1. Energy and Earth's underground - Multiple sources and storage options Rome - 10 December 2014 Electricity from geothermal energy: risk, challenges and benefits Franco Barberi

2. The Earth internal heat is a very important energy resource Production world data from 2010 IGC: -Electricity generation from medium and high enthalpy resources (>90 °C) in 24 Countries: installed capacity 10,725 MWe, production 67,246 GWh; -Direct uses from low enthalpy resources (<90 °C; mostly space heating and cooling) in 78 Countries: 438,071 TJ/y; -An 80 % increase estimated in 2014.

3. Potential risks from geothermal electricity generation -Induced seismicity from fluid reinjection: no hazardous event recorded in the many exploited natural hydrothermal systems in the world with no over-P reinjection (only a few felt earthquakes); some damaging events in EGS caused by high-P injection needed to produce rock fracturation (e.g. Basel, 2006, M= 3.4) -Subsidence: negligible when extracted fluid is totally reinjected in the reservoir - Greenhouse gas emissions in atmosphere: CO 2 main incondensable gas, H 2 S frequently abated, CH 4

4. Important challenge Geothermal electricity generation with no gas emission and total fluid reinjection in the reservoir. Horizon 2020 project includes the task “low-carbon geothermal energy”; this should be changed into “no-carbon geothermal energy”. CO 2 emission Present CO 2 emissions from geothermal power plants: weighted average: 122 g/kWh, estimated world total in 2010: >8x10 6 t/h

5. Benefits from geothermal energy Reduction of greenhouse gas emission: electrical production from geothermal fluids results in one order of magnitude less CO 2 emission per kWh compared to burning fossil fuels (coal, petroleum, natural gas) A truly renewable resource: heat is generated by Earth’s internal processes of geological duration An economically competitive, local natural resource.