ERCOT LMP Components — System Lambda and Congestion

Quick Answer

In ERCOT, a Locational Marginal Price (LMP) equals System Lambda (energy) plus a congestion component. System Lambda is identical at every Settlement Point in a given interval. Congestion varies by location and can be positive or negative. Unlike some other ISO/RTOs, ERCOT does not include a marginal-loss component in LMP—transmission and distribution losses are allocated separately under Protocols Section 13.

System Lambda (Energy Component)

ERCOT Protocols Section 2 defines System Lambda as the cost of providing one MWh of energy at the reference Electrical Bus—the shadow price of the system power-balance constraint. It is the energy component of LMP at each Settlement Point. It is not simply “the most expensive unit online” or “the cheapest available source”; it is the optimization’s power-balance dual, equal to the LMP at the reference bus.

Congestion Component

When transmission constraints bind, congestion pulls location prices apart. For each binding constraint, ERCOT uses that constraint’s shadow price and each location’s shift factor (how strongly injection at that bus affects flow on the constrained element). In protocol formulas, Settlement Point prices are of the form System Lambda minus the sum of (shift factor × shadow price) across binding constraints—so congestion can raise or lower a location’s price relative to System Lambda.

Typical pattern (not a forecast): West Texas export limits with surplus wind often depress West prices relative to System Lambda; load-pocket constraints can elevate Houston-area prices. Signs depend on shift factors and which side of each constraint a bus sits on.

Where Losses Go (Not Inside LMP)

Many textbook LMP explainers use LMP = Energy + Congestion + Loss. That three-part design fits markets such as ISO-NE or CAISO. It does not describe ERCOT. ERCOT still accounts for losses: QSEs representing load are responsible for transmission and distribution losses, which ERCOT allocates during data aggregation using Transmission Loss Factors and Distribution Loss Factors (Protocols Section 13). Losses affect settlement volumes/allocation—they are not a third additive term inside the published LMP.

LMP Formula (ERCOT)

LMP ≈ System Lambda + Congestion (equivalently, congestion ≈ LMP − System Lambda for a bus in the same interval). For interval-level analysis, subtract published System Lambda from the location’s LMP to isolate congestion.

Why Prices Differ (Illustrative)

Two nodes share the same System Lambda but can post very different LMPs when congestion differs. Example numbers only: if System Lambda is $20/MWh, a West Texas resource node might clear near −$10/MWh after large negative congestion, while a constrained load-area bus might clear near $25/MWh after positive congestion—with no separate loss addend in either LMP.