Distributed generation (DG) refers to the practice of locating small-scale electric generating units at or near the load served. With distributed generation, individual buildings or complexes can have a local electric power supply that provides some or all of the facility's electric energy needs. This is in contrast to electric utilities building large multi0unit base-load power plants remote from urban load centers as they did throughout most of the 20th century. Economies of scale made these large central plants more cost-effective to build and more efficient to operate than smaller local generating stations. However, in recent years, environmental, regulatory, financial and other constraints have restricted utility expansion and made the construction of new power plants and transmission lines very difficult and expensive.
In the 21st century, many parts of the United States have experienced power shortages, disruptions and utility-scheduled load reductions (brownouts) that have led to concern about the availability and reliability of the utility grid. This coupled with technological advances in small-scale generation, along with rising utility rates and financial incentives, is making small-scale generation competitive with utility-supplied power in many locations. DG can be an attractive alternative for building owners and developers and an emerging market for electrical contractors.
Your customers can benefit from DG in a variety of ways depending on where they are located and their particular power supply needs. Facilities have different needs. For example, healthcare facilities require high reliability (backup) power and high power quality due to sensitive electronic equipment. Computer centers need steady, high-quality, uninterrupted power. Commercial buildings and industrial plants are concerned about high energy bills and reliability. DG strategies can be developed that will address your customer's need to improve power quality, increase power availability, reduce peak demand or lower energy costs. In addition, because DG involves the application of one or more small-scale generation technologies, installations are often scalable so that your customer only has to install the amount of generating capacity needed and does not have money tied up in excess generating capacity in anticipation of future needs that may never materialize.
Most electrical contractors have been involved in the DG market for years but have not realized it. The installation of an emergency generator to provide light and power for public safety and rescue operations in the event of a power outage is an example of distributed generation. Similarly, the installation of an uninterruptible power supply (UPS) to protect against economic loss in the event of power disruption to a data or telecommunications center is also an example of distributed generation. Even though these systems are very reliable and important to the business, neither offers an economically or operationally viable alternative to the utility power supply. However, the electrical contractor's knowledge and expertise in the selection, installation and maintenance of these emergency systems provides a good foundation for assisting owners in successfully integrating emerging small-scale generation technologies into specific facilities.
Utilities are using combustion turbines and combined cycle plants. Reciprocating engines, including diesel generators, have also been used extensively to provide power to rural areas and are available for building owners and developers today. Similarly, wind generation may be a viable alternative power source in rural areas. However, there are several environmentally friendly technologies that are available today and should be considered for commercial, industrial and institutional facilities. These new small-scale generation technologies include microturbines, fuel cells and photovoltaics.
Microturbines generate electricity with only one moving part, making them very reliable. Both the turbine and the electric generator are mounted on the same shaft, which rotates at a speed between 60,000 and 100,000 revolutions per minute (RPM). The high-frequency alternating current (AC) generated by the microturbine is transformed into usable 60-Hertz (Hz) power using a solid-state power converter. Microturbines can operate on a variety of readily available fuels including natural gas at efficiencies between 25 and 30 percent when generating electricity alone. However, capturing waste-exhaust heat and using it to displace energy that would otherwise have to be purchased can increase the efficiency of the overall system considerably.
Fuel cells have been around for many years. They found their first real application in the space program. Continuing research and development is increasing fuel-cell efficiency and lowering first costs. This has resulted in fuel-cell experimentation by utilities, automobile manufacturers and others. Fuel cells generate direct current (DC) power through a chemical reaction between oxygen and either hydrogen or a hydrocarbon fuel such as natural gas. An inverter is required to convert the DC to the AC needed by standard building equipment and appliances. Water and carbon dioxide are typically the only by-products of the reaction, making fuel cells environmentally friendly.
The Long Island Power Authority (LIPA) installed 75 fuel cells at a substation to demonstrate the viability of this environmentally friendly technology. Long Island's demand for electric power is growing at a rate of 3.5 percent per year, twice the statewide average (LIPA 2001). This was the first installation of its kind in New York state. Environmental News (2001) predicted that this installation would generate about one million kilowatt-hours over its life, powering about 100 average-size homes. In 2002, LIPA continued its experimentation with fuel cells and installed 17 5kW fuel cells at commercial customer locations including a McDonald's restaurant. This year, LIPA is installing another 20 5kW fuel cells to provide electric power and heat for single- and multifamily residences.
Photovoltaics (PV) are semiconductors that convert sunlight to DC. Like fuel cells, photovoltaics have been around for a long time and are just now beginning to become economically viable for the building industry, as utility rates rise and photovoltaic manufacturing costs decrease. Like fuels cells, an inverter is used to convert the DC produced by the photovoltaic cells to AC.
Integrating photovoltaics into building roofs, walls and windows is referred to as building integrated photovoltaics (BIPV). Using BIPV, the skin of a building actually generates the electric energy for some or all of the building loads. The photovoltaics are integrated with building elements, making them part of the building's architecture, which eliminates photovoltaic panels that can detract from the building's appearance; the panels are often viewed as an afterthought. Integrating photovoltaics into building elements also reduces material and construction costs because both the building elements and photovoltaic are manufactured and installed as one. The available photovoltaic surface area, which determines the amount of energy that can be produced, typically increases with building-integrated photovoltaics. In addition to generating electricity, photovoltaics can reduce the building's cooling load and increase the efficiency of the building as a whole when they are integrated into a commercial building's curtain wall.
Mary Ann Cofrin Hall is a recently constructed 120,000-square-foot classroom building at the University of Wisconsin, Green Bay, campus. It is an example of a building that uses building-
integrated photovoltaics to meet a portion of its electric power needs (Wisconsin Public Service 2002). Approximately 4,300 square feet of photovoltaics were installed that produce around 27,500kWh of electric energy for the building annually. The photovoltaics were 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 around 12,500kWh annually.
Connecting to the Grid
Besides economics, one of the major barriers to the widespread use of distributed generation has been the lack of standards for interconnecting small-scale generation with the utility's distribution system. The Institute of Electrical and Electronics Engineers (IEEE) has developed and published IEEE Standards 1547 and 929 that should help remove this barrier. IEEE Standard 1547 provides uniform standards and recommended practices for interconnecting DG installations with the electric grid. IEEE Standard 929 specifically addresses the interconnection of photovoltaic systems that generate 10kW or less with the utility grid but can be applied to photovoltaic systems of any size. Prior to this standard, many utilities required that small- to medium-sized photovoltaic systems comply with the same interconnection requirements that are applied to traditional generators, which proved impractical and restricted the application of photovoltaic systems. IEEE Standard 929 simplifies photovoltaic system interconnection with the utility grid with the goal of safety for utility linemen, safeguarding of utility equipment and the protection of the utility customer.
Owners will need help in evaluating their power supply needs, identifying alternative ways of meeting those needs and selecting the power supply option that best meets those needs. When the selected power supply option includes on-site generation using small-scale electric generating units, the electrical contractor can assist owners in the selection, installation and maintenance of the needed alternative power source. All of this represents a tremendous opportunity for the electrical contractor who is prepared to take advantage of the emerging distributed generation market. 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@example.com.