Reciprocating engine power plants are bringing reliability to the grid, addressing increasing instability as renewable generation becomes more prevalent in the energy mix.
When you think of electric power plants, "nimble" may not be the first word that comes to mind.
In fact, the entire power industry has historically been just the opposite. Coal-fired plants at the industry's core are big, centralized and designed to meet the power needs of large swaths of the population. And for many years that was just fine, because they delivered the consistent, reliable energy supply the nation desired.
But as times change, so do conditions. The power grid infrastructure is aging. Utilities are under regulatory pressure to lower carbon emissions and increase use of renewable energy sources. Other electric power producers must operate under the constraints of an electric grid challenged by renewable energy sources and outside market forces. Consumer and manufacturing shifts, meanwhile, have also thrown a wrench in historic patterns of energy use.
"It used to be, energy use peaked during the daytime hours because of the demand created by the manufacturing sector," says Tom Graves, associate for Burns & McDonnell's Energy Group. "Demand dropped in the evening when families went home to their modest, one-television homes."
Over the past two decades, however, peak demand hours have flip-flopped. "Industrial growth has slowed, and people now go home at night to larger homes and power up energy-hungry big-screen TVs and other technologies," Graves says.
Many electric power producers, meanwhile, have rebalanced their energy generation portfolios, adding wind, solar and other renewable sources to the mix.
Taken together, these factors are wreaking havoc on the electrical power grid, says Vic Ranalletta, manager of the Energy Group in Burns & McDonnell's Chicago regional office: Peak usage, net of solar and wind resources, continues after the sun goes down and the wind stops blowing.
"While beneficial in many ways, the addition of wind and solar energy has made the transmission system more unstable," adds Brian Elwell, Burns & McDonnell EPC project manager. "The industry has been searching for flexible solutions that can supplement renewable sources and help create transmission grid stability."
Enter the Reciprocating Engine Plant
Back in the late 1990s, Elwell was part of a Burns & McDonnell project team pioneering an energy-generating technology that is able to do just that.
It started when the City of Iola, Kansas, asked for the firm's help in installing two reciprocating engines in the city power plant to bolster the local power supply. "No one thought we were on the cutting edge at the time," Elwell says.
Reciprocating engines, after all, were hardly a new technology. They had been used in car engines since the late 19th century. Outside of the automotive industry, they served primarily as a source of emergency backup power.
"Because these engines ran on diesel fuel, they were fairly expensive to operate and not particularly friendly to the environment," Graves says. "They weren't considered a preferred solution for most energy needs."
But reciprocating engines had one feature that had great appeal to utilities in need of ways to quickly balance variations in energy demand: They could be started and ramped up to produce precisely the amount of power needed on — literally — a few moments' notice.
Startup time matters, especially when other generators are coming on and offline at unpredictable rates, Graves says. Power producers must balance not only the wattage, but also voltage and frequency.
"Inconsistencies can not only create power outages, they can damage the grid itself," Graves says.
A New ‘Plug and Play' Approach to Power Production
By 2007, Wärtsilä, the company that manufactured Iola's reciprocating engines, had introduced a new turbocharged version that could operate on cleaner-burning natural gas. These engines could be combined in a new kind of "plug and play" power plant that could be scaled up or down to operate during peak load times, or when facing sudden fluctuations in electrical power demand.
When Midwest Energy in Hays, Kansas, prepared to become one of the nation's first gas and electric utilities to build a power plant using the flexible technology, members of the Burns & McDonnell team called upon their work in Iola and recommended Wärtsilä's engine technology.
"That's how we got into this business on the ground floor," Elwell says.
Today — just eight years later — there are 19 reciprocating engine plants of 25 megawatts or larger operating, in design or under construction in the United States. Burns & McDonnell has provided or is now providing planning and design services for 11 of these plants, including work as the construction manager on eight.
The plants contain anywhere from three to 24 individual reciprocating engine generators, each delivering either approximately 10 megawatts or 18 megawatts of power. (A megawatt can power about 1,000 homes.)
Most of the plants are being constructed by smaller municipalities, electric co-ops and irrigation districts in search of low-cost, supplemental sources of power generation, says Joey Mashek, business development manager for Burns & McDonnell's Energy Group.But a few — including the Matanuska Electric Association in Palmer, Alaska — have built theirs to achieve a reliable baseload electric power supply.
"These plants aren't being built to replace large, 400- or 500-megawatt coal-fired plants," Mashek says. "Their owners may only need 50 or 100 additional megawatts that they can tap into. Reciprocating engine plants are appealing because they can pick the size they want."
Regulatory, Economic Motives
Municipalities and co-ops have other reasons for gravitating toward reciprocating engine plants.
Among the biggest drivers of increasing interest in reciprocating engines are regulatory bodies, such as the North American Reliability Corp. (NERC), says Sandro Tombesi, a senior project manager in the Energy Group.
"NERC used to look to the big energy players — the large coal-fired plants — to balance energy demand," Tombesi says. "Today, that responsibility is being pushed down to the local utilities."
Regional transmission operators — the traffic cops and dispatchers of the power on the grid — are likewise making local utilities and power producers financially responsible for replacing whatever loads they fail to provide.
Local power producers also have the opportunity to sell excess supply and other auxiliary services sometimes needed to manage the load on the grid.
"A well-placed reciprocating engine plant can fill that need and make significant returns," Tombesi says.
As more of the plants come online, interest from the power industry continues to grow. To help spread the word, Burns & McDonnell and current reciprocating engine plant owners head out four times a year with a traveling road show.
"More people now see that these new plug-and-play power plants are an important piece of the new, more flexible grid that is evolving nationwide," Mashek says.
Adds Graves: "As people become more conscious of power use, and we see more things like time-of-use metering, there'll be an even greater need for a grid that can adapt and change quickly. The demand for fewer emissions and lower fuel consumption will also drive change."
Most importantly, Elwell says, reciprocating engine plants do a great job of backing up renewables and stabilizing the grid.
"These plants were just what many in the power industry were looking for," he says.
For more information, contact Tom Graves, 816-822-3379.
Who: Lea County Electric Cooperative
What: 46.7-megawatt peaking plant
Where: Lovington, New Mexico
For decades, Lea County Electrical Cooperative relied on contracts with larger regional suppliers to provide power for the six rural counties it serves in southeastern New Mexico and western Texas. But with those contracts ending and new renewable energy portfolio requirements looming, the co-op decided in the early 2000s that it was time to once again generate its own power.
"Our goal was to build resources," says Gary Hurse, the co-op's general manager. "We needed to find pieces of the supply puzzle that would provide a reliable source of power, while also meeting the new standards for renewables."
The co-op's choice: a flexible gas-fired reciprocating engine plant that would work together with a wind farm they would develop nearby. With Burns & McDonnell performing engineering, procurement and construction management, the 46.7-megawatt engine plant came online in early 2012.
Now in its third year of operation, the plant has enjoyed real success, Hurse says: The plant was "built around the wind" and runs anywhere from 20 percent to 50 percent of the time.
Capable of reaching full output in less than five minutes, he says, the plant fits the market well.
"In addition to providing backup power for our wind farm, it enables us to sell ancillary services on the open market," Hurse says.Who: Mid-Kansas Electric Co.
What: The largest natural gas plant in the world driven by Caterpillar engines
Where: Ulysses, Kansas
Heightened interest in reciprocating engine technology is creating more options for utilities such as Mid-Kansas Electric Co. that seek increasingly flexible power sources.
The new 111.2-megawatt Rubart Station, which Mid-Kansas brought online in 2014, includes first-of-their-kind Caterpillar reciprocating engines. The 12-engine plant — designed to expand to 24 engines — is the largest Caterpillar natural gas plant of its kind in the world, says Kyle Nelson, the utility's chief operating officer.
Designed and built by Burns & McDonnell, the plant also includes an Emerson Ovation control system that enables the utility to monitor and operate the plant remotely from anywhere in the Mid-Kansas system. The units are designed to go from zero to full output in under 10 minutes, with complex algorithms determining how many of the station's 12 engines are needed at a given time.
The units' flexibility, operational sophistication and fast startup are all important to Nelson, given that large-scale wind development in the utility's service territory places a tremendous strain on the transmission grid.
"This technology enables us to quickly balance the load when the wind dies down," Nelson says. "It offers us something that nicely complements the mix of coal, natural gas and renewable resources in our portfolio."Who: South Texas Electric Cooperative
What: 202-megawatt power plant expansion
Where: Pearsall, Texas
Facing rising demand back in the late 2000s, South Texas Electric Cooperative (STEC) needed to expand its 1960s-era Pearsall Power Plant with 202 additional megawatts of power.
"We were looking for a power source we could operate during peak times, and we liked the efficiency that reciprocating engines offered," says John Packard, the co-op's manager of power supply, who noted that the technology's flexibility, fast start and ability to "follow the wind" also proved attractive.
With Burns & McDonnell providing design, procurement and construction services, STEC subsequently added 24 gas-fired reciprocating engines in a plant expansion that came online in early 2010.
Since then, the engines have run during peak demand times for a total of 2,000 to 3,000 hours a year. The co-op uses the power to cover its own needs, but also takes advantage of market opportunities that arise during times of excess capacity.
"It has worked out very well," Packard says. "The engines have performed well with high availability. These engines have definitely been a good fit for our application."