Course Content

Surface Footprint

Energy is a Hot Topic Environmental Considerations for Geothermal Energy Surface Footprint

All energy systems, whether they generate molecules or electrons, require construction of infrastructure, such as wells, turbines, pipelines, power plants, transmission lines, etc. Surface space to host production facilities is required across the board, whatever the energy source may be. Fortunately, given the design, deployment, and use of many different utility scale energy systems for over a century, we have a thorough understanding of the surface footprints that (at least historically) have been required for these systems. Innovation has reduced surface footprints as systems have evolved with time, experience, and an acknowledgment of the importance of land conservation as an ancillary goal.¹

At the moment, geothermal has the smallest surface footprint compared to other energy sources. Geothermal projects use 1-8 acres per megawatt (MW) versus 5-10 acres per MW for nuclear-operations and 19 acres per MW for coal power plants.² A binary plant only needs 2% of the land required for a solar energy installation with a similar capacity. However, total land use could increase as new technologies emerge that require the storage of wastewater brines and fluid cooling/condensing. With any energy technology, we must consider other indirect ways that land is altered. Researchers look at land modifications due to transmission lines, mining for infrastructure materials, vegetation removal (which can cause increased dust and soil erosion), and more. These impacts are all common with any kind of energy infrastructure, but they differ depending on the energy source and must be considered when building an energy profile for a community.³

The cooling towers of the Ormat Tungsten Mountain hydrothermal plant, located in Nevada⁴

Learnings from Oil and Gas

In research relevant to geothermal development, Pierre, et al., (2017⁵; 2020⁶) reported on a time series of land surface alteration from drilling pads (and, by extrapolation, from pipeline construction) for the Eagle Ford and Permian Basin areas of Texas, respectively. They showed a spectrum of current land alteration scenarios that depended on degree of drilling and number of multiwell drilling pads, though restoration following on-site activities have mitigated some of these impacts. Because geothermal development in Texas is likely to follow the paradigm of drilling used in oil and gas, also known as “pad drilling,” this research gives perspective of what largescale geothermal deployment might look like in Texas.⁷

Beginning in the early 2000’s, unconventional (shale and tight rock) plays became the dominant source of fossil energy exploration, leading to a larger per well support area needed for each well, particularly in the size of the drill pad; 1.5 hectares and up, much larger than typical well pads (Johnson, 2010⁸). Because of the need for tight lateral spacing and much smaller drainage volume per well, the spacing of well pads have become closer, creating denser landscape alteration patterns (McClung & Moran, 2018⁹).¹⁰

A production site representative of a multi-well pad drilling process in the Denver-Julesburg Basin (DJ Basin)

Note that, although the number of geothermal plants in the United States is relatively small, and there are currently zero geothermal plants in Texas, experience that could be transferred from the oil and gas industry is significant, especially with respect to land use needs. Both industries require drilling pads for hosting boreholes, both benefit from horizontal drilling and stimulation (in the case of EGS), and both connect wellheads to infrastructure that captures an energy product.¹¹

Wind

Renewable energy generating facilities, specifically in the form of wind and solar installations, also impact landscapes in diverse ways. Land alteration from wind energy in particular differs from other energy sources, not only because the tower, turbine, and blades are above ground, but also because the blades have a wingspan that far exceeds its surface footprint. Different researchers approach the total (direct and indirect) impact of onshore wind energy differently. One well-cited study (Denholm, et al., 2009¹²) evaluated 172 existing or proposed (at the time) projects, focusing more on land area occupied and less on intensity of the impact. These researchers illustrated nuances of the direct impact of turbine pads, roadways, support areas, etc., and a more vague, more subjective use of indirect land use that is included in total area, including spaces between turbines or the blades themselves (depending on blade length).¹³

Land alteration for wind in particular is sometimes vaguely defined, because the land between turbines, still within the facility boundary, often remains in use (e.g., for agriculture), hence the use of two different land use intensity values for wind; one for just the land use for the tower (Wind-), and the other that includes the space between the towers (Wind+). Impacts to habitats, avian species, and other site operations (for example, other infrastructure) are often site specific and would require specific analyses, sometimes down to a species level, or ecosystem service approaches.¹⁴

The Brazos Wind Farm, also known as the Green Mountain Energy Wind Farm, near Fluvanna, Texas. Note cattle grazing beneath the turbines.

Solar

Land alteration from solar energy infrastructure is easier to quantify than from wind energy because photovoltaic panels and related hardware are closer to the ground, often one to two meters above the surface. Moreover, the infrastructure is often more densely packed, removing some of the ambiguities of indirect impacts, as is the case for turbines. As reported by Lovering, et al., (2022¹⁵), the land use intensity for ground mounted solar photovoltaic panels is over 40 times higher than for geothermal.¹⁶

Geothermal

In general across all technologies, a single representative value of land use for all of geothermal facilities and designs is difficult to determine. A midrange estimate ranges from 500 megawatts per square kilometer (or 0.49 acres per megawatt) (DOE, 1997¹⁷) to approximately 1,000 megawatts per square kilometer (0.97 acres per megawatt (Lovering, et al., 2022¹⁸). A few factors relevant to geothermal land needs are the quality and lateral extent of the reservoir, the efficiency factor of the plant, and the number and interspatial distances between drilling pads and pipelines needed for moving fluids.¹⁹

A key factor in total land use is the potential need to store wastewater brines, particularly in the case of conventional geothermal systems. Though this is less likely to be relevant in Texas as next generation concepts are deployed, if necessary, these vessels could increase land use by 75 percent.²⁰

Once drilling is complete, next generation geothermal systems (EGS, etc.) offer the potential for smaller footprints relative to hydrothermal systems in two ways. First, these systems are anticipated to be in the low tens of megawatts per installation, with density of installations kept low for geophysical reasons. Generation will therefore most likely be located immediately adjacent to the drilling pad, minimizing the footprint created when above or below ground pipelines are needed to move fuel. Second, the emerging supercritical CO₂ based turbines have demonstrated an order of magnitude or greater reduction in size when compared to current state-of-the art Organic Rankine Cycle turbines, thus allowing for a small post drilling footprint. These new technologies may allow next generation geothermal plant turbomachinery components for a several megawatt pilot plant to fit within the size of a tractor trailer container (Sage Geosystems, 2021²¹).²²

That said, currently, even next generation plant concepts will require fluid cooling/condensing, which is a contributor to the surface footprint of geothermal developments. Further, the climate in summer months poses a challenge for traditional air cooling technologies in states that tend to be hot in the summer, and may increase the square footage requirement of cooling systems to maintain performance efficiency. This is an area where both innovation and piloting is needed to further understand the impact that geothermal plant cooling/condensing requirements will have on the footprint of new future developments.²³

Other Land Use Considerations

The impact of transmission lines constitutes the largest source of the range in land use estimates reported at around 0.215 to 1.485 square kilometers per 30 to 50 megawatt plant. This is equivalent to about nine acres per megawatt, assuming a 40 megawatt capacity, which is a footprint similar to that of utility-scale solar.²⁴

To further reduce an effective land footprint and potential land fragmentation issues, site remediation and conservation practices should be considered at the initial stages of facility design and then implemented as soon as practicable, so that long term impacts are minimized. Measurable reductions in regional land alteration were noted in the Eagle Ford Shale play (Pierre, et al., 2015²⁵), one of the largest in Texas, after consistent land reclamation practices were implemented.²⁶

Disturbances from removal of vegetation can increase dust emission potential, which can be a respiratory hazard in humans, especially for utility scale solar energy, with blading and grading for the panels, frames, and broads. Dust erosion, although potentially significant in long-term solar panel efficiency, is probably not an issue in the geothermal context.²⁷

Image Credits

Cooling-towers-Ormat-Tungsten-Mt-hydrothermal-plant-Nevada-FOGIT: The Future of Geothermal in Texas, Ormat Technologies
Multi-well-production-site-DJ-Basin: photo courtesy of Hilary Olson
800px-Wind_turbine_blade_transport_I-35-Wiki: Alexi Kostibas, Wikipedia
800px-GreenMountainWindFarm_Fluvanna_2004-Wiki: Leaflet, Wikipedia

Oklahoma Academic Standards

Environmental Science: 3.1, 3.2, 3.3, 3.4, LS2.7
Earth and Space Science: 3.1, 3.2, 3.5
Physical Science: PS3.1, PS3.2, PS3.3, PS3.4

TEKS Standards

Earth Systems Science: 1.A, 1.D, 2.C, 2.D, 3.B, 3.C, 4.A, 4.B, 4.C, 9.D, 12.E, 13.A, 13.B
Environmental Systems: 1.A, 1.D, 4.A, 4.B, 4.C, 6.A, 6.B, 6.C, 6.E, 6.F, 10.A, 12.A, 12.C, 12.E

College Board Units and Topics

AP Environmental Science: 5.1, 5.9, 5.11, 6.1, 6.3, 6.4, 6.5, 6.8, 6.10, 6.12

Next Generation Science Standards

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