Electricity Markets Overview
Lo-Cal seminar, 09/21/2010
Stages of Balancing
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Stages of Balancing: Day Ahead
• Load serving entities and power generators
submit hourly bids in the day-ahead market. The
day-ahead market closes at 10.00 the day before
actual operation. The OPF determines the
optimal dispatch and the CAISO publishes
instructions by 13.00 the same day. The result is
an hourly dispatch schedule for generators with
20-minute ramps between hours.
• Integrated Forward Market (financial) vs Residual
Unit Commitment (based on forecasts)
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Stages of Balancing: Hour Ahead
• As the actual operating hour approaches,
generators and loads adjust their positions to
forecast errors or unanticipated events by bidding
in the hour-ahead market. These bids are also
settled by an OPF and the results are published
by the CAISO 75 minutes before the beginning of
the operating hour. Hour-ahead schedules are
also hourly blocks with intra-hour ramps
• HASP(TH-45 to TH+60), STUC (TH-30 to TH+240),
TH-15 to TH + 60, TH to TH + 60
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Stages of Balancing: Real Time
• Within each operating hour CAISO continues to
adjust generator operating points every 5
minutes. 7.5 minutes prior to the beginning of a
5-minute operating interval CAISO uses hourahead generation bids and load forecasts to
readjust the operating point of each generator for
that interval. The prices that result from real time
dispatch, also called ex-post zonal prices, are
reported every 10 minutes and are averaged over
two adjacent 5-minute intervals
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Stages of Balancing: Regulation
• Every one minute the ISO adjusts the output
of specific generators and/or loads based on
reliability criteria. These generators and loads
provide ancillary services to the system. The
ancillary services market is cleared hourahead. The actual dispatch of regulation
resources is empirical rather than economic
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