JSDEWES: Sustainability Assessment of Innovative Energy Technologies – Hydrogen from Wind Power as a Fuel for Mobility Applications

The transformation of the German energy system (also known as "Energiewende") is of high importance. Innovative energy technologies are able to make a considerable contribution to this transformation process. However, in order to analyse greenhouse gas reduction potentials without losing track of other associated effects, a comprehensive sustainability assessment is necessary. Beside other environmental impacts, this should also include economic as well as social implications [3]. Soares et al. [4] gave a comprehensive overview of important issues for sustainability in future energy systems. Their main conclusion for future research is that an "understanding of the whole supply chain – from energy provision to end-use consumption – as well as the technical, economic, environmental and governance factors needed to manage and transition current energy systems towards sustainable energy systems" [4] is crucial. For waste-to-energy systems, Chong et al. [5] suggested a sustainability metric highlighting the importance of assessing the three dimensions of sustainability simultaneously. Generally, each technology has specific techno-economic and environmental characteristics, challenges and constraints. For their further improvement and decision regarding their implementation, a comprehensive (i.e. respecting all dimensions of sustainability) and prospective impact analysis of these technologies is needed. However, there is no agreed-upon method to assess the prospective sustainability of energy technologies contributing to the objective of European and national climate neutrality by 2050 in a holistic and systematic way, neither on technology nor on systems level [6]. Based on these thoughts, the joint Helmholtz Initiative "Energy System 2050" (ES 2050) [7] is developing an interdisciplinary approach for sustainability assessment of future-oriented technologies and applies it across different innovative energy technologies, i.e. production of fuels, electricity and heat from residual lignocellulose biomass, battery energy storage and hydrogen for cross-sectoral applications. The backbone of this approach are life-cycle oriented methodologies, i.e. Life Cycle Assessment (LCA) and Life Cycle Costing (LCC). These enable to take not only direct impacts into account but also upstream processes and possible burden shifting from greenhouse gas emissions to other environmental impacts or costs. The social dimension is assessed with a focus on more direct effects; here three aspects are picked as examples, which include social acceptance of technologies, patent analysis and added value due to new production routes.

Hydrogen is such an innovative energy technology. This energy carrier has the potential to serve as a fuel for mobility applications, as a storage medium for generated electricity to balance out the electricity grid, for heat and electricity production in households as well as businesses and as feedstock for industry, e.g. steel production or refineries [8]. The cornerstone for these applications is hydrogen production that is low in emissions. This has often been assessed from a techno-economic and environmental perspective. However, the additional consideration of social aspects to perform a comprehensive sustainability assessment is still an exception. Stefanova et al. [9] used hydrogen production from biomass as an example to perform an extensive goal and scope definition but stopped there and did not perform an analysis. Wulf et al. [10] used hydrogen production to test their indicator selection based on the Sustainable Development Goals. However, the authors have not presented a consistent description of the inventory and did not discuss the results regarding trade-offs. The group of Ren [11] focused more on the mathematical linking of indicators using multi-criteria decision analysis (MCDA). Weighting factors for the different indicators were derived by expert solicitation, but they focused on a limited set of sustainability indicators. For several hydrogen production and storage options, Acar and Dincer [12] performed a literature review and evaluated different sustainability indicators including several technical indicators. However, by taking only literature data, no joint system boundary is achieved. Furthermore, the analysis did not take the different technology readiness levels of the analysed technologies into account, which makes a comparison very complicated. Several other publications took a similar path. Ren et al. [13] developed an MCDA approach using Fuzzy Best-Worst Method to determine the weights of the criteria and the fuzzy Technique for Order Performance by Similarity to Ideal Solution (TOPSIS) for the ranking of hydrogen production technologies. For the same type of technologies, Xu et al. [14] used interval best-worst method (IBWM), interval entropy technique (IET) and interval best-worst projection (IBWP) for the ranking and Li et al. [15] applied the decision-making trial and evaluation laboratory method and the grey relational analysis. However, the merit of these publications lies in the MCDA and not in the consistency of modelling hydrogen supply chains. Valente et al. [16] followed a different procedure by performing a Life Cycle Sustainability Assessment (LCSA) on hydrogen production by biomass gasification.

The approach applied in this paper does not focus on MCDA because several papers have already tackled this problem and is out of scope of the ES 2050 approach. What is lacking is more a consistent indicator selection based on the ES 2050 approach and modelling of the three dimensions of sustainability, taking not only technical, economic and environmental aspects into account but also social aspects. Technologically, the focus is on the total supply chain of hydrogen rather than different hydrogen production technologies.

Alkaline water electrolysis has proven to be an excellent technology for hydrogen production coupled with photovoltaics or wind power [17]. Wind power is selected as the renewable energy source because it is a promising option under the circumstances given in Germany. The reference region Germany is one of the boundaries of the ES 2050 project together with the technological development until 2050. As field of application, hydrogen mobility by fuel cell electric vehicles (FCEV) is selected as an example. Within the project, the described approach is applied for the reference year 2015 as well as for the target year 2050. All aspects of the case study are developed in the respective section; but at first, the overall ES 2050 approach is introduced with a more detailed presentation of the different sustainability indicators.

Backbone of a transparent and comprehensive sustainability assessment approach is a detailed modelling of material and energy flows between processes of the systems investigated. In a future-oriented ecological and economic assessment (LCA and LCC), systems are analysed from a life cycle perspective (Figure 1). The extensively assessed economic indicators and ecological impact categories are complemented by social indicators evaluating hot spots for certain social topics. Pre-selected social issues are acceptability, innovation potential and added value. An equally comprehensive assessment of social impacts for innovative technologies is not possible at the moment and subject to further research.

The social assessment takes only specific elements of the process chain into consideration. "Social acceptance" of hydrogen transport can affect different aspects. Thesen and Langhelle [18] analysed the public perception of hydrogen refuelling stations and FCEVs in the neighbourhood of people. More questions with a broader range of technology were asked by Zimmer and Welke [19]. In their questionnaire, also risk perception and the attitude towards "green" hydrogen was assessed as well as aspects regarding hydrogen production and storage. Based on these findings, hydrogen refuelling stations turn out to be the most critical part of the process chain, because not only the person actively choosing to buy and drive an FCEV has to be convinced by the new technology, but also residents near the refuelling station should tolerate the technology. This is evaluated by analysing the public perception of this technology. A second social aspect analyses patents to express a technology’s innovation potential. This analysis is employed for alkaline electrolysers. A third social indicator reflects possible impacts of the new technology regarding local employment. This is assessed by analysing the cost structure of the technology and classifying the costs in tradable and non-tradable parts. Further information on the applied methods is provided in this section.

To test the sustainability assessment approach for innovative energy technologies that was developed for ES 2050, a case study on hydrogen mobility was carried out. The goal was to assess hydrogen as an alternative fuel for passenger cars in Germany. Although the supplied hydrogen could also be used in public buses or light duty vehicles, in this case the passenger car was chosen for the investigation.

Hydrogen for mobility applications has a chance to be climate-friendly only when produced from renewable energy sources [50]. As done in this paper, a case study for Germany is discussed with wind power as an appropriate renewable energy source. The generated electricity was used in an alkaline water electrolyser. To account for the non-stable electricity supply, the full load hours of the electrolyser are adjusted accordingly. Afterwards it was stored and transported to the hydrogen refuelling stations to be dispensed to FCEVs (Figure 2).

For transport and distribution of hydrogen, different technologies are available. Currently, the most common method of transporting gaseous hydrogen in high pressure tanks and liquid hydrogen in cryogenic tanks is by truck. Alternatively, hydrogen storage and transport in liquid organic hydrogen carriers (LOHCs) by truck was considered. The fourth alternative analysed was the construction of a new hydrogen pipeline network in Germany. In order to be independent from the fluctuations of wind power availability, hydrogen needs to be stored, if necessary for months. Therefore, for gaseous hydrogen transport, seasonal storage in salt caverns was taken into account. Liquid hydrogen as well as hydrogen in LOHCs can be stored in appropriate tanks. The most important technical parameters for the sustainability assessment are summarised in Table 3.

Most important technical parameters of the analysed systems

DE- Germany, WW- World wide, HRS- hydrogen refuelling station, GH2- gaseous hydrogen, LH2- liquid hydrogen, LOHC- liquid organic hydrogen carrier

More detailed information on hydrogen transport and storage as well as the modelling of the LCA inventory can be found in [71] and [72]. The detailed LCA for the FCEV can be found in [73]. The costs deriving from the designed system are summarised in Table 4.

Economic parameters of the analysed systems

For the calculation of the future costs of hydrogen refuelling stations, a learning and economy of scale approach (eq. (2)) is followed based on Melaina and Penev [75]:

$C_1=C_0{\left(\frac{Q_1}{Q_0}\right)}^{\alpha }{\left(\frac{n_1}{n_0}\right)}^{\beta },$ (2)

C₁ - station capital cost; C₀ - base station capital cost; Q₁ - station capacity (kg/day); Q₀ - base station capacity (kg/day); n₁ - number of hydrogen refuelling stations; n_o - number of hydrogen refuelling stations at cost status of base station; α - scaling factor (0.707); β - learning factor (-0.106).

The application of this learning curve approach requires that not only the expansion of hydrogen mobility in Germany proceeds as described in Pregger et al. [51], but also in the global scale hydrogen mobility increases in the same rate. For calculating the current capital costs of the hydrogen refuelling station, the HRSAM model from the Argonne national laboratory was used [74].

The presented approach for sustainability assessment in combination with the described case study provided a plethora of possible results. A selection of these results will be presented and discussed.

For the environmental assessment, three impact categories were selected exemplarily for all analysed impact categories (acidification, climate change and eutrophication, terrestrial). These impact categories were applied to the four options of hydrogen supply for the year 2050 and their results are shown in Figure 3.

The lowest impact was always achieved in the pipeline option, regardless of the analysed impact category. The same applies to the transport of liquefied hydrogen: it always showed the second lowest environmental impacts. Comparing the transport of gaseous hydrogen with hydrogen bound in LOHCs, no clear statement is possible. From a climate and eutrophication (terrestrial) perspective, gaseous hydrogen transport is more advantageous, while for acidification the impact is too similar in value for a differentiation to be made. The importance of the different process steps, i.e. hydrogen production, transport, storage and dispension, varied for the different impact categories. For climate change, transport was determining the results. The different characteristics of the assessed options clearly influence the results. For LOHC, the heat demand for dehydrogenation is most influential, while for compressed hydrogen, the lower transport capacity in the trucks lead to more emissions and for liquefied hydrogen, it is the electricity demand for the liquefaction. In the other impact categories, transport is less dominant and instead, hydrogen production comes into focus. More detailed results for the environmental assessment of alkaline water electrolysis can be found in [53], while LOHC based transport in 2050 is discussed further in [71] and [72].

The costs for hydrogen supply in 2050 are presented in Figure 4 in comparison to the costs that would occur if hydrogen were supplied today. The error bars show the range of results for varying discount rates (1.5 – 3.5%). It has to be noted that for the LOHC option the investment costs are connected with higher insecurities than for the other options because no commercial hydrogenation and dehydrogenation plants were running in the reference year.

For all options, a significant reduction could be achieved due to lower electricity generation costs of wind power for the hydrogen production and lower investment costs of alkaline electrolysers and hydrogen refuelling stations. The reduction of investment costs was realized by higher production volumes (economy of scale) and bigger plants. The most expensive process in the hydrogen supply chain is hydrogen production (between 57% and 65% of the total costs in 2050) due to the electricity costs of wind power. The transport options of liquid hydrogen and LOHCs, however, added significant costs to the overall process chain due to additional investment costs and higher operational costs for electricity (liquefaction) and natural gas (dehydrogenation). The costs for storage are very low for the assessed options, even though high initial investments, e.g. for the underground storage, are necessary. When allocated to the total amount of hydrogen produced, these end up very low. The costs for hydrogen supplied by pipelines and high-pressure trailers are very close together. A slight preference for high-pressure trailers can be observed (3.0% difference). A more detailed assessment of the parameters driver wage, future diesel demand for trucks, investment costs for pipelines and the electricity demand for recompression within the pipeline is necessary to conclude on the most cost efficient supply chain.

Regarding the social aspects, survey participants chose explosion hazard as the most pressing concern (Figure 5). A possible fire hazard was also a matter of concern for the respondents.

Other concerns of the people did not refer to hydrogen itself but to the refuelling station regardless of the dispensed fuel. This is not only visible in the number of answers for noise pollution and negative effects on land- and cityscape, but also in the submitted comments. Further comments dealt with the competition to other technologies, e.g. less funding for charging points for battery electric vehicles or the competition for land between food and energy crops. The interviewees were also asked to state the level of knowledge they had about the technologies. For the hydrogen refuelling station, 64% stated that they had known nothing or only very little about it before the study. This was also reflected in some of the answers. Hydrogen is an odourless gas, which makes odour pollution very unlikely. Additionally, FCEVs’ only emission is water so that from them and from a hydrogen refuelling station, very little odour pollution can be expected.

For the patent analysis, the portfolio diagram for alkaline water electrolysis for the years 2016 until 2018 is presented as one result (Figure 6). This diagram incorporates the indicators national technology share (bubble size), technology potential/ patent dynamic (y-axis) and national innovation potential/ patents per PPP (x-axis).

Over the considered time period (1995 until 2018), Japan issued most of the patents. In the past years, however, China has increased its patent activity tremendously and holds most issued patents in relation to all technologies in their country (Figure 6). Germany shows the highest patent dynamic, even though it started on a very low number of issued patents in the previous period. However, this still implies an increasing interest of alkaline electrolysers in Germany. Compared to its economic output (here described using purchasing power parity; PPP) South Korea shows the highest patent activity. Together with the rather high patent dynamic (second rank) and the high national technology share (also second rank), South Korea is well positioned in the field of alkaline water electrolysis.

For a first assessment of added value for hydrogen supply, the pipeline option is used exemplarily (Figure 7).

In future, the added value could shift slightly from domestic spending to non-domestic spending. In the base year, in particular the generation of electricity from wind power produced added value in Germany. Due to the ongoing globalization of the industrial sector, this market will not be spared. When including FCEV, however, a much higher shift to non-domestic spending is expected [49].

In this paper, an approach for sustainability assessment of innovative energy technologies was presented and applied to a case study about hydrogen supply. Well-established methods like LCA and LCC were combined with social indicators still under development. The environmental assessment showed that hydrogen transport by pipeline is the preferable option. The economic analysis returned no clear transport preference. The supplementary social evaluation highlighted some additional concerns that need to be addressed when implementing hydrogen as fuel for private cars. A risk assessment of explosion hazards at hydrogen refuelling stations would be an adequate consequence of the survey result. This would additionally take into account the general limitation of LCA not to include risks. The potential shift of local jobs to other countries is another important point that needs further addressing, even though hydrogen supply seems to have a stable share of domestic spending due to the German wind industry. Additionally, Germany needs to do more to foster innovation regarding hydrogen production if it wants to remain competitive with countries such as China, Japan or South Korea.

Next to the already mentioned limitation of LCA not to include risks, another import limitation is the dependence of economic results on the economy of scale. Only if hydrogen demand – not only in the mobility sector – is high enough, investments into a hydrogen infrastructure will be made and electrolyzers and hydrogen refuelling stations need to be produced in larger numbers to become economically viable. Another prerequisite, in particular affecting the environmental results, is the large-scale expansion of on- and offshore wind power as well as photovoltaics in Germany to deliver enough electricity from renewable sources for hydrogen production, which might face bureaucratic obstacles and public resentment.

Moving forward, further social indicators are to be developed, regarding not only their calculation method but also the interpretation of results. With reference to the case study, the model should be extended from hydrogen supply to hydrogen mobility for all indicators by including an FCEV. Especially for the discussion of "added value" a comparison with conventional reference technologies is important and should be integrated into the model. Furthermore, some refinements of the model would benefit the overall significance of the results. This includes, for example, the investment costs for the LOHC system, the environmental modelling of electricity generation technologies or the modelling of the hydrogen underground storage, which is our next focus for LCA.

This work was supported by the Helmholtz Association under the Joint Initiative "Energy System 2050 – A Contribution of the Research Field Energy".

Many thanks go to our project colleagues Martina Haase and Manuel Baumann for their critical review and much appreciated advise.

The article is based on a contribution to the SDEWES 2019 conference in Dubrovnik and was choosen for this special issue.