Shift in the energy-technology paradigm: from fossil to renewable energies
The contemporary energy system will be radically transformed in the twenty-first century, and these expected changes are often labeled as the 'new industrial revolution' . At the core of this revolution is a shift in the energy-technology paradigm away from fossil energy technologies to renewable ones . This paradigm shift is enforced through two pivotal global processes: Firstly, in the future, there will not be enough cheap crude oil for worldwide economic growth . Secondly, it has become almost indisputable that greenhouse gas emissions will lead to considerable changes in global climate. This growing awareness of climate change has strengthened environmental policies and supported the development of renewable energy technologies .
Until recently, there has been a huge schism between scientists in their prediction of future oil production. While some of them assumed that oil production has already reached its peak and will soon decline, others argued that there are large undiscovered oil reserves that will be exploited in the future. However, voices supporting the latter position have become scarce, and most scientists now believe that oil production has either already reached its peak and will not increase further  or will reach it at the latest by 2035 . Forecasts on worldwide oil demand are even more consistent. Despite the current demand collapse due to the economic crisis, it is widely believed that the demand for oil will increase again. Both the decreasing oil production and the growing oil demand will inevitably lead to a rise in oil prices. Hence, economic growth needs to be decoupled from oil, and alternative energy technologies that do not rely on fossil energy sources must be developed.
The second process that promotes this development is climate change. A rise in the global surface temperature has been observed since 1850, when instrumental recording first started . Simultaneously, the concentration of greenhouse gases in the atmosphere has increased since 1750 as a result of human activities, in particular the beginning of the industrialization at the end of the eighteenth century . Though it has been long contested, whether these two processes are related to each other, with some uncertainty still remaining, it is very likely that global warming is caused by humans . Both the concentration of greenhouse gases and the resulting rise in temperature have been characterized by exponential growth since the beginning of the twentieth century. This development has had consequences; scientists have observed several phenomena that are caused by global warming. There is a strong conviction that the rise in temperature resulting from greenhouse gas emissions will lead to considerable changes in the global climate [6, 7].
Alternative energy technologies
For all the reasons outlined above, it is necessary to decouple economic growth from fossil energies and to develop alternative energy technologies that rely on renewable energy sources. Hence, the decreasing availability and rising prices of fossil fuels, as well as climate change and its consequences, resulting from their mass usage, not merely cause the change in the energy technological paradigm, but also determine its direction. It is not only a transformation from fossil to non-fossil renewable energy sources, but also a change to those renewable energy sources whose production and consumption allows a CO2-free energy cycle. Therefore, energy technologies need to be developed, which in combination with renewable energy sources provide a CO2-free energy cycle from generation to the end use. While this at first glance may seem to be a technical endeavor, the transformation from fossil to renewable energy sources cannot be achieved by engineers alone, as diverse research strands such as, for instance, economic history perspectives (e.g., [8, 9]) or microsociological studies (e.g.,  or ) have highlighted the significance of culture in technology development. In fact, interdisciplinary collaboration is required in order to tackle this shift in the energy paradigm.
An important area of application of alternative energy technologies is the transportation sector that heavily relies on the combustion of fossil fuels and thus accounts for a large share of overall emissions. Within the range of this quest for new energy sources, various fuels such as, for example, natural gas, synthetic fuels, or fuels from biomass have been developed and tested in combination with several different propulsion systems in the automotive industry . Hydrogen and fuel cells are among the technologies that open up the chance to deploy renewable energy sources in transportation and electricity, as well as heat generation, in CO2-free energy cycles. Thus, they target an area which is currently responsible for half of the European Union's [EU] total greenhouse gas emissions .
However, for two reasons, this is not necessarily the case. Firstly, the term 'hydrogen and fuel cell technology' suggests a combination of the two technologies, which is possible, but not mandatory. Hydrogen can be used without fuel cells, for instance, as fuel for internal combustion engines in vehicles. Likewise, fuel cells can be powered by fuels other than hydrogen, such as methanol. Furthermore, there is a substantial difference between the two technologies: hydrogen is an energy carrier, while fuel cells are energy converters. Hydrogen and fuel cells are, therefore, the combination of an energy carrier and an energy converter technology. This combination is a broad application area of both technologies, but not the sole one.
Secondly, it should be noted that both technologies are not ecological per se. As hydrogen rarely exists in its pure gaseous form in nature, it has to be obtained from hydrogenous compositions. There are a variety of possible production processes, and hydrogen can be generated from coal, natural gas, biomass, and water. Each production process results in a different energy cycle. Fuel cells present a similar picture. They can be powered by methanol and hydrogen, which can be produced from several different raw materials and in a variety of ways, so that both result in completely different energy cycles.
Therefore, the supporters of hydrogen and fuel cell technologies do not promote them in general, but with regard to their ecological potential. They envisage 'green' hydrogen and fuel cell technologies that rely on renewable energies and contribute to a CO2-free energy cycle instead of 'black' technologies that are based on fossil energy sources. In order to speak of a CO2-free energy cycle, the entire fuel process chain has to be considered. This concerns the fuel pathway from 'fuel processing from the primary energy source' to its use 'by the propulsion technology that converts fuel to motion on board the vehicle' . In the case of hydrogen, only hydrogen production from renewable energies can contribute to a CO2-free energy cycle . This green potential of hydrogen and fuel cell technologies and their wide variety of applications are what attract the interest of many diverse actors. Hydrogen and fuel cells can, for instance, be used to generate power and electricity as well as to run small-scale heating devices for private households and large-scale devices for industry. They can not only provide power for small, portable applications such as mobile phones and notebooks, but can also serve as a propulsion system in large vehicles.
The history of hydrogen and fuel cells
The basic inventions of hydrogen and fuel cell technologies (hydrogen combustion engine and fuel cell) were made at the beginning of the nineteenth century and are today closer to societal usage than ever before. However, the history of hydrogen and fuel cell technologies presents by no means a linear process. Their development for the transport sector is illustrated in detail on the website 'H2Mobility' of TÜV-SÜD , the technical inspectorship for vehicles in southern Germany, and is briefly summarized in the following paragraphs.
The first hydrogen-driven combustion engine was constructed by Issac de Rivaz in 1806. The invention did not receive much attention in the societal discourse for the next 50 years, and it was not until 1863 that the next vehicle driven by a hydrogen-powered combustion engine was constructed by Étienne Lenoir. Nevertheless, the technology has disappeared once again from the scene until the late 1920s when Rudolf Erren constructed a hydrogen-powered two-stroke engine. This development was followed by single concept studies during the following decades, but none of them passed beyond the laboratory stage.
The history of fuel cells is characterized by a similar trajectory. The mechanisms of fuel cell technologies were discovered in 1838 by the German-Swiss chemist Christian Friedrich Schönbein and the British lawyer and natural scientist Sir William Grove, who did research independently of one another. The fuel cell gained its actual name in 1889 from Ludwig Mond and Charles Langer who conducted thorough investigations into this technology. Still, it was not until 1932 that the first model of an alkali electrolyte fuel cell was constructed by Francis Thomas Bacon. This development was followed by the construction of the first vehicle with fuel cell propulsion in 1959.
The development of hydrogen-powered combustion engines and fuel cell propulsion systems exhibited a similar picture until the late 1960s. Both began with basic inventions by a single person, followed by single inventions and wide temporal intervals during which the technologies did not gain societal attention. However, by the end of the 1960s, the initiatives aiming at the societal acceptance of hydrogen and fuel cell technologies started to increase all over the world. This rise in interest was the result of two separate developments: First, hydrogen and fuel technologies were successfully applied in spacecrafts in the 1960s and 1970s where they not only demonstrated their technical functionality, but also gained a high value as key technologies that enabled travel to the moon. Second, the 1973 oil crisis fostered the development of alternative technologies for the transport sector that should decouple modern mobility from crude oil.
Various indicators could clarify the dynamics in the development of hydrogen and fuel cells from the 1970s to the present. One could, for example, take media attention (cf. [16–18]) or the number of constructed prototypes and optimistic statements by the industry (cf. ) as a standard for the upgrading or downgrading of these technologies. However, we decided to focus on the statistics of the German Federal Republic regarding the funding of hydrogen and fuel cells as these illustrate very well the societal and, in particular, the political valuation of these technologies.
Public funding increased continuously from 1974 and reached a temporary peak in 1994 . However, from 1994 onwards, funding decreased and reached its lowest point in 1999 when it fell back to the 1988 level. The end of the lighthouse projects 'HYSOLAR' and 'NECAR' accompanied this development. HYSOLAR, an abbreviation for 'Hydrogen from Solar Energy', was a German-Saudi-Arabian research, development, and demonstration program to assess the chances of CO2-free hydrogen production from solar energy in Saudi Arabia that then should be transported to Germany . The program ran from 1985 to 1995 without a follow-up project . NECAR, an abbreviation for 'New Electric Car' and 'No Emission Car', was initiated and accomplished by the German car manufacturer Daimler. The objective of this project was to develop a fuel cell propulsion system for vehicles. For this purpose, five fuel cell-powered vehicle prototypes were constructed between 1994 and 2000, when the project had finished.
The end of these projects and the decrease in funding clarify that hydrogen and fuel cell technologies at the turn of the millennium reached the bottom of their history in Germany, but then, a short period from 1999 to 2005 followed in which funding again began to rise and was stabilized at a comparably high level of above €20 million/annum. Thereafter, funding increased vastly, and hydrogen and fuel cell technologies should be funded by at least €100 million/annum from 2008 to 2016 , which exceeded the average annual funding from 1974 to 2004 by more than a factor of 10 . This development raises the question: What factors led to this rapid increase in funding in a technology field that appeared to have lost its attraction?