HYDROPOWER

Hydropower

Hydropower

Introduction

Many hydropower plants built at the beginning of the 20th century are still operating today. The turbines installed at that time are still running at very high efficiencies of 80-90%. Indeed, hydropower is based on a simple process, taking advantage of the kinetic energy freed by falling water. In all hydroelectric generating stations, the rushing water drives a turbine, which converts the water's motion into mechanical and electrical energy. This simple process makes it the most efficient, reliable and versatile source of electricity. In practice, this process is applied in many different ways depending on the electrical services sought and the specific site conditions. Accordingly, there are a wide variety of hydroelectric projects, each providing different types of services and generating environmental and social impacts of different nature and magnitude.

The necessity to evaluate each hydroelectric project in relation to the services it offers and to compare electricity supply projects on the basis of equivalent services provided to society. The article first describes the role of hydropower in electricity supply. It then describes various types of hydropower projects, with the specific electricity services they provide and how they differ in terms of environmental impacts.

Hydropower and electricity supply

Although electricity demand varies significantly during any given day and throughout the year, electricity cannot be stored, unlike energy sources such as wood, petrol, or gas. Electricity is thus characterized by the fact that any change in demand for power must instantly be matched by an equivalent adjustment in power generation. If demand increases and supply is not able to increase accordingly, then the voltage or “pressure” of the electric current drops, which can generate “brownouts”, stress on electric systems and power outages. This can result in major impacts on economic activities, basic services such as health, education, and security.

In order to face the wide range of power demand, utilities combine diverse power plants whose services differ in terms of continuity of services. Some electricity generating plants are better suited to be operated as base plants, others as peaking plants. For example, nuclear power plants run optimally at a stable output, making them essentially base load generators. Hydropower plants in contrast may, depending on their design, provide electricity for base or for peak demand or both. This flexibility in energy supply is one of the specific technical advantages of hydropower.

Hydropower, then, may fulfill different electricity services:

Base load and peak load generation: In regions where hydropower is very abundant, it satisfies both base and peak loads. The base load is produced by large or numerous reservoir-type projects, which store sufficient energy to cover several seasons of consumption and periods of dry weather, possibly combined, if available, with run-of-river plants (hydroplants which use the water flows in a river but which do not have a reservoir). The electricity needed to meet peak load is generated by installing extra water turbines at some power plants. This additional capacity—that functions only a few hundred to a thousand hours per year—provides extra power when ...