14 The Distributed Generation Technologies

Distributed generation is any small-scale electrical power generation technology that provides electric power at or near the load site; it is either interconnected to the distribution system, directly to the customer's facilities, or both. According to the Distributed Power Coalition of America (DPCA), research indicates that distributed power has the potential to capture up to 20% of all new generating capacity, or 35 Gigawatts (GW), over the next two decades. The Electric Power Research Institute estimates that the DG market could amount to 2.5 to 5 GW/year by 2010. DG technologies include small combustion turbine generators (including microturbines), internal combustion reciprocating engines and generators, photovoltaic panels, and fuel cells. Other technologies including solar thermal conversion, Stirling engines, and biomass conversion are considered DG. In this book, the term DG is limited to units below 10 MW electrical output.

DG can provide a multitude of services to both utilities and consumers, including standby generation, peak shaving capability, peak sharing, base-load generation, or combined heat and power that provide for the thermal and electrical loads of a given site. Less well understood benefits include ancillary services — VAR support, voltage support, network stability, black start, spinning reserve, and others — which may ultimately be of more economic benefit than simple energy for the intended load.

DG technologies can have environmental benefits ranging from truly green power (i.e., photovoltaics) to significant mitigation of one or more pollutants often associated with coal-fired generation. Natural gas-fired DG turbine generators, for example, release less than one-quarter of the emissions of sulfur dioxide (SO2), less than 1/100th of the nitrogen oxides (NOX), and 40% less carbon dioxide (CO2) than many new coal-boiler power plants; these units are clean enough to be sited within a community among residential and commercial establishments (DPCA, 1998).

Electric restructuring has spurred the consideration of DG power because all participants in the energy industry — buyers and sellers alike — must be more responsive to market forces. Central utilities suffer from the burden of significant "stranded costs," which are proposed to be relieved through tem porary fixed charges. DG avoids this cost. DG is a priority in parts of the country where the spinning reserve margins are shrinking, where industrial and commercial users and T&D constraints are limiting power flows (DPCA, 1998).

Additional impetus was added to DG efforts during the summer of 1998 due to the heat wave that staggered the U.S. and caused power shortages across the Rust Belt. The shortages and outages were the result of a combination of factors such as climbing electricity demand, the permanent or temporary shutdown of some of the region's nuclear facilities, unusually hot weather, and summer tornadoes that downed a transmission line.

In spite of several notable reasons for DG growth discussed throughout the book, it must be recognized that DG is a disruptive technology and, as was the case with past technologies, may initially offer worse economic or technical performance than traditional approaches. As commercialization continues, however, these new technologies will be characterized by rapid performance improvements and larger market share. But, because the products described below tend to be simpler and smaller than older generations, they may well be less expensive to own and operate, even in the near-term. Table 1.2 provides an overview of feasible present or near-term DG technologies. Each technology summarized below is described fully in separate chapters later in the book.

TABLE 1.2

Summary of Distributed Generation Technologies

TABLE 1.2

Summary of Distributed Generation Technologies

IC Engine

Microturbine

PVs

Fuel Cells

Dispatchability

Yes

Yes

No

Yes

Capacity range

50 kW-5 MW

25 kW-25 MW

1 kW-1 MW

200 kW-2 MW

Efficiencya

35%

29-42%

6-19%

40-57%

Capital cost ($/kW)

200-350

450-1000

6,600

3,750-5,000

O&M costb ($/kWh)

0.01

0.005-0.0065

0.001-0.004

0.0017

NOx (lb/Btu)

Nat. Gas

0.3

0.10

0.003-0.02

Oil

3.7

0.17

Technology status

Commercial

Commercial

Commercial

Commercial

in larger sizes

scale demos

a Efficiencies of fossil and renewable DG technologies are not directly comparable. The method described in Chapter 8 includes all effects needed to assess energy production. b O&M costs do not include fuel. Capital costs have been adjusted based on quotes. Source: Distributed Power Coalition of America; Kreider and Associates, LLC (with permission).

a Efficiencies of fossil and renewable DG technologies are not directly comparable. The method described in Chapter 8 includes all effects needed to assess energy production. b O&M costs do not include fuel. Capital costs have been adjusted based on quotes. Source: Distributed Power Coalition of America; Kreider and Associates, LLC (with permission).

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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