DG fundamentals challenged.(Letters)(Letter to the Editor)

Dear Editor:

In the article "Distributed Generation" (September 2003) the author John Fetters offered all erroneous statement in regard to the use of combustion gas turbines.

He wrote: "Low efficiencies make their [gas turbines] use for peak shaving or for CHP installations where a continuous supply of hot water or steam is needed uneconomical". This sentence includes two incorrect statements.

1. As mentioned later in the same article, "peak-shaving units operate infrequently, often less than a thou sand hours annually." For the above reason the efficiency is a much less important factor in the selection of a peak-shaving unit than the installed cost of it, therefore gas turbines are used for this application.

2. The second error relates to the role of gas turbines in CHP applications. For those readers unfamiliar with this term: CHP (combined heat and power) is the modern term for cogeneration. Although gas turbines are less efficient than combustion turbines, in a CHP application where most of the wasted heat is utilized, the prime driver efficiency is, again, of lesser importance as compared to the electrical-to-thermal load ratio that a specific unit is able to provide.

Therefore, depending on the road profile and type of thermal energy used (steam or hot water), in a CHP application gas turbines can be more feasible than combustion engines. In addition, in a so called Cheng cycle mode, gas turbines offer more flexibility in switching between the thermal and electric loads.

For ...