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The specific business case for the electrolyser will also affect the optimisation of these parameters. For example, an electrolyser that is coupled with PV could only operate typically less than 2000 hours in a year, making the capital cost a critical parameter to tackle. With such limited operating hours, durability might be less of an issue, since a short operating lifetime still translates into a longer actual lifetime. This could lead to using materials that are cheaper, but degrade faster. This case is different to one where the electrolyser is coupled with a concentrated solar power that has higher operating hours in a year, but that delivers a higher electricity price, making efficiency more important to reduce the operational cost. Improving the performance of the electrolyser in one dimension usually goes along with reduced performance in other parameters. This leads to trade -offs during the innovation process instead of having a single best-performing design Broadening the scope and looking beyond cost also influences the tradeoffs between these parameters. Considering the revenue side could lead to changing the operating strategy of the electrolyser. For instance, bidding in the balancing market to complement the revenues from hydrogen sales. This could have a negative effect on durability, since it could result in faster membrane degradation, requiring a more frequent replacement of membranes and consequently all other related components, but could also slightly reduce the contribution of the capital cost given increased operating hours (i.e. times when the electrolyser would not be operating based on hydrogen sales only, but doing so based on the additional revenues from balancing). Similarly, increasing the current operating density can create higher production flow at the expense of faster degradation. SCALING UP ELECTROLYSERS TO MEET THE 1.5°C CLIMATE GOAL Lifetime aspects related to materials and components The lifetime of electrolyser technologies is a function of the cumulative current passing through the stack, which can be represented by the number of full load hours13 as well as the number of operating hours – the number of hours during which the facility is on, regardless of load operating levels. Alkaline electrolysers are the most robust, with proven lifetimes of over 30 years. Some of the factors that affect their lifetime are: Gas permeation: The diaphragm is exposed to a continuous flow of KOH, gas permeation, and local hot spots created by the deposition of impurities on electrode coatings. This eventually causes small, pin-hole failures that increase in size over time and lead to gas contamination. Since the stacks usually have large areas, reaching up to 3 m in diameter and hundreds of cells, inspecting is not a feasible option. Instead, the oxygen stream is monitored and when the hydrogen concentration reaches 2% on the oxygen side, the stacks are sent for repair or disposal. One solution is to use polyphenylene sulphide fabric diaphragms. This negatively impacts the hydrogen production efficiency, but has a positive effect on lifetime, since it limits gas permeation. These negative aspects have been constantly changed for new generation diaphragms and under low pressure operation, and a few companies have claimed to have already solved these issues. Electrodes: Deactivation of electrodes on the cathode and anode sides have been prevented in some systems by using small idle protective currents within a few microamperes of current to avoid reversal of potentials of cathodes, potentially leading to less active electrodes overtime. 13 Full Load hours are the number of hours the electrolyser would have taken to consume the amount of energy current consumed over a period of time (typically one year), had it been operating at full capacity, in relation to the electrolyser plate capacity. 43PDF Image | GREEN HYDROGEN SCALING UP ELECTROLYSERS
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