A hydroelectric plant is a set of hydraulic engineering works together with a series of suitable machines. The objective of a hydroelectric plant is to obtain electricity from the potential energy of moving masses of water.
These types of power plants take advantage of the potential energy of water to generate electrical energy.
The energy produced by hydroelectric plants must be classified in all respects as renewable energy. Thanks to the water cycle, this resource can be endlessly reused for the same purpose without undergoing a purification process. The concept of renewability is subordinated to the constancy of the annual volume of total inputs.
Hydroelectric plants have the peculiarity of being activated and deactivated in a few minutes with the immediate opening of the hydraulic gate valves. This feature provides the possibility of easily covering sudden peaks in electrical energy demand that may occur.
How does a hydroelectric plant work?
A modern hydroelectric power plant consists of: a reservoir, a dam, gates, turbines and generators.
The tank stores the "fuel" and allows operators to control the amount of water fed to the turbines. It also serves as a settling tank: most of the dirt and debris in the water settles to the bottom and away from the suction area.
Water coming from the basin is transported to the turbines through an inlet (gate dam) and a penstock. An inlet filter system further cleans the water to ensure it is relatively free of suspended solids, which could damage the turbine blades.
Hydraulic systems work together to open and close gate valves that allow water flow to flow downstream of the basin. These systems are: the regulator, the brakes, the gate controls, etc.
Regardless of the type of design, the turbine transforms the kinetic energy of the movement or fall of water into mechanical energy.
The turbine is connected through the shaft to the rotor of an electrical generator that converts mechanical energy into electricity.
For maximum efficiency, the turbines are custom made for each hydroelectric plant.
Types of hydroelectric plants
The classification of hydroelectric plants depends on factors such as water storage (reservoirs or run-of-the-river), geographical location, size and capacity, and available water flow. Each type is chosen based on local geography and power generation needs
Some of the most common types are:
- Reservoir hydroelectric plants: They store water in a reservoir, gradually releasing it to drive turbines and generate electricity. They are the most common.
- Run-of-the-river plants: They do not store water and depend on the constant flow of rivers or streams to generate energy.
- Pumping stations: They store water in two reservoirs at different heights and generate electricity by pumping water from the lower reservoir to the upper one during periods of low demand, and then releasing it downwards during peak demand.
- Tidal power plants: Capture tidal energy by allowing water to flow to and from a tidal basin through turbines.
- Underground hydroelectric plants: They use underground caverns or cavities to store water and generate energy, which minimizes the environmental impact on the surface.
- Small hydroelectric or microhydroelectric plants: These are smaller facilities used in remote areas or rural communities to generate local electricity.
- Continuous flow plants: These plants use the constant current of small rivers to generate electricity continuously.
Pumped storage plants are power plants that fill their own storage basin with water when electricity is produced in excess of consumption.
The power plant then purchases electricity at a price below its average price, at which point it changes its configuration and pumps water to its storage tanks. When consumption exceeds the supply of electricity, the power plant sells the electricity it produces from its storage tanks to consumers at a price that is more expensive than its average price.
The pumping stations use two reservoirs located at different heights. When there is demand, the plant generates electricity like a conventional plant. Water falls from the upper reservoir, drives the turbines and is stored in the lower reservoir.
When demand is low, water is pumped again from the lower reservoir, at the foot of the dam, to the upper reservoir.
The production capacity of a hydroelectric plant is determined by several key factors:
- Height difference: The power generated depends on the height difference between the average level of the reservoir and the water level at the foot of the dam.
- Maximum flow: The capacity of the water flow to pass through the turbines is an essential factor.
- Characteristics of turbines and generators: The efficiency of the turbines and electrical generators used in the plant influences energy production.
- Annual energy capacity: The amount of energy that the plant can generate in a given period, generally a year, is an indicator of its capacity.
Types of hydraulic turbines
The hydraulic turbines used to convert mechanical energy into electricity are:
- Pelton turbine: Suitable for high water falls and low to moderate flows.
- Kaplan turbine: Ideal for variable flow rates and moderate heads.
- Turgo Turbine: Used in medium flow and moderate head applications.
- Francis turbine: Versatile and suitable for a variety of flows and heights.
Advantages of hydroelectric plants
The benefits of electricity generation through hydroelectric plants compared to other alternatives are:
Low economic cost
The main advantage of hydroelectric energy is the elimination of fuel costs. The cost of running a hydroelectric plant is almost immune to increases in fossil fuel costs.
Fuel is not necessary and does not need to be imported.
The overall labor cost is low, as the plants are automated and are lightly staffed during operation.
A hydroelectric power station can be established with relatively low construction costs, providing a useful source of income to offset base operating costs.
This way of generating energy does not emit greenhouse gases.
Being a renewable energy, it does not consume fossil fuels. Therefore, it does not emit greenhouse gases such as carbon dioxide, among others.
Other types of activities: Recreational activities, sports and tourism
The reservoirs located in the central area sometimes offer facilities for water sports, becoming tourist attractions in themselves.
In some countries, base-raising of fish is common.
Of the multiple uses of dams for installed irrigation, it can support relatively constant crop establishment with the reach of water.
Disadvantages of hydroelectric plants
A problem related to hydroelectric plants is the accumulation of sediment in the upper reservoir. This problem inevitably appears over time.
To avoid this, accumulated sediment must be dredged periodically.
The presence of a dam implies certain complications at the environmental level:
Dams block the transport of river solids (sand and gravel).
The water leaving the plant is free of sediment, which upsets the balance between the solid supply and erosive activity in the downstream waters. Due to reduced or no solid contribution, the phenomenon of coastal erosion exists.
Destruction of natural habitats.
Many of these environmental problems do not occur in "MINI-HYDRO" systems, which in most cases do not require the construction of dams.