Geothermal

Question 1

what is geothermal energy

Answer 1

energy using heat from the earth (e.g magmatic heat)

Question 2

where does geothermal energy come form

Answer 2

1. release of stored gravitational energy from the formation of the earth
2. radioactive decay of heat producing elements (e.g. uranium) in the mantle and crust

Question 3

what is the geothermal gradient

Answer 3

increase in temperature with depth

Question 4

what are the 3 geothermal energy extraction methods

Answer 4

volcanic source
geothermal aquifer
hot dry rock (HDR) source

Question 5

how do you extract from a VOLCANIC SOURCR

Answer 5

hot (ground)water is heaed by magma and rises into permeable rocks (with overlying impermebale rocks)
Pressure makes it SUPERHEATED
A bore hole allows water to rise up the pipe, reduction in pressure caused water to FLASH into steam
this steam drives turbines/heats water to drive turbines GENERATING ELECTRICTY
used water is sent back down to maintain pressure and avoid waste

Question 6

how do you extract from a GEOTHERMAL AQUIFER

Answer 6

geothermal aquifers in deeo sedimentary basins are interbedded with impermeable mudstones and shales
hot water is pumped to the surface, passed through a heat exchanger and used for space heating and hot water supply
the cooled water is then injected back into ground

Question 7

how do you extract from a HDR

Answer 7

granite intrusions contain highest concentration of RADIOACTIVE HEAT producing elements. (low groundwater content)
2 boreholes and explosives fracture the rock
cold water pumped down one bore hole its heated and rises up the other

Question 8

advantages of geothermal

Answer 8

cheap
less fossil fuels
susatinable (water reinjection)
no co2 emmisons
day and night/not affected by weather

Question 9

disdavtages of geothermsl

Answer 9

geographically restrictive
danger of volcanic erupttion
extracting groundwater may cause subsidence/trigger earthquakes
each geothermal well only lasts 20-30
groundwater is saline/toxic can precipitate in borehole

Question 10

example of geothermal in uK

Answer 10

eden project - cornwall/devon

redruth granite

Question 11

geothermal GRADIENT calculation

Answer 11

gg= increase in temp (C) / depth in earths crust

Question 12

geothermal GRADIENT avergae

Answer 12

25C/km

Question 13

what is the lowest viable temp for energy extraction

Answer 13

180C

Question 14

iceland geothermal energy what % of mix?

Answer 14

30%