Geothermal

Geothermal electrical power generation schematic from Canadian Energy Commission

Geothermal has been used by some countries for the warming of buildings and electricity generation, and has been promoted as a key alternative energy technology that can help mitigate climate change impacts. 

The US Department of Energy (DOE) lists several benefits of geothermal power, including the following:

• 24-hour continuous production of geothermal electrical power regardless of weather conditions.
• Geothermal has a small footprint that use only 1,046 GWh/km2, as compared with coal (9433 GWh/km2). wind (3458 GWh/km2) and solar (8384 GWh/km2)
• Life cycle greenhouse gas emissions are 4 times less than solar, and 6-20 times lower than natural gas. 

Iceland leads the world in use of geothermal energy. 54% of the country’s total energy use is supplied by direct heat and electrical energy from geothermal sources, and more than 89% of the population have geothermal heating in their homes. (Lund, 2010)

Most geothermal heat pumps (GHPs) operate within 6 metres of the Earth’s surface that maintains a stable temperature of 10 to 16 °C (EncyclopaediaBritannica, 2013). The efficiency of a geothermal technology is typically expressed by its Coefficient of Performance (CoP), which measures the thermal energy generated as a ratio of the the electrical power consumed. CoPs typically range around 2-6. (Tong et al, 2010, Ozcan and Ozgener, 2011). GHPs could present an average savings in GHG emissions of above 50% in comparison to conventional heating systems. (Saner, 2010)

Heat from depths of around 2-6km has also been extracted for generating electricity, using steam with temperatures ranging from 120 to 370 °C. (Zaigham and Nayyar, 2010). In terms of costing, electrical energy generation costs 2–10 US¢/kWh for geothermal and hydro, 5–13 US¢/kWh for wind, 5–15 US¢/kWh for biomass and 25–125 US¢/kWh for solar photovoltaic (Fridleifsson, 2001).

Geothermal fluids may contain traces of chemicals such as hydrogen sulfide, ammonia and mercury which are largely reinjected into drillholes and not released into the environment. Thus far, national and legally binding regulations for geothermal technology only exist in few countries such as Denmark or Sweden. Haehnlein (2010) suggests that to avoid detrimental environmental impacts, it is necessary to define groundwater temperature limits for heating and cooling and minimum distances between such geothermal systems.  

Geothermal electricity generation has been made available commercially since 1913 but so far the focus has been largely on hydropower (Fridleifsson, 2001). For developing countries like Kenya, Ogola (2012) argues that the use of geothermal energy will improve food security, mitigate the impact of climate change, and provide employment opportunities. 

With a small footprint and limited greenhouse gas emissions, the arguments so far gives support to the potential of geothermal energy as a cost-effective and viable alternative energy source. There is however a need to strengthen national legislation to ensure minimal environmental impact arising from geothermal energy use.