<HTML><BODY style="word-wrap: break-word; -khtml-nbsp-mode: space; -khtml-line-break: after-white-space; "><FONT class="Apple-style-span" color="#0000FF">Tom,</FONT><DIV><FONT class="Apple-style-span" color="#0000FF"><BR class="khtml-block-placeholder"></FONT></DIV><DIV><SPAN class="Apple-tab-span" style="white-space:pre"> </SPAN><FONT class="Apple-style-span" color="#0000FF">You mentioned 90% as best performance for flat glass. Do you have a corresponding number for tubes, in terms of losses due to reflectance? Anyone else have any data to share?</FONT></DIV><DIV><FONT class="Apple-style-span" color="#0000FF"><BR class="khtml-block-placeholder"></FONT></DIV><DIV><FONT class="Apple-style-span" color="#0000FF">Thanks,</FONT></DIV><DIV><FONT class="Apple-style-span" color="#0000FF"><BR></FONT><DIV> <SPAN class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica"><FONT class="Apple-style-span" color="#0000FF">Jim Grundy</FONT></FONT></P><P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica"><FONT class="Apple-style-span" color="#0000FF">NABCEP Certified Solar PV Installer</FONT></FONT></P><P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT class="Apple-style-span" color="#0000FF">Vermont Solar Specialist Plumber PS-279</FONT></P><P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica"><FONT class="Apple-style-span" color="#0000FF">Elemental Energy, Inc.</FONT></FONT></P><P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica"><FONT class="Apple-style-span" color="#0000FF">1750 Clark Rd</FONT></FONT></P><P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica"><FONT class="Apple-style-span" color="#0000FF">E. Montpelier, VT</FONT><SPAN class="Apple-converted-space"><FONT class="Apple-style-span" color="#0000FF"> </FONT></SPAN><SPAN class="Apple-converted-space"><FONT class="Apple-style-span" color="#0000FF"> </FONT><SPAN class="Apple-converted-space"><FONT class="Apple-style-span" color="#0000FF"> </FONT></SPAN></SPAN><FONT class="Apple-style-span" color="#0000FF">05651</FONT></FONT></P><P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica"><FONT class="Apple-style-span" color="#0000FF">802-476-3441 (p)</FONT></FONT></P><P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica"><FONT class="Apple-style-span" color="#0000FF">802-476-5680 (f )</FONT></FONT></P><P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica"><FONT class="Apple-style-span" color="#0000FF">802-272-8933 (c)</FONT></FONT></P><BR class="Apple-interchange-newline"></SPAN> </DIV><BR><DIV><DIV>On Jul 22, 2009, at 6:15 PM, <A href="mailto:re-wrenches-request@lists.re-wrenches.org">re-wrenches-request@lists.re-wrenches.org</A> wrote:</DIV><BR class="Apple-interchange-newline"><P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">Message: 3</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">Date: Wed, 22 Jul 2009 14:29:29 -0400</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">From: "Tom Lane" <<A href="mailto:tom@ecs-solar.com">tom@ecs-solar.com</A>></FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">Subject: [RE-wrenches] tubes versus flat surfaces</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">To: <<A href="mailto:re-wrenches@lists.re-wrenches.org">re-wrenches@lists.re-wrenches.org</A>></FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">Message-ID: <00e401ca0afa$5b06e240$1114a6c0$@com></FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">Content-Type: text/plain; charset="us-ascii"</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px Helvetica; min-height: 14.0px"><BR></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">Glazed collectors: i.e.<SPAN class="Apple-converted-space"> </SPAN></FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px Helvetica; min-height: 14.0px"><BR></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">evacuated tubes and flat plate collectors - the single one factor that</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">effects the collectors efficiency is most is the Angle of Incidence of</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">sunlight to the flat glass or curved glass cylinders. Typically in the best</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">low iron glass at perfect orientation to the sun - only 90% of the sunlight</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">gets through the glass while at least 10% gets reflected off the surface. No</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">matter how efficient the absorber is in capturing the solar thermal energy -</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">if only 90% get through - then 90% insolation x 90% efficiency means at a</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">theoretically best is 81% efficient<SPAN class="Apple-converted-space"> </SPAN>collector under optimal conditions.</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">Evacuated tubes have an obvious distinct disadvantage to a flat surface - as</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">the plane rotates away from the south. On east or west facing roofs, the</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">back side of the tube curvature will typically be greater than a 40 degree</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">angle of incidence from September 21st to March 21st above 40 degrees</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">latitude. Rotating the absorber in the tube will not change the angle of</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">incidence to the glass. In the summertime above 40 degree latitude the</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">morning<SPAN class="Apple-converted-space"> </SPAN>and/or afternoon<SPAN class="Apple-converted-space"> </SPAN>sun will be north of a south facing absorber in</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">the glass tube. IT IS IMPOSSIBLE for a tubular surface<SPAN class="Apple-converted-space"> </SPAN>that covers the same</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">area TO CAPTURE AS MUCH SUNLIGHT AS A FLAT SURFACE -<SPAN class="Apple-converted-space"> </SPAN>as much of the surface</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">on one side<SPAN class="Apple-converted-space"> </SPAN>will always be curved AWAY from the sun. Even at direct 0</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">orientation at solar noon to a flat plate or evacuated tube facing south</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">only the 10 o'clock to 2 o' clock position on a tube is in excellent</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">orientation to the sun. TOTAL NONSENSE IS TUBULAR PEOPLE CLAIMING THE TUBES</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">TRACK THE SUN! Please take a geometry class! PLEASE NOTE THIS IS TRUE FOR</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">SOLAR ELECTRIC OR SOLAR THERMAL COLLECTORS THE ANGLE OF INCIDENCE TO THE</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">GLASS IS CRITICAL. NOTE TO FOLLOW - IT IS ILLEGAL TO TO PUT ANNEALED GLASS</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">ON A ROOF. Only tempered glass can legally be put on a roof.<SPAN class="Apple-converted-space"> </SPAN>Gator tom</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px Helvetica; min-height: 14.0px"><BR></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px Helvetica; min-height: 14.0px"><BR></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px Helvetica; min-height: 14.0px"><BR></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">Tom Lane</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px Helvetica; min-height: 14.0px"><BR></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">Energy Conservation Services</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px Helvetica; min-height: 14.0px"><BR></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">6120 SW 13th ST, Gainesville, FL 32608</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px Helvetica; min-height: 14.0px"><BR></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">(352) 377-8866<SPAN class="Apple-converted-space"> </SPAN>F (352) 338-0056</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px Helvetica; min-height: 14.0px"><BR></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">Give Your Sun A Job <<A href="http://www.ecs-solar.com/">http://www.ecs-solar.com/</A>><SPAN class="Apple-converted-space"> </SPAN></FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px Helvetica; min-height: 14.0px"><BR></P> </DIV><BR></DIV></BODY></HTML>