Ross McCluney wrote: > For those interested, my reply to Fernando Cabral about solar water > heating is attached, or can be seen below. One thing I forgot to say is > that when you have one collector facing East toward the morning sun, if > the panels are placed in series, the heat collected by the East panel > will be radiated out by the West panel facing away from the sun. If > they are in parallel, the same problem is experienced, but it is the > heat the "hot" panel has put in the tank which is radiated by the "cold" > panel.
Ooops! This is a possibility I had not thought about. You are100% right (albeit for people living near the Equator the problem is much less acute than for people living in temperate zones, I guess). - fernando > The only way to avoid this problem would be to make a special > plumbing system which made the circulating water go through only the > East panel in the morning, shutting off flow through the West one, and > reversing this arrangement in the afternoon, a complex solution and the > reason all installations have all panels facing the same direction. > > An extreme version of this problem was tested (against our protest that > the test was not worth doing) by FSEC in the late 70s. It consisted of > a cylindrical hot water tank, painted black all around, and covered by a > cylindrical transparent glazing all the way around. We pointed out that > the sides of this tank in shade would be radiating while the sides in > sun would be collecting. The collector was tested for the inventor > anyway, and he was very disappointed with the poor results. > > Another solar collector tank, similar to the one described, was slightly > taperd at the top, and we called it the "suppository solar collector." > > Another one we tested was a fairly conventional flat plate collector in > an insulated box and the inventor had a good idea of putting folded > transparent plastic in the space between the glass and the blackened > metal fin and tube absorbing plate. Solar water heating collectors have > to be tested both in simulated actual opertion, with water in them, and > empty, dry. The latter test is to make sure they won't have any > problems when sitting in the sun, on the roof or ground below, while the > plumbing and wiring are being done. This collector failed the dry, > "stagnation," test when the plastic inside melted, ran through some > cracks in the case, and pooled on the ground below. > > Ross McCluney, Cocoa, FL > > > ------------------------------------------------------------------------ > > Subject: Re: Best angle to catch sun light - off topic > Date: Fri, 15 Jan 1999 10:00:38 -0500 > From: Ross McCluney <[EMAIL PROTECTED]> > Organization: Florida Solar Energy Center > To: [EMAIL PROTECTED] > References: <[EMAIL PROTECTED]> > > Fernando Cabral wrote: > > > One thing I have noticed is that no one plans the roof in order to take > > advantage of the sun in an optimized way. They build their house and > > than the best place for the panel is found. Usually this just means > > deciding > > which side of the house is facing North. That where the panel is placed. > > > > Also, the angle the panel makes with the horizon is just an accident: > > whatever > > the inclination of the roof is. > > > > Now I am planning to build a house for a small farm I have. I've been > > thinking > > on how to take the best advantage of the solar power. This includes > > where > > to have a garder with a nice sundial and where to place the solar panels > > for water heating as well as (perhaps) electricity (at least in Brazil > > solar panels for electricity are very expensive). > > > > At 19 37' 57" S, it is clear that the panel should be facing North. > > But what is the best angle with the horizon. And, if I can have several > > panels, is there a practical to calculate the best angle of each > > so as I can guarantee the highest possible insolation level? > > > > Say, if I have three panels, is it best to place them side by side, with > > > > the same inclinatation and declination? Perhas if one is a inclined > > towards > > the East with a certain angle and the other to the West with a proper > > angle I can capture more light? > > I suggest that you visit our web site and explore the available options for > getting information from our documents section. Most of our publications > are free. Though oriented mainly for northern latitudes in the U.S., I > think you should be able to translate the recommendations to your location. > > A couple of conclusions I remember from years ago when I did a little work > in this field: > > Solar water heater collectors, and solar photovoltaic cells for generating > electricity, are not overly sensitive to small changes away from the optimum > direction for them to face. Normally we recommend pointing the normal > (perpendicular) of the flat plate collector surface due south (north in the > southern hemisphere) and at an elevation from the horizon that is half way > between the sun's solar noon summer and winter solstice positions, putting > this direction close to the solar noon equinox position. > > Since summer months are longer than winter months, and winter months are > colder, some people alter this direction, facing the collector closer to the > lower-in-the-sky winter solstice, by 10 to 20 degrees, depending upon what > is desired, to slightly improve performance in the winter at the expense of > summer output. Furthermore, if you want to accentuate afternoon performance > over morning performance, you can change the azimuth as well, but don't > overdo it, because these alterations probably will reduce the total amount > of solar energy collected over the course of a year slightly, or a lot if > the direction is too far away from the primary recommendation. I say > "probably" because so far I haven't considered the effect of clouds, haze, > and other atmospheric variables. If your site has more sun in the morning > than the afternoon, due to afternoon cloud buildup, for example, you can > increase overall annual performance by rotating the collector slightly to > the East. > > The above recommendations apply to all the solar panels. They should all > face the same way--be parallel to each other. If you face one more toward > the East and another more toward the west, you are in some respects shooting > yourself in the foot. The East one will do better in the morning, but the > west one will do worse, probably a lot worse, and vice versa in the > afternoon. I know of no solar installation anywhere that has its solar > collectors in different directions, at least on purpose and for optimum > performance. > > The problem of facing buildings in the wrong direction is a very very common > one. It might be forgiven for relatively uneducated people, but for > architects it is inexcusable, but alas common. > > The problem is not as crucial for solar collectors for heat or electricity, > since they are generally somewhat independent from the building. It just > means that the support structure holding the solar panels has to be more > complex, and probably unsightly, in order to face them in the proper > direction on a roof facing the wrong direction. My field is the daylight > illumination of building interiors--daylighting, and in this case > mis-orientation can be devastating. In hot climates, such as found within > 20 or 30 degrees of the equator, facing windows west without adequate > shading produces horrible afternoon heat loads, localized thermal > discomfort, and terrible glare. We recommend avoiding facing windows in > this direction, or shading them with good exterior shading devices. Visit > our fenestration web site for more information about this, shown below. You > can use the main screen menu or just add "/~fen" at the end of the site > address to go directly to the proper page. > > > I know this information can probabily be found in some book about > > photometry or perhaps archtecture/engineering. I couldn't find > > them... > > Look for books on solar energy or solar engineering. The "bible" is a book > by Duffie and Beckman called "Solar Energy Thermal Processes" or something > like that, but there are others. If it is photometry that interests you, > try my book, listed below. > > I hope this helps. > -- > Ross McCluney, Ph.D. Principal Research Scientist > Florida Solar Energy Center, 1679 Clearlake Rd., Cocoa, FL 32922-5703 > Voice: 407-638-1414 Fax: 407-638-1439 e-mail: [EMAIL PROTECTED] > Florida Solar Energy Center: http://www.fsec.ucf.edu > Sundials: http://www.sunpath-designs.com > Introduction to Radiometry and Photometry: http://www.artech-house.com > -------------------------------------------------------------- -- Fernando Cabral Padrao iX Sistemas Abertos mailto:[EMAIL PROTECTED] http://www.pix.com.br mailto:[EMAIL PROTECTED] Fone: +55 61 321-2433 Fax: +55 61 225-3082 15º 45' 04.9" S 47º 49' 58.6" W 19º 37' 57.0" S 45º 17' 13.6" W
