EM Feature

30 January 2003EM

EMEMFeature

INTRODUCTIONDistributed generation, a concept first promoted by ThomasEdison in the 19th century, is rewiring the way facility opera-tors and environmental managers think about how electricpower can be produced and distributed. For decades, energyusers have waited for the promise of fuel cells, solar panels,and wind turbines to translate into reliable and economicallyviable sources of power. That wait continues. But with clean,safe, reliable, and cost-effective applications, microturbinesare quietly delivering on those promises and proving to be asupplement to traditional forms of power generation.

Moving away from 100% dependence on the utility powergrid to having an onsite microturbine power supplement is,admittedly, a paradigm shift. But for progressive environmen-tal managers worldwide, microturbines are quickly becomingan energy management solution that saves money, resources,and the environment in one compact and scalable package—be it stationary or mobile, remote or interconnected with theutility grid.

THE POWER BASICSMicroturbine technology is based on the design heritage of jetengine technology and large power turbines that span a widthof a dozen feet or more. A major advantage of microturbinetechnology is that it is properly scaled for small installations,able to serve power needs ranging from a few kilowatts to a

few megawatts, and that it meets those needs with low-pollut-ant emissions, regardless of the fuel used. Whether operatedwith natural gas, propane, diesel, kerosene, JP8 military fuel,oilfield “flare” gas, or biogases from landfills, microturbinestypically emit low levels of nitrogen oxides (NOx) emissionswithout the need for post-combustion catalysts or other tem-peramental exhaust cleanup devices. Microturbines are evenchanging the way people perceive fuel. Think diesel is dirty?So did the California Air Resources Board (CARB)1 before ittested a microturbine fueled by diesel. CARB certified that theNOx emissions per brake-horsepower-hour of a diesel-fueledmicroturbine were half those of the cleanest, certified naturalgas-fueled engine (see Figure 1).2 Furthermore, CARB notedthat particulate emissions were almost undetectable—essen-tially the same as those of a natural gas engine—straight outof the combustion chamber, without any particulate trap.When using natural gas or renewable biogases as a fuel source,microturbine emissions are lower still.

Capstone Turbine Corporation (www.microturbine.com) hasdeveloped microturbine systems since 1988. To date, the com-pany has shipped more than 2400 units worldwide. Incor-porating patented design features, such as air bearings andadvanced digital power electronics, Capstone MicroTurbineshave just one moving part and do not require the use ofoil, lubricants, or coolants (see Figure 2). With a low-NOx

combustion system, these scaleable, state-of-the-art onsite

by Dr. Ake Almgren

Microturbines are an innovative and environmentally friendly alternative powersolution for applications from resource recovery to hybrid electric vehicles. In thisarticle, a developer of microturbine systems describes how microturbines are quietlyproving to be a serious competitor to traditional forms of power generation.

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generators are making their mark globally across five pri-mary applications: self-generation, micro-cogeneration,renewable resource recovery, power quality and reliability,and hybrid electric vehicles. With more than three millionhours of operating time since commercial production beganin 1998, the information presented below by Capstone Tur-bine represents an amalgamation of real-world experience.

ENVIRONMENTAL BENEFITSMicroturbine energy production offers environmental benefitsin terms of both emissions reduction and resource preservation.

Emissions ReductionUnlike diesel generators, which are limited in California andseveral other states to 100–200 hr of use per year, use ofmicroturbines is unlimited. A recent study by Cambridge

Energy Research Associates (CERA)3 reports that one of theCapstone MicroTurbines installed at the University of Califor-nia, Irvine emits an average of 1.3 parts per million NOx emis-sions when operating at maximum output. That equates to 0.15lb/MWh versus the 2.26 lb/MWh average of natural gas-fueledcentral power plants, according to current U.S. EnvironmentalProtection Agency (EPA) data. In fact, microturbine technologyhas so impressed California’s South Coast Air Quality Manage-ment District (SCAQMD) that in 2001 the district committed$8 million of its own funds in an effort to increase deploymentof microturbines to replace traditional diesel generators and otherpolluting sources in public facilities throughout California, as

part of its clean air technology program.4 SCAQMD hopes that

installing microturbine technology will improve the California

environment, through emissions reductions, and ensure a sourceof backup power in case of power outages.

Source: Data obtained from CARB for all diesel, compressed natural gas (CNG), and liquid propane gas (LPG) on-road heavy-duty truck and bus engines

under 400 bhp approved for sale in California for model-year 2000. Data listed are cleanest emissions available from each manufacturer meeting regulations.

Capstone CNG, LPG, and diesel actual emissions results per CARB certifications. C60 CARB certification pending — results are per pre-certification testing

only. Capstone emissions are per modified Federal Test Procedure for Heavy-Duty Diesel Engines, approved by CARB for use with microturbine engines.

Figure 1. NOx emissions comparison results from CARB tests of a microturbine fueled by diesel, liquid propane gas, and natural gas.

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Resource PreservationIn regions like the Southwest, where water usage is an im-portant concern, microturbines could prove to be even morevaluable, since microturbine power systems do not requirethe use of water. A combined-cycle 500-MW utility powerplant, in contrast, typically consumes up to 300,000 gallonsof water per day. Microturbines are also successful in resourcerecovery applications. For example, they can directly trans-form harmful waste gases emitted from oil and gas explora-tion sites, as well as renewable biogases from landfills,wastewater treatment plants, and livestock/agriculturalanaerobic digesters, into usable electricity. The advantagesare clear, bearing in mind that waste gases are usuallycollected and flared off into the atmosphere. This partial

combustion process releases enormous amounts of unburnedmethane, a greenhouse gas (GHG) that is 20 to 60 times moredamaging than carbon dioxide (CO2),

5 into the atmosphere.

APPLICATIONSThe following applications best illustrate the environmentalbenefits of microturbine technology, which include resourcerecovery, hybrid electric vehicles, and micro-cogeneration.

Resource RecoveryAccording to the Energy Information Administration,6 GHGemissions amount to more than 28 million metric tons peryear in the United States.5 Microturbines can use these “prob-lem” methane gases as renewable fuel. Flared gases oftenhave low-energy yields or high contents of corrosive “sour”(hydrogen sulfide, or H2S) gas, making them an infeasiblefuel source for conventional generators. Microturbines, onthe other hand, have no problem operating exclusively onlow-energy gases—as low as 350 Btu/scf—and are imperviousto H2S content up to 7%. Capstone also offers a simple-cyclemicroturbine for specific applications where it is advanta-geous to consume up to twice the amount of waste gas perkilowatt generated.

A core component of a system implemented for landfillgas resource recovery is a treatment system that removes moist-ure, solids, and siloxanes (a component of degrading tooth-paste that creates gummy or crystalline residue in anycombustion device) from the gas stream. The resultant mix-ture of a dozen or more noxious and toxic gases can then becompressed and injected directly into the microturbine, wherethe gases and odor are destroyed. Because microturbine sys-tems are typically small and modular, incremental additionsor reductions to generating capacity can be easily accommo-dated and microturbines can simply be moved to anotherlocation if necessary.

An example application is the deployment of 50 biogas-fueled microturbines at a closed landfill in Los Angeles County.The project was initiated by the Los Angeles Department ofWater and Power (LADWP), as part of a cooperative agreementwith SCAQMD, in which LADWP is installing more than 100Capstone MicroTurbines within its service territory. In 2001,the installation was cited as one of the leadership actions thatwon the LADWP the Renewable Company of the Year Award at

the Financial Times Global Energy Awards (the “AcademyAwards” of the international energy industry). The site is ex-pected to eliminate more than 20,000 pounds of NOx emis-

sions each year, while at the same time generating enough powerto meet the needs of approximately 1500 homes (see Figure 3).

Microturbines can also be used in oil and gas recoveryapplications. With the ability to convert unprocessed casinggas that contains up to 7% corrosive H2S gas, microturbinescan eliminate the need for flaring. At the same time, their power

Figure 2. Capstone MicroTurbine generators have just one movingpart and use no oil, lubricants, coolants, or other fluids.

Figure 3. Capstone MicroTurbines generate 1.5 MW of power fromwaste gas at this Los Angeles landfill, enough to serve 1500 homes.

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output reduces or eliminates the need for additional electricitysources. Microturbines can operate onsite without the need forcostly intermediary equipment and do so with near-zero sched-uled maintenance requirements (Capstone MicroTurbines, forexample, are able to operate at full load for one year beforescheduled maintenance is recommended). This makes it pos-sible to deploy microturbines directly at the site, at the well-head, or on offshore platforms, and to generate enough powerto fulfill the requirements of the whole site. Although still afledgling application, there is enormous potential in this area.

CogenerationCogeneration, or combined heat and power (CHP) generation,refers to the process of utilizing the heat produced by acombustion engine as energy output. During normaloperation, microturbines produce significant quantities ofhigh-temperature exhaust that can be easily integrated withheat exchangers and a hot water loop to produce valuableenergy output. From a cost–benefit perspective, this can yieldsignificant savings compared to purchasing power and heat-ing fuel. When the heat energy is utilized, overall system fuelefficiency can range between 70 and 90+%.7

Cogeneration is not a new concept, but the systems thatare currently in operation are generally large, gas-powered tur-bines or large, slow-speed reciprocating engines. Small recip-rocating engines have also been applied, but high maintenanceand exhaust filth make these undesirable. The advent ofmicroturbine technology, and its voluminous, oxygen-richdry exhaust, has positioned micro-cogeneration as a viablesolution for a wide range of facilities. Building engineers nowhave a scalable cogeneration tool, which offers decided ad-vantages for environmentally sound energy management bybeing able to make use of the clean microturbine exhauststream for heating purposes.

Approximately 1000 microturbines are operating world-wide in CHP applications. One example installation is HarbecPlastics, a plastics manufacturer located near Rochester, NY,where 25 microturbines generate all the power needed at thefacility (see Figure 4). Harbec uses the utility grid only as abackup source. The primary goal of the installation was toensure continuous power, since even a brief power fluctua-tion would cause days of lost production time and costs ex-ceeding $15,000. Heat output from the microturbines is routedinto four heat-exchange units to create a 210 °F water loopthat goes to the facility’s radiant floor heating and ventilationsystem. During the summer, the hot water drives an absorp-tion chiller, which converts the heat input into cold output. Asa result, Harbec can air condition its plant with no appreciableelectrical load. Harbec’s average cost-per-kilowatt-generated is7.5 cents versus 10.5 cents for utility power. Harbec is contractedto a long-term gas delivery rate of $6.85 per million Btu. Inmany parts of the country, however, delivered gas can range to

as low as $4 per million Btu, making the economic advantages

of microturbine power even more significant.

Hybrid Electric VehiclesAll-electric buses are clean alternatives to traditional diesel- orcompressed natural gas (CNG)-powered public transportation,but they are limited in terms of the distances and terrain

Figure 4. A 750-kW microturbine power, heat, and chilling systeminstalled at a NY-based plastics manufacturer.

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they can travel between battery charges. Microturbine tech-nology can serve as the onboard battery charger for hybridelectric vehicles, extending operating range and providingadditional power for passenger comforts, such as air condi-tioning, which are too energy-intensive for most electricvehicles. In addition, the use of microturbine technologycan dramatically lower NOx emissions, while cutting oper-ating and maintenance costs. (The cleanest CARB-certifiedexperimental [i.e., not in real-world operation] compressednatural gas [CNG] engine emits 1.3 grams of NOx per brake-horsepower-hour; Capstone MicroTurbines are CARB-certifiedat 0.70, 0.53, and 0.26 grams of NOx using diesel, propane,and natural gas, respectively.2)

Using a microturbine-powered system eliminates the needto routinely remove vehicles from daily service for batterycharging or swapping. Hybrid electric vehicles can plug direc-tly into the local grid at night, recharging batteries when elec-tricity utility rates are at their lowest. This, along with theregenerative braking power functionality of hybrid electricvehicles, makes the total fuel cost significantly lower than forconventional diesel- or natural gas-powered vehicles. Further-more, microturbine-powered hybrid electric vehicles can beeasily integrated into existing transportation infrastructures,since they can run on virtually any mass transportation fuel:CNG, liquefied natural gas (LNG), liquid propane gas (LPG),or diesel. The implementation of microturbine technologyallows transit authorities with limited funds to implement acleaner than CNG fleet, while still using diesel. Greater fuelefficiency, coupled with lower maintenance costs (virtuallyzero downtime and maintenance) and a smoother, quieter ridefor passengers translates into practical and affordable publictransportation.

Microturbine-powered hybrid electric vehicles are in usetoday in the United States, Europe, Japan, New Zealand,and China. The buses and shuttles that use microturbines

produce emissions that are 70% below EPA’syear-2004 requirements. Among the first hy-brid electric buses to utilize microturbines asonboard battery rechargers are three publictransit buses that have been operating inChristchurch, New Zealand for more thantwo years. The buses operate an average of14 hr per day, seven days per week. So far,they have amassed more than a quarter of amillion miles of operation with only one un-scheduled microturbine maintenance, whichinvolved the replacement of a failed igniter(spark plug). A fourth bus was added to theChristchurch fleet in 2001 (see Figure 5).

ADVANTAGES OF MICROTURBINESMicroturbines offer a number of advantages

compared to similarly sized reciprocating engine generators.These include lower energy and maintenance costs, increasedreliability and safety, and the ability to easily and safely connectto the utility power grid.

Lower Energy CostsMicroturbines reduce reliance on the utility power grid and,thus, higher, peak-demand utility rates, particularly duringsummer months. Onsite generation allows the reductionor elimination of energy drawn from the power grid, result-ing in both energy (kWh) and demand (kW) savings. Inaddition, microturbines offer some protection againstrising electricity rates. A micro-cogeneration system allowsfacility managers increased energy cost control: as grid elec-tricity costs increase, so do self-generation savings.Microturbines also provide users with the flexibility andopportunity to participate in rebate programs or voluntarycurtailment programs. State and federal regulators arebeginning to recognize the value of distributed generationand cogeneration to the power grid, the economy, and theenvironment. For example, cogeneration capital incentivefunding and time-of-use rate structures with demand chargesencourage distributed generation. Severe power shortages—when loads must be reduced to maintain grid reliabilitysafety margins—force “interruptible” customers to shutdown operations or suffer heavy penalties. Distributed gen-eration, however, offers facilities the flexibility to partici-pate in the most advantageous scenarios, including ratesthat allow curtailment of service, while limiting negativeimpact to operations and productivity.

Maintenance and ReliabilityWith only one moving part, microturbines are designed tooperate at full output continuously for five to 10 years (40,000–80,000 hr) between major service intervals. Reciprocating

Figure 5. These microturbine-powered buses in New Zealand have surpassed 250,000miles in operation with virtually no downtime.

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About the Author

Dr. Ake Almgren is president and chief executive officer of CapstoneTurbine Corporation, Chatsworth, CA, a developer of microturbinepower generation technology. Dr. Almgren is a leading advocate ofclean, efficient distributed generation. Inquiries may be addressedto info@microturbine.com.

engines usually require major service every 5000–10,000 hr.Typically, microturbine generators are implemented in ar-rays, linking several units together. Other generators—newand old—require expensive external switchgear and otherdevices to accomplish this level of functionality. Up to 20Capstone MicroTurbines can be multipacked (arrayed) withno external hardware other than computer cables. (An un-limited number of units can be arrayed using a utilitygrid connection, but, if the power grid blacks out, so doesthe array communication right when you would need itthe most.) Monitoring, control, dispatching, diagnostics,and other adjustments to all systems in the array are madethrough the control panel on a single designated masterunit, or via a single modem or TCP/IP Internet connection.Should one unit in the array go offline, or be taken downfor maintenance, the remaining machines automaticallypick up the lost load. In this way, an array can achieve ex-tremely high reliability and availability, responding instan-taneously to a facility’s power needs as they fluctuate. Alow-cost Capstone PowerServer option is also available thatis designed to network together as many as 100 grid-inde-pendent units.

One of the longest running applications of a CapstoneMicroTurbine operates at an oilfield in Consort, Alberta,Canada. The unit is fed a constant stream of 2% sour gas at a

production site owned by Shell and has operated virtually

nonstop for three years, surpassing 25,000 hours of full-load,

round-the-clock operation. The only required maintenance

has been air filter changes and a few simple injector cleanings.

In contrast, a traditional reciprocating engine generator

operating under similar conditions would most likely have

required at least four major overhauls and countless “minor”

service intervals during the same time period.

Operation, Interconnection, and SafetyFor onsite generators to routinely generate power when grid

demand and utility rates peak, they must be interconnected

with the utility grid. Microturbines are designed to operate

in parallel with or independently of the utility power grid.

The three-phase power output from the generator is syn-

chronized with the electricity provided via the grid to an

energized circuit. The current, frequency, and voltage are

sampled at a rate of 15,000 times per second to ensure clean

power and protection for sensitive equipment, and also to

ensure that its output can have no adverse effect on power

grid operation. Intended to interconnect with utility sys-

tems throughout the world, Underwriters Laboratory has

certified Capstone MicroTurbines to its UL1741 grid

interconnectivity safety standard. The systems have also

been tested and approved by the states of New York and

California—the only states that have currently mandated

statewide standards—for direct-to-grid interconnection.These certifications ensure to all parties—end user facili-ties, utility grid operators, and other facilities on thatparticular grid circuit—that these interconnected systemsare proven safe and can have no adverse effects. To date,Capstone MicroTurbines are the only generating productsof their kind that meet these standards. No external syn-chronizing equipment or protective relaying is required—everything is built into the microturbine. The Capstonesystems are also UL listed to the 2200 generator safetystandard, and are compliant with Europe’s CE, Canada’s CSA,and a number of other international quality and safetystandards.

CONCLUSIONDistributed generation technologies, and microturbines inparticular, offer a new perspective on clean, efficient powergeneration and distribution. The benefits of microturbine tech-nology translate into increased functionality that rapidly paysfor itself before becoming a source of cost containment. Gen-erating energy with half the fuel input required by conven-tional power and heat generation sources—or creating energyfrom renewable waste sources—benefit both the environmentand the bottom line.

REFERENCES1. California Air Resources Board (CARB). See http://www.arb.ca.gov/

homepage.htm.2. “CARB Certifies Diesel Capstone MicroTurbine for Commercial Hy-

brid Electric Vehicles”; press release dated March 21, 2001; CapstoneTurbine Corporation: Chatsworth, CA; available online at http://microturbine.com/whatsNew/pressrelease.asp?article=66 (accessedJune 2002).

3. Cambridge Energy Research Associates (CERA). See http://www.cera.com.4. “SCAQMD OKs $6.2M to Buy, Install Capstone MicroTurbines”; press

release dated November 19, 2001; Capstone Turbine Corporation:Chatsworth, CA; available online at http://microturbine.com/whatsNew/pressrelease.asp?article=147 (accessed June 2002).

5. Emissions of Greenhouse Gases in the United States, 2000; DOE/EIA-0573(2000); Energy Information Administration, Office of IntegratedAnalysis and Forecasting, U.S. Department of Energy: Washington, DC,November 2001; available online at http://www.eia.doe.gov/oiaf/1605/ggrpt/pdf/057300.pdf (accessed June 2002).

6. Energy Information Administration. See http://www.eia.doe.gov.7. “Capstone30 at Bosbad Putten: Longest running unit in Europe!”; press

release dated October 19, 2001; Geveke Power Systems: Papendrecht,The Netherlands; available online at http://www.microturbine.nl (ac-cessed June 2002).