Fuel Cell Technology

by Brian Walsh and Robert Wichert
Breakthrough Technologies Institute and U.S. Fuel Cell Council

Last updated: 04-13-2007

Introduction

Fuel cell power systems are quiet, clean, highly efficient on-site electrical generators that use an electrochemical process—not combustion—to convert fuel into electricity. In addition to providing power, they can supply a thermal energy source for hot water and space heating, or absorption cooling. In demonstration projects, fuel cells have been shown to reduce facility energy service costs by 20% to 40% over conventional energy service.

First discovered in the early 19th century, fuel cell technology remained a laboratory experiment until space exploration required a new energy source. In the 1960s, NASA dramatically advanced fuel cell technology for use in American space vehicles, using hydrogen fuel. Current land-based fuel choices include natural gas, propane, methane gas from landfills, anaerobic digester gas, methanol, and hydrogen.

At present, there are only a few companies that manufacture fuel cells commercially for building applications. Nevertheless, interest in the technology is intense and demonstration plants are being deployed all over the world. Fuel cell power systems have been proposed as the environmentally friendly, reliable, decentralized electricity generation solution of the future. High efficiency building cogeneration systems using fuel cells are expected to be one of the key technology options for improving building energy efficiency.

Description

A. How Fuel Cells Work

Fuel cell power systems convert the chemical energy of a fuel and an oxidant directly into electrical energy and heat using electrochemical processes—not combustion. In a fuel cell system, individual fuel cells can be combined in series into a fuel cell "stack" to achieve the desired voltage. The fuel cell "stack" is the principle component of a fuel cell power system. The total fuel cell power system consists of:

• Fuel Cell "Stack" or Fuel Cell Power Section
• Balance-of-plant
  • Fuel Reformer or Processor—to extract hydrogen from the fuel
  • Power Conditioner—to condition DC electric current to meet AC electrical grid requirements
  • Cogeneration or Bottoming Cycle (optional)—to utilize the waste heat

Perhaps the simplest system, a Proton Exchange Membrane Fuel Cell (PEMFC), combines hydrogen fuel with oxygen from the air to produce electricity, water, and heat. This process is essentially the reverse of electrolysis of water. The electricity results from free electrons liberated from hydrogen at the anode flowing through an external electrical circuit before recombining with hydrogen ions and oxygen at the cathode to produce water.

A Basic Proton Exchange Membrane Fuel Cell consists of 3 components: an anode (a negative electrode that repels electrons), an electrolyte in the center, and a cathode (a positive electrode that attracts electrons). The animated illustration shows how the hydrogen gives up electrons at the anode of a PEMFC and how they recombine with the hydrogen ions (the protons) and oxygen at the cathode to form water. As hydrogen flows into the fuel cell anode, a catalyst, often a platinum coating on the anode, helps to separate the gas into protons (hydrogen ions) and electrons. The electrolyte membrane in the center allows only hydrogen ion protons to pass through the membrane to the cathode side of the fuel cell. The electrons cannot pass through this membrane and instead flow through an external circuit in the form of DC electricity. Meanwhile, as oxygen from air flows into the fuel cell cathode, another catalyst helps the oxygen, protons, and electrons combine to produce pure water and heat.

The processes in a Phosphoric Acid Fuel Cell (PAFC) are similar, but the electrolyte is phosphoric acid instead of a proton exchange membrane. The ions formed and utilized in other fuel cell types are different, but the general concept is the same—a fuel is oxidized without flame to produce highly efficient electrical energy.

B. Types of Fuel Cells

The most common classification method for fuel cells is naming based on the type of electrolyte used in the cell stack. The most common, listed in the ascending order of their operating temperatures, are:

1. Proton Exchange Membrane Fuel Cells (PEMFC)
2. Alkaline Fuel Cells (AFC)
3. Phosphoric Acid Fuel Cells (PAFC)
4. Molten Carbonate Fuel Cells (MCFC) and
5. Solid Oxide Fuel Cells (SOFC).

C. Characteristics of Fuel Cell Power Systems

Although fuel cell power systems are currently more expensive than some other power systems, they have several characteristics that make them attractive for specific applications. First, fuel cells generate power continually, eliminating the need for backup generators or Uninterruptible Power Supply (U.P.S.) units. Second, they are efficient, converting approximately 40%-50% of the available fuel to electricity (up to 85% or higher with cogeneration heat recovery) compared to 20%-40% for traditional fossil fuel-fired power plants. Third, fuel cells emit 60% less carbon dioxide than combustion-fired reciprocating engines per unit output, and operate at lower noise levels (60 decibels at 100 feet) so that soundproofing and hearing protection are not required. In addition, fuel cells are fuel flexible and can operate with most hydrocarbons, such as natural gas, methanol, ethanol, propane, diesel, and gasoline. And lastly, there is significant potential for waste heat utilization using affiliated cogeneration systems.

By having electricity produced near the end-users, there is improvement in the overall conversion efficiency of fuel to end use electricity due to reduced transmission losses, and reduction in capital investment for new electric utility infrastructure. Also, fuel cells can "cold start" within hours, and idle to full load in seconds. Their higher efficiency at lower power levels makes them easy to leave in operation, even during low-load conditions. They are an uninterruptible power supply that is as efficient as the highest efficiency power plant. The modular nature of fuel cells can mean that units are added "just in time" to meet electricity power needs, saving capital costs and keeping the power distribution system flexible.

However, it should be noted that because fuel cells are an emerging technology, at the moment there are few suppliers, no comprehensive buyer's guide, and some risk involved in installing demonstration fuel cell power systems.

D. Fuel Cell Economics

Companies seeking to produce fuel cells for residential and commercial buildings are competing to bring the cost of their devices into a competitive range, which is generally considered to be between $1,000 and $2,500 per installed kilowatt (kW). At present, fuel cells prices range from $3,000 to $4,000 per kW. The actual life-cycle cost of fuel cell generated electricity depends on the relative price of electricity and natural gas (or whatever fuel is being used), the value of waste heat generated, maintenance costs, and the anticipated life of the fuel cell. In addition, the costs saved due to reliability gains and avoided transmission and distribution system costs must be taken into account.

E. Useful Life

While the fuel cell system as a whole should last a long time—the industry goal is 40,000 hours lifetime—the stacks within the cell may need to be replaced periodically. Stacks in today's phosphoric acid fuel cells are expected to need replacement after five to ten years, but the Department of Defense is investigating electrolyte replenishment as an alternative to stack replacement. In any case, there is little track record for the fuel cell industry, and some experts believe that early fuel cells will require major service every two to three years.

Application

Currently, approximately 35 buildings in America receive their primary power source from a fuel cell, with the grid as the back-up. In general, for fuel cells to be financially viable, they must run almost continuously. This requires a large continuous demand for electricity and heat. Buildings with little electrical use at night may not be suitable for large scale fuel cell technology. Smaller systems may be more appropriate in some instances. With this in mind, fuel cells can be installed in a variety of new and retrofit building projects. For applications including assured-power, back-up power generation, cogeneration, and distributed generation, fuel cells can provide significant cost savings. Another niche market for fuel cells is off-the-grid applications, where they will have to compete with solar and wind generation.

Below are links to some functioning fuel cell demonstration projects.

• PEM Oberhausen Demonstration (PEM CHP)
• Bewag Fuel Cell Innovation Park
• Residential Buildings—DOD Residential Demonstration
• Demonstration site evaluations—DOD PAFC Demonstration
• Worldwide list of fuel cell installations—Fuel Cells 2000

Relevant Codes and Standards

• Executive Order 13423, "Strengthening Federal Environmental, Energy, and Transportation Management"
• American National Standards Institute (ANSI)—ANSI/CSA America FC 1-2004, Stationary Fuel Cell Power Systems (this document supercedes ANSI Z21.83)
• American Society of Mechanical Engineers (ASME)—PTC 50 Performance Test Code—Fuel Cell Power Systems Performance
• The Institute of Electrical and Electronics Engineers (IEEE)—IEEE 1547, Standard for Interconnected Distributed Resources with Electric Power Systems
• International Code Council (ICC) (model building, mechanical, and fire protection codes covering buildings and their systems)
• National Fire Protection Association (NFPA)—NFPA 853 Standard for the Installation of Stationary Fuel Cell Power Plants
• National Fire Protection Association (NFPA)—NFPA/NEC 70, Article 692, Fuel Cell Systems (interconnection with building wiring)
• Underwriters Laboratories (UL)—UL 1741 Standard for Safety Inverters, Converters, and Controllers for Use in Independent Power Systems

Additional Resources

WBDG

Products and Sytems

Federal Green Construction Guide for Specifiers

Companies Developing Fuel Cells for Building Applications.

Fuel Cell Design and Analysis Tools

• Federal Technology Alert: Natural Gas Fuel Cells. November 1995. (FTA-1195a Natural Gas Fuel Cells) Contains detailed information to evaluate most natural gas fuel cells (NGFC) applications, including procedures for preliminary sizing of equipment, estimating energy savings, and calculating life-cycle costs (LCC).
• The National Renewable Energy Lab's, A Phosphoric Acid Fuel Cell Cogeneration System Retrofit to a Large Office Building, provides design guidance as well as economic analysis examples that can be used for many systems.
• U.S. Fuel Cell Council's Fuel Cell Energy Cost Model, is a product of the U.S. Fuel Cell Council's Power Generation Working Group, which makes calculations of estimated fuel cell energy costs given fuel, load, and other user input.

Fuel Cell Associations

• American Hydrogen Association
• California Stationary Fuel Cell Collaborative
• Fuel Cell Europe
• National Hydrogen Association
• U.S. Fuel Cell Council
• World Fuel Cell Council

Independent Fuel Cell Testing Programs

• Department of Defense (DoD) Fuel Cell Test and Evaluation Center (FCTEC) Fuel Cell Testing Program
• National Fuel Cell Research Center

Fuel Cell Incentives and Programs

• Database of State Incentives for Renewable Energy
• Updike, Kelly & Spellacy, P.C. (Guide to state fuel cell incentives and programs)

Others

• Department of Defense Fuel Cell Demonstration Projects
• Monthly Fuel Cell Connection Newsletter—Free Subscription
• Online Fuel Cell Information Center—developed by Fuel Cells 2000