The surface of the earth receives a tremendous amount of energy from the sun. It is estimated that the amount of solar energy that strikes the earth's surface daily is greater than the amount of energy used worldwide in 25 years. Even that amount can vary with latitude, time of day, season, sky conditions and other factors, sunlight is available throughout the United States for conversion to electric power using photovoltaics (PV). But PV is not just for the sunny regions.

What about Alaska?

When considering the use of PV in the United States, Alaska is not the first state that usually comes to mind. Even though sunlight is scarce between November and January, there are actually 230 more hours of possible sunlight available at the Arctic Circle than at the equator.

The problem is that sunlight in Alaska is more dynamic and less reliable than in the Lower 48, making it difficult to harvest the available sunlight using PV.

However, proper orientation and design of the building to optimize the use of PV can greatly improve the system's performance. PV can provide an alternate source of energy for grid-connected commercial and residential buildings in Alaska, but it is particularly well-suited for remote buildings that do not have access to utility-supplied power such as summer cabins. This is the same as for remote vacation homes in such areas as Colorado where connection to the utility grid is not possible or practical.

Northern PV applications

Mary Ann Cofrin Hall is an example of a building in the northern United States that uses building-integrated PV to meet a portion of its electric power needs. Cofrin Hall is a 120,000-square-foot classroom building on the campus of the University of Wisconsin-Green Bay.

A total of 4,300 square feet of PV was installed that produces 27,500 kilowatt hours (kWh) of electric energy for the building annually. The PV was integrated into 2,300 square feet of standing-seam metal roofing that produces about 15,000kWh annually and 2,000 square feet of glass curtain wall that produces 12,500kWh annually.

Snow is often a concern when it comes to installing PV on roofs on buildings in northern climates. The Jarecki Center of Advanced Learning at Aquinas College in Grand Rapids, Mich., is a 21,000-square-foot building that has a 12kW PV array installed on its pitched roof.

Thin-film PV laminate produced by United Solar Systems Corp. that is installed on the roof produces an average of 8.5kW in the summer and 7.0kW during the remainder of the year. According to United Solar, one of the advantages of the thin-film laminate on a steep-slope roof is that it sheds snow faster than traditional roof-mounted PV panels, allowing the PV array to quickly resume electricity production.

Another example of PV being used successfully is the 3,000-square-foot, six-story Intercultural Center at Georgetown University in Washington, D.C. Installed in 1984, this building has a 300kW polycrystalline array installed on a sawtooth roof that provides both shading and power production. This installation was originally considered experimental but today is considered an integral part of Georgetown's power supply. The electricity produced by the PV array serves the Intercultural Center's loads, and any surplus is fed back into Georgetown's distribution system to serve other campus loads.

Local conditions to consider

Local climate and conditions need to be taken into account when selecting the particular PV technology to be used and planning the physical installation. For instance, thin-film PV conversion efficiency is better than crystalline silicon PV in low or diffuse light making it more efficient in cloudy regions.

Similarly, PV cells have a higher output at lower temperatures and lose efficiency the hotter they get. This makes thin-film PV a better choice in desert regions because its cell temperature remains lower than crystalline silicon PV, making it more efficient.

Finally, the actual installation of the PV technology has a major impact on its efficiency and buildings should be designed to optimize PV performance. Small things such as using a sloped roof that will shed snow quickly following a snowstorm can improve the performance of the PV installation.

This article is the result of a research project investigating the investigating the potential of the emerging PV market for the electrical contracting firm being sponsored by The Electrical Contracting Foundation Inc. The author would like to thank the foundation for its support. EC

GLAVINICH is an associate professor in the Department of Civil, Environmental and Architectural Engineering at The University of Kansas and is a frequent instructor for NECA’s Management Education Institute. He can be reached at 785.864.3435 or [email protected].