Renewable Energy Technology Assessments - Kauai Island Utility ...

Kaua’i Island Utility Cooperative
Renewable Energy Technology Assessments 3.0 Renewable Energy Technology Options
permanent power and intermittent power demands. Figure 3-24 shows an example of a
fuel cell in operation.
Figure 3-24. 200 kW Fuel Cell (Source: UTC Fuel Cells).
Operating Principles
Fuel cells convert hydrogen-rich fuel sources directly to electricity through an
electrochemical reaction. Fuel cell power systems have the promise of high efficiencies
because they are not limited by the Carnot efficiency that limits thermal power systems.
Fuel cells can sustain high efficiency operation even under part load. The construction of
fuel cells is inherently modular, making it easy to size plants according to power
requirements.
There are four major fuel cell types under development: phosphoric acid, molten
carbonate, solid oxide, and proton exchange membrane. The most developed fuel cell
technology for stationary power is the phosphoric acid fuel cell (PAFC). PAFC plants
range from around 200 kW to 11 MW in size and have efficiencies on the order of 40
percent. PAFC cogeneration facilities can attain efficiencies approaching 88 percent
when the thermal energy from the fuel cell is utilized for low grade energy recovery. The
potential development of solid oxide fuel cell/gas turbine combined cycles could reach
electrical conversion efficiencies of 60 to 70 percent.
21 March 2005 3-84 Black & Veatch