TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Components: The energy-capturing device comprises a conduit for holding production fluid flowing from a well; a turbine hydraulically connected to conduit; and a generator mechanically connected to the turbine and electrically connected to the power converter. The energy-capturing device includes choke hydraulically connected to the conduit and arranged in parallel with the turbine. The energy-capturing device comprises a thermoelectric generator electrically connected to the power converter. The thermoelectric generator is adapted to generate electrical energy from heat transfer across a temperature differential. The thermoelectric generator is arranged in a wellbore adjacent to a conduit for injecting a fluid into the wellbore. The temperature differential is between the wellbore and the fluid within the conduit. The thermoelectric generator is arranged in a wellbore. The temperature differential comprises a vertical temperature gradient of fluid in the wellbore. The thermoelectric generator is arranged in seawater outside a wellbore adjacent to a conduit carrying production fluid from the wellbore. The temperature differential is between the seawater and the production fluid. The system includes conduit loops branching from and reconnecting to the conduit; thermoelectric generator(s) arranged adjacent to each conduit loop; a valve arranged between each conduit loop and the conduit; energy storage device electrically connected to the power converter; electrical device (20) for performing subsea operation. The energy storage device is adapted to receive electrical energy from the power converter to be delivered back to the power converter as needed; and damper electrically connected between the power converter and the electrical device; fuel cell; hydrogen storage vessel; interface; subsea vehicle; electrolyzer. The electrical device is electrically connected to the power converter the damper being adapted to condition the electrical energy from the power converter for use by the electrical device; and oxygen storage vessel. The fuel cell is electrically connected to the power converter. The oxygen storage vessel is connected to the fuel cell. The hydrogen storage vessel is connected to the fuel cell. The interface is connected to the oxygen storage vessel and the hydrogen storage vessel. The subsea vehicle has separate oxygen and hydrogen storage tanks. The subsea vehicle is adapted to be deployed subsea and engage the interface to deliver oxygen from the oxygen storage tank to the oxygen storage vessel and to deliver hydrogen from the hydrogen storage tank to the hydrogen storage vessel. The electrolyzer is connected to the oxygen storage vessel and the hydrogen storage vessel. The electrolyzer is adapted to receive seawater, break down the seawater into oxygen and hydrogen, and deliver the oxygen and hydrogen to the oxygen storage vessel and the hydrogen storage vessel respectively. The electrolyzer is electrically connected to the power converter.