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Fuel for Thought: Some Questions on the Future of Gas-Fired Generation

Fortnightly Magazine - December 1999

these constraints, a substantial global market for microturbine generators still should develop in the 25- to 500-kilowatt range, especially the design that is based on established aerospace technology and large-volume automotive production for turbocharger applications. It has high reliability and minimal service requirements, thanks to a single moving part supported by air bearings and thereby requiring no lubrication. This design also is relatively light and compact, generates little noise and emits low concentrations of nitrogen oxides. Moreover, although natural gas is the preferred fuel, microturbine generators can operate with other premium hydrocarbon fuels.

Fuel Cell Uncertainties. Compared with microturbine generators for DG applications, the prospects for fuel cells in the single-digit-kilowatt to single-digit-megawatt capacity range are even more poorly defined. As noted before, the only commercial product is the 200-kW PC-25 of International Fuel Cells Corp./ONSI, a joint venture of United Technologies Corp. and Toshiba Corp. Over 200 units have been sold and the operating experience has been satisfactory.

Typical economics, again based on a promotional gas rate of $3.50 per million Btu, are shown in Table 2. Even with the hot water credit, power costs exceed average commercial electricity prices. However, for high load factor operation in areas where commercial electricity rates are high and gas is relatively cheap, where there is a premium on reliable power supply, in remote locations, or where the cost of bringing in additional grid power is high, these systems obviously are finding a niche. With large-volume production, equipment costs also could be reduced substantially.

Clearly, however, the marketing experience with this excellent system illustrates the limitations of the inherently high first-cost fuel cell technologies as distributed power sources. The efficiency advantage over other DG options of fuel cell technologies that operate at much higher temperatures than PEM and phosphoric acid fuel cells - notably molten carbonate electrolyte and solid oxide systems - cannot at present compensate for these high costs.

Success Stories: Where Gas

Gensets Work Best

Table 3 summarizes my estimates of the performance characteristics and costs of available gas-fired distributed and modular generation options, based on various literature sources. The most widely used systems for emergency and back-up power systems are proven reciprocating-engine-driven gensets of up to 5- to 6-MW capacity. The performance of these units, which generally have the lowest first cost, continues to improve. However, they require a great deal of maintenance to ensure reliable operation and have not been used extensively for DG or cogeneration in areas with access to reliable grid supplies.

Turbine-driven gensets are popular for on-site large commercial and industrial cogeneration applications. In fact, gas-fired cogeneration's market penetration has grown in recent years. In 1997 there were 34 gigawatts (GW) of such capacity in the United States, compared with 745 GW of conventional power generation capacity. However, this market is projected to grow only to 39 GW by 2020.[Fn.11]

The biggest market for combustion turbines is in various forms of grid power supply. Simple-cycle combustion turbines, because of their low first cost and low non-fuel O&M costs, traditionally have been the preferred option for meeting peaking needs