What Is PJM? The Grid Behind Your Electric Bill

Every time you flip a light switch in northern Illinois, the electricity flowing to your home was bought and sold on a wholesale market you've probably never heard of. That market is run by PJM Interconnection, the largest grid operator in the United States, and its decisions directly shape what you pay on your ComEd bill every month.

PJM doesn't generate electricity and it doesn't send you a bill. But as the organization that coordinates the power grid across 13 states and D.C., it runs the auctions and markets where wholesale electricity prices are set. When PJM's capacity auction prices spiked nearly 10x in 2024, ComEd customers saw their supply rates jump 53% the following June.

Understanding PJM helps explain why your electricity bill keeps climbing and what forces are driving those increases.

What Is PJM Interconnection?

PJM is a Regional Transmission Organization (RTO) — a federally regulated entity that coordinates the generation and transmission of electricity across a multi-state region. Think of it as the air traffic control system for the power grid: it doesn't own the planes (power plants) or airports (utilities), but it manages who flies where and when.

Founded in 1927 as a power-sharing agreement between utilities in Pennsylvania, New Jersey, and Maryland (hence "PJM"), it has expanded to cover all or parts of 13 states plus the District of Columbia. Today PJM manages a grid serving 67 million people — about one in five Americans.

PJM's territory stretches from Chicago to the Atlantic coast. The states it covers include Delaware, Illinois, Indiana, Kentucky, Maryland, Michigan, New Jersey, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia, and West Virginia. In Illinois, ComEd's service territory in the northern part of the state falls under PJM, while Ameren's downstate territory is part of a different grid operator called MISO.

How PJM Sets Wholesale Electricity Prices

PJM operates two main markets that determine the price of electricity: the energy market and the capacity market. Both feed into what you ultimately pay on your utility bill.

The Energy Market: Real-Time Supply and Demand

PJM uses a pricing system called Locational Marginal Pricing (LMP). At its core, LMP reflects the cost of delivering one more megawatt of electricity to a specific point on the grid, taking three factors into account:

• Energy cost — the marginal cost of generating the next unit of power
• Congestion cost — added cost when transmission lines are bottlenecked and cheap power can't reach where it's needed
• Loss cost — energy lost as electricity travels across wires

PJM calculates LMP prices at thousands of nodes across its grid every five minutes in real time and every hour on a day-ahead basis. Generators get paid the LMP at their location, and utilities pay the LMP at theirs. This creates price signals that encourage power plants to locate where power is needed most and incentivize new transmission to reduce congestion.

Day-Ahead vs. Real-Time Markets

PJM runs two energy market timelines. The day-ahead market lets generators and utilities lock in prices for the next day based on projected demand. The real-time market handles actual conditions as they unfold, adjusting for unexpected demand spikes, plant outages, or weather shifts. Most electricity (roughly 95%) trades in the day-ahead market, with the real-time market handling the balance.

If you're on ComEd's hourly pricing program, the prices you see are derived directly from these PJM wholesale markets. When PJM's real-time prices spike during a heat wave, your hourly rate spikes too.

The Capacity Market: Paying to Keep the Lights On

The energy market pays generators for electricity they actually produce. The capacity market pays them to simply exist — to guarantee they'll be available when needed. PJM holds capacity auctions three years in advance to ensure enough power plants will be online to meet projected peak demand plus a safety margin.

These capacity charges have become the most significant driver of rising electricity costs in PJM territory. Here's how dramatically prices have escalated:

The 2025/2026 auction cleared at $269.92/MW-day for most of PJM — a staggering increase from the $28.92/MW-day in the prior year. The 2026/2027 auction hit the FERC-approved price cap at $329.17/MW-day. Without the cap, prices would have exceeded $530/MW-day.

For consumers, these aren't abstract numbers. Capacity charges are baked into the supply portion of your electricity bill. When PJM capacity prices jump 10x, those costs flow directly to your monthly statement.

Data Centers: The Demand Surge Driving Up Prices

The biggest single factor behind PJM's price explosion is the rapid growth of data centers across its territory. AI training facilities, cloud computing, and cryptocurrency mining operations have created an unprecedented surge in electricity demand.

PJM's independent market monitor estimated that data centers were responsible for 63% of the capacity price increase in the 2025/2026 auction, translating to $9.3 billion in costs passed along to electricity customers across the region.

Preliminary utility forecasts project that data centers could require more than 50 GW of peak capacity by 2030 — enough to power over 20 million homes. The grid is struggling to keep up: data centers are connecting faster than new power supply can be built. PJM has warned that starting in summer 2026, it will have just barely enough power to meet reliability standards, and by 2027 the region could fall below them entirely.

How PJM Prices Show Up on Your Electric Bill

Your ComEd bill has two main sections: supply (the electricity itself) and delivery (the wires, poles, and infrastructure to get it to your home). PJM's wholesale markets affect the supply side.

ComEd purchases electricity from the PJM wholesale market on behalf of its default-service customers. The price ComEd pays — shaped by LMP energy prices and capacity auction results — becomes the per-kWh supply rate on your bill.

Capacity charges typically account for about 20% of your supply cost. But with the recent auctions clearing at record levels, that share has grown substantially. Looking ahead, experts at the Citizens Utility Board and NRDC project that cumulative capacity costs through 2033 could reach $163 billion across PJM states, with $21.4 billion falling on ComEd's territory alone — translating to roughly $70 per month in additional costs for the average household.

PJM's Generation Mix and Its Price Impact

What fuels the power plants in PJM's territory also shapes prices. The most recent capacity auction cleared with the following resource mix:

Natural gas dominates at 45%, making PJM prices sensitive to gas market volatility. While Illinois itself is heavily nuclear, PJM's broader mix is still fossil-fuel dependent. Coal and gas plants are also retiring faster than replacements are being built, tightening supply and pushing capacity prices higher.

PJM has over 170,000 MW of new generation requests in its interconnection queue — mostly wind and solar — but the queue has been notoriously slow. Getting a new power plant connected to the PJM grid can take 5-7 years, creating a bottleneck right when new supply is needed most.

What's Being Done About Rising Costs

The scale of PJM's challenges has drawn attention from governors, regulators, and consumer advocates across the region. Several efforts are underway:

What You Can Do About Rising Electricity Costs

You can't control PJM's capacity auctions, but you can take steps to reduce the impact on your wallet:

• Reduce your Peak Load Contribution (PLC). Your capacity charges are partly based on your usage during the grid's peak hours. Cutting consumption during summer afternoon peaks can lower your capacity costs in future years.
• Consider dynamic pricing. ComEd's hourly pricing program lets you pay real-time wholesale rates, saving money by shifting usage to low-price hours.
• Invest in energy efficiency. Reducing overall consumption directly reduces your exposure to rising supply costs. Start with the biggest energy users in your home: HVAC, water heating, and appliances.
• Explore rooftop solar and battery storage. Generating your own power during peak hours shields you from the highest wholesale prices.
• Track prices and set alerts. Knowing when wholesale prices are high or low lets you make smarter decisions about when to run major appliances. Tools like Electrac provide real-time price tracking and SMS alerts for ComEd customers.

The Bottom Line

PJM Interconnection is the invisible infrastructure behind your electricity bill. Its wholesale markets and capacity auctions set the foundational prices that flow through to what ComEd charges you every month. With data center demand surging, power plants retiring, and capacity prices hitting record highs, PJM's decisions are going to matter more — not less — in the years ahead.

The good news is that policy responses are in motion. FERC price caps, state-level grid legislation, and faster interconnection processing are all aimed at keeping costs in check while maintaining grid reliability. But these fixes take time, and experts expect prices to stay elevated for several more years.

For now, the best thing you can do is understand how these markets work, reduce your consumption during peak periods, and stay informed about the wholesale prices that drive your bill.