1. What Is Hydropower?

Hydropower (from hydro meaning water) is energy that comes from the force of moving water.

The fall and flow of water is part of a continuous natural cycle. The sun draws moisture up from the oceans and rivers, and the moisture then condenses into clouds in the atmosphere. The moisture falls as rain or snow, replenishing the oceans and rivers. Gravity drives the water, moving it from high ground to low ground. The force of moving water can be extremely great. Anyone who has been white water rafting knows that!

Hydropower is called a renewable energy source because it is replenished by snow and rainfall. As long as the rain falls, we won't run out of this energy source.

2. History of Hydropower

Hydropower has been used for centuries. The Greeks used water wheels to grind wheat into flour more than 2000 years ago. In the early 1800s, American and European factories used the water wheel to power machines.

The water wheel is a simple machine. The water wheel picks up flowing water in buckets located around the wheel. The weight of the water causes the wheel to turn. Water wheels convert the kinetic energy (energy pertaining to motion) of water to mechanical energy. The mechanical energy can then be used to grind grain, drive sawmills, or pump water.

In the late 19th century, the force of falling water was used to generate electricity. The first hydroelectric power plant was built at Niagara Falls in 1879. In the following decades, many more hydroelectric plants were built. At its height in the early 1940s, hydropower provided 33 percent of this country's electricity.

But by the late 1940s, the best sites for big dams had been developed. Inexpensive fossil fuel (coal, oil) plants also entered the picture. At that time, these plants could make electricity more cheaply than hydro plants. Soon they began to underprice the smaller hydroelectric plants. It wasn't until the oil shocks of the 1970s that people showed a renewed interest in hydropower.

3. Hydroelectric Power Plants

As people discovered centuries ago, the flow of water represents a huge supply of kinetic energy that can be put to work. Water wheels are useful for generating mechanical energy to grind grain or saw wood, but they are not practical for generating electricity. Water wheels are too bulky and slow.

Hydroelectric plants (or hydro plants, as they are usually called) are very different. They use mode turbine generators to produce electricity just as thermal (coal, oil, nuclear) power plants do.

How a Hydro Plant Works

A hydro plant uses the force of falling water to make electricity. A typical hydro plant is a system with three parts:

To make electricity, a dam opens. its gates to allow water from the reservoir to flow through a large tube called a penstock. At the bottom of the penstock, the fast-moving water spins the blades of a turbine. The turbine is connected to a generator to produce electricity. The electricity is then transported via huge transmission lines to a local utility company.

Head and Flow

The amount of electricity that can be generated at a hydro plant is determined by two factors: head and ,flow. Head is how far the water drops. It is the distance from the highest level of the dammed water to the point where it goes through the power-producing turbine.

Flow is how much water moves through the system. The more water moving through a system, the higher the flow. Generally, a high-head plant needs less water flow than a low-head plant to produce the same amount of electricity.

More about Dams

It's easier to build a hydro, plant where there is a natural waterfall. That's why the first hydro plant was built at Niagara Falls. Dams, which are artificial waterfalls, are the next best way.

Dams are built on rivers where the terrain will produce an artificial lake or reservoir above the dam. Today there are about 80,000 dams in the United States, but only three percent have power-generating hydro plants. Most dams are built for flood control and irrigation, not electric power generation.

A dam serves two purposes at a hydro plant. First, a dam increases the head or height of a waterfall. Second, it controls the flow of water. Dams release water when it is needed for electricity production. (Special gates called "spillway gates" release excess water from the reservoir during heavy rainfalls.)

Storing Energy

One of the biggest advantages of a hydro plant is its ability to store energy. The water in a reservoir is, after all, stored energy.

Water can be stored in a reservoir and released when needed for electricity production. During the day when people use more electricity, water can flow through a plant to generate electricity. Then, during the night when people use less electricity, water can be held back in the reservoir. Storage also makes it possible to save water from winter rains for summer generating power, or to save water from wet years for generating electricity during dry years.

Pumped Storage Systems

Some hydro plants also use pumped storage systems. A pumped storage system operates much as a public fountain does. The same water is used again and again.

At a pumped storage hydro plant, flowing, water is used to make electricity and then stored in a lower pool. Depending on how much electricity is needed, the water may or may not be pumped back to an upper pool. Pumping water to the upper pool requires electricity so hydro plants usually use pumped storage systems when there is a big demand for electricity.

Pumped hydro is the most reliable energy storage system used by American electric utilities. Coal and nuclear power plants have no energy storage systems. They must turn to expensive gas and oil-fired generators when people demand lots of electricity. They also have no way to store any extra energy they might produce during normal generating periods.

4. Hydropower Production

How much electricity do we get from hydropower today? Quite a bit. Depending on whether the year has been wet or dry, hydro plants produce from eight to 10 percent of the electricity produced in this country (almost 8.5 percent in 1994), far more than any other renewable energy source. In Oregon and Washington, hydropower supplies over 85 percent of the electricity each year.

Currently, there are about 75 million kilowatts of hydroelectric generating capacity in the United States. That's equivalent to the generating capacity of 70 large nuclear power plants. The biggest hydro plant in the country is located at the Grand Coulee dam on the Columbia River in northern Washington.

The United States also gets some hydropower electricity from Canada. Some New England utility companies buy this imported electricity.

What does the future look like for hydropower? The best sites for hydropower dams have already been developed so the development of big hydro plants is unlikely. But existing plants could be enlarged to provide additional generating capacity. Plus, many flood-control dams not equipped for electricity production could be outfitted with generating equipment. The Federal Energy Regulatory Commission estimates 60 thousand megawatts of additional generating capacity could be developed in the United States.

Good source of baseload power

Demand for electricity is not steady; it goes up and down. People use more electricity during the day when they are awake and using electrical appliances, and less at night when they are asleep. People also use more electricity when the weather is very cold or very hot.

Electric utility companies have to produce electricity to meet these changing demands. Baseload power is the electricity that utilities have to generate all the time. For that reason, baseload power should be cheap and reliable. Hydropower meets both these requirements. Generating, electricity from flowing water is the cheapest way to generate electricity in the United States, and the fuel supply-flowing water is always available, especially at plants with pumped storage systems.

Hydro plants are more energy efficient than thermal power plants too. That means they waste less energy to produce electricity. In thermal power plants, a lot of energy is lost as heat.

Hydro plants also run 85 percent of the time, about 50 percent more than thermal plants.

5. Economics of Hydropower and the Environment

Hydropower is the cheapest way to generate electricity today. No other energy source, renewable or nonrenewable, can match it. In 1994 it cost less than one cent per kWh (kilowatt-hour) to produce electricity at a typical hydro plant. In comparison, it costs coal plants about four cents per kWh and nuclear plants two cents per kWh to generate electricity.

Producing electricity from hydropower is cheap because, once a dam has been built and the equipment installed, the energy source-flowing water-is free.

Another reason hydro plants produce power cheaply is due to their sturdy structures and simple equipment. Hydro plants are dependable and long-lived, and their maintenance costs are low compared to coal or nuclear plants.

There is one thing that may increase hydropower's costs in the future. The procedure for licensing a dam has become a lengthy and expensive process. Many environmental impact studies must be undertaken. And some times as many as 13 state and federal agencies must be consulted. It takes anywhere from five to seven years just to get a license to build a dam.

Hydropower and the Environment

Hydropower does present a few environmental problems. Damming rivers may destroy or disrupt wildlife and natural resources. Fish, for one, may no longer be able to swim upstream.

Hydro plant operations may also affect water quality by churning up dissolved metals that may have been deposited by industry long ago. Hydro plant operations may increase silting, change water temperatures, and lower the levels of dissolved oxygen. To some degree, these problems can be managed by constructing fish ladders, dredging silt, and carefully regulating plant operations.

On the plus side, hydropower's fuel supply (flowing water) is clean and is renewed yearly by snow and rainfall. Unlike fossil fuel plants, hydro plants do not emit any pollutants into the air because they bum no fuel.

Hydropower is also the only energy source that offers a whole range of added benefits. Dams control flood waters, and reservoirs provide lakes for boating, fishing, and swimming.