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Distributed Energy Systems

Achieving Low Unit Production Costs

Commercially developed simple cycle gas turbine generators without recuperators sell for around $700/kW. Single recuperator open cycle gas turbines are priced at about $800/kW.

By those standards, the CEC concept sets out to achieve exceptionally low unit costs for turbo generators in quantity production. Much of this stems from a basic design philosophy to eliminate manufacturing complexities. Fewer parts, elements serving dual functions, elimination of conventional fasteners, design for mechanized processing and selection of materials with particular characteristic, are all a part of this process. Previous use of this philosophy by CEC' technical leadership was successfully applied to the Capstone Micro Turbine which set new low cost standards for its generation of commercial gas turbine designs.

The Requirement for Low Cost Production of the CEC Turbo Generator

The CEC turbo generator improves on those standards, applying them to much smaller power units. The purpose is to get away from the historically high cost capital equipment syndrome that prevails in most gas turbine development organizations. This is accomplished by imparting to CEC units the expendable feel that one has for commercial appliances. For example, a vapor cycle refrigeration unit, for all its complexity, has become accepted as an inexpensive, hermetically sealed device that delivers unattended, trouble-free service for decades. Similarly, at a fraction of the cost that gas turbine engineers would expect, the common household clothes drier features combustion arrangements very similar in performance, to that of the CEC turbo generator.

 

Heat Exchangers

The recuperator, combustion heat exchanger, and combustion air recuperator are all plate-fin heat transfer units made of conductive ceramic materials. The external utility and heat sink heat exchanger is a conventional counter-flow steel heat exchanger. Heat exchangers account for a large part of the cost of any recuperated gas turbine system. As such, CEC pays close attention to the development of designs and manufacturing processes to automate the mass production of the heat transfer items. The heat transfer items represent a little more than one third of the system's factory cost.

Packaging

The turbo generator comes packaged as a plug-compatible, sealed assembly with minimal installation requirements, as expected from a commercial appliance. There is a standard natural gas connector, a combustion air exhaust duct connection, a duct connection for the hot air supply to other services and a wild frequency electrical output connector.

Simple Controls

Since a wild frequency alternator is used, control of the rotor speed is quite tolerant. This allows for the use of self-powered pneumatic control of fuel flow on the one hand, and the pressure of the working fluid on the other. The resulting proprietary control system is indeed very simple, highly reliable, and inexpensive to manufacture.

Relative to the kinds of digital electronic controls used on conventional open cycle gas turbines, the cost advantage of the mechanical system is considerable.

Turbo Generator Rotor

As explained elsewhere in more detail, the rotating part of the turbo generator is made in one piece out of precision ceramics, except for the permanent magnet for the generator. Once in quantity production, ceramic parts of this nature can be replicated at very low cost.

In addition to low specific weights comparable to that of aluminum, ceramics offer the added advantage of very low coefficients of thermal expansion. To maintain tight clearances at all temperatures, the turbine housing and nozzle and compressor diffuser are also made of ceramics. The small clearances allow for the achievement of higher higher compressor and turbine efficiencies. In essence, all the high precision parts are ceramic, and will account for less than 18% of system factory cost.

High Speed Alternator

The stator of the alternator is made of laminations that are wound with thin copper wire held in place by wedges. The magnetic media inserted into the shaft represents roughly a third of the alternator cost and the stator with windings accounts for the rest. Together, they add up to about 13% of the system's factory cost.

Combustor and Sheet Metal Parts

Apart from the porous burner element which glows brightly while flames hardly penetrate beyond its surface (like the bag in a propane lantern), the combustor is essentially a low cost ceramic plenum and heat exchanger through which the combustion gasses pass. This part and other sheet metal frames, housing and manifold parts along with sound attenuation, filter and hardware elements taken together account for about 16% of system factory costs.

Overall System

The factory cost of the entire turbo generator modestly exceeds $300/kW. With distribution costs included its selling price is targeted to be $400/kW.

Proprietary Rights

There is nothing patentable about the form of Brayton cycle used, nor the basic operational concepts employed. The real value of the design lies in the proprietary features and processes used to make the system affordable to a very wide commercial audience. The Company believes at least two such features to be patentable. It purposely has delayed filing for such patents until it becomes necessary to start disclosing some specifics about these features for manufacturing or marketing purposes, by which time the Company should be much more capable of vigorously defending its proprietary rights.