Name: 地球的热量能否解决我们的能源问题（Could Earth's Heat Solve Our Energy Problems?）
Uploaded: 2021-06-05T17:46:10.000Z
Duration: 13 min 48 s
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基礎被動語態

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

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

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

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.

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

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

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

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地球的热量能否解决我们的能源问题（Could Earth's Heat Solve Our Energy Problems?）

potential

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common

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