Where Is Geothermal Renewable?

What is Geothermal Energy?

Geothermal energy refers to thermal energy generated and stored within the Earth. The word “geothermal” comes from the Greek words geo (earth) and therme (heat). Geothermal energy originates from the heat retained within the Earth since its formation billions of years ago, as well as from the ongoing decay of radioactive materials.

This energy can be tapped and utilized for electricity generation and direct heating and cooling purposes. Geothermal power plants use steam or high-temperature fluids from geothermal reservoirs to drive turbine generators and produce electricity. Geothermal heating and cooling systems use lower temperature ground or water as an exchange medium to control building temperatures.

How Geothermal Energy Works

Geothermal energy harnesses the natural heat from deep within the Earth to generate renewable power. The technology relies on accessing reservoirs of hot water or steam located in permeable rock or fractures beneath the Earth’s surface. Wells are drilled into these geothermal reservoirs to tap the heated fluid.

Once a geothermal reservoir is accessed by drilling, a circulation system is installed. Pipes are used to carry the hot fluid up through the well to a power plant or heating system. The heated water or steam then turns turbines at the power plant which activate generators and produce electricity. For direct heating applications, the hot fluid is piped directly into buildings or facilities to provide heat.

After the geothermal fluid passes through the system, it is returned to the reservoir through separate injection wells, completing the loop. The fluid is constantly replenished naturally by rain and snow melt filtering down into the hot rock layers beneath the surface. This cycle allows geothermal power plants to operate continuously as long as the reservoir is effectively managed.

Types of Geothermal Energy Systems

There are two main types of geothermal energy systems used to generate electricity – hydrothermal systems and enhanced geothermal systems (EGS).

Hydrothermal systems utilize naturally occurring reservoirs of steam or hot water that exist below the Earth’s surface to generate power. Hot water and steam are accessed by drilling wells into the geothermal reservoir. The steam rotates a turbine which activates a generator, thereby producing electricity. Any leftover water or condensed steam is injected back into the reservoir to recharge it. Hydrothermal systems are capable of providing consistent, baseload power.

Enhanced geothermal systems (EGS) can be engineered in areas that lack the natural geothermal reservoirs required for hydrothermal power plants. With EGS, fluid is injected into hot rocks found deep below the surface through strategically drilled wells, creating an artificial geothermal reservoir. The fluid absorbs heat from the rocks as it travels through fractures in the reservoir. It returns to the surface as hot water and steam, which is used to power a generator.

Geographic Locations for Geothermal

Geothermal energy requires specific geological conditions to be harnessed effectively. The Earth’s crust contains hot molten rock and trapped steam or water that can be tapped for geothermal power. This type of geothermal energy is mainly found along plate boundaries and seismically active areas where the Earth’s crust is thinner. This allows the magma and heated underground reservoirs to be closer to the surface.

The world’s most active geothermal resources are usually found along major plate boundaries like the Pacific Ring of Fire, which runs along the west coasts of North and South America. Countries like the United States, Mexico, El Salvador, and Costa Rica in the Americas have substantial geothermal capabilities thanks to their location on this plate boundary. Other geologically active areas like Iceland, New Zealand, Indonesia, and The Philippines also have excellent geothermal potential for energy usage.

Areas far away from tectonic plate boundaries generally do not possess the ideal underground heat reservoirs at shallow enough depths to make geothermal energy extraction feasible. The geologic activity that builds up heat underneath the Earth’s crust over time is what provides the temperature gradients needed for geothermal systems. This limits extensive geothermal development to mountainous regions, volcanically active zones, geyser fields, and similar hot spots situated near moving tectonic plates.

Major Geothermal Sites Around the World

Some of the major geothermal sites utilized for energy production around the world include:

The Geysers, California: The Geysers is located in the Mayacamas Mountains north of San Francisco and is the largest geothermal field in the world. It has been in operation since the 1960s and provides around one-fifth of the average electricity demand for Northern California.

Wairakei, New Zealand: Wairakei was the first wet steam field to be commercially developed in the world. Located in the Taupo Volcanic Zone, it supplies electricity to the North Island grid and provides hot water to an industrial park. It generates around 25% of New Zealand’s geothermal electricity.

Kenya’s Rift Valley: Kenya generates a substantial amount of its electricity from geothermal energy due to the geologically active Rift Valley that runs through the country. Major geothermal plants are located at Olkaria and Eburru in the valley. Kenya ranks 8th globally in geothermal electricity generation.

Iceland: Iceland is a leader in geothermal energy, with around 25% of its primary energy usage derived from geothermal sources. Major geothermal fields include the Reykjanes system near Reykjavik and the Krafla system in the northeast of the country. Iceland generates over 25% of its electricity from geothermal power.

Japan: Japan generates more geothermal power than any other country in the world. Major geothermal fields are found at Hatchobaru and Otake in the southern island of Kyushu. Japan has over 500 geothermal plants in 18 locations and derives 16% of its electricity from geothermal sources.

Environmental Advantages of Geothermal

Geothermal energy has significant environmental advantages over conventional fossil fuel power plants.

Geothermal plants emit very low levels of greenhouse gases like carbon dioxide. The emissions from geothermal plants are estimated to be just 5-10% of the emissions from a natural gas power plant. This makes geothermal an attractive renewable energy source for reducing carbon emissions and mitigating climate change.

Geothermal plants also have a small physical footprint compared to other renewable energy sources like solar or wind farms. While a large solar farm can cover many square miles of land, a geothermal power plant uses relatively compact wells and power generation facilities. This reduces overall land usage and habitat disruption.

Finally, geothermal plants use minimal water for power generation. The geothermal fluid is pumped in a closed loop system so water consumption is low. This gives geothermal an advantage over other thermal power plants that require large volumes of water for cooling or steam generation.

Limitations of Geothermal

While geothermal energy has several advantages, it also comes with some limitations that restrict its wider adoption and feasibility in all locations. Here are some of the main challenges and restrictions facing geothermal energy production:

High upfront costs for drilling and exploration – Developing geothermal power plants requires significant upfront investments for exploration, drilling and well construction to reach the deep hot reservoirs needed. This can cost several million dollars before a single kilowatt of energy is even produced, posing financial risks and uncertainty.

Limited to specific geographic locations – Geothermal energy sources are location dependent, as they rely on heat naturally available in certain underground rock formations and aquifers. This restricts geothermal plants to tectonically active areas like Western North America or Pacific Rim volcanic belts.

Potential for localized seismic activity – The pumping and reinjection of geothermal fluids and wastewater can potentially trigger small, localized earthquakes near the power plant if not managed carefully. While rare, this remains a concern and risk factor for geothermal.

Global Geothermal Energy Production

Indonesia, the Philippines, and Turkey currently lead global geothermal capacity. Indonesia has the highest geothermal generation worldwide, with over 2,000 megawatts of installed capacity providing about 5% of the country’s electricity. The Philippines follows closely behind with 1,900 megawatts of geothermal capacity. Turkey has seen rapid growth in geothermal in recent years, reaching 1,500 megawatts of installed capacity in 2017. While the United States has the largest geothermal energy production overall, it lags behind the growth rate seen in some other countries. Total U.S. geothermal capacity is around 2,500 megawatts, meeting about 0.4% of national electricity demand. Compared to Indonesia and the Philippines where geothermal accounts for a significant portion of the energy mix, the U.S. has ample room to further develop its abundant geothermal resources.

Future Outlook for Geothermal

The future looks bright for continued growth and expansion of geothermal energy globally. There are several key factors driving increased adoption of geothermal technology:

Improving technologies like enhanced geothermal systems (EGS) are greatly expanding the potential to utilize geothermal energy in areas without naturally occurring hydrothermal resources. EGS works by injecting fluid into hot dry rock to create an artificial geothermal reservoir.

The costs of geothermal energy have been declining, making it more competitive with conventional power generation. Drilling accounts for a large share of geothermal project costs, but those costs have fallen substantially in recent years.

Geothermal power generation and direct heating/cooling applications are expected to see continued growth worldwide. The global geothermal power market is projected to reach over 18 GW by 2026. Geothermal heat pumps are also seeing rapid global growth as an efficient heating/cooling solution.

With technology improvements, declining costs, and supportive policies, geothermal energy is poised to provide a growing share of the world’s energy needs in a sustainable manner.

Conclusions

To summarize, geothermal energy refers to the heat energy that can be generated from the Earth’s core and harnessed for electricity production and direct heating applications. It is considered a renewable energy source as the heat emanating from the Earth’s interior is constantly replenished. Geothermal energy is produced by drilling wells into areas with hot underground aquifers or rock and using the steam or hot water to drive turbines and generate electricity. There are three main types of geothermal systems – hydrothermal, enhanced geothermal, and geothermal heat pumps.

When developed responsibly, geothermal energy offers many environmental benefits compared to fossil fuels, like low emissions and a small land footprint per kWh generated. However, there are limitations, such as geographical availability and potential seismic impacts if not managed properly. Globally, geothermal energy generates around 90 TWh per year, supplying about 0.3% of total electricity demand. Significant potential remains largely untapped in countries with suitable geological conditions like Iceland, New Zealand, Indonesia, the Philippines, and parts of North and South America.

With continued technology improvements and growing interest in renewable energy, the future outlook for geothermal seems positive. Expanding geothermal capabilities could play an integral role in the global transition to cleaner energy sources. Overall, geothermal power represents a sustainable, renewable energy option that can help reduce reliance on fossil fuels – when developed and managed conscientiously.