Scientists from Birmingham University (the UK) proposed a system allowing for producing green hydrogen right in the open sea without connecting to the on-shore power grid. To do that, they combined several technological solutions: hybrid waves and tides energy converter, supercapacitors and batteries, electrolysis unit with proton-exchange membrane and sub-sea hydrogen storage facility.
The researchers’ idea was not only to collect the sea energy, but to make it usable for permanent operation of the equipment. The waves provide energy in an uneven manner, with surges, while tidal streams are more stable. The developed hybrid converter uses both sources simultaneously: vertical motions of a buoy due to the waves and horizontal motion of water during the tides. These motions are combined and rotate one generator. Due to this, the fluctuations of one source are partially compensated by the other one, and power generation becomes more even.
The scientists evaluated the operation of such system based on 2024 actual data about waves and tides in British waters. In their simulation, the platform is equipped with six hybrid units of such type. Their average cumulative output made 64.8 KW, and in peak hours 108 KW. This is about the amount consumed by a small office or an autonomous sea platform with residential and technical modules. In winter and spring, each unit could generate over 20 KW, in summer – about 7-11 KW, demonstrating the seasonal nature of the sea energy. To avoid the negative effects of such fluctuations on the system’s performance, supercapacitors and energy storage facilities were included. They mitigate short-term variations of output and maintain stable voltage.
The generated electricity is used by electrolysis units splitting water into hydrogen and oxygen. In the computational configuration, their rated output is 78 KW, and their load factor – circa 72%, which is considered optimal for such equipment. In the stable operation mode, the system produces from 1.2 up to 1.4 kg of hydrogen per hour. It means 12.4 tons of hydrogen annually. For example, such amount is enough to provide fuel to several dozens of hydrogen-fueled vehicles during one year.
The energy consumption per 1 kg of hydrogen made from 46.8 to 55.7 KW·h depending on the season. This is compatible with on-shore hydrogen units despite the fact that the open sea conditions are much harder. The overall efficiency of the entire chain (from moving water to commercial hydrogen) is at the level of circa 20%. For off-shore energy systems this is believed to be good performance.
The research gives a special focus on storing hydrogen. The scientists proved that it is economically unfeasible to keep big reserves of hydrogen right on the platform in pressurized bottles: it requires a lot of space and makes the project significantly more expensive. Instead of that they propose to use the worked-out gas fields as storage facilities. This will allow for reducing the amount of storage equipment approximately 18 times and decrease storage costs down to circa USD 1.5 per 1 kg of hydrogen. And 170 kg of hydrogen can supply over 40 KW to the platform during three days without additional generation.
