Geothermal

Question 1

Describe TWO types of power plants that are commonly used to generate electricity from natural geothermal energy systems. Why is there a difference in greenhouse gas emissions?

Answer 1

• Flash steam power plant: use hot water reservoirs. As hot water is released from the pressure of the deep reservoir in a flash tank, some of it flashed to steam. Remaining water/steam goes back to source.
• Binary power plant: heat from water is used to vaporize a “working fluid” in sperate adjacent pipes. The vapour powers the turbine. No emissions as gets pumped around again.

Question 2

List the most common applications for which geothermal energy can be used directly (i.e. as opposed to ‘indirect’ electricity generation).

Answer 2

• Electricity generation: distributed power, central station power
• Heat producing: district heating, process heat, agriculture, aquaculture

Question 3

Briefly discuss whether or not conventional geothermal power production is sustainable.

Answer 3

• Natural rate of recharge of geothermal reservoirs varies from a few to 1000 thermal MW. This is the minimum rate at which geothermal systems could be used for tens of thousands of years
• However, in commercial systems extraction rate usually exceeds the natural recharge rates
• Therefore, Geothermal systems have a finite lifetime during which they will produce economic electrical power

Question 4

With the aid of a schematic diagram, describe the principles underlying research into Enhanced Geothermal Energy (also known as “Hot Rock” geothermal energy). How does it differ from conventional geothermal energy, for electricity generation?

Answer 4

• go down a lot deeper into rock and try to create artificial geothermal power plants in many more locations across US and even Europe
• drill into different type of rock and pump down water under pressure to crack rock and then push down cold water and suck up hot water
• flow rate of hot water coming out is too slow as no one has created a network of cracks.

Question 5

What are the main technical barriers to the commercial introduction of Enhanced Geothermal Energy?

Answer 5

• Societal acceptance of geothermal power by local stack holders as it effects almost all other barriers such as financial, technical and political risk
• flow rate of hot water coming out is too slow for it to be economical
• Has caused earthquakes in areas of America so unsure consumers

Question 6

What are geothermal harmful effects

Answer 6

• Brine: can salinate soil if water is not injected back into reserve after heat is extracted
• Extracting large amounts of water can cause land subsidence and lead to an increase in seismic activity
• Power plants that do not inject cooled water back into ground can release H2S and CO2