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ERCOT Control Area This graph shows data for the area controlled
by Electric Reliability Council of Texas (ERCOT), which covers about 85%
of electricity use in Texas. In addition to the resources in state, DC transmission
lines connect Texas to other control areas. ERCOT, unlike the rest of the
control areas in the United States, is not under the jurisdiction of the
Federal Energy Regulatory Commission (FERC). It does operate under the safety standards of the North American Electric Reliability Council (NERC).
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Maximum Capacity
This number is an estimate of the total generation capacity within the ERCOT region.
It is computed as the sum of the online capacity of all the generators licensed to operate
according to the EIA Electric Power Annual 2000 Volume II, published by EIA and which can be found
here.
This number will be updated as appropriate.
The fact that a generator is licensed, and so included in this figure, does not
mean that it will be operating or selling electricity any given day.
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On-Line Capacity
On-Line Capacity is equal to the Maximum Capacity minus Generation Outages.
It represents the total generation capacity in the ERCOT region that can
feasibly operate that day. See Generation Outages for more detail.
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Generation Outages
A generator that is off-line (unavailable to operate under any circumstances)
is called an "outage" or a "curtailment".
Outages can be scheduled in advance (usually for maintenance purposes), in which
case they're known as "planned" outages.
Or they may occur with little or no advance notice, in which case they're called
"forced" outages.
This number is not published anywhere by ERCOT. On this website, we estimate total outages at any given time to be 15 percent of the maximum capacity.
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Potential Capacity The generation capacity potentially available to
supply electricity is computed here as the sum of
On-Line Capacity + Net Imports/Exports - Reserves .
We use a reserve margin equal to 7% of the load.
The generation capacity actually available in any given
hour will differ from our estimate of the potential capacity for a variety of reasons.
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Current Load
The current load is the total demand for electricity in the ERCOT region at the
current time. It is published in real-time on the ERCOT Real Time Data webpage
An archive dating back to July 26, 2002 is also available on the ERCOT web site. The ERCOT load accounts for about 85% of total electricity use in Texas.
Although the load varies everytime anyone flicks a switch, on the average it's fairly
predictable, with variations due to daily, weekly and seasonal patterns.
Load that is fairly constant over the entire day is referred to as the "baseload"--
for residences, it includes such things as refrigerators, water heaters, and lights
that are never turned off. Baseload for residential and commercial buildings can be
surprisingly large, considering that there is little activity at night.
Seasonal variations in load are due mainly to changes in the need for heating
and cooling, and can be quite substantial. This is somewhat inconvenient in terms
of managing supply, since generation capacity has to be built to satisfy the peak
load, but for much of the year the actual loads may be much less.
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Forecast Load
While the load changes every time someone turns on a computer or switches off a light,
on the average it can be predicted, given information about the weather,
the daily habits of individuals and businesses, etc.
Every day ERCOT publishes seven-day forecasts of loads for each hour. These forecasts are used by
the Qualified Scheduling Entities (QSEs) to
schedule delivery of adequate electricity. The curve shown here is from the most current forecast.
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Net Import/Export The electricity transmission grid
that serves the ERCOT control area is interconnected with neighbors via a DC Tie Line.
The values for imports and exports shown in the graph are real time flows, published in real time on the ERCOT web site.
On this graph a positive number indicates a net import into the ERCOT region;
negative numbers indicate a net export. This differs from the convention
used by ERCOT, which indicates net flow into the ERCOT control area as negative.
The reason we decided to display imports as positive is to keep this graph
consistent with the other graphs on this Electricity Status web site.
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