Wikipedia Deep Dive

PJM Interconnection

9 min read

In the summer of 2026, when temperatures climb above 90 degrees Fahrenheit across the eastern United States, the lights may go out. Not because the grid fails in some catastrophic collapse, but because the largest power grid operator in North America simply cannot purchase enough electricity to meet demand. That operator is PJM Interconnection—a regional transmission organization that manages the flow of electrons from Chicago to New Jersey, serving 67 million customers across fourteen states and the District of Columbia.

PJM's footprint covers some of the most densely populated territory in America: the industrial heartland of Ohio, the metropolitan sprawl of Philadelphia and New Jersey, the rolling hills of Kentucky. Its transmission lines—88,333 miles long—stretch from the Great Lakes to the Carolinas, an invisible web woven through twenty-two percent of the United States. In 2024 alone, PJM delivered over 800 terawatt-hours of electricity, enough to power millions of homes. And yet, by December 2025, the organization reported it could not purchase one hundred percent of the power it needs in its future electricity auction. Rolling blackouts may occur in 2026.

This crisis represents more than an engineering problem—it is a reckoning with the fundamental architecture of how electricity flows through the modern grid. To understand PJM's current predicament, one must trace the organization's origins back nearly a century, to an era when three utilities decided that cooperation made more sense than competition.

The Birth of a Power Pool

In 1927, at a time when the nation was still recovering from the First World War and electricity was transforming American life, three forward-thinking companies formed what would become the world's largest competitive wholesale electricity market. The Public Service Electric and Gas Company of New Jersey, the Philadelphia Electric Company, and the Pennsylvania Power & Light Company created a power pool—essentially a cooperative arrangement where electric generating plants would be dispatched on a lowest-cost basis, reducing electric costs for everyone in the pool.

This was a radical idea. At the time, utilities operated as vertical monopolies, each controlling generation, transmission, and distribution within their territories. The concept of pooling resources across state lines to minimize costs was innovative. When Baltimore Gas and Electric Company and General Public Utilities joined in 1956, the pool received its famous name: the Pennsylvania-New Jersey-Maryland Interconnection, abbreviated as PJM.

The pool operated much like an airline's reservation system—with generators scheduled like flights, each unit of electricity dispatched where it was needed. The economics were compelling. By pooling resources, these utilities could draw power from whichever plant was cheapest at any given moment, rather than forcing every utility to maintain its own expensive generating capacity around the clock.

Restructuring the Grid

For seven decades, PJM operated as a traditional power pool. Then came the late 1990s, and everything changed.

Between 1996 and 1999, the Federal Energy Regulatory Commission—FERC, the regulatory body that oversees interstate electricity transmission—issued a series of decisions that would fundamentally restructure the American electric utility industry. The intent was to open the wholesale power market to new players. FERC hoped that sparking competition would save consumers between four and five billion dollars per year while encouraging technical innovation.

Order No. 888 directed utility owners of interstate transmission lines to provide proposed terms—called tariffs—under which new market participants would gain open, non-discriminatory access to move power through the existing grid. Crucially, FERC also mandated what is known as functional separation: utilities were required to separate their transmission operations from their power plant and power marketing businesses.

This unbunnling of functions aimed to eliminate conflicts of interest that might arise when the same company owned both the transmission system and the generating plants. It was a radical break from nearly a century of integrated utility operation.

Order No. 889 went further, requiring creation of an electronic system—the Open Access Same-Time Information System—to ensure every participant in the wholesale power market had access to the same information about available transmission capacity and prices. The playing field was being leveled, but someone needed to coordinate this new competitive landscape.

FERC endorsed the concept of independent system operators—ISOs—to coordinate, control, and monitor operations of electrical power systems. This function had traditionally been the responsibility of vertically integrated electric utilities. PJM became an ISO in 1997, one of the earliest adopters of this new model.

The concept evolved into regional transmission organizations—RTOs—and FERC's Order No. 2000, issued in 1999, specified exactly what capabilities these organizations should possess for the competitive generation market to function as intended. In 2001, PJM was formally designated an RTO by FERC.

Expanding the Footprint

The transition from ISO to RTO marked a new era of expansion. Pjm's territory grew not through hostile takeover but through voluntary participation—utilities choosing to join the coordinated grid rather than operating in isolation.

In April 2002, Allegheny Power became the first external control area to join the PJM RTO as a market participant. PJM and Allegheny Power operated as a single control area, filling the roles of balancing authority, interchange authority, market operator, and transmission operator.

Two years later, in May 2004, Commonwealth Edison—known as ComEd and serving the Chicago area—joined PJM as a separate balancing authority operating under the RTO. PJM managed the two territories in a single market through what it called "the pathway": a set of firm contracts that transferred energy from ComEd through third-party control areas to the eastern PJM markets.

By October 2004, American Electric Power and Dayton Power & Light joined, allowing PJM to collapse back into a single control area. In January 2005, Duquesne Light Co. joined. Then in May 2005, Dominion Virginia Power extended PJM's southern border to North Carolina. FirstEnergy was added in June 2011, expanding the footprint across northern Ohio to the Michigan border. Areas of Ohio and Kentucky near Cincinnati covered by Duke Energy joined in January 2012.

By 2018, the Ohio Valley Electric Corporation integrated into PJM—adding another piece to what had become the largest regional transmission organization in North America.

During the Northeast Blackout of 2003, the transmission systems within PJM's operations area largely remained operational and were not affected by the widespread power failure. When the grid separated, a small portion of the Public Service Electric and Gas New Jersey zone electrically separated from the Eastern Interconnection due to over-frequency relay operations—a testament to the robustness of PJM's coordination.

The Crisis Ahead

Today, PJM stands at a crossroads. Its fifteen-year planning horizon for transmission system upgrades—known as the Regional Transmission Expansion Planning process—considers forecasts of load growth and additions of demand response, interconnection requests for new generating plants, and possible solutions to mitigate congestion on the transmission system.

But the numbers tell a troubling story. The 2024 auction cost $2.2 billion. By late 2025, total capacity costs exceeded sixteen billion dollars—eight times higher than just the previous year. PJM's anticipated future supply shortages stem from expected five percent annual demand growth, comparing sharply to no growth from 2005-2020.

This demand surge comes from an unlikely source: new data centers. AI operations and cloud computing infrastructure require enormous amounts of electricity, and the facilities serving them have grown exponentially in recent years. Combined with supply constraints from shutdowns of many generation plants for environmental or economic reasons—and the difficulty of timely permitting for new power plants—the system faces genuine scarcity.

The challenge is two-fold: availability and affordability. Rolling blackouts loom as early as 2026, sky-high capacity costs threatening to make electricity uneconomical for consumers even when it remains physically available.

Decarbonization and the Future

As the largest regional transmission organization in North America, PJM plays a significant role in reducing grid emissions. Three strategic pillars guide its operations, including "facilitating decarbonization"—the integration of renewable sources into its generation mix.

PJM presents hourly charts of its energy sources on its main website, providing transparency about the fuel types feeding the grid. A database tracking generation by fuel type shows historical hour-by-hour breakdowns—with 2022 serving as a recent benchmark.

Yet challenges persist. As of 2022, PJM has experienced difficulty evaluating and integrating proposed new renewable energy projects into its system. This resulted in delays for significant projects being built or planned, inhibiting progress toward President Biden's goal of one hundred percent carbon-free electricity by 2035.

The transition to renewables may also be slowed by features of the PJM pricing structure—a legacy of its competitive market design that sometimes rewards fossil fuel generation over cleaner alternatives.

The Grid Today

More than one thousand companies are members of PJM. The organization manages one thousand four hundred and thirty-six electric power generators, coordinating a complex dance between supply and demand across multiple jurisdictions.

What began as a cost-saving arrangement among three Pennsylvania-area utilities in 1927 has become the backbone of electricity transmission for much of the eastern seaboard. It is a remarkable story of coordination—tens of thousands of miles of transmission lines, hundreds of generators working in concert, all coordinated by an organization born from the simple insight that cooperation reduces costs.

But that very coordination now faces unprecedented pressure. The AI-driven demand surge, the retirement of aging fossil plants, the difficulty of permitting new generation—all converge to threaten the system that PJM built. What happens next may determine not just whether the lights stay on, but how the American grid adapts to a future where energy must be both clean and reliable.

The answer will come in the auctions, in the regulatory rulings, in the planning processes of an organization that has operated for nearly a century—and in the decisions made by policymakers balancing competing demands. One thing is certain: PJM Interconnection remains indispensable to understanding how electricity flows through modern America.