There is a lot of excitement and conversation in the roofing industry today about environmentally friendly roofs. You may have even read articles on green, Energy Star, recyclable and sustainable roof systems. Much of the recent interest revolves around one concept, the need to manage and conserve energy.

Many cities have or are considering enacting regulations on the reflectivity (the amount of light reflected) and emissivity (the amount of heat absorbed) of the roofing system. The reasons for these regulations are based on the need to minimize the amount of heat an urban environment absorbs. Consequently, we see the roofing industry moving towards the installation of reflective roofs that do not absorb heat. In addition, many cities have in place minimum R-value requirements for insulation, recognizing that a substantial amount of energy can escape through the roof. In terms of land use, particularly in an urban setting, the roof is a huge waste of space and consumer of resources that offers nothing in monetary return.

The next phase in energy and roofing, now in its infancy, is a roofing system that will reduce air pollution, supplement a building's energy needs, and actually provide economic return.

Roofs that generate energy through the use of photovoltaics (PV) are beginning to appear in the commercial roofing market. PV devices are small cells that have no moving parts. Due to their composition, when exposed to sunlight, they produce electricity. A single cell by itself produces very little electricity - one watt or less, but when combined with additional cells to form a module, modules of up to 200 watts can be produced. Any number of modules can be combined to form an array. Arrays can be designed to produce an unlimited amount of electricity. This electricity can be used, stored in batteries or sold back to the power company.

PV Array integrated into warehouse roof system.

The roof is an ideal place for the installation of a PV system. Typically roofs are totally exposed to the sun, a major requirement, have large areas of open space and very little traffic. To mount a PV system on the roof utilizes space that was once empty, providing an economic benefit to the building. A roof-mounted system does not require an additional investment in land or racks for the panels or security systems. In effect, the roof becomes a resource to the building owner.

The first major use of PV cells was to generate electricity on spacecraft. Since that time, photovoltaic cells have evolved into cost-effective devices. As the cost of electricity rises in some urban areas from 12 to 15 cents per kilowatt-hour and above, the attractiveness of manufacturing energy by PV becomes viable.  Through the development of thin film modules, modules that can be attached directly to a roof membrane or to a metal roof with adhesives, these large expanses of roof - of wasted space, can now become generators of energy for use in the building, or in some cases, sold back to the grid.

At the time, there are several commercial building owners in the United States that have installed PV systems into the roof to supplement their building's energy needs. The technology to produce up to 1 megawatt of electricity is currently available. As energy costs continue to rise, and as energy becomes more scarce and environmental awareness continues to shape our society, energy options will become a major consideration when selecting, designing and installing roofing systems.