Its a long article but well worth the read IMO, talks about many of the Fuel Cell players
At present, more than 50% of America's
electricity is generated from coal-fired central
plants like this one, but their days could be
numbered.
By Wallace Edward Brand
Part 1 of multi-part series on the dynamics of power
generation and the future role of fuel cell technology.
January 19,2002
By now it is pretty clear that distributed generation is the
wave of the future in electric power supply.
Are you already familiar with the concept of "distributed
generation" ? It is small scale generation based on new
technology. It is technology that is twice as efficient in turning
hydrocarbons into electrical energy as the coal fired steam
turbine. These are in much smaller generating unit sizes than
the giant generator sizes currently in use. They are small
enough to place in the cellar of your home and dedicate to
serving just your residence needs.
Some bigger models can serve an apartment building, an
office building or a small subdivision. The idea is to place the
generation close to the load rather than concentrating it in
giant plants which could be as much as one or two hundred
miles away.
We choose the coal fired steam turbine for an initial
comparison of the feasibility of this new form of generation
because it now comprises more than half of the generating
capacity of the grid. However a new form of gas combustion
turbine generator developed in the seventies called an
"aeroderivative gas turbine" has a higher efficiency.
Distributed generation is small in scale. It can include small
gas turbines called "microturbines". It can include the diesel
engine-generator set. However the revolutionary new star of
distributed generation, which will likely be commercial as of
the end of this year, is the fuel cell.
These tiny generators, 5 kW to 300 kw to 3,000 kilowatt in
size are far smaller than the giant 600,000 kW to 1,000,000
kW to 1,400,000 kW coal fired steam turbines, gas
combustion turbines and combined cycle generators currently
in use that they will likely replace. They are small enough so
they can be dedicated to serve only a single family residence,
a large office building, a large apartment house.
Slightly larger fuel cells can supply a single load center or a
discrete area of the grid containing one or two small load
centers, or can supplement grid power by supplying an island
in the grid created by limitations in transmission. In contrast,
existing generators add to an interstate pool of power from
which energy serving all loads on the grid is drawn.
Fuel Cell Basics
Fuel cells can be classified by their operating temperature,
and their electrolyte. The low temperature fuel cells are the
phosphoric acid cells (PAFC) and the proton exchange
membrane fuel cells (PEMFC). These have, respectively,
phosphoric acid and plastic as their electrolyte.
In your car battery, for example, sulphuric acid is the
electrolyte..
In some fuel cell electrolytes a hydrogen proton passes
through the exchange membrane but the electron can't get
through so it has to go around through a wire to meet up
again with its proton companions.
If you put a light bulb in the circuit, it will, if there are enough
fuel cells, light it up. There have to be quite a few for a 110
volt light bulb because each cell only provides about one volt
or less.
There are also high temperature fuel cells. These operate at
650 degrees Centigrade or even 1000 degrees Centigrade.
The FCEL fuel cell is a molten carbonate fuel cell (MCFC,
carbonate electrolyte) and operates at 650 degrees
Centigrade. The classic solid oxide fuel cell (SOFC) operates
at 1000 degrees Centigrade and has a ceramic electrolyte.
There is a variation on the theme, however, which is receiving
a lot of attention. That is the RTESP SOFC. Westinghouse,
now Siemens Westinghouse, had difficulty in sealing the
planar fuel cells because there was so much expansion
between the cool phase and the hot operating phase. So it
went to a tubular configuration which solved the sealing
problem.
However a German scientifc group, Julich, found a way to
make one with a very thin ceramic electrolyte which it
supported with one of the electrodes and found this could
operate at lower temperatures. Gobal Thermoelectric of
Calgary, Canada is makeing those RTESP SOFCs which
refers to Reduced operating Temperature, Electrode
Supported, Planar (flat rather than tubular) solid oxide fuel
cells.
PEMFC are favored for providing the propulsion for cars.
Ballard of Vancouver is leading in that field. However the
Internal Combustion Engine is a much tougher competitor
than the stationary generator. The price of the fuel cell must
be much lower to compete with it.
Electrical efficiency refers to the ratio of electrical energy
output to fuel input. The high temperature fuel cells have a
greater electrical efficiency than the low temperature cells. In
the high temperature fuel cells, when hydrocarbons such as
natural gas or diesel fuel are used to obtain hydrogen for the
fuel cells, the hydrogen can be disassociated from the
remainder of the fuel in the stack. In the low temperature fuel
cells, there must be an external reformer which uses about
one third of the energy available from the fuel.
The PEMFC has an electrical efficiency, therefore, of only
40% at best, as low level operations, and its efficiency falls
off as one reaches its continuous rating. In contrast, the
MCFC is slightly off its highest efficiency at below 20%
operation and above that loading (approximately) its
efficiency goes up to 54% - 57% and stays there until it
reaches its continuous rating. Currently, Global
Thermoelectric's RTESP SOFC has a 45% efficiency.
To put this in contrast, coal fired steam turbines have an
efficiency at best of 38% at the busbar. . US average
efficiency of coal fired steam turbines, which is more than one
half of the bulk power supply, is only 33% at the busbar
(near the point of output from the generator.) Electrical losses
from having to travel so far down transmission,
subtransmission and distribution, to get to residential
customers and small commercial loads, bring their average
efficiency down some 13% to 16%, down to 27.5% at the
customers meter.
Advances in turbine technology in the mid 70s in gas
combustion turbines raised the simple cycle gas turbine
efficiency from about 25% to 42%. When the waste heat is
collected and used to make steam for a steam generator
(bottoming cycle) the efficiency can go up to 50% to 60%;
about 16% less at the residential customer's meter. At low
loading their efficiency falls off considerably. Formerly gas
combustion turbines were only used for peakers. Since the
70s they have been used for base load as well.
Fuel cells are tiny compared with conventional generators but
are far more efficient than conventional generators of the
same size. They can be sized to match the size of a load at a
single site, and therefore are usually located on the site of the
load. That is close enough so their heat can be utilized
usefully as well as their electricity. Use of the thermal energy
inevitably produced by a generator, as well as its electrical
energy is referred to as "co-generation". The combined heat
and power efficiency or CHP efficiency may be as much as
75% to 85%.
In contrast, conventional coal fired steam turbine generators
and gas combustion turbines and combined cycles must be
large to reach needed efficiencies. Therefore their heat, which
can't travel great distances to the load, must be thrown away
except to the extent it is used for a bottoming cycle for a gas
turbine combined cycle unit.
The high temperature fuel cells can also provide heat for a
turbine bottoming cycle. These are called "hybrids" and have
electrical efficiencies as high as 78% or more.
PEM's are currently being made by Ballard in about 50 kW
sizes which is equivalent to 75 horsepower. Plugpower is
making PEM fuel cells but apparently may be having difficulty
in getting the bugs out of its reformers or its electrolyte water
management system since its introduction has been delayed..
Plugpower is also making a PEMFC for home use. It will be
sized from 5 kW to 7 kW with maybe some flywheel storage
that will give you up to one half hour at as much as 10kW. It
may go up to 35 kW or more for small commercial sales.
Vaillant, its European partner is pushing cogeneration with its
first model. It will provide both electricity and heat for its
customers.
Global Thermoelectric's RTESP SOFC will likely be made in
sizes of 5 kW to 175 kW. It can be used for small remote
power supplies, and also for an auxilliary power unit for cars
which want to keep their interal combustion engine for
propulsion.
FCEL's mature commercial stacks will have modules of 300
kW which it will also provide in systems of 1,500 kW and
3,000 kW. These can be used by apartment houses, office
buildings, small subdivisions, and can be used by electric
utilities to add to the capacity of existing distribution
substatios so they can add the capacity in small increments.
At the present the fuel cells are being produced in small
volumes and cost quite a lot. The manufacturers expect the
costs to diminish significantly at mass production volumes.
But which form of generation will win out? And will
distributed resouces really be able to displace the integrated
electric power systems, replace giant scale generators
operating in networks of transmission lines, that have been
the bulwark of electric power supply for over 100 years?
Place your bets now.
Here are the alternatives.
Will it be a 30,000 kW simple cycle aeroderivative gas
turbine developed in the mid 70's with an efficiency of up to
42%, a combined cycle steam and gas turbine with
efficiencies up to 50% or 60% but in sizes of 60,000 kw to
500,000 kW? Will it be a 250 or 300 kw molten carbonate
fuel cell with simple cycle electrical efficiencies of 55%, a 10
MW to 40 MW combined cycle (or hybrid) fuel cell/gas
turbine with electrical efficiency of up to 78%?
Or will it be small 5 to 10 kW on site proton exchange
membrane (PEMFC) with a peak efficiency of 40% or or a 3
kW to 5 kW solid oxide (SOFC) fuel cells of 45%
efficiency, able to use their thermal energy for cogeneration
with efficiencies up to 85% or more? How about a 30 kw or
75 kw microturbine or a 20 kW to 10,000 kw diesel
generator?
My money is on the small but very efficient fuel cell. Here's
why.
The key parameters, are size, efficiency, reliability, cost per
kw and per kwh, and clean air.
Starting in 1910 or 1920, when polyphase alternating current
proved its superiority over direct current, the owners of
power systems tied more and more load centers together into
a single integrated system using high voltage and then extra
high voltage transmission. Why did they do it? Principally so
they could use ever larger coal fired steam turbines.
As the generating unit size increased, the investment cost per
kilowatt decreased drastically and so did the operating cost
per kilowatt hour. A 200,000 kw steam turbine generator
cost only 150% of the cost of a 100,000 kw generator. A
400,000 kw steam turbine generator cost only 150% of the
cost of a 200,000 kw generator. A 20,000 kw steam turbine
generator might have a heat rate of 14,000 BTU's per kwh
equivalent to an efficiency of about 24%. But a 500,000 kw
to 600,000 kw steam turbine generator could achieve a heat
rate of 10,000 BTU's per kwh or lower, equivalent to
efficiencies up to 38%.
The large integrated systems also obtained significant benefits
from "load diversity". Since not everyone would be using
electricity at the same time, if everyone drew from the same
power supply, fewer generators would do the job. Also, with
integration, other large generators could be called on to
supply emergency service when the primary generator was
unavailable as they were during forced outages of 5% to
10% of the time, and for several weeks a year during
scheduled maintenance.
By the 1960s, 500,000 kw and 600,000 kw coal fired steam
turbines were being built. The "Big Allis" generator of Con Ed
broke the 1,000,000 kw barrier and was in service by 1965,
the time of the big East Coast blackout. The Federal Power
Commission's National Power Survey in the 1960s in a quest
for ever lower cost and greater efficiency stimulated even
larger power systems by urging utilities to engage in programs
of coordinated development of base load generating units and
reserve sharing. These programs made possible ever larger
units sizes without increasing reserves as they otherwise might
have.
These would be programs undertaken by the dominant
regional electric utility systems in each region which had
already obtained the benefits of large scale integration. Such
institutional power pooling arrangements made it feasible for
the dominant systems in an area to install even larger sizes
than they had been able to install as a result of their own
integration. With coordination, it became economically
feasible to install generating unit sizes of up to 1,400,000 kw.
Next Week.... Part 2 "The Decline and Fall of the Steam
Turbine"
END STORY
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