lecture 13: geothermal energy

the first geothermal power

1904 Italy

Lardello, Italy - world’s 1st commercial geothermal production plant

Geothermal energy 2024

• 16.8GW energy

• 35 countries have energy plants - mainly pacific ring of fire

• energy used in 80 countries

Heat production

primordial heat

• from formation and gravitational compression of Earth

• heat from core

• 20%

ongoing decay of long lived radioactive elements e.g. uranium

geothermal gradient

rate at which temperature of Earth’s interior increases with increasing depth

35C per km

Low temperature gradient

need very deep boreholes to reach high temperature rocks

high temperature gradient

needed to get heat from reasonable

high enthalpy

state where a substance possesses a high amount of heat or energy content

How much electricity was generated globally in 2024?

17GW (infancy stage)

What is the capacity factor of geothermal energy?

high capacity factor

Iceland:

High temperature field

200-350C

• Volcanism + close to plate boundaries 

• electricity production with conventional turbines 

Iceland:

Low temperature field

150-100C

• sedimentary basins, especially in fracture zone 

• space heating 

Full energy from geothermal resources

about 40 countries could get all their electricity from indigenous geothermal power

→ nearly all developing countries

dry steam system

hot dry steam generated in hot aquifers and erupting from geysers with temperatures greater than 235C piped directly to steam turbines

single cycle system

water pumped down into rocks → heats water → creating steam → moves turbines

Binary cycle power plants

pumping circuit heat to heat exchanger → fluid heating and moving turbine

more efficient use of lower temperature water, 100-175C

enhanced geothermal system ‘hot dry rocks'

reservoir with fracture network is created or enhanced provides well-connected fluid pathways between injection and production

Geothermal energy in Ireland

low enthalpy

Mallow - 19C

Louisa Bridge, Leixlip - 17.5%

for warm springs

Low enthalpy geothermal energy:

near surface ground

absorbs heat from Sun and stores it

stored heat can be taken from ground and used to heat buildings

Low enthalpy geothermal energy:

geothermal heat pumps

absorbs heat from ground and use it to warm the air in building

in summer process reversed - taking heat from building and transferring it back into ground

Benefits of geothermal heat pumps

• can be used almost everywhere worldwide

• energy and cost efficient

• no emissions released

geothermal energy for heating

less than 1% of Irish households are heated by geothermal enegryW

What is the estimated installed capacity for Ireland

15MW