Assessment of Fuel Cell Technologies to Address
Power Requirements at the Port of Long Beach
SUPPLEMENTAL REPORT
The Science of Fuel Cells
Prepared by
Dr. Michael A. MacKinnon
Senior Scientist
Dr. Scott Samuelsen
Professor of Mechanical, Aerospace, and Environmental Engineering
Submitted to
Port of Long Beach
Irvine, California
92696-3550
949-824-7302
In conjunction with:
Contract Number HD-8381, Job Task 1605
April 31, 2016
Contents
Nomenclature ............................................................................................................................................... 2
1. Fuel Cell Overview ................................................................................................................................ 4
1.1 Characteristics of Fuel Cell Systems ............................................................................................... 5
2. Fuel Cell Applications ......................................................................................................................... 13
2.1 Stationary Power .......................................................................................................................... 14
2.2 Motive Power Fuel Cell Applications ............................................................................................ 19
2.3 Portable Fuel Cells ........................................................................................................................ 20
3. Fuel Cell Types.................................................................................................................................... 20
3.1 Fuel Cell Types for Stationary Applications .................................................................................. 23
References .............................................................................................................................................. 25
1
Nomenclature
AB
Assembly Bill
AC
Alternating Current
AFC
Alkaline Fuel Cell
APU
Auxiliary Power Unit
CO
Carbon Monoxide
CO2
Carbon Dioxide
DC
Direct Current
DG
Distributed Generation
DMFC
Direct Methanol Fuel Cell
DOE
U.S. Department of Energy
FC
Fuel Cell
FCEV
Fuel Cell Electric Vehicle
GHG
Greenhouse Gas
HVAC
Heating, Ventilation, and Air Conditioning
MCFC
Molten Carbonate Fuel Cell
MW
Megawatt
2
NG
Natural Gas
NGCC
Natural Gas Combined Cycle
NOx
Nitrogen Oxides
OCSD
Orange County Sanitation District
PAFC
Phosphoric Acid Fuel Cell
PEMFC
Polymer Electrolyte Membrane Fuel Cell
PM
Particulate Matter
PV
Photovoltaic
SMR
Steam Methane Reformation
SOx
Sulfur Oxides
SOFC
Solid Oxide Fuel Cell
UCI
University of California, Irvine
3
1. Fuel Cell Overview
In contrast to combustion heat engines (e.g., gas turbines, diesel generators), fuel
cells convert the chemical energy in a fuel directly into electricity and water by
electrochemical reactions that are similar in concept to battery electrochemical reactions.
The key difference between fuel cells and batteries is that fuel cells operate on an
external fuel source rather than stored chemical reactants. Thus, fuel cells do not run
down or require charging. Instead, they continuously provide electricity as long as fuel
is provided in the same manner as heat engines.
A diagram of how a phosphoric acid fuel cell works is provided in Figure A.1.
Hydrogen is fed on the anode side where it combines reacts to form two protons (H+)
and two electrons (e-). The protons are allowed to move through the electrolyte to the
cathode while the electrons are rejected by the electrolyte.
The electrons take an
alternative path to the cathode, serving loads such as lighting, motors for vehicles or
HVAC fans, and plug-in appliances. While “spent” of energy as they leave the load, the
electrons are able to react at the cathode with the oxygen in the air entering the fuel cell
and the protons emerging from the electrolyte. The product of the reaction is water
(H2O).
4
Figure A.1: Overview of fuel cell technology. A Doosan PureCell is shown as an example only.
1.1 Characteristics of Fuel Cell Systems
As shown in Figure A.2, fuel cells produce electricity and heat for a diverse range
of consumer applications with attributes that include:
•
High electrical efficiencies
•
Emission of virtually zero criteria pollutants
•
Low GHG emissions as a result of the high electrical efficiency and, in
many applications, recovery of the exhaust heat for steam, hot water, or
chilled water
•
Net zero GHG emissions when operating on biogas
•
Zero GHG emissions when operating on renewable hydrogen
•
Flexible with regard to fuel (natural gas, renewable biogas, hydrogen and
renewable hydrogen)
•
Consumption of virtually zero to net negative water
•
Flexibility and modularity with regard to system sizing and siting which
broadens the scope of potential applications
5
•
Acoustically benign
•
Provide resiliency and reliability to electrical supply
•
Compatibility with renewable technologies
•
Support the grid
•
Applicable to both stationary power generation, power for mobile
transportation (e.g., automobiles, trucks, buses, locomotives), and portable
power
Figure A.2: Overview of fuel cells including fuel sources, conversion products, and applications
High Electrical Efficiencies
Fuel cells generate electricity with high electrical efficiencies compared with
combustion engines. The one step of a fuel cell in transforming chemical to electrical
energy, as compared to the multi-step process used by combustion devices of chemical
to thermal to mechanical to electrical, results in significant reductions in total energy
loss by avoiding thermal losses at each conversion step (Figure A.3).
6
Figure A.3: Differences in energy conversion steps for electricity generation from fuel cells and heat engines
Electrical efficiency is a measure of how well fuel input is converted to electrical
power. The higher the electrical efficiency, the lower the amount of fuel required per
kilowatt-hour (“kWh”) of electricity generated.
High electrical efficiency is an
important attribute of fuel cells relative to both the cost of operation and the
environmental impact. Fuel cells have demonstrated electrical efficiencies from 30% to
levels exceeding 60% [1, 2]. 1 This is significantly higher than electrical efficiencies
attained by heat engines especially at the distributed generation scale. For example,
reciprocating engines range from 27-41%, steam turbines from 5-40%, gas turbines from
24-36%, and microturbines from 22-28% [3]. As the amount of carbon dioxide (CO2)
generated per kWh of electricity produced is inversely proportional to the electrical
efficiency, fuel cells with their higher electrical efficiency emit less CO2 per kWh of
electricity produced than other electricity generating technologies using the same fuel.
High Overall Efficiencies with CCHP
Fuel cells produce high quality heat. In addition to generating electrical power,
stationary fuel cells can cogenerate a thermal product. The strategy, referred to as
Combined Cooling, Heat, and Power (CCHP), is to capture and utilize the heat
produced by the fuel cell for the provision of cooling heat, hot water, or steam. This
1
These efficiencies are for operation on natural gas and include reformation of the fuel to hydrogen.
7
results in the fuel cell’s overall efficiency (electrical power generation and use of the
captured thermal energy) ranging from 55-80% [3] and, with a judicious design,
exceeding 90% [4]. In addition, this attribute displaces the fuel and emissions that
would otherwise be associated with (1) boilers (in the case of using the thermal energy
as heat), and (2) the displaced electricity to drive chillers (in the case of using the
thermal energy for cooling).
The resultant effect is to dramatically reduce CO2
emissions, criteria pollutant emissions, and the demand on fuel reserves. Combustion
heat engines also serve CCHP opportunities.
Fuel cells are unique, however, in
providing high fuel-to-electricity efficiency and high quality (i.e., high temperature)
heat, as well as producing a virtually zero emission of criteria pollutants.
Ultra-low Pollutant and GHG Emissions
Fuel cells reduce emissions of both criteria pollutants and GHGs from
traditional power generation, mobile, and CCHP energy systems. [4] This is due in
part to the reaction chemistry. Fuel cells are driven by electrochemistry versus hightemperature combustion chemistry.
Thus fuel cells emit virtually zero criteria
pollutants including nitrogen oxides (NOx), sulfur oxides (SOx), particulate matter (PM),
and carbon monoxide (CO) [3]. Demonstrating this, Figure A.4 displays the emissions
of NOx per kWh for both traditional and advanced heat engines and fuel cells operating
on natural gas. Fuel cell conversion of electricity results in negligible emissions relative
to other common generation technologies.
If the fuel input is hydrogen, only water vapor and the nitrogen that entered
from the air are emitted in the exhaust. If the fuel is natural gas or another hydrocarbon
fuel, then CO2 is also generated. As explained above, because of the high electrical
efficiency of fuel cells, the amount of CO2 emitted per kWh of electricity generated is
substantially lower than from conventional power generation technologies. The ability
of fuel cells to capture and use the high-quality thermal energy further reduces the
8
amount of CO2 emitted, and the ability of fuel cells to operate on biogas results in net
zero emission of carbon, and the ability of fuel cells to operate on renewable hydrogen
results in zero emission of carbon.
0.25
NOx from Natural Gas Power Generation
g NOx/kWhr
0.2
0.15
0.1
0.05
0
Fuel Cell
NGCC
Combustion Microturbine Reciprocating
Turbine
Engine
Figure A.4: Emissions of NOx from Natural Gas Power Generation Devices. Data for NGCC [5-7], Data for others [3].
Therefore, fuel cells can generate clean power (i.e., virtually zero emission of
criteria pollutants) that benefits regional air quality while, at the same time, supporting
California’s GHG reduction goals under AB 32 even while using fossil fuels such as
natural gas, and renewable fuels such as biogas and bio-hydrogen and renewable
hydrogen. Additional benefits of fuel cells include suitability for citing near or even
inside buildings (due to being virtually zero emitting of pollutants and acoustically
benign) and the avoidance of hurdles related to permitting and zoning. For example,
the South Coast Air Quality Management District waives permitting for fuel cells
operating on natural gas due to their favorable environmental performance.
Fuel Flexible
Fuel cells are fuel flexible and can be effectively operated on a diverse range of
gaseous fuels including natural gas, renewable fuels (such as biogas and renewable
9
hydrogen [8]), propane, diesel, methane, methanol, and syngas produced from solid
biomass or coal [9]. While hydrogen can be used directly in a fuel cell, hydrocarbon
fuels must be “reformed” to liberate the hydrogen using, for example, steam methane
reformation (SMR). For some fuel cell types (e.g., phosphoric acid), the steam and
elevated temperatures are combined with the fuel into a SMR reformer that is external
to the fuel cell stack. For the fuel cells that operate at high temperatures (e.g., molten
carbonate and solid oxide), the reformation can be supported within the fuel cell stack
where steam is available from the fuel cell exhaust.
This flexibility allows for mixtures of fuels to be used with the particular benefit
of facilitating biogas supplementation of natural gas (or vice versa). This is beneficial in
that fuel cells can operate on natural gas, biogas, and mixtures of the two. Biogasderived fuels have low or even net negative GHG emissions.
However, current
strategies to manage biogas in California include flaring to prevent methane release or
conversion in heat engines that can result in detrimental levels of criteria pollutant
emissions. By using biogas, or mixtures of biogas and natural gas in fuel cells, the
environmental benefits are achieved without the barrier of point-of-generation criteria
pollutant emissions.
Low to Negative Water Consumption
Fuel cells require very little to no water during operation and can even be a net
water producer by generating more water than they consume due to electrochemical
reactions between the reactants, oxygen from the air, and hydrogen.
This has
importance from concerns regarding the sustainability of fresh water supply with
potential climate effects and expanding demands from population and infrastructure
growth. Fuel cells require no water beyond small initial injections at start-up [10].
Therefore, fuel cells achieve significant reductions in water consumption relative to
conventional power generation technologies. For example, a median estimate for water
10
consumption by efficient combined cycle natural gas plants is 210,000 gallons per
kilowatt-hour [11]. Doosan Fuel Cell America estimates that the use of its 400 kW fuel
cell systems saves approximately 1.6 million gallons of water annually relative to the
U.S. electric grid [10].
Commercial fuel cell deployments in California are reporting
significant reductions in water consumption.
A 1-MW fuel cell system at a food
processing facility has been reported to reduce water use from a conventional power
plant by 99.99% and CO2 emissions by 30% per unit generated electricity 2. Installation
of a 500-kw fuel cell system at the LPL financial building in San Diego is expected to
reduce 3.4 million gallons of water annually relative to the U.S. grid [10]. Similarly, a 1MW system at a corporate campus will save more than 3.25 million gallons per year
relative to the average water demands of California power plants [10].
Modularity, Scalability, and Flexibility of Installation
Fuel cells are highly scalable and flexible. Fuel cells are modular and can be
scaled up depending on the power needs of the consumer, thereby allowing them to be
installed and operated in a variety of ways and applications. Smaller installations in the
kilowatt range can meet the power needs for residential, telecommunications or small
commercial facilities. Larger commercial installations may require several hundred kW
to multiple MW scale fuel cell systems while utility applications may reach hundreds of
MW scale.
Acoustically Benign
Unlike heat engines, fuel cells have few moving parts and subsequently
operate with little noise. The market is familiar with reciprocating engines, gas turbine
engines, and the associated electric generators, all of which depend on many moving
parts and produce a distinctive acoustic emission. With few moving parts, fuel cells are
2
http://www.thepacker.com/fruit-vegetable-news/Taylor-Farms-flips-switch-on-solar-system.html
11
more closely aligned to the acoustic emission of a transformer and it is often challenging
to convince the market that a fuel cell is actually generating electrical power.
Provide Resiliency and Reliability to Electrical Supply
Fuel cells can significantly increase the resiliency and reliability of electricity
supply to consumers. The ability of fuel cells to provide constant and high quality
power to consumers in a primary or backup role has increasing importance due to the
reliance on electronics for many essential industries including banking, communication,
and teleworking. This is in addition to concerns over the vulnerability of an aging
electrical grid in many locations that could have increasing vulnerability to outages. As
grid outages incur significant costs and other detriments, the ability of fuel cells to
generate backup power independent of the grid to grid-connected buildings (or to
operate as a building’s primary source of power) is beneficial – particularly to
consumers who prioritize the constant availability of high quality power to maintain
critical operations. Examples of such entities include data centers, banks, hospitals,
grocery stores, and government agencies. Fuel cells have successfully demonstrated
this ability through several recent natural disasters including providing power to
essential telecommunication technologies, grocery stores, and storm shelters during
Superstorm Sandy and Hurricane Irene. 3
Compatibility with Renewable Technologies
Fuel cells are complementary with other electricity generation technologies –
most notably renewable generation. Stationary fuel cells are load-following capable
with fast ramp rates and a significant degree of turndown depending on the fuel cell
type. Furthermore, fuel cells can operate on several different renewable fuels providing
dispatchable renewable generation.
3
This allows fuel cells to be integrated with
http://www.fuelcells.org/uploads/Fuel-Cells-in-Storms.pdf
12
distributed solar PV, wind turbines, and battery storage systems to provide stable, baseload power supply that supports and enhances the power supply from the intermittent
renewable technologies. On the larger scale, fuel cell power plants can support the
integration of intermittent renewable resources into the utility grid by providing clean,
24/7, load-following power generation.
Support the Grid
Fuel cells can provide important energy services to both the micro- and macrogrids in which they are deployed. Fuel cells can provide support to the existing and
future electrical grid that can result in various benefits to both customers and utilities –
including reduced costs. Stationary fuel cells have load-following capabilities with fast
ramp rates and a significant degree of turndown depending on the fuel cell type. Fuel
cells can deliver peaking or intermediate load service which can prevent the need for
new transmission and distribution infrastructure and provide peaking capacity in
constrained areas.
The load-following capabilities of fuel cells are particularly
important in California as expected increases in intermittent wind and solar power
generation will necessitate increasing amounts of clean, efficient, load-following power
generation. Additionally, power conditioning inverters in fuel cell systems needed to
transform DC electricity into AC can be used even independently of the fuel cell for
system power factor correction and voltage support.
2. Fuel Cell Applications
Fuel cells suit a wide variety of applications in different market sectors, including
stationary power generation, transportation motive power, and portable power
generation. Stationary applications include the needs of utilities, commercial buildings,
homes, government and military complexes, and large institutional, medical and
industrial centers.
To serve these applications, systems ranging in capacity from
13
several hundred kilowatts to multi-megawatts are now available commercially and
larger systems are being developed for central plant applications. For transportation,
fuel cells have been used in many different mobile technologies in conjunction with
hydrogen including automobiles, heavy-duty trucks and buses, and materials handling
equipment (e.g., forklifts). For portable applications, fuel cells could replace batteries
for laptops, cell phones, and other personal power devices.
2.1 Stationary Power
The generation of electricity for stationary power applications is a principal
function of fuel cell technology. Stationary fuel cells are commercially available across a
wide range of sizes from kilowatt to megawatt installations. Stationary fuel cells can be
used to provide primary power from the small distributed to utility-scale, backup
power, emergency power, auxiliary power units (APU), and battery and electronics
charging. The modularity and distributed nature of stationary fuel cells makes them
well suited for CCHP applications to facilitate the capture and use of waste heat to
potentially provide heating, cooling, and hot water.
Fuel cells can also provide
hydrogen as an output when operating on natural gas or biogas allowing for trigenerations 4 systems with very high net energy efficiencies [12]. Fuel cells are capable
of being combined with traditional heat engines (i.e., hybrid fuel cell heat engine
systems) in a manner that captures synergies and allows for very clean and efficient
energy conversion.
Stationary fuel cells are often used as a clean and efficient form of distributed
generation (DG). In contrast to large, centralized power plants far from electricity users
that require the transmission and distribution of generated electricity, the use of DG
The term tri-generation refers to stationary fuel cell technologies that generate both electricity and heat
as well as hydrogen as a transportation fuel.
4
14
allows for electricity to be produced at or near the site of use. Typical DG systems
range in size from the kW to hundreds of MW. Benefits of using DG include potentially
lower costs, reduced emissions, higher power quality, reliability, and security.
Market acceptance has been driven by the capability of fuel cells to provide high
quality power with high efficiencies over a broad range of load profiles, high
availability, power quality, and compatibly with zoning restrictions, and small
footprint. Consumers seeking high quality power may value reliability and power
quality over costs and may prioritize low-emitting technologies due to potential
interactions with zoning issues and emissions credits.
Table A.1: Potential roles and benefits of fuel cells in DG applications
Potential Roles of Fuel Cells for DG
•
•
•
•
•
•
•
Benefits of Using Fuel Cells for DG
Primary Power
Backup Power
Emergency Power
Auxiliary Power Units
Combined Cooling, Heating and Power (CCHP)
Tri-generation (Power, Heat, Hydrogen)
Load-following power to complement
intermittent renewable resources
•
•
•
•
•
•
•
•
High electrical and CCHP efficiencies
Virtually zero emissions and water
use
Low vibration and noise
High power availability/quality/
reliability
Modular/flexible/scalable
Small footprint/space requirements
Avoidance of zoning restrictions
Manage and enhance renewable
resource integration
Large stationary fuel cell applications include utility and distributed-scale power
plants. Electric utility companies around the world have integrated fuel cell power
plants at the MW scale including the U.S. and South Korea. Stationary fuel cells can
provide primary or backup power to data centers, grocery and retail operations, mixeduse buildings including hospitals/healthcare centers, universities and schools,
government buildings, corporate headquarters/campuses, and hotels, and industrial
applications such as agriculture or food processing facilities. Small fuel cell applications
15
include residential, small commercial, and telecommunications to provide backup
power to cell towers and other critical communication equipment.
Table A.2: Commercial Fuel Cell Applications
•
•
•
•
•
•
•
Commercial Fuel Cell Applications
Utilities
Government Offices and Public
Buildings
Fire Departments and Law
Enforcement
Wastewater Treatment Plants
Landfills
Zoos/Parks/Gardens
Grocery/Retail
•
•
•
•
•
•
•
•
•
Telecommunications
Data Centers
Corporate Headquarters/Campuses
Public School and Universities
Hospitals/Healthcare
Hospitality/Hotels
Industrial Settings
Food Production Facilities
Agricultural Processing Facilities
Combined Cooling, Heating, and Power
Due to their suitability for DG and other benefits, fuel cells are commonly
considered for use in CCHP applications. CCHP is a method of generating electric
power and useful thermal energy to provide services to the consumer potentially
including cooling, heating, hot water and steam. Typically CCHP systems consist of a
number of individual components comprising (1) prime mover, (2) generator, (3) heat
recovery, and (4) electrical interconnection configured as an integrated whole.
Stationary fuel cells can provide the prime mover in CCHP systems. Benefits of CCHP
include reduced energy related costs, increased reliability and resiliency of power
supply, increased energy efficiencies, reduction in GHG and pollutant emissions, and
provision of macro and microgrid support via various services [3].
An example of a real-world CCHP fuel cell installation is displayed below in
Figure A.5 for a 1.4 MW of clean electricity and 200 tons of clean cooling used for air
conditioning at the University of California, Irvine Medical Center (UCIMC). Predicted
16
system efficiency is 74% during the provision of 24/7 generation of electricity from
natural gas.
Figure A.5: 1.4 Megawatt fuel cell installation at the UCI Medical Center providing 200 tons of cooling used for air conditioning
with a 74% predicted efficiency operating on natural gas
Production of Transportation Fuels in Tri-Generation
A distinctive attribute of fuel cell systems is that some can produce hydrogen
fuel as an output when operating on gaseous fuels including natural gas and biogas.
This allows fuel cells to operate in “tri-generation” systems producing electricity, heat,
and hydrogen from a single fuel input stream (Figure A.6) [12].
Incorporating
hydrogen production further increases the energy efficiency of the system relative to
solely using waste heat and provides additional benefits – including fuel production for
mobile fuel cell applications such as forklifts, buses, or fuel cell electric vehicles (FCEV).
High temperature fuel cells are suitable for tri-generation as available heat can facilitate
internal reformation in the fuel cell stack.
A particularly attractive fuel pathway for tri-generation systems is biogas
(produced via anaerobic digestion at sites including wastewater treatment plants,
landfills, and agricultural operations) as this allows for a means of coupling very low
emission GHG and criteria pollutant strategies in the electricity and transportation
sectors [13]. This concept was demonstrated in real-world settings with a 300 kW
MCFC Fuel Cell Energy system operated at the Orange County Sanitation District
17
(OCSD) (Figure A.7).
Biogas produced during anaerobic digestion at OCSD was
cleaned and fed to the fuel cell to produce electricity and heat (available for use in plant
operations such as meeting the thermal requirements of digesters) and a third product,
hydrogen, that was provided to an on-site vehicle refueling station.
Figure A.6: Overview of Tri-generation Fuel Cell Systems
18
Figure A.7: Tri-generation Fuel Cell System Operating on Biogas at the Orange County Sanitation District
2.2 Motive Power Fuel Cell Applications
Fuel cells can provide motive power in transportation applications with many of
the same benefits of power generation – including very high efficiencies and ultra-low
emissions. Fuel cells have been demonstrated or deployed in nearly all sectors of
transport including light-, medium-, and heavy-duty vehicles, buses, and a variety of
material handling vehicles and specialty vehicles. In addition to providing primary
motive power, fuel cells can be included onboard other vehicle types with conventional
internal combustion engines as APU and battery-electric vehicles to provide range
extension.
Fuel cells are commercially available to power automobiles in fuel cell electric
vehicle (FCEV) applications being developed by major automakers including Hyundai,
Toyota, Honda, Volkswagen, Daimler, and General Motors [14]. FCEVs are highly
efficient and environmentally friendly and have benefits over other alternative
technologies including a short refueling time and similar range per tank as a gasoline
vehicle. To encourage the commercial deployment of FCEVs, California is supporting
the construction of public hydrogen refueling stations via substantial funding [14].
19
Fuel cells have been demonstrated as particularly suitable for material handling
and have achieved success with forklift deployments at distribution and warehouse
centers for Walmart, Ace Hardware, and Central Grocers [10]. Fuel cell-powered fork
lifts improve operation efficiencies by completing a 6 to 8 hour shift on a single tank of
hydrogen while delivering constant power free of voltage sag [10]. Fuel cell forklifts
also have benefits over electric battery powered fork lifts including easy and rapid
refueling by the operator which negates the need for dedicated staff to perform battery
swaps and recharge. Additionally, the avoidance of batteries and associated activities
can free up warehouse space and prevent the need for handling and disposal of toxic
lead acid batteries. Reflecting the benefits of fuel cell use for materials handling, in 2014
North American fuel cell-powered forklifts totaled 7,500 located within 60 warehouses
and distribution centers in 20 states and Canada [14].
2.3 Portable Fuel Cells
Portable fuel cells can be used to charge non-stationary products with the
primary characteristic being they are designed to be moved.
Portable fuel cell
applications are used in recreational settings, military applications, portable products,
and small personal electronics. Typically portable fuel cells range in size from 1 W to 20
kW and are most often PEMFC and direct methanol fuel cells (DMFC).
3. Fuel Cell Types
Five principal types of fuel cells are currently deployed commercially – alkaline
(AFC), proton exchange membrane (PEMFC), phosphoric acid (PAFC), molten
carbonate (MCFC), and solid oxide (SOFC) based technologies [15].
Each type is
distinguished by the material used for the electrolyte and the operating temperature.
The fuel cell types also vary in efficiency, range of sizes, fuels used to power the fuel
20
cell. These differences in characteristics directly impacts the suitability of each fuel cell
type for various applications.
•
Alkaline – AFCs contain a potassium hydroxide solution as an
electrolyte and typically operate at temperatures (225-475°F) lower than
SOFCs and MCFCs. A benefit of AFC is the ability to use a variety of
non-precious metal catalysts. AFCs are generally considered for use in
military, space, and underwater applications as they require controlled
environments to avoid poisoning by carbon dioxide (CO2). For example,
NASA has used AFCs since the 1960s to provide electricity and water to
space missions.
•
Proton Exchange Membrane – PEMFCs use a solid polymer membrane
as an electrolyte typically with platinum acting as a catalyst and
typically range in size from several watts (w) to 1 megawatt (MW).
Most PEMFCs operate at low temperatures (175-200°F) and pressures
allowing for short startup times, have a high power density, and can
quickly ramp output up or down to meet dynamic power needs.
PEMFCs are thus well suited for applications requiring fast startup and
dynamics including motive power in light duty vehicles, buses, and
forklifts. Additionally, PEMFCs systems are available for primary or
backup power in telecommunications, data centers, and residential
markets.
hydrogen.
Low-temperature PEMFCs are limited in fuel choice to
However, high temperature PEMFCs (250-390°F) are
available that can be integrated with fuel reformers to permit increased
fuel flexibility.
21
•
Phosphoric acid – PAFCs use an electrolyte of phosphoric acid soaked
in a matrix with a carbon-supported platinum catalyst.
PAFCs can
operate using reformed hydrocarbon fuels (e.g., natural gas) or biogas.
PAFCs operate similarly to PEMFCs but are more tolerant of fuel
impurities due to higher operating temperatures (350-400°F). The higher
operating temperatures of PAFCs increases their suitability in CCHP
applications.
PAFCs have experienced widespread commercial use
including hospitals, schools, office buildings, grocery stores, and waste
water treatment plants.
•
Molten Carbonate – MCFCs use a solution of lithium, sodium, and
potassium carbonates in a ceramic matrix as an electrolyte and operate
at high temperatures (1,200°F). High temperature operation gives the
MCFC fuel flexibility, avoidance of expensive catalyst, and high CCHP
suitability. MCFCs are not susceptible to CO or CO2 poisoning and can
even be operated on syngas produced from coal. MCFCs are ideal for
large stationary applications including utility-scale power plants,
manufacturing plans, hospitals, prisons, hotels, universities, and
wastewater treatment plants.
•
Solid Oxide – SOFCs use a solid ceramic (often yttria-stabilized
zirconia) as an electrolyte and operate at very high temperatures
(1,800°F). High temperature operation gives SOFCs the ability to use
low-cost, non-precious metal catalysts, operate on a range of
hydrocarbon fuels directly by internal reformation, and provides ideal
suitability for CCHP applications that capture and utilize waste heat for
useful purposes. SOFCs are excellent for stationary power applications
22
from the distributed up to the utility scale.
SOFC are also being
demonstrated for use as vehicle auxiliary power units (APUs).
3.1 Fuel Cell Types for Stationary Applications
Among stationary applications, different types of fuel cells are better suited to
serve different market segments, based on size and customer needs (especially for heat
and/or cooling), fuel availability, etc.
PEMFCs are well suited for backup power and intermittent power demand (e.g.,
peak load shaving) compared to incumbent combustion-based generating technologies
for the following reasons:
•
•
•
•
•
•
Lowest environmental impact of any power generation system using similar
fuels
Generation of high quality power
Ease of siting at or near the point of use
Unattended operation, low maintenance, high availability
Readily turned on and off as required on demand
Minimal licensing, permitting and installation time
PAFCs, MCFCs, and SOFCs are well suited for continuous, baseload generation
of electricity and heat compared to incumbent combustion-based generation
technologies for the following reasons (Table A.3):
Table A.3: Typical Operating Characteristics and Applications of Fuel Cell Categories
Fuel Cell
Type
External
Reformer
for NG
Operating
Temp
[◦F]
Electrical
Efficiency
[%]**
Avg. Size
[kW]
Potential
Fuels*
Solid Oxide
700-1000
NG, H2,
Biogas
No
~1800
60%
Molten
Carbonate
600-700
NG, H2,
Biogas,
Syngas
No
~1200
50%
Potential
Applications***
•
23
•
•
•
•
Utility/distributed
power
CCHP
Vehicle APU
Utility/Distributed
power
CCHP
Alkaline
PEM
Phosphoric
Acid
90-100
H2
Yes
225-475
60%
80
H2
Yes
175-200
30-40%
150-250
NG, H2,
Biogas
Yes
350-400
40%
•
•
•
•
•
Military and Space
Mobile
Distributed/backup
power
Utility/Distributed
power
CCHP
*Refers to direct use of fuel. External reformer can allow any fuel cell to operate on natural gas, NG = natural gas, H2 =
hydrogen, **Electrical efficiency calculated while operating on natural gas, CCHP = Combined cooling, heating and power, APU =
auxiliary power unit
•
•
•
•
•
•
•
•
•
Highest electrical efficiency of any comparable-sized system
Lowest environmental impact of any power generation system using similar
fuels
Amenable to operation on natural gas, industrial waste hydrogen, digester
gas and other biofuels fuels (i.e., the operation does not require pure
hydrogen).
Generation of high quality power
Ease of siting at or near the point of use
Unattended operation, low maintenance, high availability
Minimal licensing, permitting and installation time
Some are air-cooled, most need limited water during normal operation
Moderate (200°C) to high (1000°C) operating temperatures assure that the
exhaust heat is of unusually high quality for waste heat recovery and
utilization (e.g., the production of chilled water, steam) with overall
efficiencies exceeding 80%
24
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15.
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