Energy Storage

Borehole Battery: A Promising Solution for Energy Storage

For more than a century, fossil fuel companies have drilled oil and gas wells to increase the production, consumption, and export of fossil fuels. These wells are often abandoned once they are no longer profitable, and are sometimes left unplugged or improperly plugged, causing local environmental hazards and contributing to global climate change. There are more than 3 million abandoned oil and gas wells in the U.S. and, according to Reuters, there may be as many as 29 million oil wells abandoned globally. Abandoned and orphaned oil and gas wells pose significant public health problems and threats to the environment.

A properly abandoned oil well is permanently taken out of production and is typically sealed or plugged to prevent the release of oil, gas, or other substances into the environment. The responsibility for properly abandoning a well usually lies with the well operator. An orphaned oil well is one where the original well operator is no longer in business or cannot be identified. Orphaned wells pose environmental and financial challenges because there may be no responsible party to carry out proper closure and environmental remediation. An idle oil well refers to a well that is temporarily not producing oil or gas but has the potential to be brought back into production. It might be shut down for maintenance, repairs, or due to economic factors such as fluctuating oil prices.

There is a growing discussion that idle wells could be plugged while also repurposing the existing infrastructure for social and environmental benefits. Idle wells are preferred over abandoned and orphaned wells for repurposing because 80% of U.S. oil and natural gas production sites are documented as low production averaging less than 15 barrels of oil equivalent per day. Furthermore, choosing to plug and repurpose a low-producing well offers owners a strategic advantage in preparing for the “end-of-life” of thousands more wells that will soon become idle with the enforcement of costly penalties for methane emissions.

To repurpose and plug an idle oil well, Geo2Watts has developed a “Borehole Battery” comprised of a concentrating solar power (CSP) parabolic trough (Figure 1), paired with silicon dioxide (sand) packed into a borehole to plug and store thermal energy for generating dispatchable electricity from renewable sources. With this concept solar power heats sand in a closed-loop pipe extended into the borehole, storing heat at about 200C. When solar irradiance decreases during cloudy days and at night, the stored heat is released to an Organic Rankine Cycle (ORC) power plant, operating optimally at 150C. This integrated plugging system for continuous heat storage and extraction can provide both baseload and dispatchable electricity, commanding premium prices.

1. The Borehole Battery uses a concentrating solar power parabolic trough to heat sand in a closed-loop pipe, which extends into an idle oil well borehole, storing heat at about 200C. Courtesy: Geo2Watts

Sand’s ability to serve both as a heat transfer and insulating material is intriguing. This dual functionality is attributed to significant variations in thermal conductivity influenced by factors such as porosity, granularity, moisture content, and mineralogy. This unique characteristic allows sand to be effectively utilized for storing heat energy in idle oil wells whereby the heat can be produced by solar energy and circulated throughout the borehole. After extracting the heat from the sand, the cooled sand can be reheated with solar energy for storage within the well until the next cycle. This creates a closed-loop system, whereby the sand is repeatedly heated and cooled for continuous energy storage and extraction.

California’s electricity grid heavily relies on solar and wind energy, posing challenges in balancing supply and demand due to their intermittent nature. The state’s ambitious renewable energy goals sometimes result in surplus solar and wind power, particularly during certain times of day or year. To address this, the demand for dispatchable long-duration energy storage (LDES) could potentially reach 52 GW by 2045, if California’s plan to retire gas generation is successful. LDES will be increasingly more in demand for grids as global clean power generation increases and thermal energy storage emerges as a key competitive option offering lower lifecycle costs, better safety, easier maintenance, and less dependence on critical raw materials. Consider that lithium-ion batteries currently supply more than 90% of the world’s battery energy storage with short-duration eight-hour capacity.

In comparison to a lithium-ion battery, the Borehole Battery emerges as a more economical and environmentally friendly LDES option for producing dispatchable electricity. Its abundance, affordability, versatility, and non-toxic favorable thermal properties position it as a sustainable energy storage solution capable of meeting the demands of an increasingly renewable energy–dependent grid.

Phil Cruver is founder and CEO of Geo2Watts, which has developed a novel thermal energy storage technology using sand as a Borehole Battery. Geo2Watts is targeting California’s 37,000 idle oil wells for repurposing to produce dispatchable zero-emissions electricity energized by Inflation Reduction Act tax benefits.

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