Photovoltaic (PV) Roofing - 11/15/2004 - House Solar Energy Efficiency

Photovoltaic (PV) Roofing

Photovolatic modules that are integrated directly into a roof's surface to provide more aestethic appeal.

Many homeowners recognize the value of solar technologies but have been leery of the highly visible collectors on their roofs. Although the term "solar power" may be synonymous with best of environmental-friendliness, and freedom from fossil fuel dependence, some types of solar systems have been avoided because of their unattractive curb appeal. For this reason, photovoltaic (PV) modules (which convert sunlight directly into electricity) that are integrated into roofing materials have been developed as an alternative to traditional PV modules that are mounted above the roof on racks. The result is a solar system that is difficult to notice on the roof but has benefits that are hard to miss. Once installed, PV roofing not only protects the home from storms and rainy weather but on sunny days produces free electricity for use in the home.

Different types of photovoltaic roofing products compliment many different types of roofing materials including asphalt shingles, standing seam metal roofing, and slate or concrete tiles. The PV roofing products are produced separately from the standard roofing products by PV manufacturers whose products are designed to serve both functions – as a roofing material to protect the home and as an electrical device to produce electricity. In addition to the PV-active roofing, an inverter, located near the electrical panel converts the PV produced electricity into utility compatible ac electricity for the home. PV systems that utilize battery storage can produce electricity for the home even when the sun is not shinning. PV systems of any type can be small to produce a limited amount of energy or very large with enough power for the home and even at times with excess that is sent back to the utility.

Most residential PV systems are used in conjunction with utility-supplied power. Excess power produced during daylight hours can be fed back into the utility's lines, while utility electricity is used in the home when the house demand is greater than can be supplied by the PV roofing. Typical residential PV systems commonly have a peak power production of between 1,200 and 5,000 watts, ac – requiring from between 150 to over 1000 square feet of roof area depending on the efficiency of the PV technology used.

PV systems reduce the amount of electricity purchased from the utility.

Electricity produced using the sun’s energy reduces the amount of energy used from non-renewable resources such as coal, gas, oil and nuclear. In addition, there are significant environmental benefits resulting from reductions in air pollution from burning fossil fuels, reductions in water and land use from central generation plants, reductions in the storage of waste byproducts. In addition, the solar technologies produce energy with little noise and few moving parts.

Expected cost of electricity produced from a PV system is equal to about 25 to 50 cents per kilowatt-hour (kWh) when considering initial cost spread over the lifetime of the system, plus maintenance costs. This compares with an average rate of about 8 cents per kWh for utility supplied power (utility rates can range from anywhere between 6-17 cents and peak rates can be over 20 cents per kWh in the United States).

For homes not in proximity of electric power lines, PV systems may be less costly than extending power lines to the home. Unlike generators, they operate silently and require little maintenance.

Because reliability has proven good thus far, PV cells actually reduce the cost of powering homes and other buildings. The amount varies depending on the size of the system, the building's location, and the building's energy needs.

Most PV products have undergone extensive testing and certification for fire, wind uplift, and electrical safety performance. Some have obtained evaluation reports from major model building codes to assure their acceptance. Many PV products are listed through a testing laboratory such as Underwriters Laboratory.

John Wesley Miller Companies: Armory Park del Sol, Tucson, Arizona

Shea Homes: San Diego, California

PV roofing systems are ready to install and supplied by distributors. PV roofing installations require a portion of the roof to be exposed to direct sunlight-in North America, for example, the southern roof must be unshaded. Depending on the PV roofing product, they can be installed by either a roofing professional, an electrician, or both. They must be wired to the house power supply by an electrician.

Manufacturing warranties vary from 2 to 5 years for workmanship and defects. However, many companies also guarantee a certain percentage of home's peak power to be produced by the PV cell for a certain number of years. The percentage depends on the length of warranty and the period of peak power.

PV roofing products provide environmental benefits because they do not produce pollution or carbon dioxide emissions like fossil fuel-based utility power. They are also more attractive than many other solar systems, which increases consumer acceptance.