Underwater Geothermal: Prototype Briefly Produces Surplus Power

Two boreholes, about 61 centimeters apart, on the seabed at a water depth of roughly 1.5 kilometers. There, at the Axial Seamount volcanic belt about 480 kilometers off the Oregon coast, the young US company Endurance Energy has tested a geothermal power plant. On September 27, it placed a prefabricated device weighing about 3 tonnes at the same spot. The company said on Monday that the plant produced more electricity than it needed itself, but only for 8.7 seconds.

Geothermal energy taps heat from the Earth’s interior, and there is plenty of it beneath the volcano: both boreholes struck hydrothermal fluids. One of them was cased, cemented and fitted with a valve; afterward it showed 260 °C. The prepared well nevertheless went unused, because the hot fluid encountered too much flow resistance. The engineers turned to a natural vent nearby, where fluids emerge at up to 281 °C. Their heat drove a turbine that reached 26,000 revolutions per minute.

The figures remain small. On a net average, the turbine delivered 2 kW, with a peak of 16.5 kW. The run ended in an emergency shutdown triggered by the batteries’ overcurrent protection. A second start attempt failed due to the failure of a power cable supplying the coolant pump. The measurements therefore describe a brief trial, not continuous operation.

The plant was controlled in real time from Seattle throughout the entire period, via a fiber-optic link of the Regional Cable Array, part of the US National Science Foundation’s research funding. The team tested both optical and acoustic communication channels. The drilling also ran as part of a voluntary environmental protection program: the site was chosen to minimize impact on marine fauna, and potential effects on animals and water were documented. According to the company, there was no unusual seismic or volcanic activity during or after the drilling.

For Endurance Energy, the trial proves that the entire chain works: drilling, placing and operating equipment on the seabed, converting geothermal heat into electricity, and controlling the system from onshore. The collected data is to feed into the development of an improved generation of plants. The company gives no timeline, customer or deployment site. For now, what has been shown is that the steps work together, and that in this run the plant delivered more electricity than it consumed, for 8.7 seconds.