Most buildings get their electricity the same way, by being connected to a huge power grid, where the energy is supplied by gigantic power plants.
But Princeton University is showing that when it comes to power plants, sometimes smaller and more local is better. Princeton’s campus is the size of a small town, and all of its utility needs are met by a 15-megawatt power plant that burns natural gas or diesel to provide steam (for heat and hot water), chilled water, (for air conditioning) and electricity to all 12,000 people and 180 buildings. The campus is connected to the power grid too, so it can still get power when the turbine goes offline for maintenance.
But why does it make economic sense for Princeton to build and run its own tiny power plant when it could instead buy electricity from the power grid? After all, the people at Public Service Electric & Gas are no dummies when it comes to creating power. Their plants are highly efficient and located near fuel sources or rivers, and can use economies of scale to make electricity for cheap.
Edward T. Borer, Princeton’s energy plant manager for the last 22 years, will explain exactly how his engineering and campus energy department is able to beat the big power company at a free lecture at the Princeton Plasma Physics Lab on Wednesday, December 14, from 4:15 to 5:30 p.m. For more information, visit www.pppl.gov.
It turns out that Princeton is something of a leader when it comes to cogeneration, which is the practice of using the leftover steam from electricity generation for other purposes. Earlier in December, Borer gave a talk on Princeton’s power plant to the U.S. Senate, which is looking to Princeton as a model for other facilities and even entire cities.
The secret to the success of cogeneration is twofold. First is the location. While large power plants are very efficient, they are typically located far away from the places where the power is used, meaning that an elaborate transmission system must be built to get the electricity to where it is needed. This adds to the cost.
The second factor is waste. At a natural gas power plant, gas is burned to boil water, which drives turbines, which rotate magnetic coils, which creates electricity. The waste heat from this process is dissipated in a smokestack or cooling tower. Borer says about two-thirds of the heat is wasted at a typical power plant.
But at a cogeneration facility, that excess heat isn’t just blasted into the air. Instead, the steam from the turbine is pumped into nearby buildings where it is used for heat and hot water. The ratio is reversed: only one third of the heat is wasted.
“I cut my fuel spend in half compared to doing heat and power separately,” Borer says. “Doggone, that’s really good savings, and it also translates into a lower carbon footprint. With combined heat and power district energy, I can basically double utility efficiency.”
Borer says district power makes sense in universities, hospitals, military bases, airports, and research campuses. It is especially valuable at those places, because a local power plant can stay online even in a natural disaster. During Hurricane Sandy, when the storm knocked out power to most of New Jersey, Princeton kept its lights on thanks to a crew of engineers who worked in shifts to keep the cogeneration plant running throughout the crisis.
Cogeneration is common in Europe, and some American cities even use it. Philadelphia, New York, and Chicago all have municipal steam heat systems that serve the citizens well but which are barely noticed because the pipes are underground and out of sight. Atlantic City pumps chilled water to casinos and hotels so they can use less space on air conditioning equipment and more on revenue-generating gambling floors.
The advantages of small, localized power plants are endless, in Borer’s view. It would even make sense for a suburban neighborhood to have its own cogeneration facility as long as the community could bite the up-front costs of building one. It would even have the bonus of providing local employment.
Borer grew up in Swarthmore, Pennsylvania. “I was the kid who took everything apart,” he says. “I needed to understand how things worked. It was a visceral need. Eventually, somebody said, ‘You are a total nerd. You should be an engineer.’” Following this advice, Borer earned a bachelor’s in mechanical engineering at Union College and then a master’s at Drexel. He worked for PECO for 10 years after graduation before joining Princeton in 1994, when the university was just building the plant. Borer oversaw its construction.
At that point, cogeneration was nothing new for the university, but it wanted to invest in a modern facility.
Borer says the history of the plant goes back to the 1860s, when Princeton first made steam in a plant and distributed it to the dozen buildings that made up the campus at the time. By the 1890s, the plant was also generating electricity. For most of the 20th century, the steam came from boilers that were built in the 1920s, and by the 1980s, those boilers were wearing out. The university was faced with the decision of replacing the old boilers or building new ones. “After a lot of math and a lot of thought, we realized the best lifecycle cost decision would be to build a new plant, not just a boiler,” Borer says.
Since then, the university has upgraded various systems of the plant, and also taken steps to reduce energy use around campus. It is currently in the middle of a project to change 100,000 lightbulbs from incandescent and fluorescent to LEDs. It’s also adding insulation, improving the steam system, and finding ways to use waste heat from the plant. All over campus, engineers are replacing single-speed fans and pumps with variable speed models. Each one is a small improvement, but Borer says it’s resulting in “tremendous” energy savings.
All this has resulted in Princeton attracting the attention of the Senate and other groups interested in how micro power grids should be operated. “The size of our power plant is not special, and the equipment is not really unique, but the way we use it is on the cutting edge,” Borer says. “People come to see the thought process of how we decide what to use, and not only what piece of equipment to use, but what load level to set it at for best economic efficiency and lowest carbon footprint. We are one of the leaders in this particular area.”
Borer hopes that more people come to realize the advantages of cogeneration.
“The energy plant of Princeton not only saves a considerable amount of money from the energy budget, but it is one of our most impactful ways to reduce our carbon footprint.”