The decarbonisation of the energy sector is increasing the need both for hydrogen and for demand flexibility in an increasingly variable power system. Coupling a small modular nuclear reactor with a hydrogen electrolysis system can provide both. No such hybrid system is yet in operation, so its economic value remains unmeasured.
The modelled system consists of an ACP100 nuclear reactor with a net output of 100 MW and a proton exchange membrane electrolysis system made up of eight identical 5 MW units, 40 MW in total. The operation is modelled with an optimisation model that, for each day and in fifteen-minute intervals, selects the electrolysis power and the reserve offer so that the monetary value of the day is maximised. The daily schedules for two years of market data are extended to thirty years by alternating the two years, while the degradation of the cell stacks and their replacements are accumulated along the way. The profit from flexible operation is measured as the difference between three operating strategies. The first operates rigidly, producing hydrogen at full power at all times. The second adjusts the production power to the electricity price. The third additionally offers balancing reserves to the transmission system operator. The model uses actual market data from the European Network of Transmission System Operators for Electricity for the years 2024 and 2025. Each strategy is valued by its average annual operating cash flow, derived from the thirty-year cash flow of operation. The calculation also accounts for the degradation of the electrolysis system and covers 38 European bidding zones, 27 of which also have reserve data.
Adjusting consumption to the price pays off in all 38 zones, on average by about 3.4 million euros per year or 10.7 % compared with rigid operation. Its magnitude is determined by the level of electricity prices. Participation in the reserve market yields a profit in all 27 zones with reserve data, on average about 6.2 million euros per year or 19.6 %. On this narrower set, adjustment yields about 2.7 million euros per year or 8.6 %, so reserves yield more than twice as much. They are driven by an entirely different factor, namely revenue on the reserve market and in particular the availability payment. Because the two drivers differ, the two profits are unrelated across zones, as the correlation coefficient between them is 0.23. The most attractive zones are those that combine high electricity prices with well paid reserves. Even under the most flexible strategy the system remains primarily a hydrogen producer, since hydrogen sales yield just over two thirds of the annual operating cash flow. Together, price adjustment and reserves raise the operating cash flow of rigid operation by about 8.9 million euros per year or just over 28 %, while the system produces between 5.0 and 6.2 thousand tonnes of hydrogen per year and releases up to 70 GWh of electricity to the market. Twelve repetitions of the full calculation confirm that both average profits remain positive across the entire range of uncertain assumptions tested, only their ratio changes, since at the lowest hydrogen price tested the adjustment yields more than the reserves.
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