leading energy

Profile: Former Shell VP helps create a new way of making clean electricity with Houston company

Cindy Taff of Sage Geosystems shares her vision for her company and for the future of energy. Photo courtesy of Sage

When Cindy Taff was a vice president at the giant oil and gas company Shell in Houston, her middle schooler Brianna would sometimes look over her shoulder as she worked from home.

“Why are you still working in oil and gas?” her daughter asked more than once. “Is there a future in it? Why aren’t you moving into something clean?”

The words weighed on Taff.

“As a parent you want to give direction, and was I giving her the right direction?” she recalled.

At Shell, Taff was in charge of drilling wells and bringing them into production. She worked on oil and natural gas that's called unconventional in the industry, because the oil or natural gas is difficult to get out of the ground — it doesn't naturally gush out like in movies. It's a term often used for oily shale rock. Taff was somewhat unconventional for the industry, too. Her coworkers used to tease her for driving an efficient hybrid.

“You’re not helping oil and gas prices by driving a Prius," they'd say.

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EDITOR’S NOTE: This is part of an occasional series of personal stories from the energy transition — the change away from a fossil-fuel based world that largely causes climate change.

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Taff wanted Shell to pursue the energy that comes from the Earth's natural heat — geothermal. Her team looked into it, but Shell never greenlit any of those projects, saying it would take too much time to recoup the investment.

When Brianna went to college, she was passionate about energy too, but she wanted to work on renewables. After her sophomore year, in the summer of 2020, she got an internship at a geothermal company — one that in fact had just been launched by Taff's former colleagues at Shell — Sage Geosystems in Houston.

Now it was Taff looking over her daughter's shoulder and asking question as she worked from home during the pandemic.

And Sage executives were talking to Brianna, too. “We could use your mom here," they said. "Can you get her to come work for us?” Brianna recalled recently.

That's how Cindy Taff left her 36-year career at Shell to become chief operating officer at Sage.

“I didn't understand why Shell wasn't pursuing it,” she said about applying the company's drilling expertise to heat energy. "Then I got this great opportunity to pivot from oil and gas and work with these guys that I have the utmost respect for. And also, I wanted to make my daughter proud, quite frankly.”

Brianna Byrd, now 24, is the operations engineer and spokesperson at the company. She's glad her mother, now CEO, left oil and gas.

“Of course I’m biased, she’s my mom, but I don’t think Sage would be where it is without her,” she said.

The United States is a world leader in electricity made from geothermal energy, but this kind of electricity still accounts for less than half a percent of the nation’s total large-scale generation, according to the U.S. Energy Information Administration. In 2023, most geothermal electricity came from California, Nevada, Utah, Hawaii, Oregon, Idaho and New Mexico, where there are reservoirs of steam, or very hot water, close to the surface.

The Energy Department estimates this next generation of geothermal projects, like what Sage is doing, could provide some 90 gigawatts by 2050 — enough to power 65 million homes or more. That hinges on private investment, and on companies like Sage introducing this form of energy to regions where, until now, it’s been thought to be impossible.

How it works

Sage has two main technologies: The first makes electricity out of heat. The company drills wells and fractures hot, dry rock. Then electric pumps push water into those fractures, heating it up, and the hot water gets jettisoned to the surface where it spins a turbine.

But a funny thing happened during testing in Starr County, Texas. In late 2021, the team realized much of their technology could also be used to store energy.

If that works, it could be a big deal. Currently, to store energy at large scale, the United States is adding batteries, mostly lithium-ion type, to solar and wind projects, so they can charge up and send electricity back to the electric grid when the sun is not shining or the wind is not blowing. These batteries typically supply four hours maximum power.

Sage envisions some of its technology placed at solar and wind farms, too. When electricity demand is low, they'll use extra energy from a solar or wind farm to run electric pumps, pumping water into the underground fractures, leaving it there until demand for electricity increases — storing the energy beneath the Earth's surface for hours, days or even weeks.

It's a novel way to use the technology, said Silviu Livescu, lead author on a report looking at the future of geothermal in Texas. Livescu knows Taff and has followed the company's progress.

“It’s the right moment for companies like Sage with a purpose, with a mission and with the technology to show that geothermal indeed is the energy source we need to address climate change,” said Livescu, who co-founded a different geothermal startup in Austin, Texas.

These days, Taff is often out in front, talking with politicians and policymakers about the potential of geothermal. She attended the United Nations COP28 climate talks last year to share her vision for this kind of energy.

Sage has raised $30 million so far and is growing.

It's building a small (3-megawatt), geothermal energy storage system at San Miguel Electric Cooperative, Inc., south of San Antonio this year. It's working with U.S. military facilities in Texas that see geothermal as a way to power their bases securely. Sage recently announced partnerships for heating communities in Bucharest, Romania; clean electricity from geothermal for Meta's data centers, and energy storage and geothermal projects in California.

The company is final-testing a proprietary turbine to more efficiently convert heat to electricity.

Because of her oil and gas background, Taff said she knows geothermal will only be adopted widely if the cost comes down. The mantra at Sage is: It's going to be clean and it's going to be cheap. She's excited to be working in a field she feels is on the cusp of playing a big role in cleaning and stabilizing the electrical grid.

“I’ve never looked back,” she said. “I love what I’m doing and I think it’s going to be transformative.”

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A View From HETI

A key threshold for limiting global warming will be nearly unavoidable, scientists say. Photo via Pexels

Humans are on track to release so much greenhouse gas in less than three years that a key threshold for limiting global warming will be nearly unavoidable, according to a study released June 19.

The report predicts that society will have emitted enough carbon dioxide by early 2028 that crossing an important long-term temperature boundary will be more likely than not. The scientists calculate that by that point there will be enough of the heat-trapping gas in the atmosphere to create a 50-50 chance or greater that the world will be locked in to 1.5 degrees Celsius (2.7 degrees Fahrenheit) of long-term warming since preindustrial times. That level of gas accumulation, which comes from the burning of fuels like gasoline, oil and coal, is sooner than the same group of 60 international scientists calculated in a study last year.

“Things aren’t just getting worse. They’re getting worse faster,” said study co-author Zeke Hausfather of the tech firm Stripe and the climate monitoring group Berkeley Earth. “We’re actively moving in the wrong direction in a critical period of time that we would need to meet our most ambitious climate goals. Some reports, there’s a silver lining. I don’t think there really is one in this one.”

That 1.5 goal, first set in the 2015 Paris agreement, has been a cornerstone of international efforts to curb worsening climate change. Scientists say crossing that limit would mean worse heat waves and droughts, bigger storms and sea-level rise that could imperil small island nations. Over the last 150 years, scientists have established a direct correlation between the release of certain levels of carbon dioxide, along with other greenhouse gases like methane, and specific increases in global temperatures.

In Thursday's Indicators of Global Climate Change report, researchers calculated that society can spew only 143 billion more tons (130 billion metric tons) of carbon dioxide before the 1.5 limit becomes technically inevitable. The world is producing 46 billion tons (42 billion metric tons) a year, so that inevitability should hit around February 2028 because the report is measured from the start of this year, the scientists wrote. The world now stands at about 1.24 degrees Celsius (2.23 degrees Fahrenheit) of long-term warming since preindustrial times, the report said.

Earth's energy imbalance

The report, which was published in the journal Earth System Science Data, shows that the rate of human-caused warming per decade has increased to nearly half a degree (0.27 degrees Celsius) per decade, Hausfather said. And the imbalance between the heat Earth absorbs from the sun and the amount it radiates out to space, a key climate change signal, is accelerating, the report said.

“It's quite a depressing picture unfortunately, where if you look across the indicators, we find that records are really being broken everywhere,” said lead author Piers Forster, director of the Priestley Centre for Climate Futures at the University of Leeds in England. “I can't conceive of a situation where we can really avoid passing 1.5 degrees of very long-term temperature change.”

The increase in emissions from fossil-fuel burning is the main driver. But reduced particle pollution, which includes soot and smog, is another factor because those particles had a cooling effect that masked even more warming from appearing, scientists said. Changes in clouds also factor in. That all shows up in Earth’s energy imbalance, which is now 25% higher than it was just a decade or so ago, Forster said.

Earth’s energy imbalance “is the most important measure of the amount of heat being trapped in the system,” Hausfather said.

Earth keeps absorbing more and more heat than it releases. “It is very clearly accelerating. It’s worrisome,” he said.

Crossing the temperature limit

The planet temporarily passed the key 1.5 limit last year. The world hit 1.52 degrees Celsius (2.74 degrees Fahrenheit) of warming since preindustrial times for an entire year in 2024, but the Paris threshold is meant to be measured over a longer period, usually considered 20 years. Still, the globe could reach that long-term threshold in the next few years even if individual years haven't consistently hit that mark, because of how the Earth's carbon cycle works.

That 1.5 is “a clear limit, a political limit for which countries have decided that beyond which the impact of climate change would be unacceptable to their societies,” said study co-author Joeri Rogelj, a climate scientist at Imperial College London.

The mark is so important because once it is crossed, many small island nations could eventually disappear because of sea level rise, and scientific evidence shows that the impacts become particularly extreme beyond that level, especially hurting poor and vulnerable populations, he said. He added that efforts to curb emissions and the impacts of climate change must continue even if the 1.5 degree threshold is exceeded.

Crossing the threshold "means increasingly more frequent and severe climate extremes of the type we are now seeing all too often in the U.S. and around the world — unprecedented heat waves, extreme hot drought, extreme rainfall events, and bigger storms,” said University of Michigan environment school dean Jonathan Overpeck, who wasn't part of the study.

Andrew Dessler, a Texas A&M University climate scientist who wasn't part of the study, said the 1.5 goal was aspirational and not realistic, so people shouldn’t focus on that particular threshold.

“Missing it does not mean the end of the world,” Dessler said in an email, though he agreed that “each tenth of a degree of warming will bring increasingly worse impacts.”

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