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.

Or you could complete one of Brilliant's daily challenges. Each day Brilliant presents

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

learn more, there's a course quiz that explores the same concept in greater detail. If you

are confused and need more guidance, there's a community of thousands of learners discussing

the problems and writing solutions. Daily challenges are thought provoking challenges

that will lead you from curiosity to mastery one day at a time.

If I have inspired you and you want to educate yourself, then go to brilliant.org/RealEngineering

and sign up for free.And the first 500 people that go to that link will get 20% off the

annual Premium subscription, so you can get full access to all their courses as well as

the entire daily challenges archive.

As always, thanks for watching and thank you to all my Patreon supporters. If you would

like to see more from me the links to my instagram, twitter, subreddit and discord server are

below.