Texas Reliability Entity generating capacity margin chart

Power generators in Texas have come under criticism this week over the possibility of buying power from Mexico to meet high consumer demands because of extreme winter weather.  However, power suppliers have been able to meet those demands for the most part.  Below is chart of the demand and capacity resources in the region.

The Texas Reliability Entity (TRE) ensure the reliability of the bulk power system in the Electric Reliability Council of Texas (ERCOT) region.  TRE serves 85% of the Texas load and 75% of the Texas land mass. 

The chart plots consumer demand and capacity resources in megawatts.  The difference between the two, called capacity margin, is reserve generating capacity utilized during extreme winter and summer peak loads.  While having a large reserve is desirable in extreme conditions, idle capacity is costly.  Power generators have to balance the trade off, maintaining just enough reserve capacity to meet emergencies but not over building the system.  Note the difference between the blue and green columns.  TRE systems maintains a certain percentage of excess generating capacity over consumer demand.  This capacity margin is represented by the red line, expressed in percent on the right.

Data Source: U.S. Energy Information Administration

Related Article: Number of new power plants down in 2009, capacity up

Update on February 11, 2011 by ed

The American Wind Energy Association reports wind generated turbines produced 3,500 - 4,000 megawatts of capacity last week, playing "a critical role in limiting the severity of the blackouts, [and] providing enough electricity to keep the power on for about three million typical households." Wind generated power in Texas accounted for 7% of ERCOT's needs at its most critical juncture.