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GREEN HYDROGEN COST REDUCTION Water and land use for green hydrogen production Green hydrogen production uses water as a key feedstock and renewable electricity as an energy source to separate hydrogen and oxygen from water in an electrolyser. Water, as pure as possible, is therefore a key input. While the purity level required varies depending on the technology, the cost of water purification is marginal, starting from desalinated sea water (well below USD 1/cubic metre (m3) of water (Reddy and Ghaffour, 2007)). Impurities in the water, however, will have a major impact on the lifetime of the electrolyser stack (see Chapter 2, Section 4), which can in turn affect hydrogen cost by increasing the annuity of the electrolyser in the cost of hydrogen. In addition to desalination costs, the need for any water treatment in the electrolyser stack requires additional costs (e.g. deioniser). These can potentially become significant, depending on the purity level required, but are still of low impact on the overall cost of hydrogen, as in general they remain around USD 1/m3 (Hand, Guest and Cusick, 2019), or less than USD 0.01/kg H2. Water use is not barrier to scaling up electrolysis. Even in places with water stress, sea water desalination can be used with limited penalties on cost or efficiency From a pure, stoichiometric perspective, 1kg of hydrogen requires 9 kg of water as input. Due to some inefficiencies in the process, however, taking into account the process of water demineralisation, with typical water consumption, the ratio can range between 18kg and 24kg of water per kilo of hydrogen. The largest water consumption is actually upstream and it is the highest when the electrolyser is coupled with PV. Water consumption for green hydrogen from PV can vary between 22 and 126kg of water per kg of hydrogen depending on the solar radiation, lifetime and silicon content (Shi, 2020). The water scarcity is highly specific to a region since it compares the water use to the replenishment of water in the area, so local impact assessments are needed when there is hydrogen production in water- stressed regions. One of the methods to assess the impact from water use at the midpoint level is the Available WAter REmaining (AWARE) method developed by a working group of the UNEP-SETAC Life Cycle Initiative (Mehmeti, 2018). In terms of the impact of hydrogen production on water availability, this is clearly not an issue, as long as the assumption is that desalinated sea water is used. If freshwater is the preferred water source, a comparison can be made with current freshwater consumption for thermal power plants. Considering a very large 1 GW electrolyser, operating with an efficiency of 75% for 8 000 hours per year, the annual hydrogen production would be 0.15 million tonnes of hydrogen and 3 million tonnes of water (assuming 20kg of water use per kilo of hydrogen). This corresponds to the consumption of water of a small city(around70000inhabitants)withaconsumption of 45 m3 per inhabitant. The acceptability of this will depend on the water availability at the location of the plant, with desalination remaining a key option to be part of the design of the plant, especially in water-stressed regions. The water source for large scale hydrogen production should be explicitly accounted for in hydrogen strategies, as the volumes might be significant for water-stressed regions. Desalination can, however, be deployed jointly for hydrogen production as well as other uses (e.g. human consumption and agriculture), with hydrogen production helping to increase water supply by driving the deployment of multi-purpose desalination facilities in water-stressed regions. For the expected 19 exajoules (EJ) of green hydrogen (approximately 160 megatonnes [Mt]) in the Transforming Energy Scenario of the IRENA Global Renewables Outlook, we would require around 3 billion m3 of water per year in 2050. This is 0.08% of the current global consumption of freshwater. As freshwater is used for a multiplicity of non-energy uses (e.g. agriculture), a better comparison is the current consumption of thermoelectric power plants, which is significantly higher: for instance, the estimated water consumption by thermal power plants in the United States in the 2030 reference case was 5.8 billion m3 (IRENA, 2015). Even for more ambitious scenarios, where decarbonisation is 40PDF Image | GREEN HYDROGEN SCALING UP ELECTROLYSERS
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