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The Battery Beneath Our Feet
The Battery Beneath Our Feet

 

When it comes to clean energy sources, solar, wind, and hydro often dominate the conversation. Moreover, when it comes to geothermal energy, Portland isn't the first place that usually comes to mind. A study led by Portland State University's Dr. John Bershaw may change all that.

Bershaw is an Assistant Professor in PSU's Geology Department, a fellow in the university's Institute for Sustainable Solutions, and a geochemist whose research focuses on the geochemistry of the sedimentary and layered volcanic rocks below our feet. He also heads a multidisciplinary team of researchers evaluating the feasibility of storing thermal energy generated during Portland's warm summers deep underground for use in winter—an emerging technology called Deep Direct-Use thermal energy storage. The US Department of Energy's (DOE) Geothermal Technology Office supports the study through a two-year, $720,000 grant. The project's partners include PSU geologists Dr. Ben Perkins and Dr. Ashely Streig, and PSU economist Dr. Jenny Liu. The US Geological Survey (USGS), the City of Portland, Oregon Health and Science University (OHSU), and AltaRock Energy, a geothermal development firm based in Seattle, Washington, are also involved.

Deep Direct-Use (DDU) is a highly efficient, emerging technology in the geothermal sector. DDU taps into heretofore unusable brackish or saline aquifers below the serviceable water table to store thermal energy at temperatures between 100° F and 300° F for direct applications such as heating and cooling large-scale residential, commercial, industrial, and agricultural buildings.

While China and several European nations have increased DDU capacity over the past decades, in the US adoption has been hampered by economic, regulatory, and geothermal resource barriers. Seeking viable options for diversifying the nation's energy supply and providing site-specific resilience to meet lower-temperature energy demands, the DOE last year invested $4 million in six geothermal DDU feasibility studies, including the project led by Bershaw.

If these comprehensive feasibility studies demonstrate the proof of concept of implementing DDU here in the US, the technology could supplement energy resources and provide an alternative to fossil fuels like natural gas currently used to condition indoor environments in many large-scale buildings. To warm or cool buildings using thermal energy from below our feet, however, requires reliable subsurface energy sources at implementation sites. The obstacle to deploying DDU in Portland and throughout much of the US is a lack of sufficient thermal resources in the layers of rock beneath us.

Bershaw's team proposed a novel solution to this problem: thermal energy storage. In regions like Portland where there is a shortage of subsurface thermal energy, it may be possible to transfer wasted heat generated by sources including HVAC systems and solar arrays into untapped and otherwise unusable salty aquifers where we could store the energy for later use.

Project partner Dr. Erik Burns, a research hydrologist at the USGS's Oregon Water Science Center in Portland, along with colleagues at the Menlo Park campus of the USGS in California, originally hatched the plan. The proposal was the only one of its kind to have received support from the DOE. The study aims to evaluate the feasibility of implementing a DDU thermal energy storage system at a new building on OHSU's South Waterfront location. Bershaw and his team will look at the project's feasibility from multiple angles, taking into account factors including geochemical and geophysical constraints, the regulatory environment, and the project's economic and carbon footprints. The team will also create a generalizable probabilistic model that others will be able to use to determine if the technology is viable in their regions.

"The challenge with conventional geothermal in places like the Cascades where there is a source of thermal energy has been circulating fluids below the surface to capture that energy," Bershaw said. "In the Portland metro, we don't have circulation problems, but we lack geothermal heat. So, we thought, why not try to capture the wasted thermal energy generated by cooling buildings during the summer, use it to heat fluids at the surface. Then we could inject that heated fluid deep underground, well below our usable aquifers, and store it there until we need the heat in winter."

The plan sounds simple enough. but determining whether it's feasible requires addressing layers of complexity. For one, the research team needs to evaluate the geology and geochemistry of the project's implementation site. While the plan is to collaborate with OHSU to consider what it would take to implement a DDU thermal energy storage system at one of the university's new buildings in the South Waterfront neighborhood, the question the study asks is, could this work anywhere in the Portland Basin? The basin encompasses a 770-square-mile area from roughly Southwest Washington's Lewis River to the north, to the Clackamas River to the south of Portland. To the east, the basin in hemmed in by the foothills of the Cascades. Portland's West Hills form the basin's western boundary. The study aims to determine the feasibility of deploying DDU thermal energy storage technology across the entire region.

Bershaw and a graduate student are compiling and analyzing data from a variety of sources to map the basin's geometry to understand its stratigraphy and the dynamics governing the circulation of fluids within the basalt rocks targeted for thermal storage. Streig and a graduate student are examining basin seismicity, and regional fault geometries, and assessing earthquake risk factors. Models and maps produced by Burns at the USGS will incorporate Bershaw's and Streig's contributions. Perkins is investigating the chemistry that could come into play in the surface/subsurface exchange of fluids and how the mineralization could affect the infrastructure circulating fluids from the source of thermal energy at the surface to the brackish aquifers and back again. Liu, meanwhile, is evaluating the technology's market potential and economic and operational feasibility in relation to existing energy options and the environmental benefits and impacts. In collaboration with the City of Portland, the team is conducting a regulatory review through engagement with relevant local and state agencies to identify and overcome potential regulatory hurdles. AltaRock Energy, the team's industry partner, is playing a critical role in designing infrastructure necessary to deploy DDU thermal energy storage technology.

"To the best of our knowledge, no one in the US has tested a project like this," said Burns. "And we know we have these deep saline aquifers with thermal storage potential throughout much of the country. There's the potential that this technology could be deployed almost anywhere in the US where there are cool winters and warm summers."

In 1948, J.D. Krocker, an engineer in Portland, Oregon, introduced the city to geothermal energy when he deployed the first commercial building use of a groundwater heat pump in the nation. Seventy years later, Bershaw and his team are asking if Portland could be the first city in the country to experiment with using DDU thermal energy storage technology to capture wasted heat and store it deep underground for later use as if there were a battery below our feet. If Bershaw's feasibility study can demonstrate the potential for overcoming the economic, regulatory, and technical barriers to adopting this new technology, buildings across the city, if not throughout the country, could one day capture what would otherwise be wasted energy. By putting that energy to use we could diversify the nation's energy supply and provide an alternative to fossil fuels like natural gas currently used to condition the indoor environments of many buildings throughout the US.

By Shaun McGillis - Research & Strategic Partnerships