Editing Energy development (section)

=== Geothermal ===
{{Main|Geothermal energy}}
[[File:NesjavellirPowerPlant edit2.jpg|thumb|Steam rising from the [[Nesjavellir Geothermal Power Station]] in [[Iceland]]]]

Geothermal energy is [[thermal energy]] generated and stored in the Earth. Thermal energy is the energy that determines the [[temperature]] of matter. The geothermal energy of the Earth's [[Crust (geology)|crust]] originates from the original formation of the planet (20%) and from [[radioactive decay]] of minerals (80%).<ref name=ucsusa>[http://www.ucsusa.org/clean_energy/our-energy-choices/renewable-energy/how-geothermal-energy-works.html How Geothermal energy works] {{webarchive|url=https://web.archive.org/web/20140925080922/http://www.ucsusa.org/clean_energy/our-energy-choices/renewable-energy/how-geothermal-energy-works.html |date=2014-09-25 }}. Ucsusa.org. Retrieved on 2013-04-24.</ref>  The [[geothermal gradient]], which is the difference in temperature between the core of the planet and its surface, drives a continuous conduction of thermal energy in the form of [[heat]] from the core to the surface. The adjective ''geothermal'' originates from the Greek roots ''γη (ge)'', meaning earth, and ''θερμος (thermos)'', meaning hot.

[[Earth's internal heat budget|Earth's internal heat]] is thermal energy generated from [[radioactive decay]] and continual heat loss from Earth's formation. Temperatures at the [[core mantle boundary|core-mantle boundary]] may reach over 4000&nbsp;°C (7,200&nbsp;°F).<ref>{{cite journal | author = Lay T., Hernlund J., Buffett B. A. | year = 2008 | title = Core–mantle boundary heat flow | journal = Nature Geoscience | volume = 1 | issue = 1| pages = 25–32 | bibcode = 2008NatGe...1...25L | doi = 10.1038/ngeo.2007.44 }}</ref> The high temperature and pressure in Earth's interior cause some rock to melt and solid [[mantle (geology)|mantle]] to behave plastically, resulting in portions of [[mantle convection|mantle convecting]] upward since it is lighter than the surrounding rock.  Rock and water is heated in the crust, sometimes up to 370&nbsp;°C (700&nbsp;°F).<ref>{{cite web|last=Nemzer|first=J|title=Geothermal heating and cooling|url=http://www.geothermal.marin.org/|url-status=dead|archive-url=https://web.archive.org/web/19980111021839/http://geothermal.marin.org/|archive-date=1998-01-11}}</ref>

From [[hot springs]], geothermal energy has been used for bathing since [[Paleolithic]] times and for [[space heating]] since ancient Roman times, but it is now better known for [[electricity generation]]. Worldwide, 11,400 [[megawatts]] (MW) of geothermal power is online in 24 countries in 2012.<ref>{{cite web |url=http://www.bp.com/en/global/corporate/about-bp/statistical-review-of-world-energy-2013/review-by-energy-type/renewable-energy/geothermal-capacity.html |title=Geothermal capacity &#124; About BP &#124; BP Global |publisher=Bp.com |access-date=2013-10-05 |url-status=live |archive-url=https://web.archive.org/web/20131006185306/http://www.bp.com/en/global/corporate/about-bp/statistical-review-of-world-energy-2013/review-by-energy-type/renewable-energy/geothermal-capacity.html |archive-date=2013-10-06 }}</ref>  An additional 28 gigawatts of direct [[geothermal heating]] capacity is installed for district heating, space heating, spas, industrial processes, desalination and agricultural applications in 2010.<ref name="IPCC">Fridleifsson, Ingvar B.; Bertani, Ruggero; Huenges, Ernst; Lund, John W.; Ragnarsson, Arni; Rybach, Ladislaus (2008-02-11), O. Hohmeyer and T. Trittin, ed., The possible role and contribution of geothermal energy to the mitigation of climate change (pdf), IPCC Scoping Meeting on Renewable Energy Sources, Luebeck, Germany, pp. 59–80, retrieved 2009-04-06</ref>

Geothermal power is cost effective, reliable, sustainable, and environmentally friendly,<ref>Glassley, William E. (2010). ''Geothermal Energy: Renewable Energy and the Environment'', CRC Press, {{ISBN|9781420075700}}.</ref> but has historically been limited to areas near [[tectonic plate boundaries]]. Recent technological advances have dramatically expanded the range and size of viable resources, especially for applications such as home heating, opening a potential for widespread exploitation. Geothermal wells release greenhouse gases trapped deep within the earth, but these emissions are much lower per energy unit than those of fossil fuels. As a result, geothermal power has the potential to help mitigate [[global warming]] if widely deployed in place of fossil fuels.

The Earth's geothermal resources are theoretically more than adequate to supply humanity's energy needs, but only a very small fraction may be profitably exploited. Drilling and exploration for deep resources is very expensive. Forecasts for the future of geothermal power depend on assumptions about technology, energy prices, [[energy subsidies|subsidies]], and interest rates. Pilot programs like EWEB's customer opt in Green Power Program <ref>[http://www.eweb.org/greenpower Green Power] {{webarchive|url=https://web.archive.org/web/20141015040912/http://www.eweb.org/greenpower |date=2014-10-15 }}. eweb.org</ref> show that customers would be willing to pay a little more for a renewable energy source like geothermal. But as a result of government assisted research and industry experience, the cost of generating geothermal power has decreased by 25% over the past two decades.<ref>{{Citation|last=Cothran|first=Helen|title=Energy Alternatives|year=2002|publisher=Greenhaven Press|isbn=978-0737709049}}</ref> In 2001, geothermal energy cost between two and ten US cents per kWh.<ref>{{cite journal|last=Fridleifsson|first=Ingvar|title= Geothermal energy for the benefit of the people|doi=10.1016/S1364-0321(01)00002-8|volume=5|issue=3|journal=Renewable and Sustainable Energy Reviews|pages=299–312|year=2001|bibcode=2001RSERv...5..299F |citeseerx=10.1.1.459.1779}}</ref>