Hydroelectric Energy: A Comprehensive Overview

Posted on Sep 11, 2024 in Geology

Hydroelectric Energy

0. Introduction

The movement of water can be an excellent source of energy, and sometimes we don’t make good use of it. However, nowadays, many dams utilize the pressure created by water flowing out of the reservoir or lake where it is stored.

0.1. Definition

Hydroelectric energy harnesses the natural movement of water to spin a turbine and generate electricity. Water power is transformed into mechanical energy to move the turbine blades in a hydroelectric plant.

0.2. History

Water power has been used by humans since ancient times. The history of tidal power stretches back to antiquity. In the Middle Ages and Roman times, there were devices like “molinillos” (small mills) where water’s force created circular motion, used to turn mechanisms. However, the first true tidal power station, converting water movement into electricity, was built in 1966. Today, numerous tidal power stations worldwide represent one of the most common forms of electricity generation.

1. Theoretical Bases

1.1. Where Does It Come From?

Hydroelectric power is the most utilized form of solar power, albeit indirectly, through the hydroelectric cycle.

Hydroelectric Cycle:

  • The cycle begins when the sun heats water in seas, rivers, and lakes, causing evaporation.
  • The evaporated water is then transported to different parts of the world by warm air currents, forming clouds.
  • When the clouds cool, the water falls as rain or snow, returning to rivers, lakes, and seas.
  • Hydroelectric power capitalizes on the potential energy of water falling from a height.
  • This potential energy is converted into kinetic energy, then into mechanical energy, and finally into electricity through hydropower installations.
  • The hydroelectric cycle can then begin anew.

1.2. Operating Technology

Water power is harnessed in hydroelectric power stations, typically located within hydroelectric reservoirs.

1.3. Hydroelectric Station

Hydroelectric plants are facilities that transform the potential energy of river water into electrical energy using turbines coupled to electric generators.

1.3.1. Parts of a Hydroelectric Plant

A hydroelectric plant consists of:

  1. Reservoir: A place where river water is stored. It also controls the water’s flow rate.
  2. Dam: A thick wall that retains the reservoir’s water.
    • Spillway: Regulates the water volume.
    • Discharge Channel: A channel where water is released back into the river.
  3. Central or Mechanical Room: A building housing:
    • Turbines: Machines that convert water’s kinetic energy into rotational energy.
    • Generator-Alternator: Working in conjunction with the turbine, the generator converts rotational energy into electrical power.

1.4. Types of Hydroelectric Stations

Different types of hydroelectric power exist, categorized by their size, location, and energy production capacity (in megawatts, MW).

Categorization by Production:

  • Large Hydro: Produces more than 10 MW.
  • Small Hydro: Produces between 1 and 10 MW.
  • Micro-Hydro: Produces less than 1 MW.

In Spain, there are 41 hydroelectric stations. Only Small and Micro hydro are considered renewable due to their lower environmental impact. Large Hydro is not considered renewable because of its significant environmental footprint.

2. Advantages

  • Long-lasting resource: Hydropower is inexhaustible as long as the water cycle remains constant.
  • Low maintenance costs.
  • Low environmental impact (for Small and Micro hydro).
  • Suitable for both small-scale and industrial consumption.
  • Clean energy: Does not emit greenhouse gases or toxic emissions, and does not produce pollution.
  • Affordable energy: Technological advancements are helping to exploit hydropower more efficiently.
  • Renewable resource: Utilizes the energy of flowing water to generate electricity.
  • Eco-friendly.
  • Very quiet.
  • Available in all climates and seasons.
  • Instrument for sustainable development: Hydroelectric projects can be developed and operated in an economically viable and environmentally responsible manner.

3. Disadvantages

  • Land inundation: Dam construction can flood large areas of land, potentially leading to the loss of fertile land and displacement of communities.
  • Ecological disruption: Dams and reservoirs can disrupt aquatic ecosystems, although solutions like fish ladders are being implemented to mitigate this.
  • Downstream ecosystem changes: Water released from turbines lacks sediment, potentially causing riverbank erosion.
  • Flow fluctuations: Repeated opening and closing of turbines can cause dramatic changes in river flows, impacting ecosystems.
  • Obstacles for fish migration: Dams can impede the movement of migratory fish species like salmon.
  • Transmission costs: Dams are often located far from population centers, requiring costly electricity transmission networks.
  • High initial investment: Plant construction requires significant investment, and suitable construction sites are limited.
  • Climate dependency: Hydropower generation is affected by climatic factors like droughts.

4. Environmental Impact

The environmental impact of hydropower is primarily associated with dam construction. While mini-hydro projects can have minimal impact, large dams can cause significant environmental consequences, including:

  • Partial water stagnation.
  • Microclimate creation, potentially harming wildlife and vegetation.
  • Disruption of fish migration.
  • Spread of waterborne diseases.
  • Flooding of farmlands and displacement of communities.

However, hydropower can also offer environmental benefits, such as flood control and water flow regulation during droughts. In some cases, the environmental impact can diminish over time due to ecosystem adaptation.

Nevertheless, severe consequences can occur. For example, the Akosombo Dam on the Volta River in Ghana, opened in 1966, flooded 8,482 square kilometers of tropical forest, displaced 80,000 people, and contributed to the spread of diseases. The electricity generated was primarily destined for aluminum production by a U.S. multinational corporation.

5. Cost

  • The cost of a hydroelectric plant with a 50-year lifespan is estimated at 2 euros per kWh (kilowatt-hour).
  • The cost of a plant with a 20-year lifespan is estimated at 2.4 euros per kWh.
  • Plant maintenance is relatively inexpensive and requires minimal staffing.
  • Dam construction costs vary depending on location, size, and terrain. However, as a general estimate, building half a dam can cost roughly the same as constructing a 100 km highway. For instance, the Hoover Dam, one of the world’s largest, cost 31 million USD (22 million euros).