<div dir="ltr"><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">There are two issues that make the article overly simplistic I think.</div><div class="gmail_default"><ul><li><font face="arial, helvetica, sans-serif">As the author admits, the calculations only work for arrays with due south orientation and states that "Solar panels should always face true south."</font></li><li><font face="arial, helvetica, sans-serif">The article ignores weather/temperature, which is one reason the statement above is not completely accurate.</font></li></ul><span style="font-family:arial,helvetica,sans-serif">For example, where I live the summer afternoons are cloudy and very hot just about every day. Winter days are crystal clear with little haze. For fixed arrays the annual optimum array orientation is about latitude minus three degrees and 170 degrees from true north. The benefit you get here from adjusting tilt twice a year is less than other areas may be for weather reasons. In fact, you could possibly gain more by keeping the same annual optimum tilt and adjusting the orientation twice a year (in a pole mount scenario). In the summer the best orientation is somewhere east of 170 and west of 170 in the winter (presumably close to 180).</span></div><div class="gmail_default"><span style="font-family:arial,helvetica,sans-serif"><br></span></div><div class="gmail_default">Granted, I’m now at 25 degrees north latitude, so the article is on the edge of being accurate in my situation, but I know for a fact that local weather patterns make the “due south” recommendation inaccurate in many places, and the benefits of tilt changes can’t be optimized without taking weather into account.</div><div class="gmail_default"><br></div><div class="gmail_default"><br></div><div class="gmail_default">Jason</div><div class="gmail_extra"><br clear="all"><div><div class="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div>
<br><div class="gmail_quote">On Mon, Feb 27, 2017 at 2:10 PM, Sindelar Solar <span dir="ltr"><<a href="mailto:Allan@sindelarsolar.com" target="_blank">Allan@sindelarsolar.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
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<p>Wrenches,</p>
<p>One of my clients sent me this article on seasonal array tilt
angles: <a href="http://www.solarpaneltilt.com/#2season" target="_blank">http://www.solarpaneltilt.com/<wbr>#2season</a></p>
<p>It challenges some of the long-held numbers, although not
substantially, and I found it worth a review.</p>
<p>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:</p>
<blockquote>Bill,<br>
Thanks for this. I'll assume that you're welcoming my response, so
in short...<br>
<p>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.</p>
<p>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. <br>
</p>
<p>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.</p>
<p>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.</p>
</blockquote>
<div class="gmail-m_7542748100153908312moz-forward-container">I'll be interested in any
comments from other Wrenches who take the time to review the link.<br>
Allan<br>
<p class="MsoNormal" style="margin-bottom:0.0001pt;line-height:normal"><span>-- <u></u><u></u></span></p>
<p class="MsoNormal" style="line-height:normal"><b><span>Allan
Sindelar</span></b><span><br>
</span><a href="mailto:allan@sindelarsolar.com" target="_blank"><span>allan@sindelarsolar.com</span></a><span><br>
</span><span>NABCEP
Certified PV Installation
Professional<br>
NABCEP Certified Technical Sales Professional<br>
New Mexico EE98J Journeyman Electrician<br>
Founder (Retired), <span>Positive
Energy,
Inc.</span><br>
<b><a href="tel:(505)%20780-2738" value="+15057802738" target="_blank">505 780-2738</a> cell</b></span><span><u></u><u></u></span></p>
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