Operational Issues & Risks ERCOT Operations Planning August 22, 2008

August, Topics Covered Risks Associated with Wind Generation Ramp Rate Challenges WGR Survey Meteorological Data Requirements High Frequency Relay Proposal SPS Operation Requirements

August, Risks Associated with Wind Generation Forecasting Accuracy –Addressing with PRR 763 & Ancillary Services –Meteorological data needed to improve forecast –Continue to work with AWS Truewind to identify additional forecasting tools and techniques Voltage Control challenges Ramp Rate Changes that create large frequency deviations –PRR 771 addresses ramps associated with deployment instructions –PRR 771 does not address ramps associated with changes in wind speed Possible Solutions for decreasing wind speed that results in low frequency –Additional Regulation Up procurements –Governor like response from wind turbines –Additional Responsive Reserve –Fleet VDIs –Non-Spin procurement to ensure that proper reserves are maintained Possible Solutions for Ramp Rate Changes that result in high frequency –Ramp rate limits –Governor like response from wind turbines –Regulation Down deployments for wind turbines –High frequency relays to protect against high frequency events –Additional Regulation Down procurements

August, WGR Ramp rate limitation Wind QSE Frequency impact -As shown from the graph below, the ability of the WGRs to almost instantaneously ramp up and down has in the past caused RRS to be deployed -A 5% ramp rate for the WGRs was initially proposed by ERCOT -Eventually, a 10% ramp rate was agreed upon by ERCOT and the wind community taking into consideration the economical impact a smaller ramp rate could have on the WGRs

August, Examples of near instantaneous wind ramps

August, High Ramp Rates Due to Wind Speed Increase Total ERCOT wind generation increased from around 700MWs at 3:40 to 2310MWs at 4:10. A ramp rate of 54 MWs/Min for 30 minutes

August, High Ramp Rates Due to Wind Speed Increase An other example of high wind generation ramp rate due to increasing wind speed Total ERCOT wind generation increased from around 992MWs at 3:40 to 1938MWs at 4:00. A ramp rate of 47 MWs/Min for 20 minutes

August, WGR Ramp Rate Limitation…Continued WGR Ramp Rate Limitations Each Wind-powered Generating Resource (WGR) shall limit its ramp rate to 10% per minute of its online installed capability when responding to or released from an ERCOT deployment. PRR 771 has been proposed to implement a ramp rate limitation on the Wind Generation Resources (WGRs) when responding to or released from an ERCOT deployment. The intent of this PRR is to maintain system reliability as it allows ERCOT to avoid frequency spikes due to the WGR’s ability to ramp up or ramp down almost instantaneously. The proposed language for the PRR is as follows

August, Intent of WGR Surveys The intent of the wind surveys is to understand the capabilities of each WGR ERCOT plans to use this information to educate the system operators on the capabilities / limitations of each specific WGR The goal is to make available to the system operators a book with all the necessary information for the WGRs. Information provided in the book will include –Installed Capacity –Make and model of turbines –AVR capabilities –24X7 contact information –One-line schematic of the stations –Net MVAR import / export with zero MW output –Wind speed / temperature restrictions –SPSs involving the WGR and its operation

August, WGR Surveys…Continued Other important topics discussed in the surveys include –Response to balancing energy deployments –How long does it to take to make a voltage set point change –On-site or remote control room –Cap and reactors banks in the facility –Any agreement with the TSP to provide a portion of voltage support –Ramping ability –Status of the meteorological data requested by ERCOT –Meet the 0.95 PF requirement –Any agreement with the TSP to provide a portion of your voltage support requirements

August, Proposed High Frequency Relay Requirement for WGRs All WGRs connected to ERCOT Grid shall install high frequency relays to disconnect the resources during system events ERCOT will divide and assign each WGR a frequency level at which their relay must be set. Possible setting assignment will be HZ, HZ, HZ, HZ and HZ. Assignment will be based on total MWs needed at each frequency level as well as control capabilities of WGR. –Control capabilities include – ramp rate limit & Governor like response

August, Meteorological Station Data ERCOT has requested the WGRs to provide the meteorological station data through the respective QSEs Required Data Points: –Wind speed (MPH) –Wind direction (Degrees – 0 to 360) –Temperature (ºC) –Barometric pressure at 2 m above ground level on the meteorological tower (hPa (mb)). All barometers must be set as “Unadjusted for Sea Level”. ERCOT will be polling the data at a frequency of every 10 seconds. ERCOT expects to see the values from the QSE every 5 minutes or less Data must be submitted by each QSE via ICCP

August, Meteorological Station Data…Continued Collection Station Height Requirement –None - height does not matter as long as the elevation is provided. –AWS will provide calculations to insure all are in compliance. A Meteorological Collection Station is required for each Wind Farm. If a Wind Farm is jointly owned each QSE is responsible for the Split Generation Resource (SGR) to supply ICCP Meteorological data. All barometers must be set at “Unadjusted for Sea Level”. All directions are to be reported in “Degrees” (360 o ).

August, Special Protection Schemes 4 SPSs modeled in the ERCOT system have a protective action to trip a WGR when a trigger condition is met ERCOT believes that a SPS should only be triggered as a last option for reliability concerns. ERCOT’s philosophy on SPSs - A WGR is expected to back its generation down when the trigger conditions are met and the SPS is armed, instead of letting the turbines trip due to generation output exceeding the trip point.