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?
- 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.
List the most common applications for which geothermal energy can be used directly (i.e. as opposed to ‘indirect’ electricity generation).
- Electricity generation: distributed power, central station power
- Heat producing: district heating, process heat, agriculture, aquaculture
Briefly discuss whether or not conventional geothermal power production is sustainable.
- 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
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?
- 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.
What are the main technical barriers to the commercial introduction of Enhanced Geothermal Energy?
- 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
What are geothermal harmful effects
- 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
