[Creative Cultivation Program] Geothermal Energy Exploitation: Digging deep into the earth to get thermal energy, is it reliable?

Author: Niu Mingmin

Reviewed by: Zhang Yuxiu, Professor Wang Lu from China University of Geosciences (Wuhan)

With the frequent occurrence of natural disasters and extreme weather around the world, it is urgent to protect the ecological environment and implement emission reduction tasks. In the current new energy track of "practicing dual carbon and green development", many outstanding players have emerged, such as wind energy, hydropower, geothermal energy, solar energy, nuclear energy, etc. Among them, geothermal energy is highly expected due to its outstanding advantages such as large reserves, wide distribution, high efficiency, stability, safety and quality. Digging a hole 10,000 meters deep to get heat energy from the earth sounds like a feasible method, but the depths of the earth that humans can currently peek into are extremely limited. Will there be new technologies that can make the earth "generate electricity for love"?

"Enthusiastic" Earth

We always say that space is vast and boundless, but in fact, the interior of the earth is also full of different wonders. If we go down to the land beneath our feet, through the loose soil layer, the hard crust, and the hot mantle, we will find that the deep interior of our blue earth is actually an ocean of molten rock.

The gravitational collapse energy accumulated when the earth was born combined with the decay energy of radioactive substances to form heat that accumulates inside the earth's core, with the temperature reaching about 5200°C. It is a veritable "hot" earth. These heats are the driving force behind the formation and development of our planet.

Some of the heat from the Earth's interior reaches the surface and is released into the form of hot springs, volcanoes, earthquakes, etc., while more heat is stored deep underground. It is estimated that the Earth's total internal heat is 170 million times the global coal reserves, equivalent to 500 trillion tons of standard coal, which can meet human energy needs for hundreds of thousands of years.

Geothermal energy has unparalleled advantages over other energy sources. Traditional thermal power generation requires continuous fuel consumption and pollutes the environment. Wind power, hydropower and solar energy fluctuate too much and cannot be output stably. The ultimate energy source, controlled nuclear fusion energy, still has a long way to go. In this context, geothermal energy, which seems to be "within reach", has become a "seed player" for dual carbon. You only need to dig a deep enough well to obtain a steady supply of geothermal energy, which is stable, environmentally friendly and has zero emissions.

The advantages are so obvious, but in fact, geothermal power generation currently accounts for less than 1% of the world's electricity supply. Why is this? Because compared with human "sky" technology, our "underground" technology is obviously much more clumsy.

The "Dig Through the Earth" Project

If you want to reach the center of the earth infinitely, the current method is still simple and crude, that is, digging a hole. The theory and method used in this are not difficult, the most important thing is cost and efficiency.

The deepest hole dug by humans so far is the "Earth Telescope" project of the Soviet Union in the last century.

Officials claimed that this scientific research would drill 15,000 meters underground, with the goal of letting humans learn more about the structure of the earth's interior. This plan naturally attracted attention from all walks of life. But unfortunately, this project, which lasted for 24 years, finally stopped at a depth of 12,262 meters. It was so close to the goal but chose to terminate, which also attracted many speculations at the time. But in fact, there is no mysterious reason, it is simply because it is too expensive.

Traditional hole digging technology has obvious defects: high cost and limited depth. The drill bit itself is very expensive and needs to be replaced frequently. It costs about $30 million to dig a hole with a diameter of 20 centimeters and a depth of 10 kilometers. In addition, the deeper the hole is dug, the worse the environment becomes. At 10,000 meters underground, the temperature reaches 300 degrees Celsius. Both the temperature and the hardness of the rock formation are beyond the ability of ordinary drill bits to withstand.

Therefore, due to economic and technical difficulties, the Soviet Union eventually stopped the exploration, and the scientific community's development of deep geothermal energy almost came to a standstill.

At present, the exploitation of geothermal energy is only concentrated in the cracks of some crustal plates or in the middle and shallow layers, and the utilization rate of this part is very limited compared with the overall geothermal energy. Most of the high-quality geothermal energy with a temperature of about 500 degrees Celsius is distributed about 10 kilometers underground, which is still "out of reach" for us.

Wave drilling technology: A new era for geothermal mining?

In April this year, the American technology company Quaise Energy announced that it was developing a "wave drilling" technology that can drill 20 kilometers into the ground and release unlimited geothermal energy.

The technology originated from a hypothesis proposed by American scientist Voskov during his research on nuclear fusion: if high-intensity electromagnetic waves are directed at stones, heating them until they evaporate, can the purpose of drilling underground be achieved? In the following decades, Voskov has been devoted to this research and founded Quaise, which has received over $70 million in investment.

The principle of wave drilling technology is not complicated. It uses a high-power millimeter wave transmitter to emit a strong beam of electromagnetic energy to melt and evaporate the rock in front of the drill bit. This digging technology has obvious advantages. Because the emitted light waves melt the rock, the drill bit itself does not come into contact with the rock. This has two advantages. First, the drill bit wears less and does not need to be frequently replaced with expensive drill bits. The cost is mainly in power consumption, which is almost 1/60 of the traditional digging method. Second, it is more conducive to the heat dissipation of the excavation equipment, which allows the drill bit to explore deeper and mine geothermal energy with better quality and higher temperature.

Wave drilling technology seems to have perfectly solved the problem of deep geothermal exploitation. Quaise currently claims in its plan that it will put millimeter wave technology into use in 2024 and conduct drilling experiments in combination with mechanical drill bits. In 2026, it will officially start drilling down to obtain heat energy and convert it into electricity. This news is undoubtedly exciting for all walks of life. After all, we don’t have much time left to reduce carbon emissions and control global warming.

If this technology can successfully meet expectations, it will usher in a new era of deep geothermal mining. Perhaps before the breakthrough of controlled nuclear fusion technology, humans can really realize the beautiful wish of having unlimited energy. Let us wait and see!

References:

Huttrer G W. 2020. Geothermal power generation in the world 2015-2020 update report[C]//Proceedings World Geothermal Congress 2020. Reykjavik: WGC.

Zheng Ke, Pan Xiaoping, Ma Fengjing, et al. Geothermal Utilization Technology[M]. Beijing: China Electric Power Press, 2018.

[3] Popular Science Black Hole: Drilling 20 kilometers into the Earth's crust! Releasing unlimited energy, what kind of technology does the wave drill of an American company have? [N/OL]. [2022-06-08]. https://baijiahao.baidu.com/s?id=1735063446249977548&wfr=spider&for=pc

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Reviewer: Professor Wang Lu from China University of Geosciences (Wuhan)