Distributed generation (DG) can be configured in many different ways, with many kinds of technologies and equipment. Among the choices are gas turbines, reciprocating engine-generator sets, photovoltaic arrays, and wind turbines. Fossil-fueled DG systems can take the form of cogeneration or combined heat and power (CHP) plants. On-site power systems that partially shed electrical load or remove load during peak demand periods also fit the definition of DG. All of these systems reduce the load that the local utility must serve and benefit the end user with lower energy bills and improved reliability.
Perfectly matching a DG system to its application isn't always easy, but it is usually well worth the effort. The choice of the system's fuel is determined by local availabilities and the fuels' relative Btu content and impact on the environment. Money matters, too; being able to use all of the energy produced by a DG system is a key aspect of its financial viability.
DG's high efficiency, compared with that of utility power (85% to 90% for CHP applications, vs. 33% for central station units), affords tremendous potential for conserving energy and reducing greenhouse gas emissions. Efficient, fossil-fueled DG systems release less CO2 per kWh or Btu generated than less-efficient generation.
Recips dominate
While exotic generating technologies capture the attention of the media, the most widely used on-site generating technology is the workhorse reciprocating engine-generator, fueled by natural gas, landfill methane, or diesel. If the application can make use of the waste heat from the engine, the installed system will also include heat-recovery equipment to produce hot air, hot water, and/or steam.
Economics also plays a big role in the decision to generate your own power. Favored locations have both relatively high electric rates and low prices for natural gas or diesel. Another plus is a government subsidy or incentive to increase efficiency or reduce air pollution. Interconnecting to the local utility still poses a problem in some areas, but the financial viability of most on-site power systems has not hinged on the willingness of utilities to buy surplus electric power produced by end users. The fact is, the power and heat have much more value when they can be fully utilized on-site.
The variability of DG applications is quite broad, and although the hardware may be similar from one application to the next, the ways in which the electric power and/or heat are used vary widely. The following six case studies represent a spectrum of applications that use reciprocating engine technologies to generate on-site power and heat.
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