Power supplied must always be equal to power being consumed. To achieve this balance, our System Controllers constantly monitor demand across Alberta and match it with available supply. System Controllers use Operating Reserves (OR) to maintain system reliability when there is an unexpected imbalance between supply and demand due to various system conditions or contingencies.
Regulating, spinning and supplemental reserves
In Alberta, OR are categorized as regulating reserves, spinning reserves and supplemental reserves, where each type of reserve performs a unique function.
Due to the size and complexity of the Alberta Interconnected Electric System (AIES), the balance between generation (supply) and consumption (demand) is not instantaneous—often there is a lag while generation is catching up to supply or while generation is decreasing in response to lower demand. Regulating reserves instantaneously provide the power difference between supply and demand required during that lag period.
Spinning and supplemental reserves (collectively referred to as contingency reserves) are used to maintain the balance of supply and demand when an unexpected system event occurs. These reserves provide capacity the System Controller can call on with short notice to correct any imbalance. These reserves can come from the supply side (generators) or from the demand side (load curtailment by reducing demand from large electrical consumers immediately).
Spinning reserves are the fastest acting contingency reserve. Generators or loads providing spinning reserves are synchronized to the grid (the turbine is “spinning” but not generating power). This unique feature allows the reserve to be provided very quickly. In addition to responding quickly, spinning reserves also provide frequency support to the system. Supplemental reserves on the other hand are not required to be synchronized to the grid.
Operating Reserve Procurement
The amount of OR the AESO procures is determined by reliability standards set by the Western Electricity Coordinating Council (WECC) of which the AESO is a member.
Everyday, the AESO procures OR from generators and loads through Watt-Ex, an online exchange. Prices for OR vary daily by each product type procured.
Visit the Watt-Ex web page.
Active vs. standby Operating Reserve procurement
The AESO procures both active and standby OR. The purpose of active reserves is to meet the requirements of the AIES under normal operating conditions. Assets who are successfully procured will normally be dispatched.
The purpose of standby reserves is to provide additional reserves for use when the resources available under the active portfolio are insufficient. Generally, before any resources are dispatched from the standby portfolio, all resources from the active portfolio have been dispatched.