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2. Centre for Alternative Technology Solar Water Heating (2013);
http://go.nature.com/9mwhyT
3. Roddy, D. J. Biomass and Biofuels (Elsevier, 2012).
4. http://www.ipcc.ch/report/ar5/wg3
5. Massachusetts Institute of Technology The Future of Geothermal Energy. Impact of Enhanced Geothermal Systems (EGS) on the United States in the 21st Century (US Department of Energy, 2006).