Hydropower Scheduling in Large Scale Power Systems

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Hydropower is the most important and widely-used renewable source of energy. Nearly one-fifth of the world’s energy each year is supplied by hydroelectric power generation, which is more than solar, wind, biomass and all other renewable sources combined. Brazil is the third largest ...

Brazil is the third largest producer of hydroelectricity in the world, preceded only by China and Canada. (Source: In 2009, hydropower accounted for 87 percent of 
Brazilian electric power generation, with smaller amounts coming from conventional thermal, nuclear, and other renewable sources. But managing a power system with over 110 GW of 
installed capacity, most of it coming from around 150 hydro plants, is a daunting task.

Hydro plants are located in 8 River Basins with specific hydrologic characteristics. Many of them are capable of storing water on reservoirs that can be used to regulate the river stream 
flow throughout the year, others are run-of-river plants and are subjected to seasonal river flows. Reservoir operations at a hydro plant affect the whole cascade downstream and the 
benefits of holding water for future use are not easy to estimate.

To illustrate these characteristics let us observe Itaipu Hydro Plant, with 14 GW of installed capacity, the hydro plant with the greatest generation in the world, located downstream 
from the Paraná River Basin on the frontier with Paraguay. Fig. 1 shows the average and standard deviation of its monthly inflows.

The seasonal behavior of the stream flow in the Parana River Basin is easily observed in Fig.1. The dry season goes from May to October, with average inflows around 6,000 m³/s in 
August. The wet season goes from November to April, with average inflows around 16,000 m³/s in February. Inflow variability is much higher during the wet season, as indicate the 
standard deviation values which are near 5,000 m³/s in February and around 2,000 m³/s in August.

Seasonal fluctuations are common in stream flow data and being able to smooth it and hedge unexpected events such as droughts and floods is a major concern in reservoir 
operation problems. Consumption of potable water, water usage for industrial and irrigation purpose, and also river flow control for navigation are some of the issues that 
constraint reservoir operation for hydropower generation.