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Water photoelectrolysis cells based on photoelectrochemical water splitting seem to be an interesting alternative to other traditional green hydrogen generation processes (e.g., water electrolysis). Unfortunately, the practical application of this technology is currently hindered by several difficulties: low solar-to-hydrogen (STH) efficiency, expensive electrode materials, etc. A novel concept, based on a tandem photoelectrolysis cell configuration with an anion-conducting membrane separating the photoanode from the photocathode, has already been proposed in the literature. This approach allows the use of low-cost metal oxide electrodes and nickel-based co-catalysts. In this paper, we conducted a study to evaluate the economic and environmental sustainability of this technology, using the environmental life cycle cost. Preliminary results have revealed two main interesting aspects: the negligible percentage of externalities in the total cost (<0.15%), which means a positive environmental impact, and as evidenced by the net present value (NPV), there are potentially financial conditions that favour future investment. In fact, an NPV higher than 150,000 EUR can be achieved after 15 years.

The goal that the international community has set itself is to reduce greenhouse gas (GHG) emissions in the short/medium-term, especially in Europe that committed itself to reducing GHG emissions to 80-95% below 1990 levels by 2050. Renewable energies play a fundamental role in achieving this objective. In this context, the policies of the main industrialized countries of the world are being oriented towards increasing the shares of electricity produced from renewable energy sources (RES). In recent years, the production of renewable energy has increased considerably, but given the availability of these sources, there is a mismatch between production and demand. This raises some issues as balancing the electricity grid and, in particular, the use of surplus energy, as well as the need to strengthen the electricity network. Among the various new solutions that are being evaluated, there are: the accumulation in batteries, the use of compressed air energy storage (CAES) and the production of hydrogen that appears to be the most suitable to associate with the water storage (pumped hydro). Concerning hydrogen, a recent study highlights that the efficiencies of hydrogen storage technologies are lower compared to advanced lead acid batteries on a DC-to-DC basis, but "in contrast, [...] the cost of hydrogen storage is competitive with batteries and could be competitive with CAES and pumped hydro in locations that are not favourable for these technologies" (Moliner et al., 2016). This shows that, once the optimal efficiency rate is reached, the technologies concerning the production of hydrogen from renewable sources will be a viable and competitive solution. But, what will be the impact on the energy and fuel markets? The production of hydrogen through electrolysis will certainly have an important economic impact, especially in the transport sector, leading to the creation of a new market and a new supply chain that will change the physiognomy of the entire energy market.

Energy communities (ECs) are widely recognised for their potential to generate renewable energy. By contrast, the capacity of ECs to reduce energy demand and foster flexibility has attracted little attention to date, despite their theoretical potential to do so. To address this gap, we apply three perspectives - social representations theory, actor-network theory, and business models - to the analysis of nine case studies based in six European countries (Germany, Italy, Slovenia, Sweden, Netherlands, and United Kingdom). The core of the article comprises analysis of the nine cases from each perspective. Our results highlight the (un)intended effects of ECs on the energy representations of members; the configurational work required by focal actors to assemble new sociotechnical configurations; and the value creation and capture opportunities open to ECs in the creation of novel business models; These factors in turn impact whether and how ECs achieve demand reduction and flexibility. We summarise and discuss these results in a process of meta-theoretical triangulation to produce a multifaceted and relational account of the potential of ECs to develop demand-side solutions. This leads us to conclude that ECs have a distinct capacity to develop demand-side solutions, rooted in the creation of innovative sociotechnical configurations; and that this distinct capacity of ECs has the potential to complement and extend the contemporary focus on the use of market mechanisms to achieve demand reduction and increase flexibility.

Green hydrogen is considered the most suitable choice for the future energy market, both as energy storage media, energy vector and fuel for transportation, industry and other applications.In the last twenty years, increasing efforts have been dedicated to green hydrogen technologies development, but still today a number of issues are claimed in justifying the delay in its large scale application and the starvation of its market. Moreover, some new questions seem ready to be put on the table for justifying the delay in green hydrogen technologies applications.In this paper, a critical analysis of recent literature and institutional reports is carried out with the aim of understanding what is the real state of the play. In particular, peculiar advantages and shortcomings of different green hydrogen technologies (biomass pyrolysis and gasification, water electrolysis, etc.) have been analysed and compared, with a focus on the electrolysis process as the most promising method for large scale and distributed generation of hydrogen.Some geopolitical and economic aspects associated with the transition to a green hydrogen economy-including the feared exacerbation of the water crisis -have been widely examined and discussed, with the purpose of identifying approaches and solutions to accelerate the mentioned transition.

The potential reshaping of global energy markets by hydrogen: Following the trend of interest in hydrogen in recent history, there is a growing belief that green and low-carbon hydrogen will play a critical role in the transition to a zero-carbon economy. This is evidenced by the breadth and depth of hydrogen strategies and roadmaps that have emerged around the world in recent years [1-2]. The goals of a new clean hydrogen sector go far beyond decarbonisation. Clean hydrogen offers the opportunity to develop new supply chains, jobs and innovation, and to radically reshape the global economy and the geopolitics of the energy sector more generally. For countries without fossil fuel resources, hydrogen could reduce their dependence on imports or even turn them into energy exporters. For countries that are rich in fossil fuels, hydrogen may be able to be used as part of a just transition to a more sustainable future. Hydrogen, by democratising the means of production, coupled with abundant and cheap renewable electricity, could help to reduce instability in global energy markets and alleviate energy poverty. For this reason, some researchers argue that the growth of green hydrogen within the global economy could lead to such geo-economic and geopolitical changes, in which new scenarios and interdependencies will be shaped [3,4,5]. In this scenario, traditional oil and gas trade is expected to shrink. According to the outlook drawn up by IRENA, green hydrogen will cover 12% of global energy consumption by 2050. This will be due to targeted investments in the sector that will increase economic competitiveness and change the current hydrocarbon-based relationships [6]. The consequences will be a different geography of energy trade with the emergence of new centres of geopolitical influence, based on the production and use of hydrogen. With regard to future value chains for the production of green hydrogen-based ammonia, methanol and green steel, according to Eicke & De Blasio [7], changes can be expected within the global market that will lead some countries to take other positions than they currently have. For instance, with respect to the production of green hydrogen-based methanol, four countries - Saudi Arabia, Trinidad and Tobago, Oman and the United Arab Emirates - with a total world market share of 39%, are limited in their potential for green methanol production. The consequence of this will be that these countries will have to rely on imports to maintain their position in the future green methanol market. On the contrary, countries such as New Zealand, Norway or Chile, which currently do not have significant market shares in this sector, could, given their resources and economic conditions, sharpen their positions. The issue of renewable fresh water: One issue that is at the centre of the debate on what the impacts of a widespread deployment of green hydrogen might be concerns water resources. Researchers from various scientific fields are comparing and assessing the effect of green hydrogen on the global water resource. The key question is: will there be enough water to meet our future demand for green hydrogen? The views and scenarios that can be drawn from the literature and reports by various international bodies make different predictions. A research conducted by Newborough & Cooley [8] states that if all current fossil fuels used were converted to green hydrogen, the need for water for electrolysis would amount to 1.8% of the current global water consumption. However, even if the consumption of water to produce hydrogen is less than that required to produce energy from fossil fuels, concerns over the scarcity of fresh water call for a reduction in the use of water sources. Some researchers see a feasible and concrete solution in utilising the Earth's vast salt water resources, which can further reduce the water footprint of hydrogen. Some of them, however, highlight the technical challenges that still need to be addressed in order for this technology to be fully deployed. But beside the technical issues, Khan et al. [9] noted that there are limited economic and environmental incentives in pursuing R&D on the up-coming technology of direct seawater electrolysis. For Pflugmann & De Blasio [4] the issue of water resources is particularly important for countries where fresh water is scarce. The authors focus on the case of Saudi Arabia, which can rely on an abundance of renewable energy but limited water resources. It would be possible to address this shortcoming by desalinating sea water. To produce an amount of hydrogen equivalent to about 15% of Saudi Arabia's annual oil production, 26 million tonnes of renewable hydrogen would be required per year. This amount of hydrogen would require 230 million m3 of fresh water. In order to obtain the freshwater Saudi Arabia's needs, at least five desalination plants would need to be added to its existing 31 large desalination plants. Referring to Africa, the World Energy Council [10] also points out that, in the short term, access to water suitable for electrolysers might require upstream investments to desalinate water in some parts of the continent. Terlouw et al. [11] argue that the large-scale spread of hydrogen production in combination with other factors - such as climate change, population growth, economic development and agricultural intensification - could lead to water scarcity. The World Economic Forum [12] carried out an analysis estimating what the impacts on water resources could be from the transition to a hydrogen economy. The research was carried out by analysing data, concerning energy demand and water withdrawal, from 135 countries. According to the estimates derived from the analysis, only nine of the 135 countries studied would need to increase their current freshwater withdrawal by more than 10% to fully switch to hydrogen-based energy, while 62 countries would need to increase their freshwater withdrawal by less than 1%. The average value for all 135 countries is 3.3%. The increased demand for water resources would affect desert countries with low annual rainfall (e.g. Qatar, Israel) or small island states (e.g. Singapore, Malta) which would also experience difficulties due to limited freshwater reserves. According to analysts at the World Economic Forum, the hydrogen economy can open up interesting prospects not only for the energy system, but also for addressing the issue of water scarcity. Countries with water shortages are unlikely to be able to produce their own hydrogen and will therefore have to rely on imported hydrogen. This, which can certainly be seen as a disadvantage, will however allow these countries to use the water produced by the conversion of hydrogen back into energy, either through combustion or fuel cell technology, and to reuse this high-purity water locally.

Given the gaps between EU ambitions regarding energy community development and the current reality of clean energy communities in Europe, we explore a research framework enabling viable multi- and interdisciplinary research into new clean energy communities. We offer a definition of new clean energy communities, discuss their potential for wider dissemination and identify four factors that contribute to the current mismatch between ambitions and reality in energy community development. As a broader framework for interdisciplinary research into the field of new clean energy communities, we propose polycentric governance theory, considering the fact that the area of community energy systems is essentially multi-scalar, and that the rules of engagement in such systems are of great significance. This opens up four avenues for research on energy communities, which we outline in terms of enabling institutional contexts, potential for learning and transferability, business models and value propositions, and evaluation of outcomes and processes.