AltaRock Energy is developing a breakthrough new energy source called Super Hot Rock. This new form of energy uses an Enhanced Geothermal System (or EGS) to mine heat from below the earth’s surface and produce electricity. Unlike conventional geothermal resources that rely on naturally occurring steam or hot water (like hot springs), hot rocks below the ground are everywhere and heat (thermal energy) can be extracted in every country in the world. Super Hot Rock uses temperatures above 400 °C where a single geothermal well, just 8 inches in diameter, produces the same amount of power as 320 acres of solar PV. Unlike solar and wind, however, geothermal is a reliable way to generate electricity 24/7 and is even more dependable than natural gas, coal and nuclear power. The earth contains over twenty billion times more heat energy than the entire planet consumes in a year. If we tap just 0.1% of this energy, we will have enough clean electricity for the next twenty million years. There would be no need for fossil fuels.
What is Super Hot Rock geothermal power and why is so important?
Super Hot Rock is a way to generate electricity while leaving all the carbon in the ground. Instead of extracting fossil fuels that move carbon from its natural state and into the atmosphere, Super Hot Rock uses heat from below the earth’s surface. The earth started as a sphere of molten rock 4.5 billion years ago and has been slowly cooling ever since. The center of the earth is still over 6,500 degrees Celsius, hotter than the surface of the sun. Radioactive components contained within the earth decay and release heat that reaches the surface. In some places heat can be found at very shallow depths, but everywhere, the deeper you go the hotter it gets.
An important threshold is reached around 400 °Celsius (675 °F). Water becomes a supercritical fluid and transports heat more efficiently than hot water or even steam. The rock mechanics, or how the rock behaves, also become consistent across rock types. Because of these special properties, we call this Super Hot Rock. In some places, Super Hot Rock is found as shallow as 5 kilometers below the surface and the average depth is 20 kilometers. Water is circulated to mine heat from the rock and bring it to the surface, in the form of superheated steam. It then drives a steam turbine connected to a generator and electricity is transmitted to your home.
Super Hot Rock is vital to the future of energy. Today, we are making great progress integrating solar and wind into the power grid. But it is not enough. We need to begin to retire all fossil energy, including natural gas, to remove carbon emissions from the electric grid entirely. This means replacing older forms of power generation with clean energy sources that are less expensive and more reliable. Super Hot Rock has the ability exceed the reliability (how consistently a power plant produces electricity) of both coal and nuclear, at lower cost, which makes it a superior form of energy. Furthermore, a power plant using Super Hot Rock has the highest energy density of any utility power source; 100 MW/km2 for Super Hot Rock heat production + power generation vs. 35 MW/km2 for uranium production + nuclear fission. The amount of energy per unit of land area will become increasingly critical as we move to a planet with 10 billion people.
Why has geothermal energy been limited?
There are many successful examples of enhanced geothermal systems (EGS) around the world today. Researchers and engineers have demonstrated the basic tools necessary to drill to depths where 200 C (400F) rock is found, open the rock fractures to create a geothermal reservoir and circulate water to extract heat. However, to achieve the performance necessary to scale EGS as a global energy source, we must go hotter and deeper. Specifically, we must access temperatures above 400 °C at depths over 5km, to efficiently produce Super Hot Rock. This requires special tools that are designed to withstand ultra-high temperatures and special techniques to extract the heat. AltaRock is developing the technology to achieve this.
What is the cost of the power?
Electricity generated from geothermal energy has historically been competitive with other forms of baseload power (coal and nuclear). In the last fifteen years, however, the cost of solar power has come down by a factor of over six and is now one of the cheapest sources of energy. What is not included in the cost of solar power is the cost of reliability. In order to rely on solar 24/7 as your only source of energy requires it to be available any time of day and night. This means you need to have a reliable power grid as backup or you need energy storage that provides power when the sun is down. At AltaRock, we think a better approach is to develop a low-cost energy resource that is inherently reliable. Super Hot Rock is capable of delivering power at a levelized cost of electricity equal to $0.05/kwh (5 cents per kilowatt hour), making it competitive with low-cost natural gas.
What is holding this energy source back?
Reproducibility of a product, any product, is critically important to maintaining consistent and expected results over-and-over again. It comes from minimizing, or eliminating, variation from the manufacturing process. This is true for making cars, appliances, drugs, food, and in the production of energy.
Geothermal electricity production started in the U.S. in 1960, and grew rapidly until the 1990s. The U.S. is the largest producer of geothermal electricity, but growth has slowed because geologists have found all the big reservoirs. Today, new geothermal reservoirs are smaller and harder to find. Future growth of geothermal is held back by a lack of consistent reproducibility, which makes it risky and prevents costs from coming down through repeatable methods.
So how do we overcome this?
We already know that a reproducible approach to energy production can substantially reduce development risk. For decades, geologists and geophysicists searched for reservoirs of oil and gas trapped in porous rocks. These reservoirs were getting smaller and harder to find because each one was different. Geologists had long known that hydrocarbons begin in rock called shale before migrating to a reservoir, but didn’t know how to extract the oil and gas directly from these nearly impermeable source rocks. Advances in 3-D seismic mapping aided by super computers, horizontal drilling with precision downhole guidance, and hydraulic fracturing converged and allowed developers to create permeability necessary for oil and gas to flow directly from this source rock. This breakthrough in the reproducibility of oil exploration and production arguably led to the largest energy transformation in history.
The way to overcome this hurdle for geothermal energy is to eliminate variability and allow the production of geothermal heat to be reproducible, anywhere in the world. Just like shale, this means developing tools to directly tap the source rock rather than exploring for unique locations containing geothermal fluids. The source rock for geothermal energy is found at depths where the temperatures exceed 400 °C, where the rock mechanics are consistent and predictable. This means that no matter where you are, if the temperature of the rock is “Super Hot” it will behave the same way whether you are developing geothermal in California, the Middle East or China. This enables the design of tools that are common across all geothermal resources and dramatically increases the predictability of drilling a successful production well. It reduces exploration time and expense, improves success rate and leads to reproducibility that dramatically lowers the cost of Super Hot Rock energy.
Ok, but why can’t we do this today?
There are several reasons;
- Conventional geothermal exploration still involves the production of naturally occurring geothermal steam or hot water, not the source rock.
- Geothermal drilling and completion cost is exponential with depth. The deeper you drill, the more expensive it becomes (especially so in hot rock). The rate of drilling also decreases with depth.
- Conventional hydraulic stimulation is only suitable for temperatures up to 150-200 °C, the maximum temperature encountered in oil and gas. This makes stimulating high temperature rock a challenge.
- The performance of most geothermal wells is far too low, producing only 2-5 MW’s on average per well. To achieve a low levelized cost of electricity, geothermal wells must exceed 10-20 MW’s per well.
Where do we go from here?
- Rather than producing locations where geothermal fluids circulate near the earth’s surface, we are developing tools to directly mine heat from the source rock. Geothermal heat is everywhere at an average temperature gradient of 35 Celsius per kilometer. So as long as we reach the necessary depth, we will always hit our target.
- The cost of drilling and completing a well is exponential with depth. This can be overcome using directed-energy, which transfers heat from the energy source directly into the rock and causes it to soften and break apart. With energy-drilling, rock hardness and temperature are no longer a limitation, casing can be replaced with in-situ rock melt (or case-as-you-go) and the cost of drilling a deep well becomes linear (constant) with depth.
- Altarock is a leader in the development of specialized materials that are used for high temperature stimulation. These materials are designed to withstand temperatures greater than 200 °C and can divert fluids without being limited to conventional oil and gas temperatures.
- Altarock has already successfully achieved temperatures capable of producing 10 MW’s per well at 300 °C and can produce over 40 MW’s of electricity from a single well when the temperature exceeds 400 °C.
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