References:

http://education.nationalgeographic.com/education/encyclopedia/tidal-energy/?ar_a=1

http://www.nrel.gov/learning/re_biomass.html

http://www.energyquest.ca.gov/story/chapter10.html

http://spectrum.ieee.org/green-tech/solar/solar-energy-isnt-always-as-green-as-you-think

http://greenliving.lovetoknow.com/Advantages_and_Disadvantages_of_Biofuels

http://www.asiabiotech.com/articles/readmore/1605-article01.html

https://www.nccs.gov.sg/news/straits-times-biofuels-development-singapore-powering-ahead-gaps-remain

http://pubs.iied.org/pdfs/15504IIED.pdf

http://www.straitstimes.com/breaking-news/singapore/story/singapores-first-tidal-energy-generator-launched-sentosa-20131106

http://wildsingaporenews.blogspot.sg/2008/11/can-tidal-energy-work-in-singapore.html#.VQWo5uFMg2Y

http://education.nationalgeographic.com/education/encyclopedia/tidal-energy/?ar_a=1

http://www.ucsusa.org/clean_energy/our-energy-choices/renewable-energy/environmental-impacts-solar-power.html#.VPQMRPmUeSo

http://news.nationalgeographic.com/news/energy/2014/11/141111-solar-panel-manufacturing-sustainability-ranking/

http://www.ucsusa.org/clean_energy/our-energy-choices/energy-and-water-use/water-energy-electricity-cooling-power-plant.html#.VP-48fmUeSo

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1567741/?page=1

http://fs-unep-centre.org/publications/gtr-2014

Images:

http://upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Reverse-Biased_pn_Junction.svg/400px-Reverse-Biased_pn_Junction.svg.png

http://www.linesolar.com/wp-content/uploads/2013/02/dreamstimelarge_21984550.jpg

http://oldblog.orbitingfiles.com/wp-content/uploads/2008/03/four_solaire_odeillo.jpg

http://media-1.web.britannica.com/eb-media/49/121649-004-16E15661.jpg

http://www.energy.ca.gov/biomass/images/biomass_graphic.jpg