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Harnessing geothermal energy from the seafloor could power the future

SHNELL, Jim, et al. “Energy from Ocean Floor Geothermal Resources.” Energy 19 (2015): 25.

Clean energy and resource management are hot topics when it comes to power. Currently the majority of power is from fossil fuels, like coal and oil, which have controversial impacts on the environment and are only available as reservoirs;  eventually they could run out. Nuclear power is another method for power, but waste disposal is always a lingering concern and research and development still have a lot of work. There is also energy from wind, water, and solar power, but these methods have yet to be economically feasible or practical on a grand scale; they are speculated not powerful enough to replace the global reliance on fossil fuels.  Another method to derive energy from the environment is to use heat generated from the inside of the earth. Currently on-land holes called enhanced geothermal systems (EGS) have been drilled that reach geothermal water and steam, at temperatures as high as 250°C, to generate power. Higher temperatures could be achieved by drilling deeper holes; however, deeper holes cost money and the seismic consequences of drilling have high uncertainty. A natural exception to this conundrum is Iceland, a unique geological hotspot that sits on a spreading center.  This means that shallower holes will reach higher temperatures, as high as 500 or 600°C.   It is suggested by the Iceland Deep Drilling Project (IDDP)  that the supercritical temperatures and pressures of deep wells may produce ten times the amount of energy per hole (5 MW versus 50 MW of electric power).  The drilling concepts and findings of the IDDP are a model for the future of clean energy harvested from the ocean floor.

An estimated 100 million quads of energy could be harvested annually from geothermal resources, compared to the 472 quads consumed globally in 2006. However, current methods of tapping this resource are not sufficient to replace global needs. So why not move it to the ocean floor? It is known that there is abundant geothermal energy on rift zones, they are relatively uniform, and they are plentiful.   The ocean crust is also considerably thinner at rift zones (5km) than continental crust (30-100km).

Self-sustaining, submersible, remotely controlled turbine generators on the ocean floor would convert energy to electricity at mid ocean rift zones, which reduces the energy loss from transferring heat to the surface. The generator would be placed at a single injection well connected to four production wells, each 500 lateral meters from the injection well and 1600 meters below the sea floor.  Direct current electricity generated from the turbines would be transferred to the continents by high voltages direct current transmission lines. This practice is already used between Norway and the Netherlands, as well as Oregon-Washington to Los Angeles. Although, these amounts (3.1 gigawatts over 846 miles) are less ambitious than what new technology would strive to achieve (10 gigawatts over 2000 miles).

The depth of the rift zone is not an issue because gas and oil industries have already drilled holes as deep as 8000 meters into the crust.   Water depth is not an issue either because the oil and gas industries can drill in water as deep as 2800 meters.   A potential difficulty is however, that the rock type is basalt, a much harder material than the shale and other sedimentary deposits that house gas and oil. The deep water also has potential advantages, like high pressure, cool bottom temperature (> 4°C), and low dissolved oxygen levels compared to the surface. There is also the potential to harvest the mineral deposits that will inevitably form. Operations could be limited to producing energy only during off peak hours, and if CO2 turbines were used there is potential for 50% efficiency. Sea floor geothermal harvesting has the potential for six times as much power generation than current EGS methods. A summary of the economics can be found in Table 1.

Harvesting energy from the seafloor to power the future seems like a potentially great idea. If it can be pulled off it will likely prove to be a cost comparable, but clean alternative, to the burning of fossil fuels.

Capacity per station Production per well Plant availablilty Duration Capitiol cost Operating cost Cost with transmission per kWH Potential offset
100 MW 50 MW 90% 30 years 1.365 billion 215 million for 30 years (7.16 million per year) $.073 Harvested mineral resultant mineral deposits

Table 1: Summary of ocean floor geothermal resource economics

 

 

Anne M. Hartwell
Hello, welcome to Oceanbites! My name is Annie, I’m an earth scientist (geology and oceanography). My favorite job as a scientist is working in the laboratory and the field because I love interacting with my research!

Discussion

2 Responses to “Harnessing geothermal energy from the seafloor could power the future”

  1. In this article I learned that instead of drilling the crust we should drill the ocean floor. I already knew that geothermal energy was a thing and that you could get energy from heat, however I didn’t know that the ocean floor would give more energy. I also didn’t know that the ocean floor was hotter than the crust from land, it certainly isn’t getting that heat from the sun because it’s farther away from the sun than the land as well as there is water that blocks the sun’s heat. So I wondered were the heat came from and then I realized that the ocean floor is farther from the surface and so the core would be closer to it and that made me realize, the heat comes from the Earth’s core.  My questions for the author are that, you talked about how the drilling on the crust would harm the environment , well wouldn’t drilling on the ocean floor harm the environment as well? Will it not harm the animals that are around the drill? As well as your drilling a hole in the ocean and you don’t think fishes are going to swim near that. Wouldn’t fish die from the extreme temperatures?

    Posted by Arslan | March 5, 2017, 1:07 pm
    • Anne M. Hartwell

      Hey Arslan,

      Thank you for visiting Oceanbites.org and thank you for submitting a comment!

      I appreciate that you question the impact that a drilling site might have on the environment, particularly the biological inhabitants. The potential of harming the environment is always a risk with human mitigation. We cannot say the precautions that a drilling team will make before drilling a hole in Earth. At each drill site various factors could impact the decisions, like if there is even a biological community present and if the community is alive, and of course, relevant regulations and laws related to marine preservation and seafloor rights. We can hope that the leaders of the mission will take due diligence to limit their footprint.

      You may be interested to learn that there are many holes in the sea floor already (and not just for oil), the Integrated Ocean Drilling Program drills sections of the seafloor so that scientists can study earths history and the deep biosphere. Some of the holes are even set up so that we can visit them again and again to make long term observations. The rock and sediment collected is stored in mutliple repositories, one of the them is on the URI GSO campus!

      With regards to extreme temperatures, some fish and organisms really prefer them. Around the mid-ocean ridges there are venting sights that reach can reach 400 degrees C that host diverse micro and macro ecosystems. Also, the holes that would be drilled to harvest heat energy wouldn’t necessarily change the heat at the seafloor. The goal of the expeditions would be to keep the heat to get energy, not let it be released to the environment.

      Here is a link to the original article!

      I hope this helps answer your questions. Thanks again for your contribution!

      Annie

      Posted by Anne M. Hartwell | March 5, 2017, 2:00 pm

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