A DISTRUPTIVE TECHNOLOGY
by Chuck Tanner
(originally published in the Cogeneration and Competitive Power Journal. For subscription information, call (770) 925-9388)
PARADIGM SHIFT IN POWER GENERATION
a new 2 MW steam turbine was installed 1900 in Hartford, it represented a
step function change. It was four times bigger than any existing steam
then on economy of scale meant bigger and bigger. By the end of the 1970s
and largely driven by nuclear power plants, steam turbines exceeded 1000
MW. The electric efficiency of steam turbine power plants eventually
trend was broken in the 1980s. More efficient gas turbines combined with
steam turbines could produce electric power with efficiencies up to 55%.
This new technology, combined cycle power plants, was the technology of
choice for independent power producers. It was now possible to build
competitive power plants down to the range of 100-200 MW. One may say that
new technology (combined cycle power plants) together with regulatory
changes (the PURPA Act) jointly drove this paradigm shift.
trend to commercially viable smaller power plants has continued. Technical
development as well as the advantage of economy of scale (mass production)
for established technologies, in particular reciprocating engines, are
increasingly replacing the old paradigm of economy of size. In the power
generation industry 500 $/kW is generally very competitive, while in the
automotive industry an engine must be below 50 $/kW to be competitive!
generation is generally used for power generation less than I MW. Some
stretch the definition up to 5 MW. In any case distributed generation is
not only a matter of power generation. It brings transmission and
distribution (T&D) into the equation.
costs for T&D are significant. For a traditional vertically integrated
electric utility they could represent 400-500 $/kW. During the
transmission and distribution from a large central power plant up to 7% of
the power is lost. Consequently if distributed generation can offset all
or parts of the T&D costs we talk about some serious/significant
money. Distributed generation is another way to distribute power, rather
than just a smaller scale of generating power.
generation is already very significant. It has grown steadily during the
1990s and may now represent up to 20% of all new installed power.
According to E-Source roughly 10 GW is in the size range of 1-10 MW units.
Eighty percent of these units are reciprocating engines. In addition we
have even more reciprocating engines used for stand-by power.
has captured a big part of this growth and is now a major manufacturer of
power equipment along with GE, Siemens and ABB-Alstohm. Far more
Caterpillar engines are used for power generation than to propel
engines have a huge advantage of the economy of scale and the maturity of
the industry/product. First price is low and spare parts and service are
available most everywhere in the world. There are two disadvantages with
reciprocating enginesemissions and maintenance. Even though there is a
continuous effort to improve reciprocating engines, new technologies such
as microturbines are better in regards to both emissions and maintenance.
energy sources such as photovoltaics and wind turbines are gaining
acceptance and presence thanks to being "green." However, they
have their disadvantages in addition to a higher cost. Both technologies
require large physical space and without their primary energy sources, sun
and wind respectively, there is no power! They are better but not perfect.
cells hold many promises of becoming a clean and relatively efficient
energy source. However there is still a long way to go. Commercial units
have a cost at 4000 $/kW. The challenge of establishing a methane or even
more a hydrogen infrastructure may be an even bigger challenge.
Capstone introduced its Model 330 MicroTurbine it represented the
commercial introduction of a new technology, microturbines.
is no scientifically correct definition of microturbines, but the term is
generally used for high speed gas turbines in the size range of 15-300 kW.
technology has emerged from four different technologies: small gas
turbines, auxiliary power units, automotive development gas turbines and
core of the microturbine is the high speed compressor-turbine section,
which rotates very fast96,000 rpm in the Capstone Model 330. On the
same shaft is generally a high speed generator using permanent magnets. A
key element for the best designs are air bearings (or more correctly gas
bearings). Air bearings enable the high speed with only air cooling and a
long life almost maintenance free.
high speed generator delivers a high frequency power, in Capstones case
1600 Hz. To "gear it down" to useful 50/60 Hz power electronics
is the way to go.
in general offer two big advantages: low emissions and low maintenance. As
illustrated below the Capstone MicroTurbine has one of the best emission
performance of any fossil fuel combustion system.
x CO THC
Engines (500 kW) 2,100 340 150
Turbines (4.5 MW) 25 50 10
Fired Steam (500 MW) 200 n/a n/a
<9 <25 <9
maintenance there are some very strong indications that the required
maintenance is radically less. One example is three units at Williams
Energy in Tulsa: more than 20,000 hours and the only maintenance has been
air filter changes.
are also smaller, lighter, and operate with no vibration and less noise.
All of those features help. make on-site installations possible without
compromising the environmental aspects.
are facing some tough challengesrobustness, interconnection with the
grid and costs.
robustness there has been steady improvement. An endurance test of a
Capstone Model 330 has now logged more than 4000 hours and has had more
than 99% availability. Still more can be done and will be done. This is
probably the least difficult challenge.
interconnection challenge is shared with other distributed generation
technologies. The challenges are both technical and tactical. The latter
are nothing but a barrier to entry. However, there is a lot of progress on
both the federal and state level for much more simple interconnection
requirements. Having said that, one should not neglect or underestimate
the technical aspects. E.g., for safety reasons the grid operator cannot
accept uncontrolled power being fed into the grid, especially in case of
an outage for maintenance. Fortunately power electronics and
microprocessors have opened up new approaches. Thus in Capstones case
we have among others included all protection relay functionality in our
related to the interconnection issue are the communication challenges.
Low-cost "mass communication" with the units is a prerequisite
for large-scale use of distributed generation. Thanks to the rapid
development of all communication technologies, not least wireless and
internet, solutions are now available for the virtual power plant concept.
biggest challenge is probably the cost. For large scale acceptance the
cost must eventually be in the range of the reciprocating engines, i.e.,
400-600 $/kW. It does not help that microturbines in quantities of single
units are already at 1100 $/kW and less, much lower in costs than
photovoltaics, wind turbines and fuel cells. With its inherent simplicity
with fewer parts and electronics instead of mechanical devices, the
economy of scale is faster for microturbines. At annual volumes of 100,000
units, microturbines should have costs equal to or better than those of
only problem is how to get to those volumes. The answer is to sell
microturbines initially for applications where their unique features bring
extra value, or for applications difficult or even impossible for other
combined with energy storage devices, e.g., batteries or flywheels, will
enable a new set of solutions for improved power reliability and quality.
The internet infrastructure as well as the "everywhere" use of
fast but sensitive microprocessors has created another growth dimension
for electric power. Power is not only a matter of kWh but is increasingly
a matter of reliability and quality. Most interruptions occur in the
distribution side of the system. The best solution in many cases is
distributed generation, or more correctly, distributed resources.
very low emissions and very low maintenance microturbines hold promise to
enable small scale cogeneration. The exhaust heat can be used for hot
water heating, absorption cooling, dehumidification, etc. It should be
possible to reach efficiencies of 70-80%. Thanks to the clean exhaust with
no risk of any oil film (due to the air bearings) it should be possible to
use the exhaust gas directly in some industrial processes.
deferral is a great potential application. Why tear up streets for
additional cables in the case of an established infrastructure that cannot
support additional load? Installing microturbines may be a better
alternative. In our own case at our "Capstone West facility"
reciprocating engines would have been impossible due to the Los Angeles
air quality requirements.
application of great interest is hybrid electric vehicles (HEV). Using the
microturbine as a clean and low maintenance onboard battery charger makes
it possible to run e.g., a bus for a whole day without any stops for
recharging of batteries or swap of batteries. The CARTA 714 HEV bus in
Chattanooga built by AVS and using a Capstone MicroTurbine is a real
success story. In fact we see it as one of our first major commercial
very interesting field of applications is the resource recovery market. It
covers oil and gas fields, where the flare gas can be used as energy
instead of just being a pollutant waste. Also landfill and other digester
gases are of great interest for microturbine applications.
believe also the combined peak-shaving and standby application holds a
great potential. In a perfectly deregulated electricity market one may
expect more price volatility as well as more price differentiation for
time of use. Microturbines should be very suitable for mitigating such
generation, including microturbines, will replace the old model of large
centralized power plants. However, the new model will not mean just
islands of power and no electric grid. On the contrary the new model will
take advantage of the grid. Power will be transmitted "both
ways." It will be a network connecting large scale power plants with
midsize power plants as well as power generating devices all the way down
to residential level. The analogy with the computer network is close. The
large scale introduction of PCs did not mean the death of mainframes. They
are still there and without a huge quantity of servers and an ever
increasing bandwidth there would not be the explosive growth of the
Tanner has a BS in mechanical engineering, Penn State University, and an
MS in mechanical engineering, University of California, Berkeley.
of his article are based on documents prepared by Ake Almgren, the
president and CEO of Capstone Turbine Corporation. Capstone Turbine
Corporation, 6430 Independence Ave., Woodland Hills, CA 91367; www.capstoneturbine.com