Geothermal Energy

Geothermal energy uses heat from within the earth to provide power. It is considered renewable
because of the constant supply of heat from the earth and is “green” because there are minimal
emissions.

Geothermal plants are developed after exploration for a suitable location. Plants need access to
aquifers that are adjacent to hot rock. A production well is drilled to access the heat and steam used to
generate electricity. Once brought to the surface, there are three methods used to produce electricity.
They are flash, dry steam, and binary. 

Geothermal plant (US Energy Information Administration)

A flash plant uses a steam separator to separate steam from water. Steam goes to turbines that power a
generator, while the water is reinjected into the ground where it becomes steam to start the cycle over.
A dry steam plant functions similarly, but there is no water and no need for a steam separator. Steam
alone turns the turbines. As it cools and condenses into water, it is reinjected back into the ground.

Binary geothermal plants use hot water from beneath the surface to boil another liquid, such as
isobutene, that has a lower boiling point than water. The vaporized fluid powers the turbines. The
water is reinjected into the ground, while the vaporized fluid goes through a condenser and a preheater
before returning to the vaporizing chamber and powering the turbines again.

How a geothermal plant works (Mechanical Technology)

A geothermal heat pump is similar to passive solar heating and cooling. Water circulates into the
ground to bring up the earth’s heat or to carry indoor heat underground to cool a building. Direct use
geothermal uses geothermal heat without use of a plant or heat pump. Hot water or steam is brought to
a plate heat exchanger for heating and cooling of a building.

Geothermal plants emit low levels of carbon dioxide and sulfides (hydrogen sulfide mainly) that occur naturally in the subsurface water and steam. Scrubbers can remove most of the hydrogen sulfide. Sulfide emissions are generally lower than fossil fuel plants (US Energy Information Administration, 2015).

This week's information comes from Geothermal Energy Association and US Energy Information Administration. Next week we'll be taking a break for the Species of the Month before returning to check out the pros and cons of nuclear energy.