1. How stuff works, http://auto.howstuffworks.com/fuel-efficiency/fuel-economy/hydrogen-economy1.htm; 2012 [accessed 10.01.12].
2. http://upload.wikimedia.org/wikipedia/commons/b/bb/Major_greenhouse_gas_trends.png.
3. Air Now, US air-quality summary, http://airnow.gov/index.cfm?action=goodup.page1; [accessed 20.02.12].
4. Holcomb Station Expansion Project. Power plant major components, www.holcombstation.coop/Technology/Components.cfm; 2010 [accessed 12.05.10].
5. Wikipedia. Francis turbine, http://en.wikipedia.org/wiki/Francis_turbine; 2010 [accessed 12.05.10].