As part of the study, different variants of electrolyzer plant construction with standard fixed typical nominal powers and electrolyzer plant powers that were optimized using a developed optimization model were considered, which simultaneously takes into account the increase in investment costs and the increase in income from the provision of mFRR auxiliary services, i.e. the reduction of operating costs in the part of electricity procurement of energy in the event of an increase in the rated power of the plant. Based on the results of the optimization model, an analysis of the profitability of the investment in the electrolysis plant was performed, and the levelized cost of green hydrogen production was calculated, taking into account the detailed investment and operating costs.