over the summer months
without a second pair of adjustments. I have long figured that the
fewer required maintenance operations the more they'll actually get
done. After reviewing this article I replied to the client who sent it
to me, whose home is at 7,000' at 35.5 ° latitude:
Bill,
Thanks for this. I'll assume that you're welcoming my response, so
in short...
For me as an advisor principally to off grid homeowners, I'll err
on the side of practicality, simplicity and ease of remembrance
over accuracy. That's why, for example, I recommend two angle
adjustments/year over four. Also, as Landau himself states, "A
difference of a few degrees will make very little difference in
the energy you gather". This information was of greater
consequence when PV was far more expensive than it is today.
My original and purposely simplistic recommendation was to adjust
to latitude +15 for winter and back to latitude for the rest of
the year. I gave an approximate date around November 10th, (midway
between the fall equinox and the winter solstice) to increase the
tilt, with a return to latitude around February 10th (midway
between the winter solstice and the spring equinox). Extrapolating
using his calculations for 4X/year, I would adjust to winter angle
earlier (his target is October 7th), such as "during October" and
returning later (his target is March 5th), such as "late February
or early March". Using Landau's figures for 35°, that suggests
32.0 for spring/summer/fall and 55.2 for winter, adding half a
degree or so for your location, with an unknown adjustment for the
higher elevation.
Given your DP&W pole-top rack with its 10-degree adjustment
increments, this means only that we have no need to drill the
additional hole in the adjustment bar at 50 degrees. The supplied
holes at 35 and 55 are best. You'll want only to broaden the
duration of your winter tilt angle on both ends.
Good exercise! I appreciate your sending this along, as I have
always worked from longtime collective-wisdom guidelines, having
never seen these calculations laid out with such accuracy.
I'll be interested in any comments from other Wrenches who take the
time to review the link.
Allan
--
*Allan Sindelar*
[email protected] <mailto:[email protected]>
NABCEP Certified PV Installation Professional
NABCEP Certified Technical Sales Professional
New Mexico EE98J Journeyman Electrician
Founder (Retired), Positive Energy, Inc.
*505 780-2738 cell*
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