MISO PRA vs PJM BRA: What's the Difference?
By Illinois Commercial Energy editorial team
Reviewed by JakenEnergy commercial energy team
If your business operates in Illinois, the wholesale capacity market that sits behind your electricity supply cost depends on where you are. A facility in northern Illinois and a facility a few hours south can face two entirely different capacity constructs, run by two different grid operators, under two different sets of rules. This guide explains the conceptual difference between MISO's Planning Resource Auction (PRA) and PJM's Base Residual Auction (BRA), and why that difference reaches Illinois buyers in ComEd and Ameren territory in distinct ways.
Two Grid Operators, One State
Illinois is unusual in that it straddles two regional grid operators. ComEd serves northern Illinois and sits inside the PJM Interconnection. Ameren Illinois serves central and southern Illinois and sits inside MISO, the Midcontinent Independent System Operator. Both PJM and MISO are responsible for keeping the lights on across large multi-state regions, and both run markets to make sure enough generating capacity is committed in advance to meet future peak demand. But they do this through separate auctions with separate designs.
Capacity, in both regions, is not the energy you consume. It is a commitment that generation and other resources will be available when the grid is most stressed. Grid operators procure that commitment ahead of time so that reliability does not depend on hoping enough supply shows up on the hottest or coldest day. The two auctions below are how PJM and MISO each secure that commitment. For a broader primer on where capacity fits among your supply costs, see capacity, energy, and transmission: the three supply cost buckets.
PJM's Base Residual Auction
PJM procures capacity through its Reliability Pricing Model, and the central mechanism is the Base Residual Auction. The word "residual" reflects the design idea that the auction secures the capacity still needed after accounting for resources that participants self-supply or arrange outside the auction. The BRA looks ahead to a future delivery year and procures commitments from generators, demand response, and other qualifying resources to be available during that period.
The BRA produces a clearing price for capacity, and PJM applies locational structure so that constrained zones can clear at different prices than the broader region. This locational element exists because moving power into some areas is limited by the transmission system, so capacity located where it is needed most can carry a different value. For a business in ComEd territory, the BRA is the auction that shapes the capacity component of supply pricing.
PJM's construct has centered on a capacity product tied to a delivery year, paired with performance obligations that hold resources accountable for actually delivering when called during system emergencies. The specifics of PJM's rules evolve over time through its stakeholder process and federal oversight, so the durable point is the structure, not any single past result.
MISO's Planning Resource Auction
MISO secures capacity through its Planning Resource Auction. Like PJM's BRA, the PRA is designed to confirm that enough resources are committed to meet forecast peak demand across MISO's footprint while respecting the limits of the transmission system between zones. MISO's construct also uses zonal structure, so different local resource zones can reflect different conditions rather than treating the whole region as one undifferentiated pool.
A defining feature of MISO's approach is that its Planning Resource Auction moved to a seasonal construct. Rather than procuring capacity as a single annual product, MISO procures it across separate seasons. The reasoning is that reliability risk is not the same in every season. Summer peaks driven by air conditioning, winter peaks driven by heating and cold-weather generator stress, and milder shoulder seasons each present different challenges. A seasonal auction is intended to value capacity in a way that reflects those differences rather than averaging them into one annual number. For a business in Ameren territory, the PRA is the auction that shapes the capacity component of supply pricing.
Why the Difference Reaches Illinois Buyers
The practical consequence for an Illinois buyer is that the capacity construct behind your supply cost is determined by your utility's grid operator, not by the state. A multi-site company with locations in both ComEd and Ameren territory is effectively operating across two capacity markets at once. The timing of the relevant auction, the way zones are drawn, and whether capacity is annual or seasonal all differ between the two.
This matters when you plan a procurement. Because these auctions run on their own schedules and set wholesale inputs for future delivery periods, the timing of when you lock supply can interact with when capacity results become known. We discuss that interaction in how to time your supply RFP around PJM auctions, and the broader process in our overview of commercial energy procurement.
One caution applies equally to both auctions. A clearing price from the BRA or the PRA is a wholesale result for a region, zone, or season. It is not your bill rate. What you actually pay depends on that wholesale input combined with your account's peak contribution and the way your supply contract treats capacity. Treat auction outcomes as market context, not as a quote.
How the Two Constructs Compare Conceptually
It helps to hold the comparison at the level of design rather than numbers. Both auctions exist to answer the same question: will there be enough committed capacity to serve the region reliably during peak conditions? Both use zonal boundaries to reflect that the transmission system cannot move unlimited power everywhere. Both produce a wholesale price that becomes an input to what customers ultimately pay. Where they diverge is in the shape of the product. PJM has organized its capacity primarily around a delivery-year framework with explicit performance accountability. MISO has organized its capacity around seasons, so a resource's value can differ between, say, a summer season and a winter season. Neither design is inherently superior; they are different answers to the same reliability problem, reflecting the different resource mixes and conditions of each footprint. For an Illinois buyer, the takeaway is simply to know which construct applies to each of your sites and to interpret auction news in that context.
Sources
This article is educational and does not promise any specific savings, price, or outcome.
Frequently Asked Questions
QWhat is the difference between MISO's PRA and PJM's BRA?
Both are capacity auctions that secure enough resource commitments to meet future peak demand, but they are run by different grid operators under different rules. PJM's Base Residual Auction is the centerpiece of its Reliability Pricing Model. MISO's Planning Resource Auction serves its footprint. They differ in timing horizon, how zones are treated, and whether capacity is procured annually or by season.
QWhy does an Illinois business see a different capacity construct depending on its utility?
ComEd territory in northern Illinois is inside PJM, so capacity there is shaped by PJM's Base Residual Auction. Ameren Illinois territory in central and southern Illinois is inside MISO, so capacity there follows MISO's Planning Resource Auction. The two regions belong to different grid operators, so the same building would face a different capacity construct depending on which utility serves it.
QDoes the auction clearing price equal my capacity charge?
No. A capacity auction sets a wholesale price for a region or zone for a delivery period. It is an input, not a line on your bill. What you actually pay depends on that wholesale result combined with your account's peak contribution and how your supply contract treats capacity. Reading an auction headline number as your rate is a common mistake.
QWhat does seasonal capacity procurement mean in MISO?
MISO moved its Planning Resource Auction to a seasonal construct, meaning capacity is procured for separate seasons rather than as a single annual product. This structure is designed to reflect that reliability risk and resource availability differ across summer, winter, and shoulder seasons. It is a conceptual departure from a single annual capacity commitment.