This year marks the centennial of the first commercial electricity production from geothermal resources. A technology centuries in the making, thermal energy generated from the Earth was used for hot baths, greenhouses, and direct heat long before it was harnessed as a power source.
Since the first modest 250-kilowatt geothermal power plant came online near Pisa, Italy in 1913, geothermal electricity production has grown steadily, tapping a reliable, nearly inexhaustible reserve of hydrothermal systems where fluid, heat, and permeability intersect naturally in the subsurface.
While the amount of conventional hydrothermal power worldwide has reached nearly 12 gigawatts, more geothermal resources can be accessed through next-generation technologies known as enhanced geothermal systems (EGS). The nation’s first commercial-scale EGS was brought online in April, connecting tomorrow’s technology to the U.S. electrical grid today and setting the stage for future growth of geothermal power.
Expanding Potential Sources
Unlike traditional hydrothermal geothermal systems, EGS capture heat from areas that traditional geothermal energy cannot—where fluid and/or permeability are lacking. EGS inject water to tap the heat from hot rock, transforming it into a working geothermal reservoir. By engineering a natural system, geothermal energy can produce power anywhere there is heat in the subsurface.
An MIT study produced for the Energy Department (DOE) estimates the domestic EGS potential at over 100 gigawatts, enough to power a tenth of the country.
HOW EGS WORKS
- Imagine taking an elevator down 900 stories—over two and a half miles into the Earth, where temperatures are upwards of 350°F—hot enough to bake a cake. Deep below our feet, hot rocks in the Earth’s crust compress and twist over thousands of years, causing fractures to form.
- Now imagine pumping cold water down that hole. In the same way an ice cube cracks when you drop it into hot tea, cold water cracks the rock at depth along weaker, pre-existing fractures, rushing through these small fractures and picking up heat like a sponge soaks up fluid.
- The fluid is then pumped to the surface, which spins a turbine, generating electricity.
The Road Ahead
To create a roadmap for EGS at lower cost and risk, DOE’s Geothermal Technologies Office (GTO) focuses on developing technologies where no natural hydrothermal system or geothermal infrastructure exists. Today DOE funds five active EGS demonstrations and several lab-scale research projects to help achieve this potential. Two of these demonstrations have reached milestones in accelerating the adoption of geothermal energy.
At the forefront of EGS development, DOE funded the nation’s first EGS success last year at the Geysers in northern California, the largest steam field in the world. Calpine Corporation and Lawrence Berkeley National Laboratory demonstrated a five-megawatt-equivalent steam power plant following a year-long stimulation along the outer edges of an operating geothermal field. The project successfully created a distinct reservoir in the corrosive, low-permeability "high temperature zone" (HTZ) beneath a geothermal producing reservoir. By accessing existing infrastructure, this EGS reservoir demonstrated that stimulating hot rock on the margins of an existing field can greatly increase energy production while keeping operating costs low.
In April, a second DOE demonstration project at Desert Peak, Nevada, completed an eight-month, multi-stage stimulation of an existing well, dramatically increasing flow rate from near zero to hundreds of gallons per minute through fluid injection. This project is now connected to the grid, making it the first EGS project in the country to generate commercial electricity.
While it is estimated up to 90% of geothermal resources in the nation could come from EGS, there are still barriers to commercial development including:
- High costs associated with drilling into hot-rock
- The ability to create and sustain an engineered reservoir
- The availability of subsurface data
However, DOE is aggressively targeting these barriers through investments in cutting-edge research, including high-power laser drilling. Two vital initiatives—the Geothermal Regulatory Roadmap and the National Geothermal Data System—will also help resolve market barriers by establishing a conducive environment for project developers and broadly disseminating data for industry and the public.
DOE’s Geothermal Technologies Office works with industry, academia, and our national labs to create new and exciting technologies that enable EGS to drill more efficiently, circulate water through fractures in rock, and track exactly where that water is flowing. Our work is helping the nation adopt technologies that reduce the risk and costs for industry to bring more of this clean, domestic renewable energy source online.
The potential benefits of geothermal energy are promising: EGS in particular hold the key to long-term sector transformation. Unlike early developments in geothermal energy, today’s advances have accelerated this game-changing technology ahead of schedule. To keep pace, DOE investments deliver cutting edge pathways for EGS, a technology that helps reduce harmful greenhouse gas emissions and diversify our energy economy.
View this animation to learn more about how EGS works.