Case study: Microgrid at Princeton University

Microgrids can lower cost and raise reliability for the owner, and for surrounding communities.

By Paul Barter, PE, ESD; and Edward T. Borer, PE, Princeton University June 8, 2015

The most advanced microgrids use multiple fuel sources, multiple power-generating assets, energy storage, CHP production, and modern digital controls. They operate with an awareness of the real-time commodity costs of fuel and electricity.

An example is the microgrid at Princeton University (see Figure 1). Recognized among the best-in-class microgrids, Princeton’s gas-fueled CHP plant produced the heating, cooling, and electricity for the campus during Hurricane Sandy, keeping the university up and running when much of the state was dark.

While the initial motivation to build a cogeneration plant was to reduce lifecycle costs, the school also benefits from a much lower carbon footprint and the higher reliability associated with behind-the-meter CHP. Princeton’s critical research projects and computing services, for example, were able to continue uninterrupted by the storm.

The heart of Princeton’s microgrid is a gas turbine capable of producing 15 MW. On sunny days, this power is supplemented by a 4.5-MW solar field (see Figure 2). Princeton’s microgrid normally operates synchronized (connected) with the local utility. This benefits both the university and other local ratepayers. When the price of utility power is lower than Princeton’s cost to generate, the microgrid draws from the utility grid. However, when Princeton’s microgrid can produce power less expensively than the utility, it will run to meet as much of the electricity needs of the university as possible. When Princeton’s microgrid can generate more than the university needs, and when the price of power on the utility grid is high, Princeton exports some power to earn revenues while lowering the net price of power for all other grid participants.

Since the creation of new ancillary services markets, Princeton is able to use its existing cogeneration assets to produce new revenue streams by selling voltage and frequency-adjustment services back to the larger power grid. This is less costly for the utility than building up its own power grid infrastructure and increasing generation at its plant. It is implemented in a way that does not reduce Princeton’s reliability.

Basic requirements for microgrid reliability include:

  • One or more generators behind an electric meter that can meet the needs of at least the most critical loads
  • The ability to run isochronous; i.e., to control voltage, frequency, and power output without the main power grid
  • The ability to black start at least one generator, i.e., start the generator when no utility power is available
  • The ability to shed less critical loads to reduce demand during island-mode operation.

Princeton University’s system offers additional lessons for successful microgrid operation:

  • Economic dispatch
  • Underground power distribution
  • Full commissioning and periodic retesting of critical components
  • Testing using realistic conditions, not desktop paper exercises
  • Designing systems with multiple fuel and water supply options
  • Regularly practicing the use of emergency response teams
  • Planning for human needs during regional emergencies.

About the authors

Paul Barter is senior vice president, global, and high-performance buildings group leader at Environmental Systems Design. He is a patented inventor and innovation specialist with 27 years of experience in the critical infrastructure and construction industries. His main focus is on project-delivery and growth in high-performance buildings, central plants, microgrids, resilient distributed power, CHP, and high-rise designs.

Ted Borer is the energy plant manager at Princeton University. He has more than 30 years of experience in the power industry and holds leadership roles in the International District Energy Association and New Jersey Higher Education Partnership for Sustainability. He is a founding co-chair of the Microgrid Resources Coalition.