Key takeaways
- PJM operates the electric grid across 13 states, including Illinois, Ohio, Pennsylvania, and much of the Mid-Atlantic.
- Your PJM capacity tag is set once a year based on your load during five specific system-wide peak events called Coincident Peaks.
- Miss those five 15-minute windows and you overpay every month for the next twelve months.
If your facility is in Illinois, Ohio, Pennsylvania, or anywhere else in PJM territory, part of your electric bill goes to capacity charges. These are separate from consumption. They are separate from local demand. And they are calculated using a mechanism that is uniquely unforgiving to facility teams that do not know it exists.
Understanding how PJM capacity charges work is the difference between paying the full tag every month and lowering it by 20 to 40% with a well-timed load curtailment.
What Is PJM Capacity?
PJM Interconnection is the regional transmission organization that operates the electric grid across 13 states and the District of Columbia. It runs a wholesale market for both energy and capacity. Energy is what you use. Capacity is what PJM has to build and maintain to make sure you can use it.
Every commercial and industrial customer in PJM has a capacity tag, expressed in kilowatts. That tag represents the customer’s contribution to system-wide peak demand. PJM procures generation capacity to meet the total tagged load across the region and passes the cost through to customers via their utility bills.
The 5CP Method: How Your Tag Is Calculated
PJM uses the Five Coincident Peaks (5CP) method to set customer capacity tags. Every summer, PJM forecasts the five days most likely to see system-wide peak demand. These are typically hot weekday afternoons between June and September.
On those five days, PJM records the single hour of highest system demand. Your facility’s load during that specific hour on all five days gets averaged. That average becomes your capacity tag for the next twelve-month capacity period, running from June through May of the following year.
You cannot know in advance which five days will be the CPs. PJM does not confirm them until after the summer ends. But there are strong indicators: hot weather forecasts, high system load projections, and PJM-issued Load Management alerts that flag likely CP days as they approach.
Miss five 15-minute windows over the summer. Pay for it every month for a year.
Why This Method Is Uniquely Painful for Facilities
Local demand charges are set every month. If you have a bad month, you pay more that month, but next month resets. A 5CP capacity tag is different. Your performance during five specific hours locks in the capacity charge for the following twelve months.
The math is brutal. A facility with a typical CP-hour load of 800 kW pays materially less in capacity charges than one with a CP-hour load of 1,200 kW, even if the second facility uses less total energy the rest of the year. Two facilities can have identical annual kWh consumption and pay wildly different capacity charges based entirely on what they happened to be doing during those five afternoons. The trap: normal operations during forecasted peak days.
Timing is opaque. The exact CP hour is confirmed after the fact. Most facilities do not know their tag was set poorly until months later, when the new capacity charges hit their bills. The trap: discovering the tag only when the bill increases.
How Capacity Charges Show Up on Your Bill
Your utility passes PJM’s capacity costs through as a line item, usually labeled something like Capacity Charge, PJM Capacity, or Generation Capacity. The rate is expressed in dollars per kilowatt per day and is applied to your capacity tag every day of the twelve-month capacity period.
Illinois facilities in ComEd territory typically see capacity rates in the range of $3 to $9 per kW per day, depending on the specific auction year. That means a facility with a 1,000 kW capacity tag pays roughly $90,000 to $270,000 per year in capacity charges alone. Cut the tag by 20% and the savings run into six figures.
Reducing Your PJM Capacity Tag
The strategy for reducing your capacity tag comes down to load curtailment during forecasted CP days. When PJM or a third-party forecasting service flags a likely peak day, you shed non-essential load during the forecasted peak hour. If you can predict four out of five CP hours accurately and curtail effectively during each, you can cut your tag substantially.
The practical challenge is knowing when to curtail and by how much. PJM issues alerts, but they do not always land during actual CP hours, and curtailment carries its own operational cost. The goal is a program that flags true CP days accurately, curtails only what is needed, and captures the savings in the following capacity year.
Every 100 kW off your tag is roughly $9,000 to $27,000 per year in savings.
ComEd territory capacity rates
What DataWrangler Does for PJM Territory Facilities
For facilities in PJM territory (including much of Illinois, Ohio, Pennsylvania, New Jersey, and the Mid-Atlantic), DataWrangler installs interval metering, monitors PJM’s daily peak forecasts, and coordinates load curtailment during forecasted CP hours. Our analysts review each capacity year’s actual CP days after the fact, quantify the savings captured, and adjust the curtailment strategy for the following year. That is part of how DataWrangler cuts 10 to 25% off commercial and industrial electric bills in PJM markets.
Check Your Own Capacity Tag
Pull your last twelve months of bills. Find the Capacity Charge line item. Multiply by twelve to see your annual capacity cost. That number is set once a year based on five hours of load. If it is meaningful to your business, it is worth managing.
Upload your bill for a free capacity tag analysis or see how DataWrangler helps commercial facilities in PJM territory.