Today I’ll be talking about the history, the current system, and future ideas for hydroelectricity. Tomorrow I’ll talk about it’s pros and cons.
Hydropower is electricity generated using the energy of moving water. Rain or melted snow, usually originating in hills and mountains, create streams and rivers that eventually run to the ocean. The energy of that moving water can be substantial, as anyone who has been whitewater rafting knows.
This energy has been proving itself for centuries. Farmers since the ancient Greeks have used water wheels to grind wheat into flour. Placed in a river, a water wheel picks up flowing water in buckets located around the wheel. The kinetic energy of the flowing river turns the wheel and is converted into mechanical energy that runs the mill.
Hydroelectric power provides almost one-fifth of the world’s electricity. China, Canada, Brazil, the United States, and Russia were the five largest producers of hydropower in 2004.
The biggest hydro plant in the United States is located at the Grand Coulee Dam on the Columbia River in northern Washington. More than 70 percent of the electricity made in Washington State is produced by hydroelectric facilities.
Hydropower is the cheapest way to generate electricity today. That’s because once a dam has been built and the equipment installed, the energy source—flowing water—is free. It’s a clean fuel source that is renewable yearly by snow and rainfall.
Hydropower is also readily available; engineers can control the flow of water through the turbines to produce electricity on demand. In addition, reservoirs may offer recreational opportunities, such as swimming and boating.
Hydropower plants consist of these major components:
- Dam – Most hydropower plants rely on a dam that holds back water, creating a large reservoir. Often, this reservoir is used as a recreational lake, such as Lake Roosevelt at the Grand Coulee Dam in Washington State.
- Intake – Gates on the dam open and gravity pulls the water through the penstock, a pipeline that leads to the turbine. Water builds up pressure as it flows through this pipe.
- Turbine – The water strikes and turns the large blades of a turbine, which is attached to a generator above it by way of a shaft. The most common type of turbine for hydropower plants is the Francis Turbine, which looks like a big disc with curved blades. A turbine can weigh as much as 172 tons and turn at a rate of 90 revolutions per minute (rpm), according to the Foundation for Water & Energy Education (FWEE).
- Generators – The heart of the hydroelectric power plant is the generator. Most hydropower plants have several of these generators. The generator, as you might have guessed, generates the electricity. The basic process of generating electricity in this manner is to rotate a series of magnets inside coils of wire. This process moves electrons, which produces electrical current.
- Transformer – The transformer inside the powerhouse takes the AC and converts it to higher-voltage current.
- Power lines – Out of every power plant come four wires: the three phases of power being produced simultaneously plus a neutral or ground common to all three.
- Outflow – Used water is carried through pipelines, called tailraces, and re-enters the river downstream.
The water in the reservoir is considered stored energy. When the gates open, the water flowing through the penstock becomes kinetic energy because it’s in motion. The amount of electricity that is generated is determined by several factors. Two of those factors are the volume of water flow and the amount of hydraulic head. The head refers to the distance between the water surface and the turbines. As the head and flow increase, so does the electricity generated. The head is usually dependent upon the amount of water in the reservoir.
There’s another type of hydropower plant, called the pumped-storage plant. In a conventional hydropower plant, the water from the reservoir flows through the plant, exits and is carried downstream. A pumped-storage plant has two reservoirs:
- Upper reservoir – Like a conventional hydropower plant, a dam creates a reservoir. The water in this reservoir flows through the hydropower plant to create electricity.
- Lower reservoir – Water exiting the hydropower plant flows into a lower reservoir rather than re-entering the river and flowing downstream.
Using a reversible turbine, the plant can pump water back to the upper reservoir. This is done in off-peak hours. Essentially, the second reservoir refills the upper reservoir. By pumping water back to the upper reservoir, the plant has more water to generate electricity during periods of peak consumption.
The problem with the large scale projects is that there aren’t many viable sites left that don’t already have power generation facilities. With no room for expansion, we are forced to look at less than optimum sites and install smaller facilities. Continued advances in technology may reduce development costs over time, however.
The environmental and aquatic impact of these smaller projects is usually minor when compared to large scale dams. These projects usually have very limited or no storage capacity, cause little or no upstream flooding, and generate power by diverting some of the water from a stream or river to the turbine and generator and releasing it back into the stream or river.
Hydroelectric power generation may also find its future in the largest body of water – the ocean. Wave and current generation technology is making rapid strides and may soon be the standard. This technology, when used properly, can have a very limited impact on the environment, and projects are not as limited to specific locations like land based projects through the use of tidal currents, ocean currents and wave power.