<P> 2H + O → 2H O + High Energy </P> <P> High Energy + 2H O → 2H + O </P> <P> This requires a high - energy input, making commercial hydrogen very inefficient . Use of a biological vector as a means to split water, and therefore produce hydrogen gas, would allow for the only energy input to be solar radiation . Biological vectors can include bacteria or more commonly algae . This process is known as biological hydrogen production . It requires the use of single celled organisms to create hydrogen gas through fermentation . Without the presence of oxygen, also known as an anaerobic environment, regular cellular respiration cannot take place and a process known as fermentation takes over . A major by - product of this process is hydrogen gas . If this could be implemented on a large scale, then sunlight, nutrients and water could create hydrogen gas to be used as a dense source of energy . Large - scale production has proven difficult . Not until 1999, was it even possible to induce these anaerobic conditions by sulfur deprivation . Since the fermentation process is an evolutionary back up, turned on during stress, the cells would die after a few days . In 2000, a two - stage process was developed to take the cells in and out of anaerobic conditions and therefore keep them alive . For the last ten years, finding a way to do this on a large - scale has been the main goal of research . Careful work is being done to ensure an efficient process before large - scale production, however once a mechanism is developed, this type of production could solve our energy needs . </P> <P> Hydroelectricity provided 75% of the worlds renewable electricity in 2013 . Much of the electricity used today is a result of the heyday of conventional hydroelectric development between 1960 and 1980, which has virtually ceased in Europe and North America due to environmental concerns . Globally there is a trend towards more hydroelectricity . From 2004 to 2014 the installed capacity rose from 715 to 1,055 GW . A popular alternative to the large dams of the past is run - of - the - river where there is no water stored behind a dam and generation usually varies with seasonal rainfall . Using run - of - the - river in wet seasons and solar in dry seasons can balance seasonal variations for both . Another move away from large dams is small hydro, these tend to be situated high up on tributaries, rather than on main rivers in valley bottoms . </P>

Why do we need to find alternative sources of energy