Results of Wind Dispatch Pilot

Results of Wind Dispatch Pilot
Date:
February 20, 2013
Prepared by:
Mariya Goloshchapova, Wind Integration Intern, AESO
cc:
Marcy Cochlan, Director Market Regulation, TransAlta
Thanh Nguyen, Regulatory, TransAlta Corporation
Jacques Duchesne, Wind Integration Program Manager, AESO
Miranda Keating Erickson, Director Market Design, AESO
Kelly Gunsch, Vice President Market Services, AESO
Richard Penn, Senior Advisor, Market Surveillance Administrator
1. Table of Contents
1. Table of Contents ....................................................................................................... 2
2. Purpose ....................................................................................................................... 3
3. Introduction ................................................................................................................. 3
3.1
Background ................................................................................................................3
3.2
Terms and Conditions................................................................................................3
4. Results ......................................................................................................................... 4
4.1
Performance ...............................................................................................................4
4.2
Offer Analysis .............................................................................................................5
4.3
Operational Challenges .............................................................................................6
5. Recommendations and Conclusions ....................................................................... 7
6. Next Steps ................................................................................................................... 8
2. Purpose
The wind dispatch pilot was initiated in order to help the Alberta Electric System Operator
(AESO) and the industry understand whether wind aggregated generating facilities
(WAGF) can be dispatchable and participate in the Energy Market Merit Order. This
report is intended to provide market participants with preliminary results of the wind
dispatch pilot initiated on May 8, 2012 with TransAlta Corporation (TransAlta).
3. Introduction
3.1
Background
Wind generation is growing rapidly in the province. There are currently 1087 MW of
transmission connected WAGF, which represents 7.5 per cent of total installed
1
generation capacity. According to the AESO 2012 Long Term Outlook , forecast wind
capacity is expected to increase to over 2500 MW by 2022. However, currently wind
facilities do not offer their energy in the market. System controllers do not have wind
generation visibility through the Energy Market Merit Order (EMMO).
The pilot was initiated in order to help understand whether changes to ISO Rules are
required for wind to participate in the energy market on a level playing field with other
generators while recognizing the unique characteristics of wind generation.
3.2
Terms and Conditions
The pilot started with the premise of using existing AESO rules except for the restatement
period. Recognizing the variable nature of wind, the AESO placed restrictions on the
amount of volume restatements within T-2 (2 hours before the delivery hour) that could
be performed. The AESO tested different volume restatement periods varying from 20
minutes to unrestricted where volumes were restated due to Acceptable Operating
Reason (AOR) when the wind supply was different than forecast (Rule 6.6; Rule 3.5.3.2).
Also, facilities participating in the pilot were excluded from wind power management
(WPM) (Rule 304.3).
Participation in the pilot was open to all market participants. TransAlta volunteered to
participate with two wind facilities for a combined capacity of 134 MW. The AESO and
TransAlta initially agreed to run the pilot for six months (May 8 – November 8, 2012). The
following initial conditions were agreed upon:
1
•
A wind facility must offer its Maximum Capability (MC) at all times.
•
Any difference between the Available Capability (AC) and the MC due to wind
variance is an acceptable operating reason (AOR).
•
Participant will receive the short-term forecast (site specific forecast updated
every 10 minutes) and will restate their AC based on that forecast.
•
Restatements will be limited to no more than one restatement in a 20 minute
period. Restatements of AC are appropriate for both increases and decreases.
http://www.aeso.ca/downloads/AESO_2012_Long-term_Outlook_bookmarked.pdf, p.52
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•
No documented Dispatch Compliance Reporting to the Market Surveillance
Administrator (MSA) will be filed.
The AESO and TransAlta initially settled on 20 minute volume restatement periods due to
the variable nature of wind. The 20 minute period was chosen arbitrarily to test the
performance of wind generation to dispatches with further agreement between both
parties to be flexible in these terms in order to learn about wind behavior and capabilities
while being dispatched. Therefore slight changes and adjustments were expected (and
implemented) to take place over the course of the pilot. Moreover, monthly progress and
evaluation meetings were held throughout the pilot duration with the MSA, TransAlta and
the AESO.
4. Results
4.1
Performance
The market participant was allowed to do volume restatements within T-2. There were
three volume restatement periods tested: a minimum of 20 minutes between
restatements as an initial condition changing to a minimum of 10 minutes, and then
unrestricted. Performance was assessed based on whether the market participant could
maintain its generation level within +/-5 MW and +/-10 MW of allowable dispatch variance
(ADV) in both directions. Table 1 below demonstrates the performance statistics for
different restatement periods based on percentage of 10 minute clock periods.
Table 1 Performance by Restatement Interval
Restatement Interval
Within +/-5 MW ADV
+ 5 MW ADV
error %
-5 MW ADV
error %
20 minutes
92%
1.5%
6.5%
10 minutes
96%
1%
3%
Unrestricted
96%
1%
3%
Restatement Interval
Within +/-10 MW ADV
+ 10 MW ADV
error %
-10 MW ADV
error %
20 minutes
98%
0.5%
1%
10 minutes
99.5%
0%
0.5%
Unrestricted
99.5%
0%
0.5%
As Table 1 indicates, staying within the ADV on the way down is more challenging for the
market participant than on the way up. While it is technically possible to limit production
when the wind is increasing, there is no control over generation when wind is diminishing.
The results show it is possible to be in compliance more than 95 per cent of the time if
the market participant is allowed to restate AC every 10 minutes if ADV is +/-5 MW or
every 20 minutes if ADV is +/-10 MW.
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Table 2 Wind Spillage by Restatement Interval
Restatement Interval
Weekly Range %
Average for Period %
20 minutes
0.3-5.5%
1.5%
10 minutes
0.3-4.8%
1.2%
Unrestricted
0-1.0%
0.2%
The numbers in Table 2 represent the average wind spillage percentage due to dispatch
restrictions for different restatement intervals. Wind spillage is defined as the difference
between potential generation and actual generation as the asset is following is dispatch.
The second column represents weekly ranges and the third column is average for each
restatement interval. The values will vary from site to site depending on wind regime,
season and wind turbine control technology. This table is only included to indicate order
of magnitude for different restatement intervals.
Overall, the general performance did not depend on the wind capacity factor (CF) as
provided in Table 3.
Table 3 Averaged Monthly Wind Capacity Factor
Month
Averaged CF (Participating WAGF)
May
28%
June
29%
July
14%
August
14%
September
21%
October
26%
th
November (until 9 )
15%
For participating facilities monthly average wind CF ranged from 14 per cent to 29 per
cent. These numbers are slightly lower than the averages of the entire wind fleet (18 per
cent – 32 per cent) during this period.
4.2
Offer Analysis
There were no modifications to the current rules regarding offers during the pilot. Like
other market participants, wind assets were able to offer into the market and were no
longer automatically price takers. The offers were placed into the Energy Market Merit
Order (EMMO) and were dispatched accordingly.
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4.3
Operational Challenges
A challenge for the market participant was managing the variable characteristics of wind.
Numerous operating scenarios throughout the different volume restatement periods
created the majority of out of ADV generation events. These events were substantially
reduced as the restatement time periods were reduced. The two predominant factors
throughout each segment which initiated the majority of ADV generation events were
wind ramping up and wind ramping down. Specifically, high wind cut-off and turbine
pause failures in strong wind ramping up situations were operational challenges.
Performance improvements were achieved by introducing two aspects to the pilot
environment.
1. The first was to continually revise the volume restatement period. As the
volume restatement periods were reduced to unrestricted volume restatements
the performance of wind generation improved.
2. The second was to consistently refine dispatch procedures with regard to
controlling ramp rates and maintaining steady state generation.
Challenges with the different restatement periods were experienced by TransAlta
operations staff. Under the 20 minute restatement periods, TransAlta found that there
were errors with wind forecasting leading to decreased performance due to the
restatement restrictions. This was particularly the case when wind increased quickly or in
volatile conditions such as returning from a high wind cut-off event. During the 10 minute
restatement periods, the market participant was able to correct the forecast errors in a
timely manner, leading to a reduction in out of ADV events. Unrestricted restatements
removed the element of forecasting wind production, enabling the market participant to
restate to reflect wind production in real time. However, it was found that dispatches were
not issued quickly enough to avoid being out of ADV on volatile days.
AESO real-time operations definitely saw benefit in having wind dispatchable according
to EMMO, but making wind dispatchable created a dispatch side effect that the System
Controller (SC) had never encountered before. The concerns arose when dispatching
during wind ramp up events. Wind ramp up events are characterized as situations where
wind generation increases at a rate faster than dispatchable generation can respond.
This is dependent on the physical ramp rate capability of the marginal units in the merit
order and this ramp rate varies based on the generating units that are at or near the
System Marginal Price (SMP). Although these events occur rarely, the AESO needs to
explore these events in greater depth to estimate system and reliability impact.
The concern is that a wind event could still be unmanageable with large amounts of wind
generation in the merit order. If there is an increase in wind then we could potentially
have all in merit wind farms restating their volumes at the same time, causing a large
volume of wind generation waiting for dispatch. To maintain balance, the SC would need
to hold off dispatching wind, while moving slower units down. Therefore, the AESO would
still need to explore the appropriate volume restatement periods for wind to avoid
straining operations or causing compromises to dispatch order.
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Table 4 below represents average dispatches frequency over different volume
restatement periods for both facilities participating in the pilot.
Table 4 Restatement Frequency and Count by Interval
Restatement Interval
Average Restatement
Period
20 minutes
Every 49 minutes
10 minutes
Every 39 minutes
Unrestricted
Every 28 minutes
This is not an operational concern with two wind facilities but may become a challenge for
system controllers with more wind facilities participating in the energy market. During a
wind event on September 25, 2012 the entire wind fleet ramped by 322 MW within 70
minutes and both of the pilot facilities ramped by 70 MW and needed seven volume
restatements. This wind event occurred when facilities were allowed unrestricted volume
restatements. During the next hour, both facilities doubled their output and had ten
volume restatements each within 30 minutes. Further observation and study are
necessary to assess wind assets’ behavior, market and reliability impacts during such
events.
An observation was made that the majority of the time, the dispatch effective time is very
close to (within a minute or two) of the restatement time. Generally, the time difference
between the restatement and instruction time is reasonable, with a few instances where it
can be a very long time (4+ minutes) before a dispatch is received. As the time
increases to receive a new dispatch the compliance performance of wind generation
decreases and wind spillage increases.
5. Recommendations and Conclusions
Both the AESO and TransAlta deem the pilot to be a successful test of performance,
operations, and offering into the market. AESO operations see the benefit of wind
facilities participating in the merit order and the system controller is no longer responding
to unknown changes in the magnitude of wind generation. Instead, the controller would
have visibility of the wind generation before dispatch. However, further evaluation and
consultation is required to permanently allow wind to participate in the energy market
merit order. Increased grid reliability for the System Controller will be achieved through
certainty of wind output. As wind assets start to control their output according to merit
order dispatch, the need for additional Ancillary Services to balance wind generation
variability should be reduced.
Dispatchable wind will also provide a strong incentive for wind generators to provide
more accurate forecast data.
Participation in the market through dispatch is a trend for wind generation throughout the
world as the amount of wind generation increases. Independent system operators such
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as NYISO, MISO, ERCOT, and PJM are already dispatching wind. Terms and conditions
for enabling wind to be dispatchable vary from jurisdiction to jurisdiction due to differing
market designs. Their programs have proven successful and beneficial for grid reliability
and wind industry development.
In conclusion the following results of allowing wind to be dispatchable were observed:
•
Improved System Controller visibility of wind generation and ability to control
wind ramping up.
•
Wind is treated more consistently as compared to other generators.
•
Created an incentive for more accurate wind forecasting.
•
Improvements to wind performance can be accomplished by a reduced volume
restatement period and refining of operating procedures.
•
The ADV bands should be explored for wind generators given challenges with
forecasting, turbine technology, wind volatility and speed of AESO dispatches.
•
Delays in receiving dispatches via Automatic Dispatch and Messaging System
(ADaMs) once a real time restatement has been made can decrease the
performance of wind.
Dispatchable wind will also allow for market-based means to resolve supply surplus or
transmission constraints conditions.
6. Next Steps
The next steps in the Wind Dispatch Pilot initiative are:
•
Receive stakeholder comments on the Phase II wind recommendation paper.
•
Perform additional modeling and analysis by the AESO
•
Develop rule(s) and definition(s) to allow wind to participate in the energy market.
•
Initiate consultation process on market rule changes and definition in order to
enable wind to be dispatchable and offer at price into the EMMO
.
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