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  • This episode of Real Engineering is brought to you by Brilliant, a problem solving website

  • that teaches you to think like an engineer.

  • One of the biggest challenges facing mankind today is our quest to transition to renewable

  • energy. Overhauling our entire electricity grid requires drastic changes to be made in

  • the way we produce, transport, use and store electricity. We have explored in past videos,

  • that with the lowering cost of solar and wind, we are beginning to hit a point of imbalance

  • in the grid. Where places like California are wasting massive amounts of energy in the

  • summer months, when solar is at its peak and not producing enough in the winter. To deal

  • with this problem California is now installing gigantic battery storage facilities in places

  • like Moss Landing to store that excess for later use, but the amount of battery storage

  • that they will require as our percentage of renewables increases is going to cost the

  • state billions, if not trillions.

  • We could drastically decrease this dependence on batteries, if we could find a nice stable

  • energy source that did not harm our planet. Some want to turn to nuclear energy, but what

  • if I told you the solution may be lying directly under our feet.

  • Imagine an ancient, hidden energy source, deep within every square meter of our planet's

  • surface. It's clean, flexible, virtually limitless, completely renewable, never turns

  • off and virtually carbon free. Geothermal energy, the energy produced by the earth itself

  • in the form of heat, can be that solution.

  • Geothermal energy is produced by the Earth's inherent heat. The center of the earth (On

  • screen: 6500km deep) is as hot as the surface of the sun (6000 °C). Through convection,

  • that heat warms the outer layers of the planet. But where does this heat come from? Much of

  • it comes from gravitational forces when the planet first form 4 billion years ago, some

  • heat is generated from friction as denser elements make their way to the earth's core.

  • The other source of Earth's internal heat occurs in the upper mantle and crust, where

  • the decay of radioactive isotopes, like Potassium-40, creates energy, and in turn, heat. If we could

  • find a way to safely and cost effectively access that heat our energy problems would

  • be solved in years.

  • That heat does come to the surface in some easily accessible locations. At temperatures

  • of 700 °C or more, rocks become partially melted, becoming magma, driving a variety

  • of geothermal phenomena. If magma flowing underground heats gases or water it can create

  • bubbling hot springs and geysers, undersea hot vents, and natural steam vents. These

  • features can provide water that's more than 200 °C, more than enough to run a steam turbine.

  • Geothermal hot spots like this are found near the boundaries of tectonic plates, like Iceland,

  • in volcanically active areas, like Turkey, or in some places where Earth's crust is

  • thin, like America's Yellowstone National Park. These places provide low hanging fruit

  • to harvest the earth's heat for our energy needs.

  • Each year enough heat flows (44 TWth) to the planet's surface to meet total global energy

  • consumption twice over [1]. And the geothermal reservoir is boundless: heat within 10km of

  • Earth's surface contains roughly 50,000 times more energy than all fossil fuel resources

  • worldwide [2].

  • Yet geothermal energy makes up less than 1% of global installed electricity capacity.

  • This isn't even a technology issue, of the global potential for geothermal power using

  • off-the-shelf technology, only 7% has been tapped [3]. So in the fight to transform our

  • global energy system, why haven't we adopted this energy source in a serious way?

  • Let's first look at our low hanging fruit, that are not being used to their full potential.

  • Naturally occurring hydrothermal reservoirs feature hot water that percolates near the

  • surface through porous or cracked rock layers. This is the easiest form of geothermal energy

  • to harvest, and can be tapped in several ways, which we have been doing for centuries.

  • Human societies have used the heat from low-temperature (150 °C) geothermal energy for millennia.

  • Among the most famous examples may be the hot springs of Bath, England, established

  • by Roman engineers in 60 CE. Here 1 million litres of water percolate to the city centre

  • of bath every day at a temperature of about 45 degrees, heating recreational baths and

  • heating some buildings. This hot water replenishes itself as rain that falls in nearby hills

  • seeps through porous limestone deep underground where it is heated and rises back to the surface.

  • [4]

  • But convenient locations like this where the right combination of a water cycle, with porous

  • rocks underground and a heat source close enough to the surface to heat it, are rare,

  • and ones that can provide water with enough heat and pressure to run a steam turbine are

  • even rarer. This particular source is not suitable, as 45 degrees is far off the lowest

  • temperature we can employ.

  • There are three basic types of geothermal energy generators. All three share the same

  • basic idea. Take hot water or steam from a geothermal reservoir

  • and run it through a steam turbine where it loses energy and condenses before being pumped

  • back underground to keep the cycle going. Dry Steam generators take the steam directly

  • from the source to run a turbine. A flash steam power plant takes extremely hot water

  • under pressure above 100 degrees, and expands it quickly to lower its boiling point and

  • turn it steam to run the steam turbine.

  • These both require higher temperature sources that are rare, [5] but they are relatively

  • common in geothermally active regions like Iceland, Italy, Austria and around the Pacific

  • ring of fire, and in these locations geothermal energy is common and is expected to grow as

  • much at 28% in the next 4 years, with countries in South East Asia expected to see the largest

  • growths like Indonesia and the Philippines. [6]

  • But we want to exploit geothermal energy outside of these regions. No matter how much power

  • we can extract we can't transport it far before power losses due to resistance in the

  • cables saps it away. The third type of generator provides the highest potential for expanding

  • geothermal energy as it can utilise the lowest temperature sources.

  • This system is called a binary cycle system. In a binary cycle power plant, warm water

  • from a geothermal source passes through a heat exchanger where it exchanges heat with

  • a closed loop containing a fluid with a low boiling point, like pentane, which has a boiling

  • point of 36 degrees. The lower boiling point allows it to transition to a gas at a much

  • lower temperature, allowing it to run a turbine at a lower temperature.

  • This system has allowed countries like Germany [7], which lacks any shallow depth geothermal

  • resources, to grow their geothermal energy market in recent years with temperatures as

  • low as 100 degrees celsius being utilised. That figure is important, because the higher

  • the temperature the deeper we have to drill.

  • Different areas have different geothermal gradients, which is a measure of how quickly

  • temperatures rise as we drill down. This map shows a rough estimate of the geothermal gradient

  • across the US [8], with the highest gradients being found in Oregan and Idaho reaching as

  • high as 70 degrees per kilometre. This is important, as to access this heat in areas

  • where it doesn't naturally come to the surface in an accessible way we need to drill down

  • and the further down we need to drill the more expensive it becomes.

  • Typically we have only used geothermal resources where the natural permeability of the rock

  • allows a convective heat cycle, but a new technology by the name of Enhanced Geothermal

  • Systems or EGS, may open the door to geothermal energy to more regions.

  • It works like this. The first step is to drill an injection well into a formation of hot

  • rocks. Then engineers inject fluid at pressure to form cracks or enlarge existing ones, this

  • increases the area over which heat exchange with the rocks can occur. To increase this

  • area even further a non-toxic and degradable material is pumped down to fill these cracks

  • and allow the pressure to form new cracks as we drill further down. Once we have opened

  • an adequate number of passages for the water to fill we can drill additional holes that

  • can take act as an outlet for our hot water as we pump more underground.

  • A report by MIT in 2006 [9] found that EGS could provide electricity at a cost as low

  • as 3.9 cents per kilowatt hour, roughly equivalent to a coal-fired power plant. The United States

  • government estimates [10] that new geothermal power plants could produce 60 gigawatts of

  • electric power on American soil by 2050, mostly through EGS systems.

  • Now I know what you are thinking, this sounds a lot like the controversial practice of fracking,

  • but it doesn't use toxic fracking fluid which can seep into our water cycle, it uses

  • water and some safe additives, but it's not all plain sailing. [11] To make this work

  • we need to create great volumes of fractures and cracks and this can have some disastrous

  • consequences.

  • In 2017 drilling at a proposed site for EGS in Pohang, South Korea [12], is thought to

  • have triggered an earthquake of 5.4 magnitude that injured 135 people. A previous incident

  • occurred at an EGS plant in Basel, Switzerland in 2006, when drilling may have caused a quake

  • of magnitude 3.4, and several buildings were damaged. Both projects were cancelled as a

  • result.

  • Red tape is a huge obstacle for Geothermal Energy. In the United States, for example,

  • there's less environmental paperwork and fewer approvals required for drilling for

  • oil than drilling a geothermal well. Tax credits for wind and solar power project are 30% while

  • the tax credit for geothermal is only 10%. [13]

  • On top of all this, drilling is very expensive and as we have seen doesn't guarantee a

  • successful geothermal plant. You could waste months of your time digging a 2 kilometre

  • hole in the ground and the productivity of the well could be too small to make the project

  • worthwhile. That makes it difficult to find investors willing to bet their money on it.

  • It simply makes more sense to invest in solar and wind.

  • Despite the challenges, there's real hope for expanding geothermal energy. The industry

  • can build off of recent improvements in drilling technology. [14] Engineers are developing

  • new kinds of drills for geothermal wells, and better techniques for cementing wells

  • drilled into hot rocks. The earthquake risk is real, but engineers have protocols for

  • monitoring with seismometers to ensure that the seismic risk can be assessed early on.

  • In the case of the Basel accident, the EGS facility was located over a seismic fault,

  • due to the proximity of hot rocks to the surface. Once the shaking started, fluid injection

  • was halted immediately. So far, geothermal projects haven't attracted strong political

  • support in the West, but they also haven't drawn major opposition, suggesting that easing

  • permitting rules for the technology may not be so challenging. As commercial interest

  • in this clean energy source rises, political support for it should follow, especially if

  • some smart politician realises it can be a rallying call for getting out of work oil

  • drilling techs back to work.

  • Sometimes the struggle to convert the global energy system to renewables can seem out of

  • reach and feel hopeless. But in the case of geothermal energy, there's an exciting source

  • of electricity and heat that could power our future, and it's right below our feet.

  • As I said at the start of the video, much of the energy present within earth is formed

  • as a result of gravitational forces. You can learn everything gravity is capable of by

  • taking this course on Brilliant.

  • This course will take you from the very basics of what gravity is and build your knowledge

  • up to the point of being able to apply Kepler's laws of planetary motion and understand orbital

  • mechanics like using the slingshot effect where space ships using a planet's gravity

  • to increase their speed. It's a fascinating course that I can't recommend enough.

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  • with you with interesting scientific and mathematical problems to test your brain

  • Each Daily challenge provides you with the context and framework that you need to tackle

  • it, so that you learn the concepts by applying them. If you like the problem and want to

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This episode of Real Engineering is brought to you by Brilliant, a problem solving website

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Could Earth's Heat Solve Our Energy Problems?

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    joey joey に公開 2021 年 06 月 05 日
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