1. Introduction to Distributed Generation

1.1 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.

Classic Electricity Paradigm--Central Power Station Model

The current model for electricity generation and distribution in the United States is dominated by centralized power plants. The power at these plants is typically combustion (coal, oil, and natural) or nuclear generated. Centralized power models, like this, require distribution from the center to outlying consumers. Current substations can be anywhere from 10s to 100s of miles away from the actual users of the power generated. This requires transmission across the distance.

This system of centralized power plants has many disadvantages. In addition to the transmission distance issues, these systems contribute to greenhouse gas emission, the production of nuclear waste, inefficiencies and power loss over the lengthy transmission lines, environmental distribution where the power lines are constructed, and security related issues.

Many of these issues can be mediated through distributed energies. By locating, the source near or at the end-user location the transmission line issues are rendered obsolete. Distributed generation (DG) is often produced by small modular energy conversion units like solar panels. As has been demonstrated by solar panel use in the United States, these units can be stand-alone or integrated into the existing energy grid. Frequently, consumers who have installed solar panels will contribute more to the grid than they take out resulting in a win-win situation for both the power grid and the end-user.



Classic Electricity Paradigm

Distributed Generation (DG) Electricity Paradigm

(This figure has been taken from the European Commission Energy Research website: http://ec.europa.eu/research/energy/nn/nn_rt/nn_rt_dg/article_1158_en.htm)

What are 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.



Wind Turbines at Buffalo Mountain, TN



Photovoltaic (Solar) Panels help Power this Elementary School in Fairbanks, Alaska



A 300 kW Capstone Microturbine at a Demonstration Project at the Oak Ridge National Laboratory in Oak Ridge, TN

Phosphorus fuel cells also provide an alternative route to a DG technology. These are not as environmentally reliant as the previously mentioned technologies. These fuel cells are able to provide electricity through a chemical process rather than a combustion process. This process produces little particulate waste.

At the end-point level the individual energy consumer can apply many of these same technologies with similar effects. One DG technology frequently employed by end-point users is the modular internal combustion engine. For example, some departments here at Virginia Tech use these power generators as a backup to the normal power grid. These modular internal combustion engines can also be used to backup RVs and homes. As many of these familiar examples show DG technologies can operate as isolated "islands" of electric energy production or they can serve as small contributors to the power grid.

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