Cost assessment of efficiency losses in hydroelectric plants

Some important real-time tasks of the independent system operator (ISO) are the monitoring and control of power system events (load deviations and contingencies). These events are usually managed by the ISO using operating reserve ancillary services. These services represent an additional capacity (MW) available in generators and some interruptible loads. Generators must change their operating points in order that this capacity can remain available. These changes might lead to efficiency losses in energy production. In systems with a high percentage of hydroelectric production, hydroelectric plants need to know the impact of ancillary services on their profits. This work therefore analyzes the cost of efficiency losses due to operating reserve availability in hydroelectric generators. A method to calculate this cost component is proposed using a unit commitment dispatch for a single hydroelectric plant. This dispatch is performed without considering the operating reserve availability and is compared with the traditional dispatch, which takes into account the availability of operating reserve. The proposal is used to calculate the cost of efficiency losses on a Brazilian hydroelectric generator. We found that the cost of efficiency losses can be considerable when compared to the incomes of a hydroelectric plant in the short-term market. (C) 2011 Elsevier B.V. All rights reserved.