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5.5 Concluding Analysis

DG System Infrastructure and Fuel

All of the technologies chosen for the 250kW-5MW DG systems require a basic infrastructure. Of the various fuel choices, natural gas appears to be an obvious. However, diesel may be tapped from existing pipelines. Where such an installation is not possible, trucking in the fuel or constructing a pipeline could prove costly.

Some fuel cell types, such as PEMs, are very vulnerable to impurities in hydrogen fuel source. SOFCs operate with the presence of some impurties and can internally reform certain types of fuels such as natural gas, propane and gasified coal [27]. Further, their ability to use reformed gasoline, diesel, and others eliminates the need for an immediate change in infrastructure. Regardless of energy source market fluctuations, the cheapest fuel could always be used predicated upon current and predicted energy prices [28]. This facilitates a more immediate acceptance of SOFCs as a DG technology.

ICE and CTs are typically very robust and do not have any stringent fuel requirements. Their larger size, proven design, and low costs suggest a well-rehearsed series of routine maintenance requirements generated from daily use. MTs utilizing air bearing and other sensitive architectures are highly susceptible to failures from impurities in their fuel and air quality. In terms of the existing infrastructure, ICEs are the most robust. Following ICEs CTs are more mechanically robust than MTs. In the case of fuel cells, the specific technology employed determines robustness.

Technology Ranking Analysis

The ranks assigned to the four technologies should not present any surprises to the careful reader. The efficiency numbers, initial costs, and environmental issues taken as absolute indicators DG systems would not provide for the best engineering solution. For instance, a diesel ICE on the surface has the best efficiency, lowest cost, and most proven technology. However, as noted in the sections above, its emissions prevent continuous duty cycle operation. SOFCs produce prodigious amounts of heat at 1000oC requiring expensive cogeneration equipment to recover lost energy. CTs, while readily available, inexpensive, and proven, currently rely on an unpredictable natural gas market.

These contradicting indicators force the power designer to rely on developing technologies rather than classic, comfortable designs. The SOFC fuel cell will undoubtedly come down in price as international environmental interests force the United States to reduce pollutants [29]. Its inherently cleaner quieter operation and 'green image' will assure the SOFC DG system will supply base power and long term peak power (like those present during the day).

In the near future, there is little reason not to use CTs. With regards to the DG technologies discussed, combustion turbines are currently the most suited for full time generation in the 250kW to 5MW penetration level. They produce significantly less emissions, are similarly priced, and occupy roughly the same footprint as diesel generators. The technology is more proven and designed better for high power generation than solid oxide fuel cells. However, SOFCs' have higher theoretical efficiencies, lack excessive noise and pollution, and will benefit from mass production. Therefore, fuel cells could potentially replace or at the very least, supplement combustion turbines in distributed generation facilities.

Table 3. DG technology rankings.

Category

Diesel ICE

Conbustion Turbine

Microturbines

Solid Oxide Fuel Cell

Technology Status

1

2

3

4

Overall Efficiency

2

2

4

1

Environmental and Noise considerations

4

2

3

1

Device Cost per kW

1

2

3

4

Physical Size

1

2

3

4

Intended Application

2

1

4

3

Potential for Improvement

4

3

2

1

Conclusion

The authors originally intended to provide a broad analysis of many different DG technologies. Subsequent research and analysis demonstrated the need to clarify and restrict the scope to a well defined penetration depth. This document provides a solid foundation and analysis of a few distributed generation technologies on a fundamental level. There are many more various factors involved in widespread implementation. The monumental impact that many DG systems will have on the grid requi The authors originally intended to provide a broad analysis of many different DG technologies. Subsequent research and analysis demonstrated the need to clarify and restrict the scope to a well defined penetration depth res substantial investigation. Grid control, modeling, and basic assumptions will no longer be acceptable in order to maintain veracity with regards to widespread borough sized DG systems. More in depth analysis of highly dispersed generation down to the 5kW or less size level should also be investigated for benefits, and drawbacks. The ranking system has been well defined and the appropriate distributed technologies identified.

 

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