Hydropower is the energy captured from moving water. It is often used to make electricity, usually at dams. A renewable energy source, hydropower produced 6% of the United States’ total electricity and 67% of generation from renewables in 2008. Hydropower produces about 20% of the electricity used worldwide, according to the US Energy Information Administration.

How Hydropower is Formed

Nature’s water cycle is important to making hydropower work. The sun heats water on the Earth’s surface, causing it to evaporate. The water vapor condenses into clouds and then comes down as rain or snow. The precipitation collects and flows via rivers into the ocean, where it evaporates again and begins the cycle anew.

The amount of energy in water depends on its flow or fall. Swiftly flowing water and water that descends from a very high point (a waterfall) both have lots of energy.

The mechanical energy of the flowing water turns turbines to run generators that convert energy into electricity.

How a Dam Works

Most hydropower projects use a dam and a reservoir to retain water from a river. When the dam gates are opened, water flows through a pipe called a penstock and applies pressure to turbines, making them turn. Just like in other kinds of power plants, the spinning turbines power a generator to produce electricity.

Dams must have a powerful streamflow and enough vertical distance for the water to flow between the reservoir and the river below the power plant to effectively produce electricity.

Other hydropower plant projects do not require dams. Instead, the force of the river current that is diverted into canals or pipes applies pressure to the turbine blades to produce electricity.

Wave Power

If you’ve ever been to the beach and taken a dip in the ocean, you know firsthand that waves can be very powerful! Scientists want to figure out a way to harness that power to produce electricity.

The US Energy Information Administration estimates that the wave energy off the US coasts could potentially generate 7% of the country’s electricity consumption. The coasts off New Zealand, Europe and Japan are also ideal for producing wave power. The key now is to develop that potential into real results.

One way to focus wave energy is to increase waves’ power and size by directing them into a narrow channel, where they can spin turbines to create electricity. Technological advances are being made in the area of wind energy, including pumps, deep-water oscillations and more. The world’s first commercial wave farm, which opened in 2008 off the coast of Portugal, can generate enough electricity to power about 1,500 Portuguese homes.

Tidal Power

The ocean’s tides have enormous power and are caused by the moon and sun’s gravitational pull and the rotation of the Earth. That power can be used the generate electricity! One way to use tidal power for energy is by using tidal barrages, which are dams built across inlets that use gates to control water levels and flow rates. The water flows in during high tide and fills a reservoir, and as the water flows out again, it goes through a system of turbines that turn and generate electricity. Tidal fences can also be used for power. Fences differ from tidal barrages because they have vertical axis turbines mounted to a fence, and all the water that passes through is used to turn turbines. Tidal turbines are essentially the same as wind turbines, but because they are underwater and water is much more powerful than wind, they must be much sturdier than wind turbines.

History of Hydropower

People have been using hydropower for thousands of years. Greeks used water wheels to grind wheat into flour more than 2,000 years ago. And falling water has been used to create electricity for more than a century. In England, records from 1086 show that more than 5,000 waterwheel-driven mills were in use – about one for every 400 people.

2,000 years ago – The Greeks used hydropower to turn water wheels for grinding wheat into flour.

1800s – English scientists William Nicholson and Sir Anthony Carlisle discovered that applying electric current to water produced hydrogen and oxygen gases. This process was later termed “electrolysis.”

1882 – World’s first hydroelectric power plant began operation on the Fox River in Appleton, Wisconsin, US.

1886 – About 45 water-powered electric plants are operating in the United States and Canada.

1889 – Two hundred electric plants in the United States use water power for some or all generation.

1940s – Hydropower provides 40% of electrical generation. Conventional capacity tripled in United States since 1920.

Today – Hydropower currently accounts for about 20% of the planet’s electricity supply. About 150 countries have the potential to use hydropower, including many developing countries that are without electricity. But environmental concerns and cost make the construction of hydropower plants prohibitive.

Uses for Hydropower

Water has been used to power machinery for hundreds of years—water wheels have been used to grind grain into flour and pound linen to be turned into paper ever since ancient times! Today, hydropower usually refers to dams that have been built to generate electricity. Hydroelectric power accounts for about 19% of the world’s electricity, according to the US Geological Survey.

Hydroelectric energy is produced by the force of falling water. When water builds up behind a high dam, it accumulates potential energy. This is transformed into mechanical energy when the water is released and strikes the blades of a turbine. The turbine’s rotation spins electromagnets that generate a current in stationary coils of wire. Finally, the current is put through a transformer where the voltage is increased for long-distance transmission over power lines.

The power of water is harnessed to provide electricity for our homes, make machines work and more.

Demand for Hydropower

Globally, hydropower supplies nearly one-fifth of the world’s energy each year, making it the most commonly used renewable energy source. Hydroelectric power generates more electricity worldwide than solar, wind, biomass and all other renewable sources combined.

And hydropower may be gaining popularity. China’s Three Gorges Dam will be the largest power plant in the world and is expected to produce 100 billion kilowatt-hours of electricity per year. And in early 2010, the Brazilian government approved plans for a $17 billion hydroelectric dam in the Amazon rainforest.