It’s no secret that the data centers powering the AI age are enormously expensive: Annual operating costs for each are estimated to be in the tens of millions, and just getting one off the ground costs billions.

But once a data center is built, maintenance costs can be significantly reduced by fueling a majority of operations via clean energy, employing energy and water efficiency technologies, and computing sustainably. And while there’s no one-size-fits-all definition of a “green data center,” those that have been able to cut emissions and costs tend to focus on these fundamental practices.

Using idle energy: There are lots of data centers that run in part on clean energy from solar farms and rooftop and community solar, all of which can lower power prices. But to supercharge those savings, data-center developers can couple unused renewable energy with the need for more computing power.

Even though the US is facing an energy demand crisis, a lot of renewable energy actually gets wasted. States like California and Texas get a higher percentage of energy from renewables like solar and wind—but because those sources of power flow mostly during the day when energy demand is lower, large swaths of clean energy don’t get used if it’s not stored in batteries. In an effort to absorb some of that energy that would otherwise go to waste, Soluna Holdings, a data center developer, locates solar and wind farms that produce more than can be consumed and builds data centers nearby.

“There’s a lot of power in the grid,” CEO John Belizaire told Morning Brew. “You’ve just got to look in the right place.”

Once Soluna finds applicable renewable farms, it enhances the substation that connects the facility to the grid to allow it to power a data center, too. And when the data center is up and running, it’s powered mostly by clean energy (though it can draw energy from the grid when needed).

Because clean energy tax credits function on a “use it or lose it” basis, Belizaire said that Soluna eating up wasted energy benefits the renewable investors it partners with, too. The company currently has 2.8 gigawatts of data center projects in Texas.

“Where these [solar and wind farms] are located, there’s not a lot of load, and so it’s very hard for them to offload that power. They end up having to turn off the facilities, or half of the facility, and that can have a materially negative effect on their revenues and profit as an enterprise, and so we provide them a solution to that,” Belizaire said. “Computing should move closer to energy.”

Holistic efficiency: It’s not just the type of energy data centers use, but also how it’s used. Aaron Binkley, the VP of sustainability at data center developer Digital Realty, told us that energy efficiency starts with how buildings are constructed. Digital Realty’s buildings are LEED certified by the US Green Building Council “across 100+ different environmental metrics.”

“That’s the materials, that’s the construction process, it’s the water and energy performance of the data centers’ design,” Binkley said. “And then when we do need to do retrofits or refurbishments of those facilities, we’’re looking at sustainable aspects of the refurbishment over the life cycle of the building.”

Digital Realty’s green building design results in a 10%–25% improvement in energy efficiency and a 75%–90% reduction in water usage compared with a typical data center, which uses evaporative water cooling. Digital Realty uses air cooling at a majority of its data centers, and funnels recycled and reclaimed water for sinks, toilets, and landscaping.

“We’re typically using about the same amount or less water than the same size office building,” Binkley said.

All in all, Binkley said Digital Realty takes a well-rounded approach to sustainability.

“There may be some industry participants that are very good on the new construction, maybe less focused operationally. Others that are maybe very dialed in on operations, but don’t do much on the construction side,” he said. “Where I feel we’ve built a good mousetrap is to look at it holistically.”

Computing responsibly: A huge part of energy efficiency and sustainability is making sure that the computing equipment data centers are running on is efficient, too. Hillery Hunter, the GM of IBM Power and CTO of IBM Infrastructure, told us that the hardware and software used inside data centers are just as important as the type of energy being used to power the entire operation. “Because otherwise you’re just talking about, how renewable is the energy you’re wasting?”

She said when IBM operates data centers for its clients, the company recommends using up-to-date computer servers and optimizing the computers, data storage, and network for efficiency. On top of that, IBM monitors hardware efficiency so clients aren’t “just buying more and more servers, [they’re] getting the maximum out of them.”

Those optimizations can pay dividends: Hunter said that data centers using the most efficient hardware and software available can see up to an 80% reduction in their carbon footprint. And sustainability gains are more than just environmentally conscious and cost-saving—they’re also necessary for future advancement.

“If you’re not addressing sustainability, you’re not going to be able to fit the computing for AI, for example, into your data center,” Hunter said. “Sustainability isn’t a standalone topic. It’s not just a standalone goal. It’s really the foundation for growth.”