Geothermal Energy Basics


The Earth contains an abundance heat that is constantly leaking to the surface. When we generate energy, we often forget that in most cases we are using heat engines. Automobiles and most power plants heat a working fluid. That heat causes molecules to vibrate faster and creates a pressure that can be used to spin a turbine, thus spinning car wheels or a coil in a magnet to generate electricity.

From geothermal resources we harness the heat directly. We can use this to heat (or cool) a building, and we can use it to make electricity. These applications are specified in units of MWthermal or MWelectric, respectively: both of which are measures of work in physics.

Geothermal Energy

To make electricity, geothermal resources require three elements:

  1. 1)Heat

  2. 2)Permeability

  3. 3)Fractures

When one of these is missing, we can enhance or engineer the system to provide the missing element. We can drill deeper for more heat. We can pump in water to add a “working” fluid that captures heat to bring to a power plant. We can create permeability by fracturing the rock.

Doing the latter two of these effectivity is part of my research.

Engineering geothermal systems for our Energy Future

These two common terms are the keys to planning for our future energy needs. They also allow us to begin to understand how conservation and efficiency of energy use are critical elements of a sustainable energy resource.

  1. Sustainable means a resource can be maintained at a specified rate of production for a specified period of time.

  2. Renewable means that a resource is replenished at a certain rate.

These terms are meaningless when not considered against a time-scale over which the resource must last, a rate of consumption, and a rate of replenishment. Both the time-scale and rates of consumption depend on choices we make and need to be considered before any discussion of energy begins. The rate of replenishment is largely an aspect of the Earth, but actually varies depending on how a resource is generated or moved to a place we can access it.

All the resources we use for energy today are renewable and sustainable, but the rates at which we can use them and still meet this criterion are radically different and often depend on location. Utilizing many sources of energy, in combination, can meet both the renewable and sustainable criterion, as well as location limitations.

What do renewable and sustainable mean?

Photo Courtesy Gillian Foulger


© Nicholas C. Davatzes

Last Updated: 2008/12