Will The Sun Shine On Your Solar Modules All Winter? Steve Willey c.1992 Steve Willey Most solar module users know that their panels generate electricity only when mounted directly in sunlight. In fact, a shadow on even part of a solar module can stop it from producing power. I have seen solar modules installed by the U. S. Forest Service that were almost completely blocked by trees, because they had considered only the appearance of the building, and neglected practicality. It seems easy to pick out a good sunny spot for solar modules by just watching shadows outdoors to find a spot that is sunny all day long. But as the seasons change, those shadows become longer or shorter. You don't see the whole picture until you watch for a full season, unless you have a solar siting device. Winter is the most critical time since the sun is lowest in the sky and shadows are longest. This simple homebrew solar sight shows winter sunshine access at a glance. You stand at the intended PV location and site across the device to see the daily path of the sun in 5 winter months, when the sun is lowest in the sky and shadows are longest. Any trees, buildings, or things other than clear sky that are seen to be higher than the edge of the sight will cast a shadow on your spot during those winter months. This sight is simple, but accurate enough to do the job. The pattern with this article is shown for one latitude only, but you can build one for other latitudes using Part One dimensions given in Table 1. The pattern given here is for 46¡ to 50¡ latitude (north or south). Assembly The two parts of the solar sight are printed here at half their real size. Cut out pieces of plywood (or cardboard for short term use) to the measurements specified on the pattern (or Table 1 depending on your latitude). Copy the converging lines on to Part Two and press in a thumbtack where the lines come together to a point for easier visibility. Copy the hours of the day on to Part One. Join Part One at a right angle to Part Two at the dotted line. The joint can be made sturdy by gluing in a piece of quarter round moulding on the back side (see photo). Elmer's wood glue works great; do not use screws or nails unless they are brass, because they may affect your compass. To align the sight, a compass and a bubble level should be glued on the triangle surface. Round bubble levels are available that mount flat on a horizontal surface and have one bubble that you line up in a central circle for level in all directions at once. Look for one in hardware and recreational vehicle stores. Just about any compass will do, but don't believe the markings on it! True south, or solar south, is the direction of the sun at noon (don't be fooled by Daylight Savings Time). In the northwest U.S. true south is a full 20 degrees left of magnetic south shown on the compass. To point true south, just mount the compass with south mark 20 degrees right of the 0 degree line on the sight as shown on the pattern. Then when you hold the sight so that the needle points to S on the compass, the sight points to the real south. It is just the opposite on the east coast, with true south 20 degrees right from magnetic south. In mid-North America, magnetic south is right on true south. A call to local surveyors will get you the right correction angle for your area. Using the Solar Site Hold the sight level, with the 12 noon center line facing true solar south. Put the head of the thumb tack in front of your eye and gaze up across top edge of the site. Be sure you are looking right along a straight line starting at the thumb tack and rising to the upper edge of the sight, where the time of day is marked, your eye always level with the thumb tack. What you see just over the edge approximately represents the sun's path in November, December and January, at the time of day shown. Mentally add 1-1/4 inch to the height of the sight to see the sun's path in October and February. Any trees or mountains or buildings that you can see above the curved sight edge will cast a shadow on you in those months. Ideally, you want to see only sky. Other Latitudes If you live at a latitude other than 46-50¡ change the heights in Part One as follows: (TABLE 1 PART ONE LINE HEIGHTS FOR LATITUDES OTHER THAN 46¡- 50¡) These figures are derived from sun angle charts, rounded a little to average the three winter months. Access Author: Steve Willey, Backwoods Solar Electric Systems, 8530 Rapid Lightning Creek Road, Sandpoint, ID 83864 ¥ 208-263-4290.