Cogeneration Utilizing Natural Gas-fired Reciprocating Engines


“This combination of being able to provide efficient, cost effective, continuous, resilient, sustainable, and power-dense means of meeting onsite electrical and thermal demands . . . makes gas engines a great technology choice today in the US versus a multitude of other competing technologies.”
– Hari Sivadas, manager of business development at General Electric’s Distributed Power Division

Cogeneration systems, also known as combined heat and power, have traditionally been installed by larger industrial users with high steam and power demands and by smaller, institutional users such as universities and hospitals. Since the early 2000s, smaller industrial and commercial companies have discovered cogeneration utilizing natural gas-fired reciprocating engines, not only for high thermal output but also low maintenance costs, low emissions, and high reliability for onsite generation and standby power.

These findings were reported in a US Department of Energy (DOE) sponsored report written by the Gas Research Institute, which documented lower operating costs for the user and potential reductions in emissions of criteria pollutants and CO2.

The companies profiled below have claimed efficiencies approaching 90% when waste heat recovery efficiencies are included with power production efficiencies. When properly maintained, they offer excellent load-following characteristics and significant heat-recovery potential, the report says.

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To increase efficiency of the overall system, heat is recovered in the form of hot water or steam, or the hot exhaust from the system can be used directly for applications such as process heating or drying (see the profile of a tomato greenhouse below). The waste heat can also be used to drive absorption chillers or desiccant wheel regeneration for dehumidification.

Reciprocating engines can also be used for standby power and are often preferred over diesel-fired engines, due to their low capital cost, rapid start-up capability (within 10 seconds), and excellent load-following characteristics.

Diesel-fired standby units can usually be installed without meeting strict emissions standards if operation is limited to 300 to 500 hours annually.

In peak shaving applications, onsite power generation can reduce the cost of peak load power. See the profile of Cummins-Tangent Energy Solutions below, which has created a business model to help customers who wish to smooth out their energy use curves.

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There are three potential peak-shaving strategies: optimize the use of purchased versus generated power under the applicable rate structures; coordinate peak-shaving programs with utilities which offer payments for limited hours of use when requested; and last, offer customers wishing to purchase power competitively on the open market competitive power supplies that are interruptible.

The DOE report, “Gas-Fired Distributed Energy Resource Technology Characterizations,” can be found at

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Credit: Co-Energy America
A 250-kwh integrated CHP system at Cape Codder Resort & Spa, MA

Distributed Generation is a Growth Area
“I see distributed generation being adopted as part of the national energy portfolio whether it’s being built by utilities, business, healthcare, or other industry,” says Christopher Nagle, regional director for Siemens’ engine business in North America. “When it comes to distributed generation, engines offer a wide-ranging solution for electricity and heat that is as reliable as any resource available,” he adds.

Siemens inherited its Guascor line of engines when it acquired Dresser-Rand in 2015. Dresser-Rand has its founding roots in Pennsylvania in the late 1800s as S.R. Dresser before it merged with Ingersoll-Rand in 1987. Dresser-Rand acquired Grupo Guascor S.L., a European company with a 50-year history of building reciprocating engines, in 2011.

Distributed generation has been a growth area and is expected to continue to grow for the foreseeable future, Nagle says. And it has diverse applications, including wind, solar, and battery storage. Cogeneration is a particularly attractive application for hospitals and schools.

“We don’t need the wind to blow or the sun to shine. As long as the engine is properly operated and maintained, it remains a constant source of reliable power in microgrid applications,” says Nagle.

The Guascor HGM family of engines, developed over the last 15 years, has become highly efficient, Nagle says. This was done with advances in controls and combustion technology, which have brought operating efficiencies to higher levels today.

“It’s really the controls monitoring a building’s energy requirement and the utility assets needed to meet these energy needs that is the measure of how far we’ve come,” says Nagle.

The diversity of fuels that can be burned in Guascor engines is an advantage for distributed generation applications. Nagle says the company’s engines run on natural gas, digester gas, biogas, landfill gas, sewage gas, flare gas, synthetic gas, coal gas from abandoned coal beds, and digested organic wastes—at distributed energy sites throughout North America.

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Credit: Co-Energy America
A 250-kwh integrated CHP system at Cape Codder Resort & Spa, MA

Wesleyan Power System Supplies Campus
Wesleyan University in Middletown, CT, has developed a distributed power system that includes two reciprocating engine systems totaling 3 MW and two solar systems totaling 1 MW. Serving 95% of the campus, approximately 2.3 million square feet, the system was built out following the major snow storm in 2011 that shut down the university.

Alan Rubacha, the director of physical plant at Wesleyan says there are two major reasons that motivated the development of Wesleyan’s power system. First, they wanted to reduce their electrical and gas costs, and are saving $2 million a year.

The second reason is reliability. The university had installed a GE Jenbacher 2.398-MW reciprocating engine in 2008. By running it, they were able to get large parts of the campus up and running during the storm, Rubacha says.

A Dresser-Rand Guaschor 656-kW reciprocating engine was installed in 2014. A 550-kW solar photovoltaic array  was installed in 2012, and a second, 750-kW solar system  was installed in 2016. Rubacha believes the university is ready for future storms that are likely to hit Connecticut in the coming years.

The exhaust heat from the reciprocating engines is used to generate steam for the campus heating system. The heat from the intercooler loop and jacket water is used to heat domestic hot water.

Normally, its cogeneration systems plus the solar arrays provide 95% of the electricity the campus uses. In the case of an emergency, by judiciously shutting off lights, some ventilation equipment, and other demand reductions, it can keep the campus operating off the grid.

Wesleyan is designated as a distribution system for the Federal Emergency Management Administration. “We’ll be supporting the city in case of a major storm,” says Rubacha. One of the buildings will provide medical services and the campus will also provide services for feeding, showering, and housing.

Rubacha says the system always runs parallel with the utility grid under normal operations. “We have to maintain a little bit of imported power, because of public utility rules,” he says. But it is cheaper to use the power on campus. He says the university has no plans to add more generation.

Wesleyan received $600,000 from the Connecticut Department of Energy and Environmental Protection in July 2013, one of the nine grants awarded to cities to build microgrid projects. Wesleyan used the money to connect the athletic center’s 600-kW load to the campus grid. The newest solar system allowed them to connect three additional buildings in 2016.

Rubacha says they are keeping their eyes on new technologies as they develop, but he is not enamored of fuel cells. “They are expensive, use the same amount of gas as the reciprocating engines, and don’t make sense for us,” he says.

GE’s Jenbacher is Resilient, Sustainable
Jenbacher engines continue to be a strong performer in the marketplace of distributed generation, says Hari Sivadas, manager of business development for General Electric’s Distributed Power division. GE bought the 100-year old global engine manufacturer 14 years ago.

Jenbacher continues to manufacture its natural gas engines in Jenbach, Austria. Sivadas says Europe was always the bread-and-butter market for Jenbacher, where government policies supported combined heat and power systems in distributed generation applications. When the market opened up in the US, Jenbacher and GE took advantage of it.

With the cost of natural gas now around $3.00 per MMBtu, and with retail power prices high in many parts of the country, generating power onsite has become an increasingly attractive growth market for the Jenbacher engines, Sivadas says.

The engines, sized from 250 kW up to 9.5 MW, can be powered by natural gas, petroleum flare gas, propane, biogas, landfill gas, sewage gas, and coal mine gas, making them attractive to small industrial companies as well as oil and mining operations.

Post-acquisition, Sivadas says Jenbacher developed its newest and largest Type 9 J920 gas engine with a capacity of up to 9.5 MW. Its major attraction, says Sivadas, is its ability to operate in a modular fashion by combining multiple units and ramping up or down one or more engines depending on load requirements. He says this makes the model an ideal choice for integrating and balancing renewables on the grid.

The Sky Global Power One power plant in Rock Island, TX was developed by the independent power producer, Sky Global Partners, LLC. Six, 8.6-MW Jenbacher J920 units were the first installations of the units in commercial operation in the US. The plant supplies peaking power to meet the demands of the 18,000 members of San Bernard Electric Cooperative in an eight-county area. The plant also has the capability to sell power to others on a merchant basis.

This extra capacity will also give the plant the flexibility to provide grid stability to counter volatility on short notice in the area that has an increasing base of intermittent renewable power generation.

Low gas prices are forecast to remain low over the coming years and retail power prices are going up, Sivadas argues. “For our commercial and industrial customers, resiliency and sustainability are key criteria,” he says. Where power outages are possibilities, whether due to hurricanes or earthquakes, an hour of downtime is very costly.

Gas engines, in particular, are chosen for resiliency, and for the ability to operate in cogeneration fashion, Sivadas explains. Users want to save money and to have both resiliency and sustainability, making gas engines a great technology choice today in the US versus a multitude of other competing technologies, he says.

Efficiencies for the Jenbacher engines in cogeneration mode can approach 90%. For example, the Type 620, a popular gas-fired model rated at 3.3 MW, has a rated electrical efficiency of 45.2%, and a total efficiency of 87.8%. The high efficiencies can be achieved when the cogeneration unit displaces both central power in a high carbon intensity grid and when heat is recovered from engine exhaust and jackets and utilized for industrial or building use. Boilers can be turned off or shut down thereby reducing or eliminating the fuel that produces CO2. The CO2 footprint can be reduced further if biogas is used as a fuel in the gas engine, especially if it is generated from locally available waste sources.

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Credit: Generac Power Systems, Inc.
A 400-kW diesel generator from Generac Industrial Power

Jenbacher Improvements in Efficiencies
Improvements in efficiencies are evolutionary, says Sivadas. Tweaks, as he describes them, are continually made to engine sub systems to improve performance, efficiency, durability, reliability, and lower cost. Other improvements include turbocharging technology (two-stage turbo systems were introduced on the Type 6 and 9 engines), and reductions in engine parasitic and frictional losses.

Controls in engines continue to advance, Sivadas says. “Today as we continue to push the envelope on performance, electrical efficiencies, transient response, and fuel tolerance being able to still operate a gas engine in an ever tighter window between knock and misfire is even more critical,” says Sivadas.

Jenbacher and GE are increasingly focused on using digital and big data to connect, monitor, and diagnose engines, Sivadas says. All Jenbacher engines leaving the factory are connected to MyPlant, a digital connectivity and monitoring system that allows one to remotely monitor assets, diagnose faults, and predict certain failures ahead of time, he explains. “Today I can pull up and monitor any MyPlant-connected Jenbacher out there on my phone,” says Sivadas.

Waukesha Engines Ideal for Demand Response
In 2011, GE also acquired Waukesha, which is a sister to Jenbacher in the distributed power division, says Sivadas. Waukesha engines are capable of operating on a wide range of fuels, have a rich-burn combustion technology, and are known for fast response, low-exhaust emissions, and high BTU fuel flexibility capabilities. They are equipped with simple three-way catalysts and tight air to fuel ratio controls.

Waukesha’s engines are particularly attractive for demand response programs and low-operating-hour peak shaving applications given their fast start capabilities, Sivadas says. While DR has traditionally been a diesel-dominated application, recent legislative rulings are limiting its use in the US and making Waukesha engines more attractive.

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Credit: Jeffrey Sauers
A Generac Installation in the Washington DC area

A Tomato Greenhouse
The cogeneration system installed at the Houweling’s Tomato Greenhouse in Camarillo, CA, was hailed in 2012 as the first greenhouse combined heat and power project in the US.

Two 4.36-MW Jenbacher J624 two-staged turbocharged natural gas engines were installed to power and heat the large-scale greenhouses onsite and to sell extra power to Southern California Edison when needed. David Bell, chief marketing officer at Houweling’s, says a third engine was added about a year later, allowing the engines to be staged based on power needs. Bell says two identical engines were installed at its Delta British Columbia greenhouse two years later.

A GE-designed CO2 fertilization system purifies and pipes the CO2 into the greenhouse to fertilize the plants during the daylight photosynthesis process. Bell says prior to installing the engines, the CO2 was being trucked in.

The greenhouse also installed a selective catalytic reduction system for the engines to minimize carbon monoxide, hydrocarbons, nitrogen oxides, and toxic air contaminants. NOx levels have been limited to 5 ppmv to meet Ventura County’s air pollution control district.

The Jenbacher engines, operating about 16 hours daily in cogeneration mode, produce 8.7 MW of electrical power and 10.6 MW of thermal power for heating the glass greenhouses onsite. The system also powers the greenhouse’s green lights for the tomatoes. The thermal power (heat) can also be stored in existing thermal storage tanks for use at other times of the day.

The thermal energy is generated by condensing out water vapor created in the combustion process and is recovered in exhaust heat exchangers for use in the greenhouse. Houweling’s says that using the condensed water vapor in the greenhouse saves approximately 9,500 gallons per day of water from local water sources.

A 1-MW solar field was installed in 2005 which supplements the facility’s power needs. It has export capabilities, Bell says.

While Houweling’s has a demand response agreement with SCE it has not been notified in the past two years to provide power to the local distribution system. The engines have a five-minute start-up capability, allowing it to quickly respond to an SCE request for power.

In 2011, California Governor Jerry Brown honored Houweling’s with a 2011 Governor’s Environmental and Economic Leadership Award for “developing environmentally friendly practices while contributing to the local economy.”

Generac Gas Turbines Ideal for Smaller Businesses
Generac was founded in 1959 and was first known for engineering affordable home standby generators. It has since expanded its product line to commercial and industrial generators and markets them throughout North America. It also designs and manufactures manual and fully automatic transfer switches and accessories for backup power applications up to 2 MW.

Rick Lincoln, product management director for liquid products at Generac says the company is now developing larger products, spurred by the growing natural gas market, and for cost and environmental reasons.

Traditional diesel generators are no longer popular if the need is to operate outside emergency events, for example if the customer wants to participate in a demand management program. In this case, a gas engine is preferred. “Fuel spillage and supply issues go away with gas,” says Lincoln. The market for diesel generators continues to be telecommunications carriers, he adds.

Distributed generation is also a growth area, Lincoln says and he is seeing a lot of interest in demand response, where aggregators are paying customers to come off the grid or reduce usage during peak power usage periods.

Current Generac models go to 500 kW, and if the customer needs additional power, modular units tied together can boost the power supply.

In environmentally sensitive areas the debate continues over diesel versus gas. In California, for example, Lincoln says customers may fear gas lines at hospitals being cut off during an earthquake. In areas where ice storms and hurricanes are common, the roads may be closed, not allowing diesel supplies to get through. Gas is considered cleaner and will be chosen if safety is not a concern, he says.

If you have a fuel tank sized for one-half load, it may take years to use the diesel, but maintaining it is time-consuming to remove the condensation, microorganisms growing in the fuel, and other debris that falls into the tank. “Another thing we’ve seen, hazmat units are concerned about spillage during fueling,” says Lincoln. So natural gas is the preferred fuel, especially in areas with high-level water tables, he says.

Another issue relating to choice of fuel is the decision by the Authority Having Jurisdiction, such as a state agency or air quality management district. When it comes to life safety situations, either of two codes will prevail. The National Electrical Code assumes that gas is not reliable until proven it is safe. The National Fire Protection Association code 110 assumes that gas is reliable. A letter from the local gas utility may be required if the National Electrical Code is enforced in the area.

Generac is constantly working on improving the efficiency of fuel being burned by the engine, and managing how fuel and air are mixed to get the best combustion. On the back end of the engine there are emissions to be captured by three-way catalysts. “The more efficient, the less after-treatment you need,” says Lincoln.

The catalyst is not as important if the gas unit is being used on the standby market or in a demand response program, Lincoln says. It does give you a cleaner product, however, he concludes.

Cummins and Tangent Jointly Market Power Dispatch
Cummins, Inc. and Tangent Energy Solutions, Inc. formed a joint venture, Tangent Generation Resources, LLC (TGR) in October 2016 after having formed a partnership in February 2015. The purpose was to market edgeGEN, a line of Cummins natural gas generators with Tangent AMP, a distributed energy resource management system (DERMS), through municipal utilities and energy retailers to commercial and industrial customers.

The goal is to help municipal and retailer C&I customers dispatch generation during peak demand periods, when costs on the energy grid are the highest. “Distribution level energy providers and their C&I customers have become more aware of and interested in the embedded economic potential that generators represent in the new grid edge economy,” says Satish Jayaram, director Global Energy Ventures at Cummins Power Systems, in an October 24, 2016 press release. “At the same time, they do not want to be distracted from core business operations,” he adds. This creates the business opportunity for TGR.

Dean Musser, president and CEO of Tangent Energy Solutions, says the edgeGEN business is doing very well and customers are very receptive to the natural gas engines. They chose the municipal utility, coop, and energy retailer markets because of the way these entities buy energy from the grid.

“Customers include large industrials, such as chemical plants and commercial businesses, down to the grocery store level,” says Musser. “After Superstorm Sandy, everyone took notice that more resiliency was needed,” he says. “Disasters have heightened concerns of these customers. Pricing signals have increased to the point that our project investors can finance and own the onsite generation, and sell power through power purchase agreements,” he explains.

The environment for participating in ISO load-shedding programs has been changing in the past year, Musser says, and he cited events triggered by the Polar Vortex in 2014 which caused prices to soar due to supply issues. New PJM load-shedding programs, for example, are not only operating during peak summer months, but have expanded to year-round operations which adds burden to customers.

“We operate in a true economic environment where a customer’s premium priced hours are reduced or eliminated using the DERMS technology, not in a regulated demand response program,” says Musser. The DERMS technology manages behind-the-meter supply and demand to maximize the economic opportunities for the customers, while minimizing disruption to normal operations.

Currently, TGR and Tangent Energy Solutions are working in the East Coast and the Midwest, including the Pennsylvania/New Jersey/Maryland territory, ISO-North East and the New York ISO. They are now expanding into Ontario and ERCOT in Texas. Musser says the DERMS software technology is expected to be deployed in California by early 2018.

A number of companies specialize in developing turnkey CHP systems designed with optimized operations for specific sites. As an example, one of Co-Energy America’s installations in Hyannis, MA, features a 250-kW unit capable of proactively islanding from the grid in the event of an anticipated outage, and then seamlessly returning to the grid once utility power has been restored.

The company’s CHP systems come with instrumentation to measure all energy flows—natural gas feed to the engine, hot water energy from the engine, and electrical energy from the generator. These measured variables are recorded by a data logger, which links to a webpage for independent third-party verification. De Bug Web

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