A hydroelectric power station converts the kinetic, or movement, energy in flowing or falling water into electrical energy that can be used in homes and businesses. Hydroelectric energy can be generated on a small scale with a ‘run-of-river’ installation, which uses naturally flowing river water to turn one or more turbines, or on a large scale with a hydroelectric dam.
A hydroelectric dam straddles a river, blocking the water’s progress downstream. Water collects on the upstream side of the dam, forming an artificial lake known as a reservoir. Damming the river converts the water’s kinetic energy into potential energy: the reservoir becomes a sort of battery, storing energy that can be released a little at a time. As well as being a source of energy, some reservoirs are used as boating lakes or drinking water supplies.
The reservoir’s potential energy is converted back into kinetic energy by opening underwater gates, or intakes, in the dam. When an intake opens, the immense weight of the reservoir forces water through a channel called the penstock towards a turbine. The water rushes past the turbine, hitting its blades and causing it to spin, converting some of the water’s kinetic energy into mechanical energy. The water then finally flows out of the dam and continues its journey downstream. A shaft connects the turbine to a generator, so when the turbine spins, so does the generator. The generator uses an electromagnetic field to convert this mechanical energy into electrical energy.
As long as there is plenty of water in the reservoir, a hydroelectric dam can respond quickly to changes in demand for electricity. Opening and closing the intakes directly controls the amount of water flowing through the penstock, which determines the amount of electricity the dam is generating.
The turbine and generator are located in the dam’s power house, which also houses a transformer. The transformer converts the electrical energy from the generator to a high voltage. The national grid uses high voltages to transmit electricity efficiently through the power lines to the homes and businesses that need it. Here, other transformers reduce the voltage back down to a usable level.
Water Generates Electricity
So, how exactly is electricity generated from water? This usually occurs through a hydroelectric dam that is built along a flowing waterway. Think of the water at Niagara. The water flowing over the falls is travelling faster than the water approaching the falls. As water travels downhill, it picks up speed and power.
To take advantage of this, dams are constructed along the waterway where there is a large elevation drop. This is exactly why you wouldn’t expect to find dams in flat places like Florida, but would expect to find them in the hilly, mountainous regions of the Southwest U.S.
Like going down a slide at the playground, water is pulled downhill by gravity and picks up speed as it goes (you’re moving faster at the bottom of the slide than at the top, right?). Inside the dam are turbines that get spun by the moving water – similar to how a pinwheel gets spun by the wind blowing by.
The spinning turbine shafts are connected to a generator, and the spinning of the turbines themselves creates electricity inside the generator. The generator is connected to power lines, which transmit the electricity to homes and buildings just like they do with coal-fired and natural gas power plants.
Just like wind blowing past the pinwheel is not affected by the pinwheel itself, water flowing by the turbines is not affected as it passes through the dam. It flows on downstream as if nothing has happened. You can see why this is such a valuable and widely used energy resource all around the world! However, with every source of energy, there are pros and cons. Let’s look at the benefits and drawbacks that come with harnessing the amazing power of moving water.
Advantages of Hydroelectric Energy
1. Renewable Hydroelectric energy is renewable. This means that we cannot use up. However, there’s only a limited number of suitable reservoirs where hydroelectric power plants can be built and even less places where such projects are profitable.
2. Green Generating electricity with hydro energy is not polluting itself. The only pollution occurs during the construction of these massive power plants.
Hydroelectricity is very reliable energy. There are very little fluctuations in terms of the electric power that is being by the plants, unless a different output is desired. Countries that have large resources of hydropower use hydroelectricity as a base load energy source. As long as there is water in the magazines electricity can be generated.
As previously mentioned, adjusting water flow and output of electricity is easy. At times where power consumption is low, water flow is reduced and the magazine levels are being conserved for times when the power consumption is high.
Compared to among others fossil fuels and nuclear energy, hydroelectricity is much safer. There is no fuel involved (other than water that is).
Disadvantages of Hydroelectric Energy
1. Environmental Consequences
The environmental consequences of hydropower are related to interventions in nature due to damming of water, changed water flow and the construction of roads and power lines.
Hydroelectric power plants may affect fish is a complex interaction between numerous physical and biological factors. More user interests related to exploitation of fish species, which helps that this is a field that many have strong opinions on.
Fish habitats are shaped by physical factors such as water level, water velocity and shelter opportunities and access to food. Draining would be completely devastating to the fish. Beyond this, the amount of water may have different effects on the fish in a river, depending on the type and stage of the life cycle. Not all unregulated river systems are optimal in terms of fish production, because of large fluctuations in flow.
Building power plants in general is expensive. Hydroelectric power plants are not an exception to this. On the other hand, these plants do not require a lot of workers and maintenance costs are usually low.
Electricity generation and energy prices are directly related to how much water is available. A drought could potentially affect this.
4. Limited Reservoirs
We have already started using up suitable reservoirs for hydroelectric power plants. There are currently about 30 major power plants that are expected to generate more than 2.000 MW under construction. Only one of these projects was started in the last two years.
Check out our article on Tidal Energy here.