Recently on a cross-country flight, I noticed the incredible number of alternative power sources that are in the process of being installed or have already been installed and are in operation. From the air, it was easy to recognize why the wind generators are placed in long lines along cliffs and in areas where natural air movement power the generators. The wind generators seem to be located on land where farming is not feasible, but the land is now bringing clean power and income to the landowners and farmers.
There are vast fields of photovoltaic (PV) cells installed in the Sunbelt areas of Arizona, California, Nevada, New Mexico, Texas and Utah, among other states. Some of these systems are supplying industrial facilities in very remote locations, thus reducing the need for utility company power, the peak power consumption for the facility and the need for expensive power line installations to the remote facilities. Many of these PV and wind-generator systems are tied into the utility grid, helping to reduce our dependency on coal and fossil fuels.
On another trip, this one to China and Taiwan, I noticed PV power systems and passive solar water heaters installed on the rooftops of buildings adjacent to my high-rise hotels.
In my travels, I have noticed the many different uses of PV power systems. I saw a high-rise with an entire wall built from PV panels, telephone call boxes and telecommunications towers with PV panels, portable and fixed traffic control units along the highways, highway sign lighting, residential power systems, and early storm warning systems with photovoltaic backup power. Someone even sent me the picture above of a PV power supply mounted on the back of a camel for cooling vaccines while the vaccines were transported to remote locations.
Rather than installing PV systems as add-on units on the rooftops of many buildings, photovoltaic modules are now being built as part of the roofing or siding of a building.
With all of this alternative power comes the realization that these wind generator and PV systems must be installed safely, so updated requirements are being added to the National Electrical Code (NEC). The NEC does not cover wind loading and fire resistance, but building codes and listing standards are requiring recognition of these issues. Areas with high-wind loads, such as coastal areas prone to hurricanes, and areas where tornadoes are prevalent, will require substantial construction methods when incorporating wind generators and PV.
A proposal has been submitted and accepted in principle to the 2011 NEC to add a new Article 694 covering Small Wind Electric Systems (Wind Turbines). The NEC Technical Correlating Committee has directed that the scope of the new article be: “The provisions of this article apply to small wind (turbine) electric systems that consist of one or more wind electric generators with individual systems up to and including 100 kW. These systems can include generators, alternators, inverters, and controllers. FPN: These systems can be interactive with other electrical power production sources or may be stand-alone systems. These systems can have AC or DC output, with or without electrical energy storage, such as batteries.”
This new article should help provide consistency and electrical safety for new nonutility wind generators or turbines.
Technological developments in the photovoltaic industry have prompted new definitions to be added at the proposal stage to Article 690 for the 2011 NEC. For example, the 2008 NEC defines an array as “a mechanically integrated assembly of modules or panels with a support structure and foundation, tracker, and other components, as required, to form a direct-current power-producing unit.” Two new terms have been added to cover “subarray as an electrical subset of an array” and “a monopole subarray as a photovoltaic subarray that has two conductors in the output circuit, one positive (+) and one negative (–) with two monopole photovoltaic subarrays used to form a bipolar photovoltaic array.”
Proposals have also been accepted for PV circuit routing of the “photovoltaic source and PV output conductors, in and out of conduit, and inside of a building or structure, for routing along building structural members such as beams, rafters, trusses, and columns where the location of those structural members can be determined by observation. Where circuits are imbedded in built-up, laminate, or membrane roofing materials in roof areas not covered by PV modules and associated equipment, the location of circuits must be clearly marked.”
These changes will also help ensure the physical safety of the systems, whether the PV circuits are installed in exposed or concealed locations.
ODE is a staff engineering associate at Underwriters Laboratories Inc., in Research Triangle Park, N.C. He can be reached at 919.549.1726 and firstname.lastname@example.org.