Lecture 6 Review

The final lecture was on geothermal energy.  This form of energy has been used by humanity of over 10,000 years. The Roman's used heat from the earth in their spa's, and it is still effectively used in this way in Iceland currently. The heat in question comes from the earth's core, and is residual energy from the Earth's formation. The earth's crust is too thick in most places to get to a depth where the temperature is high enough. As a result the best locations are those where the tectonic plates of the Earth's crust meet, as in these seismic regions, the energy is accessible much closer, if not at, the surface.

The way in which Geothermal energy is classified is though temperature, state of water and the type of energy usage. Temperature is either low (50-200 Fahrenheit) or high (above 200 Fahrenheit). The state of water is either liquid or steam. The energy usage can be a ground source heat pump, a direct source, or commercial electricity generation.

Currently the U.S. is leading the way in the Geothermal industry, generating 2,850 MW of power. 2,500 MW of this is from California, which is the state with the greatest geothermal resources. Overall, the west of America has far more potential geothermal sites than the east. Globally, Geothermal energy is used for direct heat at a scale of 12,000 MW. Combined with electrical generation it accounts for 0.15% of the world's energy production. The U.S. potential with current technology is for 6,000 MW, however this could be increased to 20,000 MW with technological improvements.

Iceland is the model that is generally associated with geothermal energy. Geothermal and Hydro power account for 70% of Iceland's primary consumption. Due to it's cold climate, Iceland ranks first in OECD countries in the per capita consumption of primary energy. However a staggering 86% if the oil consumed there is for transportation and fishing.

There are 6 types of geothermal technolgies that we looked at.  Dry Steam was the first, and is the oldest type - an example is the Geysers in Claiforni (750MW) built in 1960.. The next was Binary Cycle Power Plant, which is very efficient, clean and reliable. The third was Flash Steam Power Plants which are the most common, used in such locations as Iceland, New Zealand and Thailand. The fourth was Hot Dry Rock, which can be used anywhere, but require a much deeper drill hole. Direct Use Applications were then examined such as Geothermal Greenhouses. The final technology that was described was Geothermal Heat Pumps of which there are currently around 1,000,000 installed in the U.S.

Overall, Geothermal energy is a very good renewable option if the location is right. It is very reliable, as it is online 95% of the time, and is a proven technology, haven been used in America for the past 40 years.It is also very environmentally friendly with very low emissions and minimal land use (1-8 acres/MW compared to 19 for coal). However it is a very localized resource, and drilling can be very expensive. It also has a poor environmental perception, and these are the factors that are preventing a more wide-scale usage currently.