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How Mini/Micro Combined Heat and Power (CHP) Can Prevent Further Growth of Large Gas Plants

Joel Gordes

Historically, it may be painful but useful to remember that a number of environmental groups, including Natural Resources Defense Council and the Sierra Club, as well as numerous other environmentalists like myself, were supportive of the use of natural gas throughout the 1980s and '90s. It was oftentimes referred to as a “bridging fuel” while other times, in the extreme, it was even looked upon as an outright solution.


Natural gas, when used with a combined cycle gas turbine (CCGT) is capable of attaining a 55% to 60% thermal to power efficiency. When compared to earlier [simple cycle] plants only capable of around 35% to 40% efficiency tops, this has been a real revolution. Unfortunately, these lower performing plants still make up the majority of plants in Connecticut and are a target for natural gas power plants trying to replace them and move in.

Fire with Fire.jpg

Photo: Natural gas power plant being build in Massachusetts

Photo credit: massmatt

Contrary to what many may assume, not all power comes from within Connecticut borders but is dispatched from ISO New England from distant but often higher efficiency sources. Even though these sources may be more energy efficient, the power is ultimately subject to lowered efficiency due to line losses and outages. These distances mean outages due to weather may become more common in the future, even if facilities are “hardened.”


Natural gas has been the fuel of choice for the CCGTs because they burn extremely clean when compared to other commercialized bulk technologies. High-grade oil (akin to kerosene) can also be used as a fuel source. Today in Connecticut there are eleven CCGTs with a combined capacity of ~3,277 Megawatts (MW) out of a total of 9,175 MW (summer). That makes up about 36% of the total supply. While more can be added, there are some serious lessons to be learned before such action is taken.


What was unknown at that time, except maybe to a few less taken with the technology, was recently recounted by Bill McKibben, possibly the best known environmental author in the nation. Here’s an excerpt from his article in a March 2018 New Yorker.


        When I think about my greatest failing as a communicator — and one of the greatest failings of the climate movement — it’s not that global warming still continues…. No, the single most annoying failing is a more technical one, but with huge consequence: Public opinion — and especially elite opinion — still accepts natural gas as a cleaner replacement for other fossil fuels. And this acceptance — nearly as strong among Democrats as Republicans — has meant that we’ve seen huge increases in the use of natural gas. In fact, our essential global warming strategy in America has been to replace coal-fired power plants with ones that run on fracked gas. The idea that natural gas combats climate change is a sleight of hand. But explaining why appears to be just slightly too technical for it ever to get across, in the media or on Capitol Hill, in statehouses or city halls.


New climate threats call for not only new emission standards but new ways of thinking. It is not good enough to call for a 45% drop in emissions by 2035 unless we also raise the bar for emission levels for all new plant construction, or upgrading and backfitting existing plants where possible (a highly doubtful option for many of them). While renewable energy technologies with zero emissions (not considering embodied energy in their construction and operations) are the gold standard, we cannot ignore that more conventional (and less efficient) plants will be built in the interim.  


Also setting standards for large, new conventional plants to even 65% to 70% efficiency would exclude most of them. This would allow us to shift toward much smaller mini/micro CHP plants.


Whether you’re a fan of this strategy or not, the 80% to 90% efficiencies of these smaller plants can significantly exceed even large plant figures. That being said, the leap to all renewables in the near term may fail to consider adaptation technologies to protect the health, safety and security aspects that may accompany intermittent sources. Mandating battery storage (a technology that currently has limited capabilities) may help, but it also brings some criticism by raising prices. In some respects, it may be viewed as “letting the perfect be the enemy of the good” when compared to the super high efficiency natural gas-fueled CHP plants.


New loads drive construction of large, gas plants, requiring sizeable pipelines, but they may run only for limited times having about a 56% capacity factor. Instead, using super high efficiency, small combined heat, and power (mini and micro CHP) can more closely match end loads, cutting down on needs for large pipeline expansion and large, less efficient combined cycle plants with lower usage rates. In addition, they can serve in microgrids in tandem with renewable resources when sun, wind, hydro, etc. are not available.

Mini/micro CHP is useful not just for the mitigation of climate change gases, but provide climate change adaptation advantages as well. With enhanced and more frequent storms that may threaten prolonged power outages, the strategic placement of mini/micro CHP provides health and safety islands. Must-run facilities such as hospitals and public safety (police, fire, ambulance) would benefit from the continuity of service provided by mini/micro CHP. These islands of safety can serve as base points for many of the early microgrids.


With the Trump administration dismantling climate scientists’ efforts at every turn, it is doubtful we will attain meaningful national greenhouse gas mitigation goals. Thus, as a more vulnerable coastal state, we must redouble our local efforts towards adaptation for the security of our citizens. (See document  Preparing the Electric Grid for Climate Adaptation.) Because of the aforementioned attributes, the mini and micro CHP make ideal candidates for local adaptation efforts, the majority of which are currently being used towards greenhouse gas mitigation efforts.


Mini/micro CHP deprive large new generators of a market through the “death of a thousand cuts.” They appeal to consumers and municipalities by having very few line losses, few transmission cost or losses and little need to build inefficient larger plants.


If any large inefficient plants are on hot standby, which promotes waste and more emissions at low efficiency, the mini/micro CHP, with rapid start-up capabilities, can eventually be used to replace them.  


Other factors favoring mini/micro CHP include:


  • At about 10 MW or less in size, there will be little risk of future stranded cost for any distribution and transmission facilities. These are usually paid for by ratepayers.

  • Since many of the customers for this already use gas for heating, only small additional gas supply that more closely match loads is required. This means we do not need to rush to judgment to expand gas capacity with large, new pipeline additions required by facilities in the hundreds of megawatts range.

  • If located within a weak point in the electric grid, it should also be afforded compensation for deferral or elimination of otherwise costly grid upgrades.

  • The construction of mini/micro CHP provides local jobs and revenues.

  • Mini/micro CHP does not require lengthy, vulnerable and costly transmission like the $1.4 billion Northern Pass project proposed by Eversource to bring power from northern Quebec (approximately 900 miles away) to Connecticut. That money would be better spent on local, more resilient solutions like the construction of mini/micro CHP.


For these reasons, this technology should be afforded some favorable rating and also considered for firm natural gas contracts rather than interruptible service.

Joel Gordes is an independent energy consultant.

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