Geothermal Energy Practice Questions

Correct answer: Gravitational pressure and radioactive decay of isotopes

Geothermal energy originates from the original formation of the planet and the continuous radioactive decay of isotopes like Uranium-238 and Thorium-232. This heat is conducted through the Earth's layers toward the surface.

Correct answer: Flash Steam Plant

Flash steam plants are the most common type. They take water at temperatures over 182°C from the ground and spray it into a tank at much lower pressure, causing it to rapidly vaporize into steam to drive a turbine.

Correct answer: It is a low-boiling-point secondary fluid that vaporizes to turn the turbine

Binary plants use a heat exchanger to transfer heat from moderately warm geothermal water to a fluid like isobutane. Because this fluid boils at a lower temperature than water, it allows energy extraction from lower-temperature reservoirs.

Correct answer: To return cooled geothermal fluid to the underground reservoir

Injection wells are critical for sustainability and pressure maintenance. By returning the cooled water to the reservoir, the plant ensures the resource is not depleted and helps prevent land subsidence.

Correct answer: Tectonic plate boundaries and volcanic 'hotspots'

Most high-temperature geothermal resources are located along the 'Ring of Fire' or mid-ocean ridges. In these areas, magma is closer to the surface, heating the surrounding rock and groundwater.

Correct answer: A method of fracturing hot dry rock to create a human-made reservoir

EGS technology is used where hot rock exists but lacks natural water or permeability. By injecting high-pressure water to create fractures (hydraulic stimulation), engineers can create a functional geothermal reservoir where one didn't naturally exist.

Correct answer: District heating and greenhouse warming

Direct use refers to using the heat itself without converting it to electricity. Common examples include heating homes, warming commercial greenhouses, and providing heat for industrial processes or fish farms.

Correct answer: They use the steady shallow ground temperature to heat and cool buildings

Geothermal heat pumps do not generate electricity from high-heat reservoirs. Instead, they take advantage of the fact that the upper 10 feet of Earth remains at a constant temperature (roughly 10-16°C) to provide efficient space heating and cooling.

Correct answer: Hydrogen sulfide

While geothermal is very clean, underground reservoirs often contain dissolved gases like hydrogen sulfide (H2S). Modern plants use 'scrubbers' to remove this gas, which has a distinct rotten-egg odour, before it can be released.

Correct answer: Vapor-dominated dry steam reservoir

Vapor-dominated reservoirs produce only steam with no liquid water. These are rare but highly efficient for power generation because the steam can be piped directly into a turbine without needing 'flashing' tanks.

Correct answer: 25-30°C per kilometer

In most parts of the world, the temperature rises by about 25 to 30 degrees Celsius for every kilometer of depth. Geothermal plants look for 'anomalies' where this gradient is significantly higher.

Correct answer: Iceland

Iceland sits on a volcanic hotspot and a mid-ocean ridge, providing it with massive geothermal resources. It uses geothermal energy to heat roughly 90% of its homes and provide a large portion of its electricity.

Correct answer: It is site-specific and requires the right geology

Unlike solar panels which can be placed almost anywhere, geothermal plants require access to hot reservoirs. This limits large-scale geothermal development to specific regions with favorable tectonic activity.

Correct answer: The ratio of actual output to maximum possible output

Capacity factor compares the electricity a plant actually produces with the maximum it could produce running continuously. Geothermal often exceeds 90% because it is not intermittent and can run 24 hours a day, 365 days a year.

Correct answer: A vent in the Earth's crust that emits steam and gases

Fumaroles are vents where steam and volcanic gases escape under pressure. They are often used by geologists as indicators of a high-temperature geothermal system located beneath the surface.

Correct answer: A zone of frequent earthquakes and volcanoes rimming the Pacific

The Ring of Fire contains the vast majority of the world's active volcanoes and geothermal potential. Countries like Indonesia, the Philippines, and the USA tap into this belt for geothermal production.

Correct answer: Organic fluids such as isobutane or pentane

Organic fluids are used because they have boiling points significantly lower than water. This allows the plant to generate high-pressure vapor even when the geothermal water is only 57-175°C.

Correct answer: Induced micro-earthquakes

The process of injecting high-pressure water to fracture rocks in EGS can sometimes trigger small seismic events. Monitoring and careful pressure management are required to ensure these tremors do not become disruptive.

Correct answer: Saline water rich in dissolved minerals and salts

Geothermal water often dissolves minerals from the surrounding rock, becoming a salty 'brine.' This brine must be handled carefully to prevent pipe scaling and is usually reinjected into the ground.

Correct answer: Larderello, Italy

Prince Piero Ginori Conti tested the first geothermal generator at Larderello, Italy. It successfully lit five light bulbs, proving that the Earth's internal heat could be converted into usable electricity.