Microsoft signs a 20-year deal to restart Three Mile Island Unit 1 as the Crane Clean Energy Center

A plant that closed for economic reasons

Three Mile Island Unit 1 stopped operating in 2019 for economic reasons, exactly five years before the September 2024 announcement. The unit was fully independent of Unit 2, the reactor that shut down after the 1979 accident.^[1] The restart plan therefore concerns a separate reactor, one that had been running until its owners concluded it could no longer earn enough to justify staying open.

The agreement

On 20 September 2024, Constellation announced that it had signed a 20-year power purchase agreement (PPA) with Microsoft. It was the company's largest-ever PPA, and it paved the way for restarting Unit 1.^[1][2]

A power purchase agreement is a long-term contract in which a buyer commits to purchasing electricity from a generator, usually at a pre-agreed price. For a plant that has already closed, such a contract is what turns an uncertain restart into something that can be financed: the buyer's commitment supplies the revenue stream that pays for the work.

The renewed plant will be renamed the Crane Clean Energy Center, after former Constellation CEO Chris Crane.^[1] The restart is expected to add approximately 835 megawatts of carbon-free energy to the grid. Microsoft will buy that energy to help match the power its data centers in PJM use with carbon-free energy.^[1]

Timeline and approvals

The Crane Clean Energy Center is expected to be online in 2028, subject to approval by the US Nuclear Regulatory Commission after a comprehensive safety and environmental review.^[1][2] Constellation will also pursue a licence renewal to extend the plant's operations to at least 2054.^[1]

The economic case

Constellation pointed to a Brattle Group study finding that the restart would create 3,400 direct and indirect jobs, add $16 billion to Pennsylvania's GDP and generate more than $3 billion in state and federal taxes.^[1]

Why it matters

Microsoft Vice President of Energy Bobby Hollis called the agreement "a major milestone in Microsoft's efforts to help decarbonize the grid in support of our commitment to become carbon negative".^[1]

Beyond one company's contract, the deal illustrates a pattern worth watching. Data center operators have large and growing electricity demand, and they are under pressure to source that demand from carbon-free generation. Existing nuclear plants offer firm low-carbon output that does not depend on the weather, unlike wind and solar. A long-term contract lets such a plant sell its output years in advance, and lets the buyer claim carbon-free electricity on the same grid where its facilities sit.

What makes this arrangement unusual is not that a technology company is buying clean power; it is that the power is coming from a plant that had already been shut down. The resurrection of a closed reactor depends on several things holding at once: a buyer willing to sign for two decades, a regulator satisfied by a fresh safety and environmental review, and a licence that can be extended far into the future. The announcement put all three in motion at once, with 2028 as the target for the plant to be generating again.^[1][2]