Background Let's say you want to place a solar collector on your home or school. There are several types of solar collectors. Collector types include passive solar design; solar thermal collectors such as flat-plate collectors, which heat water or fluids; and photovoltaic, or solar electric, collectors. The collectors can be mounted on the ground near the building, attached to the building's roof or south facing wall, or be integrated into the building design (passive solar) or construction materials (building integrated). For this activity, assume the solar collector will be used for heating water. Where would you locate it? Solar collector's cannot collect the sun's energy unless the sun shines upon them. This may seem obvious, but it can be overlooked when choosing a site for a solar energy system. The altitude of the sun is the angle between the position of the sun in the sky and a point directly below on the horizon. This altitude varies by 47° during the course of one year, and unless homeowners can observe the altitude of the sun all year long, they may be unaware of potential shading problems. The sun's greatest heating effect in Wisconsin occurs between 9 a.m. and 3 p.m. Standard Time. It is best if no more than 15 percent of a solar collector is shaded during this time (the less the better). Many obstructions may shade a collector; hills, other buildings, fences, chimneys, dormers, evergreen trees, and deciduous trees (although they lose their leaves in winter, large limbs may still cause significant shading). The use of a sun locator allows you to accurately plot the times of day that sunlight is blocked by these kinds of interferences. On the winter solstice, the sun's path follows a low arc in the winter sky, while on the summer solstice, the sun follows a much higher and wider arc across the sky. If you trace the two arcs on an imaginary dome representing our sky, and connect the winter and summer morning points of 9 a.m., as well as the two afternoon points of 3 p.m., the area within the space is the solar window. Any objects appearing within this solar window subtract from the solar gain of a collector mounted at that position. If you have a site that is generally without shadow from 9 a.m. to 3 p.m., you have a good solar site. A sun locator, or solar pathfinder, is a simple device for identifying this solar window. Procedure
Background
Let's say you want to place a solar collector on your home or school. There are several types of solar collectors. Collector types include passive solar design; solar thermal collectors such as flat-plate collectors, which heat water or fluids; and photovoltaic, or solar electric, collectors. The collectors can be mounted on the ground near the building, attached to the building's roof or south facing wall, or be integrated into the building design (passive solar) or construction materials (building integrated). For this activity, assume the solar collector will be used for heating water. Where would you locate it? Solar collector's cannot collect the sun's energy unless the sun shines upon them. This may seem obvious, but it can be overlooked when choosing a site for a solar energy system. The altitude of the sun is the angle between the position of the sun in the sky and a point directly below on the horizon. This altitude varies by 47° during the course of one year, and unless homeowners can observe the altitude of the sun all year long, they may be unaware of potential shading problems.
The sun's greatest heating effect in Wisconsin occurs between 9 a.m. and 3 p.m. Standard Time. It is best if no more than 15 percent of a solar collector is shaded during this time (the less the better). Many obstructions may shade a collector; hills, other buildings, fences, chimneys, dormers, evergreen trees, and deciduous trees (although they lose their leaves in winter, large limbs may still cause significant shading). The use of a sun locator allows you to accurately plot the times of day that sunlight is blocked by these kinds of interferences.
On the winter solstice, the sun's path follows a low arc in the winter sky, while on the summer solstice, the sun follows a much higher and wider arc across the sky. If you trace the two arcs on an imaginary dome representing our sky, and connect the winter and summer morning points of 9 a.m., as well as the two afternoon points of 3 p.m., the area within the space is the solar window. Any objects appearing within this solar window subtract from the solar gain of a collector mounted at that position. If you have a site that is generally without shadow from 9 a.m. to 3 p.m., you have a good solar site. A sun locator, or solar pathfinder, is a simple device for identifying this solar window.
Procedure
1. Download Constructing and Using a Solar Pathfinder, Activity Sheet A, and Activity Sheet B. Example sketch of Activity Sheet B indicating possible shading of solar panels.
2. Choose a site to evaluate for solar collection. This may be a window, the side of a building, a potential house site, or a solar collector site. Stand as close as is safely possible to the surface that will be collecting the solar energy. Caution: Many solar energy devices are located on rooftops. Unless you have a flat roof with easy access, do not use the rooftop as one of your locations. If you are using a window, make all measurements from inside. Readings taken outside should take place at ground level.
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