Contents

6.1 Principles of Operation

6.1.1 Fuel Cell Stack

6.1.2 Fuel Cell System

6.2 Fuel Cell Types

6.2.1 Alkaline

6.2.2 Molten Carbonate

6.2.3 Phosphoric Acid

6.2.4 Proton Exchange Membrane

6.2.5 Solid Oxide

6.3 Comparison of Fuel Cell Types

6.3.1 Fuel Cell Design

6.3.2 Fundamental Limitations

6.3.3 Practical Limitations

6.3 3.1 Activation Polarization

6.3.3.2 Ohmic Polarization

6.3.3.3 Concentration Polarization

6.4 Efficiency

6.5 Operating Parameters

6.5.1 Temperature

6.5.2 Pressure

6.5.3 Gas Concentration

6.5.4 Utilization

6.5.5 Current Density

6.6 Fuels and Fuel Processing

6.6.1 Primary Fuels

6.6.2 Secondary Fuels

6.6.3 Fuel Cell Stack Fuels

6.6.4 Fuel Processing

6.6.4.1 Hydrogen Processing

6.6.4.2 Natural Gas Processing

6.6.4.3 Liquid Fuel Processing

6.6.4.4 Coal Processing

6.6.4.5 Gas Cleanup

6.6.4.6 Other Solid Fuel Processing

6.7 Cogeneration

6.7.1 Low- and High-Grade Heat

6.7.2 Hybrid Fuel Cell — Heat Engine

6.8 Interconnection and Control

6.8.1 Power Conditioning

6.8.2 Utility Interconnection

6.9 Dispatchability

6.9.1 Control Techniques

6.9.2 Current Status

6.10 Fuel Cell Systems Costs

6.11 Technology Development and Barriers

6.11.1 Cost Reduction

6.11.2 Fuel Flexibility

6.11.3 System Integration

6.11.4 Endurance and Reliability

6.12 Summary References

Fuel cells are electrochemical devices that convert the chemical energy of a fuel directly to usable energy — electricity and heat — without combustion. This is quite different from most electric generating devices (e.g., steam turbines, gas turbines, and reciprocating engines) which first convert the chemical energy of a fuel to thermal energy, then to mechanical energy, and, finally, to electricity. In the last decade, fuel cells have emerged as one of the most promising technologies to meet the nation's energy needs for the 21st century. They produce electricity at efficiencies of 40 to 60% with negligible harmful emissions, and operate so quietly that they can be used in residential neighborhoods. Fuel cells are particularly well suited to the distributed power generation market because of these characteristics as well as their scalability, high efficiency, and modularity.

In the 1960s, fuel cells were developed for space applications that required strict environmental and efficiency performance. The successful demonstration of efficient and environmentally sensitive fuel cells in space led to their serious consideration for terrestrial applications in the 1970s. Due to the emergence of several new fuel cell types (e.g., solid oxide and molten carbonate), the last 10 to 15 years have seen a tremendous expansion and diversification of developers and manufacturers which has dramatically expanded the list of potential products and applications of fuel cells.

There are many challenges and technical hurdles, however, that the fuel cell community must face in order for fuel cells to be widely used in the distributed generation market. The first challenge is establishment of the market. Fuel cells could contribute to the establishment of a distributed generation market if they become more economically competitive with current technologies. The key challenge is to produce an ideal hydrogen-fueled engine (a fuel cell) that can cost-effectively produce power in the hydrocarbon-based economy of today. This is the most significant technical challenge with regard to integrating fuel cell systems with available infrastructure, reducing their capital cost through volume manufacturing, and achieving widespread use in various sectors.

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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