12-07-2013, 04:47 PM
DISTRIBUTED GENERATION
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INTRODUCTION
Distributed generation, also called on-site generation, dispersed generation, embedded generation, decentralized generation, decentralized energy or distributed energy, generates electricity from many small energy sources. Most countries generate electricity in large centralized facilities, such as fossil fuel (coal, gas powered), nuclear, large solar power plants or hydropower plants. These plants have excellent economies of scale, but usually transmit electricity long distances and negatively affect the environment Distributed generation allows collection of energy from many sources and may give lower environmental impacts and improved security of supply.
What is Distributed Generation
Distributed generation is an approach that employs small-scale technologies to produce electricity close to the end users of power. DG technologies often consist of modular (and sometimes renewable-energy) generators, and they offer a number of potential benefits. In many cases, distributed generators can provide lower-cost electricity and higher power reliability and security with fewer environmental consequences than can traditional power generators.
In contrast to the use of a few large-scale generating stations located far from load centers--the approach used in the traditional electric power paradigm--DG systems employ numerous, but small plants and can provide power onsite with little reliance on the distribution and transmission grid. DG technologies yield power in capacities that range from a fraction of a kilowatt [kW] to about 100 megawatts [MW]. Utility-scale generation units generate power in capacities that often reach beyond 1,000 MW.
Some Examples of Distributed Generation Technologies
Distributed generation takes place on two-levels: the local level and the end-point level. Local level power generation plants often include renewable energy technologies that are site specific, such as wind turbines, geothermal energy production, solar systems (photovoltaic and combustion), and some hydro-thermal plants. These plants tend to be smaller and less centralized than the traditional model plants. They also are frequently more energy and cost efficient and more reliable. Since these local level DG producers often take into account the local context, the usually produce less environmentally damaging or disrupting energy than the larger central model plants.
History of the Emergence of DG Technologies in the United States
Among a set of five laws proposed by Carter and passed by Congress (albeit in greatly diluted form), the Public Utility Regulatory Policies Act (PURPA) of 1978 had the most far-reaching—and least intended—consequences for power companies. It spurred creation of radical technologies; it began the process of deregulation; and it challenged the control held by power company managers. In the process, the law helped change the momentum of the utility system.
A related provision of PURPA also spurred research on environmentally preferable technologies that used water, wind, or solar power to produce electricity. More successful than anyone originally anticipated, PURPA prompted work that cut the cost of power produced by solar photovoltaic panels by about 70 percent between 1980 and 1995. More significantly, it contributed to work that lowered the cost of power produced by wind turbines; by 2002, the average cost of wind-produced electricity dropped to under 5 cents per kWh, a cost that compared favorably with electricity produced by conventional utility plants burning natural gas or coal.
These smaller-scale generation technologies challenged the established paradigm of the utility industry (and many other industries) that previously relied on large-scale equipment to produce economies of scale. Now, it appeared, power plants producing modest amounts of electricity proved economically viable. Moreover, since they were smaller, they required less time to build, and they put less capital at risk during a period of rapid price inflation. Finally, they matched the slower growth rate of consumption more appropriately: with growth rates remaining under 3 percent per year, consumers needed smaller increments of power to match their demand. Had utilities continued to build their traditional behemoths, huge chunks of power would remain unused when the plants were completed. Small scale, indeed, looked beautiful.
Potential Benefits of DG Systems
Consumer advocates who favor DG point out that distributed resources can improve the efficiency of providing electric power. They often highlight that transmission of electricity from a power plant to a typical user wastes roughly 4.2 to 8.9 percent of the electricity as a consequence of aging transmission equipment, inconsistent enforcement of reliability guidelines, and growing congestion. At the same time, customers often suffer from poor power quality—variations in voltage or electrical flow—that results from a variety of factors, including poor switching operations in the network, voltage dips, interruptions, transients, and network disturbances from loads. Overall, DG proponents highlight the inefficiency of the existing large-scale electrical transmission and distribution network. Moreover, because customers’ electricity bills include the cost of this vast transmission grid, the use of on-site power equipment can conceivably provide consumers with affordable power at a higher level of quality. In addition, residents and businesses that generate power locally have the potential to sell surplus power to the grid, which can yield significant income during times of peak demand.
Industrial managers and contractors have also begun to emphasize the advantages of generating power on site. Cogeneration technologies permit businesses to reuse thermal energy that would normally be wasted. They have therefore become prized in industries that use large quantities of heat, such as the iron and steel, chemical processing, refining, pulp and paper manufacturing, and food processing industries. Similar generation hardware can also deploy recycled heat to provide hot water for use in aquaculture, greenhouse heating, desalination of seawater, increased crop growth and frost protection, and air preheating.
Electricity Generation by Fuel, 1970-2020 (billion kWh)
The relatively minor use of renewable energy systems has created a general attitude among energy analysts, scholars, and laboratory directors that the technologies are not viable sources of electricity supply. For example, Rodey Sobin, former Innovative Technology Manager for the Virginia Department of Environmental Quality, argues that “in many ways, renewable energy systems were the technology of the future, and today they still are.” Ralph D. Badinelli, a professor of Business Information Technology at Virginia Tech, explains that renewable energy technologies do not contribute significantly to U.S. generation capacity because “such sources have not yet proven themselves … Until they do, they will be considered scientific experiments as opposed to new technologies.” Similarly, Mark Levine, the Environmental Energy Technologies Division Director at the Lawrence Berkeley National Laboratory, comments that despite all of the hype surrounding renewable energy, such systems are still only “excellent for niche applications, but the niches aren’t large.”
DG/CHP technologies have an only slightly better record. In 2004, the Energy Information Administration characterized only 3.1 percent of electricity generation capacity as commercial or industrial combined heat and power (33,217 MW out of 1.49 terrawatts [TW]). The EIA also estimated that in 2002 only 0.9 gigawatts (GW) of distributed generation capacity existed in the United States. Similarly, the EIA’s 2005 Annual Energy Outlook projected that CHP systems are not widely used in the electric power sector, amounting to 0.053% of utility generation (197 billion kWh out of 3,700 billion kWh). Tom Casten, the Chair and Chief Executive Officer of Primary Energy, a manufacturer of fuel processing cogeneration steam plants, notes that even though CHP plants can reduce energy costs for industrial firms by over 40 percent, such plants remain “the exception instead of the rule.”
Why Not Use More DG Technologies
There are a mulitude of impediments to using DG technologies. A combination of social, scientific, and technical impediments prevent a transition to a more friendly DG future. Both proponents and opponents of DG technologies acknowledge that economic considerations such as capital costs, utility preferences, and business practices tend to deter people from investing in such technologies. DG systems are believed to have higher, comparative capital costs (in dollars per kilowatt) than other generators, which places many smaller, decentralized systems out of the price range of most residential consumers. Moreover, entrepreneurs and business owners argue that the comparative higher capital cost convinces them that investing in renewable or distributed systems is too expensive and deviates from the core mission of their corporate goals. Even electric utility managers generally shun renewable energy technologies, thinking that their power output is more intermittent than their fossil-fueled and nuclear alternatives, thus making them less viable providers of base-load and peaking power. Finally, since renewable and distributed energy systems, by their very nature, are more diverse and context dependent, transmission and distribution operators argue that they tend to be more difficult to permit, monitor, interconnect, and maintain.
Economies of scale
Historically, central plants have been an integral part of the electric grid, in which large generating facilities are specifically located either close to resources or otherwise located far from populated load centers. These, in turn, supply the traditional transmission and distribution (T&D) grid which distributes bulk power to load centers and from there to consumers. These were developed when the costs of transporting fuel and integrating generating technologies into populated areas far exceeded the cost of developing T&D facilities and tariffs. Central plants are usually designed to take advantage of available economies of scale in a site-specific manner, and are built as “one-off,” custom projects.
These economies of scale began to fail in the late 1960s and, by the start of the 21st century, Central Plants could arguably no longer deliver competitively cheap and reliable electricity to more remote customers through the grid, because the plants had come to cost less than the grid and had become so reliable that nearly all power failures originated in the grid.thus, the grid had become the main driver of remote customers’ power costs and power quality problems, which became more acute as digital equipment required extremely reliable electricity., Efficiency gains no longer come from increasing generating capacity, but from smaller units located closer to sites of demand.,