How a former Shell executive became a clean energy CEO

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. 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. 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 geotherma