Editing Solar energy (section)

===Molten salt technology===

Molten salt can be employed as a [[thermal energy storage]] method to retain thermal energy collected by a [[Solar power tower|solar tower]] or [[solar trough]] of a [[concentrated solar power plant]] so that it can be used to generate electricity in bad weather or at night. It was demonstrated in the [[Solar Two]] project from 1995 to 1999. The system is predicted to have an annual efficiency of 99%, a reference to the energy retained by storing heat before turning it into electricity, versus converting heat directly into electricity.<ref>{{cite web|url=http://www.sandia.gov/Renewable_Energy/solarthermal/NSTTF/salt.htm |title=Advantages of Using Molten Salt |access-date=14 July 2011 |last=Mancini |first=Tom |date=10 January 2006 |publisher=Sandia National Laboratories |archive-url=https://web.archive.org/web/20110605094349/http://www.sandia.gov/Renewable_Energy/solarthermal/NSTTF/salt.htm |archive-date=5 June 2011 |url-status=dead }}</ref><ref>[http://adsabs.harvard.edu/abs/1977htec.proc...39J Molten salt energy storage system – A feasibility study] Jones, B.G.; Roy, R.P.; Bohl, R.W. (1977) – Smithsonian/NASA ADS Physics Abstract Service. Abstract accessed December 2007</ref><ref>{{cite web|last=Biello|first=David|title=How to Use Solar Energy at Night|url=http://www.scientificamerican.com/article.cfm?id=how-to-use-solar-energy-at-night|work=Scientific American|access-date=19 June 2011}}</ref> The molten salt mixtures vary. The most extended mixture contains [[sodium nitrate]], [[potassium nitrate]] and [[calcium nitrate]]. It is non-flammable and non-toxic, and has already been used in the chemical and metals industries as a heat-transport fluid. Hence, experience with such systems exists in non-solar applications.

The salt melts at {{convert|131|°C|°F}}. It is kept liquid at {{convert|288|°C|°F}} in an insulated "cold" storage tank. The liquid salt is pumped through panels in a solar collector where the focused irradiance heats it to {{convert|566|°C|°F}}. It is then sent to a hot storage tank. This is so well insulated that the thermal energy can be usefully stored for up to a week.<ref>[[Robert Ehrlich (physicist)|Ehrlich, Robert]], 2013, "Renewable Energy: A First Course," CRC Press, Chap. 13.1.22 ''Thermal storage'' p. 375 {{ISBN|978-1-4398-6115-8}}</ref>

When electricity is needed, the hot salt is pumped to a conventional steam-generator to produce [[superheated steam]] for a turbine/generator as used in any conventional coal, oil, or nuclear power plant. A 100-megawatt turbine would need a tank about {{convert|9.1|m|ft}} tall and {{convert|24|m|ft}} in diameter to drive it for four hours by this design.

Several [[parabolic trough]] power plants in Spain<ref>[http://www.nrel.gov/csp/troughnet/thermal_energy_storage.html Parabolic Trough Thermal Energy Storage Technology] {{webarchive|url=https://web.archive.org/web/20130901224906/http://www.nrel.gov/csp/troughnet/thermal_energy_storage.html |date=1 September 2013 }}  Parabolic Trough Solar Power Network. 4 April 2007. Accessed December 2007</ref> and [[solar power tower]] developer [[SolarReserve]] use this thermal energy storage concept. The [[Solana Generating Station]] in the U.S. has six hours of storage by molten salt. In Chile, The Cerro Dominador power plant has a 110&nbsp;MW solar-thermal tower, the heat is transferred to [[Thermal energy storage#Molten salt technology|molten salts]].<ref>[https://archive.today/20140131162845/http://www.thisischile.cl/9090/2/chile-to-welcome-largest-solar-concentration-plant-in-lat-am/News.aspx Chile to welcome largest solar concentration plant in Lat Am] www.thisischile.cl Thursday, January 16, 2014 retrieved January 27, 2014</ref>
The molten salts then transfer their heat in a heat exchanger to water, generating superheated steam, which feeds a turbine that transforms the kinetic energy of the steam into electric energy using the [[Rankine cycle]].<ref>{{cite web|url= http://www.nrel.gov/csp/solarpaces/project_detail.cfm/projectID=3275 |title=Concentrating Solar Power Projects - Atacama-1 |publisher=[[National Renewable Energy Laboratory]] |date= 1 July 2015 |accessdate=10 September 2016}}</ref> In this way, the Cerro Dominador plant is capable of generating around 110 MW of power.<ref>[http://reneweconomy.com.au/2014/abengoa-to-build-110mw-solar-tower-storage-plant-in-chile-24839 Abengoa to build 110MW solar tower storage plant in Chile] reneweconomy.com.au/ By Giles Parkinson on 13 January 2014</ref>
The plant has an advanced storage system enabling it to generate electricity for up to 17.5 hours without direct solar radiation, which allows it to provide a stable electricity supply without interruptions if required. The Project secured up to 950 GW·h per year sale. Another project is the María Elena plant<ref>[http://www.thisischile.cl/8861/2/Chile-greenlights-enormous-400-megawatt-solar-project/News.aspx Here comes the sun Chile greenlights enormous 400-megawatt solar project] www.thisischile.cl Friday, 23 August 2013 retrieved 30 August 2013</ref>  is a 400&nbsp;MW thermo-solar complex in the northern [[Chile]]an region of [[Antofagasta Region|Antofagasta]] employing molten salt technology.