characteristics, and significant heat recovery potential. Electric efficiencies of natural
gas engines range from 28% LHV for small engines (<100 kW) to over 40% LHV
for very large lean-burn engines (>3 MW). Waste heat can be recovered from the hot
engine exhaust and from engine cooling systems to produce either hot water or low
pressure steam for CHP applications. Overall CHP system efficiencies (electricity
and useful thermal energy) of 70–80% are routinely achieved with natural gas engine
systems.
5.3.5 Fuel Cell
Fuel cells provide an entirely different approach to the production of electricity
compared to traditional prime mover technologies and are currently in the early
stages of development. Fuel cell stacks available and under development are silent,
produce no pollutants, have no moving parts, and have potential fuel efficiencies far
beyond the most advanced reciprocating engine or gas turbine power generation
systems. Fuel cell systems with support ancillary pumps, blowers, and reformers
have similar advantages.
As is common with new technologies, fuel cell systems have several disadvantages, such as product immaturity, overengineered system complexities, and
unproven product durability and reliability. These translate into high capital costs,
lack of support infrastructure, and technical risks for early adopters, which cause
market resistance that reinforces these disadvantages. However, the many advantages of fuel cells over other prime movers suggest that they could well become the
prime mover of choice for many applications and products in the future.
Fuel cells produce power electrochemically from hydrogen delivered to the
negative pole (anode) of the cell and oxygen delivered to the positive pole (cathode).
The hydrogen can come from a variety of sources, but the most economic is the
reforming of natural gas or liquid fuels. There are several different liquid and solid
media that support these electrochemical reactions: phosphoric acid (PAFC), molten
carbonate (MCFC), solid oxide (SOFC), and proton exchange membrane (PEM) are
the most common systems. Each of these media comprises a distinct fuel cell
technology with its own performance characteristics and development schedule.
PAFCs are the most widely deployed fuel cells currently in commercial service,
with 200 kW units delivered to over 200 customers. PEM fuel cells are just entering
the market, and SOFC and MCFC technologies are in field test or demonstration
stages. Direct electrochemical reactions are generally more efficient than using fuel
to drive a heat engine to produce electricity. Fuel cell efficiencies range from 35 to
40% for PAFC to upward of 60% for systems still in development. Fuel cells are
inherently quiet and have extremely low emissions as only a small part of the fuel is
combusted. Like a battery, fuel cells produce direct current that must be run through
an inverter to obtain 60 Hz AC. These power electronics components can be
integrated with other power quality components as part of a power quality control
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H. Ren et al.
gas engines range from 28% LHV for small engines (<100 kW) to over 40% LHV
for very large lean-burn engines (>3 MW). Waste heat can be recovered from the hot
engine exhaust and from engine cooling systems to produce either hot water or low
pressure steam for CHP applications. Overall CHP system efficiencies (electricity
and useful thermal energy) of 70–80% are routinely achieved with natural gas engine
systems.
5.3.5 Fuel Cell
Fuel cells provide an entirely different approach to the production of electricity
compared to traditional prime mover technologies and are currently in the early
stages of development. Fuel cell stacks available and under development are silent,
produce no pollutants, have no moving parts, and have potential fuel efficiencies far
beyond the most advanced reciprocating engine or gas turbine power generation
systems. Fuel cell systems with support ancillary pumps, blowers, and reformers
have similar advantages.
As is common with new technologies, fuel cell systems have several disadvantages, such as product immaturity, overengineered system complexities, and
unproven product durability and reliability. These translate into high capital costs,
lack of support infrastructure, and technical risks for early adopters, which cause
market resistance that reinforces these disadvantages. However, the many advantages of fuel cells over other prime movers suggest that they could well become the
prime mover of choice for many applications and products in the future.
Fuel cells produce power electrochemically from hydrogen delivered to the
negative pole (anode) of the cell and oxygen delivered to the positive pole (cathode).
The hydrogen can come from a variety of sources, but the most economic is the
reforming of natural gas or liquid fuels. There are several different liquid and solid
media that support these electrochemical reactions: phosphoric acid (PAFC), molten
carbonate (MCFC), solid oxide (SOFC), and proton exchange membrane (PEM) are
the most common systems. Each of these media comprises a distinct fuel cell
technology with its own performance characteristics and development schedule.
PAFCs are the most widely deployed fuel cells currently in commercial service,
with 200 kW units delivered to over 200 customers. PEM fuel cells are just entering
the market, and SOFC and MCFC technologies are in field test or demonstration
stages. Direct electrochemical reactions are generally more efficient than using fuel
to drive a heat engine to produce electricity. Fuel cell efficiencies range from 35 to
40% for PAFC to upward of 60% for systems still in development. Fuel cells are
inherently quiet and have extremely low emissions as only a small part of the fuel is
combusted. Like a battery, fuel cells produce direct current that must be run through
an inverter to obtain 60 Hz AC. These power electronics components can be
integrated with other power quality components as part of a power quality control
116
H. Ren et al.