Supply-Demand Balance Forecast

Forecast of 3 month supply-demand balance

Forecast of year end supply-demand balance

Please note: Supply Adequacy probabilistic forecasts have been discontinued, as of July 6, 2007

  1. Introduction
    On November 3, 2000, the Alberta Department of Resource Development (now Alberta Energy) requested the Power Pool of Alberta (PPoA) to maintain more awareness of generator maintenance schedules, for the purpose of ensuring a reliable supply of electric power. Following this request, the Power Pool - through its System Controller (SC)- and the Transmission Administrator (TA) (the Power Pool and the TA are now named the Alberta Electric System Operator - AESO) organized a working group that was given the task to find the most appropriate way of establishing and implementing the coordination of generation outage schedules. The working group included Buyers of Power Purchase Arrangements and Generation Facility Owners that own and operate units with installed generation capacities of over 40 MW. The Working Group developed a scheduling coordination process. This process was subsequently reviewed and endorsed by the Electricity Supply Task Force chaired by the Alberta Energy and Utilities Board (EUB). The fundamental concept is that market forces should be the primary driver for maintenance coordination and that maintenance scheduling should not be centrally planned and controlled. Historically, there has been excellent cooperation between suppliers and the AESO to manage potential threats to reliability of supply and avoid supply interruptions - it is expected that this cooperation will continue. Key to allowing the market to react is the availability of information regarding planned outages for maintenance. Suppliers will provide information to the AESO on a confidential basis. The AESO will aggregate the information and make assessments of supply adequacy changes and post on the AESO web site. It is anticipated that market implications will cause the Participants to make, when needed, appropriate adjustments to their maintenance outage schedules. It is recognized that the supply situation can change suddenly (forced outages of generation or transmission being the primary drivers) and there may not be sufficient time for market forces to react. In such instances and when reliability of supply is threatened, the AESO, as part of its ongoing monitoring and short term operations planning processes, may contact those suppliers that have planned equipment outages for the period of concern. It is expected that to the extent reasonably possible, the suppliers will work with the AESO to ensure reliability. The following sections of this document present a more detailed description of the outage scheduling coordination process.
  2. Parties Involved
    The parties involved in the coordination process for generation outage scheduling include the Generation Facility Owners (GFOs), the Power Purchase Arrangement (PPA) Buyers and the Alberta Electric System Operator (AESO).
  3. Generating Units
    The coordination process is focused on outage scheduling for generating units with installed capacities of 40 MW or higher. Smaller units can be included due to special circumstances, eg. those designated as Transmission Must Run (TMR) units. The AESO will notify the GFOs and PPA Buyers of such units to include these units in the generation outage scheduling coordination process.
  4. Generation Outage Scheduling Procedure
    Refer to OPP–601 Outage Scheduling for details concerning the generation outage submission procedure. 
    Click here to view Rules and Procedures on the AESO website of visit http://www.aeso.ca/

    Scheduled outages are aggregated by fuel type and presented on the AESO's secure ETS website.
  5. Supply-Demand Balance Model
    The AESO will combine the unit outage schedules received from PPA Buyers and GFOs with their own system load forecasts and will estimate the adequacy of electricity supplies in the province of Alberta. 

    The Supply - Demand Balance model is a deterministic approach for comparing anticipated supply with forecast load and reserve requirements. The model has these basic components:

    Total Expected Internal Supply: indicates the expected availability of intra-Alberta generation after taking into account scheduled outages and derates, less a factor of 300 MW for accumulated small forced outages and derates.

    Import Capacity from BC and SK: indicates the maximum import available transfer capability (ATC) of both the British Columbia and Saskatchewan interties, taking into account limitations caused by outages on the Alberta grid. Refer to OPP-304 (Tables 1, 2 and 3) and OPP-312 for details of the BC intertie limits. Limitations to ATC caused by system conditions in BC and SK are not indicated.

    AIES Load + Operating Reserves: indicates the peak forecast load for each day (the 'peak hour') plus the required operating reserves for that hour.

    Surplus: equals Total Expected Internal Supply plus Import Capacity from BC and SK less AIES Load + Operating Reserves.

    Supply - Demand Balance forecasts are presented for one week (accessed via the AESO's secure ETS website), three months and to year-end (links above). Differing assumptions are used to create a range of supply-demand scenarios, such as the BC tie being unavailable or a generic 400 MW unit being unavailable.
  6. Data Confidentiality
    The unit outage schedule information submitted by PPA Buyers and GFOs will be kept and treated by the AESO as confidential. Only the aggregated results will be published in graphic format as described above. The individual unit schedules will not be made known to the public or to other competitors. The AESO has entered into confidentiality agreements with the GFOs and PPA Buyers regarding the provision and use of confidential generator maintenance outage plans.
  7. Sudden Forced Outages
    When a forced outage event occurs that requires the immediate removal of the unit from service, the PPA Buyers and the GFOs will advise the AESO System Controller right away. As soon as possible, but not later than 24 hours after the occurrence of the outage, they will submit to the AESO an estimate of the length of the time period required for repairs.
  8. Outage Scheduling Coordination
    All the PPA Buyers and GFOs are expected to review and take into account the short-term to mid-term system supply adequacy when they prepare the schedules for their unit outages. It is expected that the PPA Buyers and the GFOs, in response to market forces, will change their outage schedules when needed to avoid insufficient supply situations. The changes in the original schedules should be communicated to the AESO, as specified in OPP-601.

    Each day, the AESO will review the next 7 (seven) day schedules for generation outages. Whenever an outage is scheduled for a date/time when the supply margin appears to be insufficient, the AESO personnel will contact the Buyer or GFO involved and:

    a. advise of situation;
    b. suggest changes in schedule.

    The contacted Buyer or GFO will make changes, if any, on a "best effort" basis and immediately communicate these changes to the AESO. As specified in the existing regulations, if the security of the system operation may be endangered by the operating conditions resulting from the proposed outage schedule, the AESO may issue a directive requesting the operator to keep its unit on line. The supplier retains the right and duty to take any action it deems prudent to protect the facility, its personnel, the public or the environment.
  9. AESO Contacts for Clarifications
    If a GFO or PPA Buyer has any questions or requires clarification concerning this process, they may contact Cam Bush (Email cam.bush@aeso.ca telephone: 403-705-5204).
Posted: 7/5/2007