panel would reduce the useable space to only 22.5 square feet (15 inches by 18 feet) of every 50 square feet (2 feet by 25 feet) of each roof panel being used to mount the solar laminate. This equates to a loss of 55 percent of the roof space. On the other hand, if 16-inch roof panels are used and the length of the roof is 19 feet, then the space loss for this laminate would be quite optimal at only 11 percent. Tangential to the above, maximizing the system
output (watts per square foot of available roof space) is important because more often than not the power demand of the occupant is greater than what can be supplied by roof-mounted solar. One should also con- sider the power output of the system if roof space is limited. This varies with the technology used. Before space loss considerations, a-Si laminate modules produce about 5.5 watts per square feet of laminate as compared to crystalline, which produces about 14 watts per square feet of module area. Mono- and poly-crystalline are the oldest and
by far the most popular PV modules comprising more than 90 percent of the roof-mounted PV market. Module sizes vary but are generally around 3.5 feet by 5.5 feet and consist of crystalline cells beneath a thin layer of glass and supported by a backing and aluminum frame. Because of a rigid frame, they lend themselves to mechanical attach- ment to the SSMR. Rooftop space loss can be minimized when
utilizing a solar technology that is rigidly attached above the standing seam. Mechanical attachments to a standing seam consist of either using a sup- port rail or directly to the seam, which, in either
case, can utilize penetration-free seam clamp technology originated by S-5!. When a PV system is mounted parallel to the
roof plane there is virtually no effect on wind effect to the roof. In fact, it may actually be reduced. Ad- ditional collateral loads are negligible (2 pounds per square foot to 3.2 pounds per square foot, depend- ing on module weights and the mounting method). Attaching modules directly to the seam cre-
ates the most economical approach as it eliminates the need for an additional rail support. Using this method results in minimal space loss depending on module size and standing seam spacing. While us- ing a rail adds additional cost to the system, it may also help to achieve even better space loss ratios. Tilting the PV may create greater output per
installed watt of power, but it can also result in sig- nifi cant space loss on a SSMR due to shading ef- fects. Also, when tilting a PV array, a new and dif- ferent airfoil is created, which may introduce loads for which the roof was not engineered. These new wind dynamics result in both positive and negative point loads that will need to be supported by the roof panels and structure. Use of a wind defl ector can reduce possible loads caused by wind. Aside from space loss and wind loading, many
tilted PV arrays may also increase snow loads due to drifting. Although tilted PV arrays were a fairly com-
mon practice in the past, you must weigh the cost-benefi t ratio to determine the best possible return on investment. Due to the falling cost of PV modules and the increased relative costs associ-
ated with tilting an array, the tilting scheme is becoming less and less cost justifi ed. The price of crystalline modules dropped almost 50 percent in the last two quarters of 2011 alone. At such a reduction in cost, many installers are fi nding they can make up for the loss in module effi ciencies by utilizing the available rooftop space to mount more modules in a fl ush-mount orientation rather than spending premiums on tilting. Solar technology continues to advance at a
rapid rate. In 2012, you will see the advancement of plug-and-play technology, reduction in soft cost and balance of system material and improved codes and standards for PV assemblies being mounted on a rooftop. With constantly advanc- ing technologies and standards, your options for mounting solar on the best rooftop platform will continue to improve.
Rob Haddock is the founder of S-5! and has 35 years in the industry. Starting out as a metal building erector, today Haddock is a well-known metal roof consultant, author, speaker and inventor. For 15 years, Haddock operated one of the nation's largest metal roofi ng companies with approximately 10 mil- lion square feet of successful installations nation- wide. He also serves as director of the Metal Roof Advisory Group Ltd., a consulting fi rm performing a variety of services for a worldwide clientele.
Dustin Haddock is research and development manager for S-5! and responsible for new product development, product testing and certifi cation.