Most of the electricity in the U.S., including Texas, is produced by steam turbines. Steam turbines are two machines connected by a shaft, a turbine and a generator set. <<<>>>
Electricity is produced by a steam turbine essentially by heating water (with a fuel source such as coal, nuclear fission or natural gas) to create steam. The steam generated is forced against blades mounted on the shaft of the turbine. As the blades rotate, the shaft rotates the coils in the generator to produce an electrical current.
Texas has more than 230 electric providers and over 850 electric generating units and all of them are responsible for ensuring adequate and reliable electricity to consumers in their service areas. 6 The total U.S. "nameplate" electric generating capacity (that is, the installed generating capacity running at 100 percent) was 1,075,677 megawatts (MW) as of January 1, 2007, about 1.7 percent more than on January 1, 2006. 7 Texas' total nameplate generating capacity was 109,666 MW in 2006. 8 Most thermal power plants do not meet 100 percent of the nameplate capacity of their generators; instead, their actual output varies depending on planned and unplanned outages, the cost of power production, weather, transmission-grid constraints and system demand. Nationally, the net generation capacity (minus planned and unplanned outages) totaled 986,215 MW in 2006, or 91.7 percent of the total nameplate capacity. The nation's net generation capacity has risen by 78 percent since 1995, while demand has increased 12 percent. 9 Exhibit 27-2 shows the change in net U.S. generation capacity and demand for the last six years
In Texas, 2006 net generation capacity totaled 100,754 MW, or 91.9 percent of total nameplate capacity. Net generation capacity has risen by 72 percent since 1995. 10 The ERCOT grid contains 38,000 miles of transmission lines. Exhibit 27-3 shows the change in Texas' net generation capacity and demand for the last six years. New generating capacity added during 2006 totaled 12,860 MW nationally and 1,667 MW in Texas. 11 Demand for electricity varies throughout the year, with the greatest demand coming during the summer. During 2006, for example, ERCOT's system demand ranged from a low of 21,309 MW (Nov. 24) to a peak of 62,339 MW (Aug. 17). 12 It is not uncommon in the summer for demand to fluctuate by more than 25,000 MW within a 12-hour period and require the coordinated contributions of more than 400 electric generating units. Texas has hundreds of electricity generating facilities and a number of entities involved in the retail sale of electricity. Exhibit 27-4 lists the state's five largest retail sellers of electricity. Information obtained http://www.window.state.tx.us/specialrpt/energy/uses/electricity.php
Outages and Blackouts
Insufficient capacity can result in problems meeting electricity demands. In April 2006, for example, ERCOT ordered rotating outages across the state due to unseasonably high temperatures and limited available generation capacity. <<<>>>
Many generators were offline for seasonal (pre-summer) maintenance, and emergency conditions were triggered by the sudden, unexpected loss of multiple generators. Rotating outages are not "blackouts," they are controlled and managed, and in this case resulted in targeted 10- to 45-minute power outages for some non-critical residential and commercial customers. Within ERCOT, TDSPs controlled the outages, and continued "rolling" the outage to different sets of customers.
Rotating outages such as these help the electrical grid avoid "cascading" blackouts, which are uncontrolled outages that can shut down power across entire regions and take days to correct. Even intentional power outages can disrupt transportation and commercial activities, but cascading outages can be far more troublesome and potentially dangerous. Such an event occurred on August 14, 2003, when the largest blackout in American history affected eight states in the northeastern U.S. and parts of Canada. The blackout affected 50 million people and caused the loss of between $4.5 billion and $12 billion in economic activity.
In all, however, the U.S. electricity grid is extremely reliable, delivering uninterrupted power to customers more than 99 percent of the time each year.31 Prior to April 2006, the ERCOT grid had not experienced rotating outages since 1989.
ERCOT considers electric capacity to be "adequate" at a 12.5 reserve margin; that is, when forecast installed capacity exceeds the forecast peak hourly demand by at least 12.5 percent.
Despite its current reliability, experts say that the nation's power system is under increasing pressure, as demand for power outpaces improvements in grid transmission capacity. In the next decade, U.S. demand is projected to increase by 19 percent, while capacity is estimated to increase by just 7 percent. 34 ERCOT demand is projected to increase by 21 percent - very close to the national average - but ERCOT has been far more successful in adding transmission capacity, reporting that it will add $6.1 billion in transmission improvements over the next ten years.