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--></style></head><body lang="EN-US" link="blue" vlink="purple"><div class="WordSection1"><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Bill and Wrenches,</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">I have been battling this issue for a while. Our sales folks are up against fierce competition and want to design a system that has the best return on investment. So, they will choose a reverse tilt system over a North facing array unless there is a strong deterrent to going with reverse tilt. This deterrent could come in the form of a company policy “no reverse tilts” or by adding significant costs to reverse tilt systems. We’ve tried some of both and there are still cases where reverse tilts prevail – but we do them very seldom and only with careful consideration. </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Let’s say we have a 5 kW grid tied system (off grid is a whole other ball of wax) and we’re analyzing our options between flush mount North 18 degrees (4:12 pitch) and reverse tilt to South at 5 degrees. The North facing array will produce about 24% less than the South facing reverse tilt system assuming no differences in shade for our Bay Area location or 5126 kWh/yr for North versus 6758 kWh/yr for South. At $0.20/w for electricity this amounts to $326/yr of extra savings for the South facing reverse tilt system. We might charge about an extra $1500 to install the reverse tilt system to account for the engineering cost to check the structure and extra racking material and labor. This means that the reverse tilt system pays off in less than 5 years. The numbers would be more in favor of the reverse tilt if the North facing pitch was steeper. </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">I guess all I’m saying is that the pure numbers still support reverse tilts in some cases. Despite that, my gut is that we should avoid them for the same reasons that Bill lists below. </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Best,</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">August</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p><div><div style="border:none;border-top:solid #b5c4df 1.0pt;padding:3.0pt 0in 0in 0in"><p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> RE-wrenches [mailto:<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org">re-wrenches-bounces@lists.re-wrenches.org</a>] <b>On Behalf Of </b><a href="mailto:billbrooks7@sbcglobal.net">billbrooks7@sbcglobal.net</a><br><b>Sent:</b> Tuesday, July 28, 2015 11:16 AM<br><b>To:</b> 'RE-wrenches'<br><b>Subject:</b> Re: [RE-wrenches] Using the North Facing Roof</span></p></div></div><p class="MsoNormal"> </p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Larry and Peter,</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">You are too old-school to think outside the box. It’s not about direct sunlight—it’s all about kWh/m^2/day and those numbers don’t lie. Your analysis is not correct and this is why simple analyses will always give you a wrong answer. </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">North-facing arrays have been financially attractive for years, but many have not done it due to taboos or bad analysis. Reverse-tilt arrays often look horrible and should be avoided particularly on the street-side of a house. Also, the structural impacts of tilted arrays on residential rooftops are not well-understood so wind-loading calculations are complex at best.</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">We have been using east and west facing roofs for your years so what’s the big deal about north? I put together the one of the first tables of orientation version performance way back in 2001 for the California Energy Commission to combat the misconceptions that PV arrays had to be mounted at 45-degrees facing South (the prevailing misconception at the time). I didn’t print the North facing numbers because the concept would have blown people’s minds at the time—they weren’t ready for the truth.</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">30-degrees facing south is optimal in most latitudes from 20-degrees to 50-degrees. (perfect in most locations)</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">4:12 pitch (18-degrees) facing south is 97% of perfect.</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">4:12 pitch east or west is 88% of perfect.</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Flat is 89% of perfect.</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">4:12 pitch facing north is 75% of perfect.</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">The truth shall set you FREE.</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Bill.</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p><div><div style="border:none;border-top:solid #e1e1e1 1.0pt;padding:3.0pt 0in 0in 0in"><p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> RE-wrenches [<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org">mailto:re-wrenches-bounces@lists.re-wrenches.org</a>] <b>On Behalf Of </b>Starlight Solar Power Systems<br><b>Sent:</b> Tuesday, July 28, 2015 9:41 AM<br><b>To:</b> RE-wrenches <<a href="mailto:re-wrenches@lists.re-wrenches.org">re-wrenches@lists.re-wrenches.org</a>><br><b>Subject:</b> Re: [RE-wrenches] Using the North Facing Roof</span></p></div></div><p class="MsoNormal"> </p><div><p class="MsoNormal">In Yuma, AZ, north facing modules will have direct sunlight for small part of the year. In the picture, look at the yellow area above the East-West line. Thats direct sunlight from the north. The green top line in the picture shows summer solstice showing sunlight from sunrise to about 0930 and from 1530 to sunset. The energy harvested during those hours will be tiny compared to the peak sun hours on the south side. The angle of incidence will also reduce the total power generated during those hours.</p></div><div><p class="MsoNormal"> </p></div><div><p class="MsoNormal">The thin brown middle line is the equinox. By then, there is no direct sunlight on the north side. I can not see any benefit in AZ even at todays low prices. Now, if I were building in Quetzaltenango, Guatemala, that would be a different story. But then again, I would have to clean off the volcanic ash each morning. </p></div><div><p class="MsoNormal"> </p></div><div><div><p class="MsoNormal">Larry Crutcher<br>Starlight Solar Power Systems</p></div></div><div><p class="MsoNormal"> </p></div><p class="MsoNormal"><img border="0" width="381" height="379" id="A1B69AD4-8740-4FD6-8D8C-11FF215EC3F2" src="cid:image001.png@01D0C934.FA297E10"></p><div><p class="MsoNormal">chart came from <a href="http://www.gaisma.com/en/">http://www.gaisma.com/en/</a></p><div><div><div><div><p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-family:"Helvetica","sans-serif";color:black"> </span></p></div></div></div></div><p class="MsoNormal"> </p><div><div><p class="MsoNormal">On Jul 27, 2015, at 11:21 PM, Peter Parrish <<a href="mailto:peter.parrish@calsolareng.com">peter.parrish@calsolareng.com</a>> wrote:</p></div><p class="MsoNormal"> </p><div><div><div><p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">I recently read a short piece that caught me up short, and I quote:<br><br></span></p></div><div><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">“The fast dropping cost of solar, while a huge boon to the adoption of solar PV, has counter-intuitively altered design parameters. No longer is the north-facing roof considered unusable because limited application in less-than optimal orientations can still show a positive net benefit. Arrays are thus designed now with elements or sub-arrays in these locations, increasing overall kW installation while reducing the energy production per capacity installed. This might have been anticipated based on sheer economic analysis from a users perspective, but so long has solar been expensive that these less optimal orientations were never seriously considered.”</span></p></div><div><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p></div><div><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">I doubt that the individual who wrote this piece came to these conclusions him/herself. Does anyone know of a recent article that argued this perspective? Is this an emerging design practice? If so, I’d like to know more about it. </span></p></div><div><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p></div><p class="MsoListParagraph" style="text-indent:-.25in"><span style="font-family:"Calibri","sans-serif"">-</span><span style="font-size:7.0pt"> </span><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Peter </span></p><div><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p></div><div><div><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Peter T. Parrish, Ph.D.</span></p></div><div><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">President, SolarGnosis</span></p></div><div><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">1107 Fair Oaks Ave., Suite 351</span></p></div><div><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">South Pasadena, CA 91030</span></p></div><div><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">(323) 839-6108</span></p></div><div><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><a href="mailto:petertor@pobox.com">petertor@pobox.com</a></span></p></div></div><div><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p></div></div><p class="MsoNormal" style="margin-bottom:12.0pt">_______________________________________________</p></div></div><p class="MsoNormal"> </p></div><p class="MsoNormal" style="margin-bottom:12.0pt"> </p><div class="MsoNormal" align="center" style="text-align:center"><hr size="1" width="99%" noshade style="color:#909090" align="center"></div><table class="MsoNormalTable" border="0" cellspacing="0" cellpadding="0" style="border-collapse:collapse"><tr><td style="padding:0in 11.25pt 0in 6.0pt"><p class="MsoNormal"><a href="https://www.avast.com/antivirus"><span style="text-decoration:none"><img border="0" id="_x0000_i1027" src="http://static.avast.com/emails/avast-mail-stamp.png" alt="Avast logo"></span></a></p></td><td style="padding:.75pt .75pt .75pt .75pt"><p><span style="font-family:"Calibri","sans-serif";color:#3d4d5a">This email has been checked for viruses by Avast antivirus software. <br><a href="https://www.avast.com/antivirus">www.avast.com</a> </span></p></td></tr></table><p class="MsoNormal"> </p></div></body></html>