The euphoria over nuclear energy as a power source for data centers is “overblown,” the CEO of a major power provider for large tech companies told CNBC in an interview Monday.

AES Corporation CEO Andrés Gluski said renewable energy is the future, though natural gas will also play a role as a transition fuel. Nuclear power, on the other hand, faces challenges in meeting the growing power demand from data centers, Gluski said.

AES is a major power provider for large tech companies building out data centers, with more than 40% of its 12.7 gigawatt backlog coming from customers including Amazon, Microsoft and Google, according to its most recent earnings presentation to investors.

Some Wall Street analysts have predicted a nuclear renaissance as power demand increases thanks to artificial intelligence, data centers, re-industrialization and the electrification of the vehicle fleet. Nuclear provides reliable, carbon-free energy, though new projects have long lead times and are expensive.

Gluski said the “euphoria” over nuclear power is a “little overblown.” There is only so much existing nuclear energy that merchant power providers can re-contract to sites such as data centers, the CEO said.

“The question is, going forward, what’s the price of new nuclear,” Gluski said, adding that only one new nuclear plant has been built in the U.S. in decades and it came in far above budget.

The second of two new nuclear reactors at Vogtle Plant in Georgia came online in April, but the project was seven years behind schedule and cost double the original projections, according to the Energy Information Administration. The reactors, operated by Georgia Power, are the first newly-constructed nuclear units built in the U.S. in more than 30 years, according to the Department of Energy.

“The Street got ahead of it saying you’re not going to build renewables, it’s all going be nuclear,” Gluski said. “It’s going to be natural gas and renewables, but the bulk of it’s going to be renewables,” the CEO said.

AES current gross power generation is 54% renewables, 27% natural gas, and 17% coal. Renewables represent 89% of the company’s gross power generation under construction while gas makes up the remaining 11%.

Gluski pointed to the recent agreement between Microsoft and Brookfield Asset Management for 10.5 gigawatts of renewable energy between 2026 and 2030 as a sign of the future. Microsoft and Brookfield described the agreement as the largest renewable purchase ever between two corporate partners.

“It tells you that’s where most of the energy is going to be coming from,” Gluski said. “They are cheaper, they are clean and quite frankly easier to site, so the future is going to be renewable energy.”

The natural gas industry views data centers as major source of demand growth, arguing that renewables will need a backup power source when they are not generating enough power due to sun or wind conditions.

“I do agree that we’re going to need natural gas to shore up, if you want, renewables until batteries become ubiquitous and cheap enough to make up for that,” Gluski said.

Goldman Sachs estimates that power demand from data centers will more than double to 8% of total U.S. electricity consumption by 2030, according to an April report. The investment bank sees natural gas supplying 60% of the demand growth, and renewables 40%.

But battery prices are coming down, the CEO said, and there is as much battery storage waiting for connection to the grid as solar power. There are some hours during the day in California where storage represents the biggest source of energy being dispatched, Gluski said.

“You can do it 100% with renewables, you just need a whole lot more renewables,” he said.

Solar, storage and wind represented about 95% of the power capacity in line waiting for connection to the grid at the end of 2023, while gas was just 3% and a grab bag made up the rest, according to Lawrence Berkeley National Laboratory. Renewables and storage in line for connection is nearly twice the installed capacity of the U.S. power plant fleet.

AES has already signed long-term contracts with data centers to provide them hourly matched renewable energy 24/7, Gluski said. “We’ve done that already for two years. So we can do that today,” he said.

AES signed an agreement with Google in 2021 to power its Virginia data center campus with 90% carbon-free energy on an hourly basis using a combination of wind, solar, hydro and battery storage resources.

The power company recently signed an agreement with Amazon for an additional gigawatt of solar and storage at a site in Kern County, California, bringing the project to a total of two gigawatts in a 15-year contract that is expected to come online in 2025 to 2026. AES has described the agreement as the largest solar and storage project in the U.S.

All told, the power company has signed agreements to provide Amazon with 3.1 gigawatts of power, Microsoft with 1.7 gigawatts, and Google with 800 megawatts, according to its first quarter earnings presentation.

“All of them want to be part of an energy transition,” Gluski said. “I don’t see anybody saying build me gas and coal plants to power my data centers, unless it’s a temporary situation, give me power from your gas plant until the renewables are available.”

AES stock is up 26% over the past three months and 6% year to date. Some 67% of Wall Street analysts rate AES the equivalent of a buy, 25% have a hold on the company’s stock and 8% rate it the equivalent of a sell.