Real-Time or Security Constrained Economic Dispatch (SCED)

Zonal
  Today, all resources in a CMZ are assigned the same shift factor, with respect to the CSCs that define that zone.
 
   
  Nodal
  In nodal, we will calculate an actual shift factor for each resource.
 

As the name implies, SCED determines the most economical dispatch of individual resources across the grid. Currently, the real-time market is used to “balance� the system. ERCOT uses balanced energy to meet the short-term load forecast and manage congestion between zones.

Today, ERCOT deploys a balancing energy program every 15 minutes by QSE portfolio in each CMZ. The QSEs manage the economic dispatch of individual resources within their portfolio. If zonal congestion exists, portfolios are re-dispatched in each zone, based on zonal average shift factors.

In the Texas nodal market, ERCOT will run the security constrained economic dispatch (SCED) every five minutes using offers by individual resources and actual shift factors by each resource on each transmission element. The distinction between zonal and local congestion disappears as all congestion becomes local.

In the Texas nodal market, generation is based on the locational marginal price (LMP) of the node where the generator is located. Load is settled based on a load zone price that is a load weighted average of the LMPs in the load zone.