What process would provide the energy used to generate electricity at a power plant?

Geothermal power plants use steam to produce electricity. The steam comes from reservoirs of hot water found a few miles or more below the earth's surface.

The steam rotates a turbine that activates a generator, which produces electricity. There are three types of geothermal power plants: dry steam, flash steam, and binary cycle.

Dry Steam

Dry steam power plants draw from underground resources of steam. The steam is piped directly from underground wells to the power plant where it is directed into a turbine/generator unit. There are only two known underground resources of steam in the United States:

1. The Geysers in northern California
2. Yellowstone National Park in Wyoming, where there's a well-known geyser called Old Faithful.

Since Yellowstone is protected from development, the only dry steam plants in the country are at The Geysers.

Flash Steam

Flash steam power plants are the most common and use geothermal reservoirs of water with temperatures greater than 360°F (182°C). This very hot water flows up through wells in the ground under its own pressure. As it flows upward, the pressure decreases and some of the hot water boils into steam. The steam is then separated from the water and used to power a turbine/generator. Any leftover water and condensed steam are injected back into the reservoir, making this a sustainable resource.

Binary Steam

Binary cycle power plants operate on water at lower temperatures of about 225-360°F (107-182°C). Binary cycle plants use the heat from the hot water to boil a working fluid, usually an organic compound with a low boiling point. The working fluid is vaporized in a heat exchanger and used to turn a turbine. The water is then injected back into the ground to be reheated. The water and the working fluid are kept separated during the whole process, so there are little or no air emissions.

Currently, two types of geothermal resources can be used in binary cycle power plants to generate electricity: enhanced geothermal systems (EGS) and low-temperature or co-produced resources.

Enhanced Geothermal Systems

EGS provide geothermal power by tapping into the Earth's deep geothermal resources that are otherwise not economical due to lack of water, location, or rock type. The U.S. Geological Survey estimates that potentially 500,000 megawatts of EGS resource is available in the western U.S. or about half of the current installed electric power generating capacity in the United States.

Low-Temperature and Co-Produced Resources

Low-temperature and co-produced geothermal resources are typically found at temperatures of 300F (150C) or less. Some low-temperature resources can be harnessed to generate electricity using binary cycle technology. Co-produced hot water is a byproduct of oil and gas wells in the United States. This hot water is being examined for its potential to produce electricity, helping to lower greenhouse gas emissions and extend the life of oil and gas fields.

Additional Resources

For more information about geothermal technologies, visit the following resources:

NREL's Policymakers' Guidebook for Geothermal Electricity Generation

NREL Geothermal Research

Low Temperature and Coproduced Resources
U.S. Department of Energy  

Enhanced Geothermal Systems
U.S. Department of Energy

How do we generate electricity using gas?

There are three types of gas power stations: 

1. OCGT - Open cycle fast turbines, these are generally smaller and use gas, which when burnt produces hot air that drives the turbine and produces electricity. There are hundreds of these across the country. OCGTs are cheap to build and good for short runs in producing energy. 

1. CCGT - combined cycle gas turbines, these are primarily the same as OCGTs at the beginning, except the hot air that exits the engine is then used to heat water, this creates steam which drives another turbine producing more energy, making them much more efficient but are more costly to build. 

1. CHP - combined heat and power, these again are like OCGTs at the beginning. However, the heat from the engine is then used for other purposes, such as local district heating or larger stations using the steam to power chemical services such as oil refineries. CHPs are efficient but only when the heat can be used effectively.  

The future of gas 

Gas is a fossil fuel, meaning that we find it in pockets under the earth’s surface. It is a finite, non-renewable source of energy. The process of burning gas creates greenhouse gases which contribute to global warming. As part of GB’s ambition to reach net zero by 2050, we need to step away from using gas power.  

However, gas power remains an important part of today’s generation mix to make sure we have a secure supply of electricity across Great Britain. Gas power stations help us to manage the unpredictability of renewable energy sources by creating inertia - something which is vital as we integrate more renewables onto the system.  

Gas power stations in Great Britain 

There are over 30 gas power stations in Great Britain but the power that we require from them has reduced over recent years as renewable energy becomes more readily available. 

However, with coal power plants in Britain set to close by 2025, we’ll look to gas power stations in the short term to provide the inertia we need on our system.  

The ESO is currently running pathfinder projects to find new ways of procuring inertia that don’t rely on fossil fuels so we can become an even greener system operator.  

Hydroelectric energy, also called hydroelectric power or hydroelectricity, is a form of energy that harnesses the power of water in motion—such as water flowing over a waterfall—to generate electricity. People have used this force for millennia. Over two thousand years ago, people in Greece used flowing water to turn the wheel of their mill to ground wheat into flour.

How Does Hydroelectric Energy Work?

Most hydroelectric power plants have a reservoir of water, a gate or valve to control how much water flows out of the reservoir, and an outlet or place where the water ends up after flowing downward. Water gains potential energy just before it spills over the top of a dam or flows down a hill. The potential energy is converted into kinetic energy as water flows downhill. The water can be used to turn the blades of a turbine to generate electricity, which is distributed to the power plant’s customers.

Types of Hydroelectric Energy Plants

There are three different types of hydroelectric energy plants, the most common being an impoundment facility. In an impoundment facility, a dam is used to control the flow of water stored in a pool or reservoir. When more energy is needed, water is released from the dam. Once water is released, gravity takes over and the water flows downward through a turbine. As the blades of the turbine spin, they power a generator.

Another type of hydroelectric energy plant is a diversion facility. This type of plant is unique because it does not use a dam. Instead, it uses a series of canals to channel flowing river water toward the generator-powering turbines.

The third type of plant is called a pumped-storage facility. This plant collects the energy produced from solar, wind, and nuclear power and stores it for future use. The plant stores energy by pumping water uphill from a pool at a lower elevation to a reservoir located at a higher elevation. When there is high demand for electricity, water located in the higher pool is released. As this water flows back down to the lower reservoir, it turns a turbine to generate more electricity.

How Widely Is Hydroelectric Energy Used Around the World?

Hydroelectric energy is the most commonly-used renewable source of electricity. China is the largest producer of hydroelectricity. Other top producers of hydropower around the world include the United States, Brazil, Canada, India, and Russia. Approximately 71 percent of all of the renewable electricity generated on Earth is from hydropower.

What Is the Largest Hydroelectric Power Plant in the World?

The Three Gorges Dam in China, which holds back the Yangtze River, is the largest hydroelectric dam in the world, in terms of electricity production. The dam is 2,335 meters (7,660 feet) long and 185 meters (607 feet) tall, and has enough generators to produce 22,500 megawatts of power.