When you stream a movie, back up a photo or ask ChatGPT a question, somewhere a data center is working hard — and getting hot. Cooling those facilities already consumes a huge share of their electricity, and nearly half of that energy leaves as low-temperature waste heat that’s simply vented into the air.
A new study from Rice University shows how to turn that waste into power.
“There’s an invisible river of warm air flowing out of data centers,” said Laura Schaefer, the Burton J. and Ann M. McMurtry Chair of Mechanical Engineering at Rice and co-author of the paper. “Our question was: Can we nudge that heat to a slightly higher temperature with sunlight and convert a lot more of it into electricity? The answer is yes, and it’s economically compelling.”
Published in Solar Energy, the research introduces a novel solar thermal-boosted organic Rankine cycle (ORC) — a compact power system that uses a safe working fluid to make electricity from heat. The twist is adding low-cost, rooftop flat-plate solar collectors to warm the data center’s coolant stream before it reaches the ORC. That extra “solar bump” overcomes what has been the main technical barrier until now: Data center waste heat is typically too cool for efficient power generation on its own.
Data centers already draw hundreds of terawatt-hours annually, which equates to roughly a midsized country’s demand, and AI growth is accelerating that curve.
“Efficiency gains are being outpaced by demand,” said Kashif Liaqat, a graduate student in mechanical engineering at Rice. “If we want the digital economy to be sustainable, we have to reclaim some of the energy that is currently just thrown away.”
Traditional fixes, like using electric heat pumps to raise temperatures before recovery, can wipe out benefits because they consume significant extra power.
“Solar thermal gives us the temperature lift without adding to the plug load,” Schaefer explained. “It’s a cleaner, simpler pathway.”
Schaefer and Liaqat created detailed thermoeconomic models, which they validated against industry tools, to test performance in two of America’s biggest data center hubs with very different climates: Ashburn, Virginia, and Los Angeles. They modeled rooftop solar collectors feeding a right-sized ORC tied into a representative liquid-cooling loop.
The results were striking. The system recovered 60-80% more electricity annually from the same waste heat with a 60% boost in Ashburn and an 80% boost in Los Angeles. It also achieved over 8% higher ORC efficiency during sunny peak hours, along with an increase in annual average efficiency. Even more, the approach lowered the cost of electricity from the recovered power — by 5.5% in Ashburn and by 16.5% in Los Angeles.
“Los Angeles performed better because of stronger solar resources,” Liaqat said. “But even in Ashburn, where winters are colder and cloudier, the hybrid system meaningfully increases output and cuts costs.”
An unexpected upside: The approach performs best under the conditions most data centers already have, where modern computer servers are cooled with liquid systems that don’t get extremely hot.
“What the industry considers a weakness becomes a strength once you add solar,” Liaqat said. “That’s great news for modern data centers.”
Schaefer and Liaqat designed their system to use simple, affordable, low-profile solar collectors (like the kind often seen for heating water) mounted on rooftops and connected directly into the cooling system of the data center — an innovative use of off-the-shelf technology. Because the ORC sits on the waste-heat side, the recovered power directly offsets grid consumption for the facility.
“Think of it as adding a clean, behind-the-meter generator that gets stronger when the sun is out — right when cooling loads are highest,” Schaefer said.
The researchers said the next steps should include piloting the hybrid system at an operational site and exploring thermal storage, which could bank solar heat during the day to boost recovery at night. They also plan to evaluate other collector types for colder regions.
“We’re not saying this replaces efficiency work on servers or cooling, which is also crucial,” Schaefer said. “But we are adding a new tool to the kit — one that turns a liability into an asset.”
This research was supported by the Alliance for Sustainable Energy LLC, the National Renewable Energy Laboratory and the U.S. Department of Energy.