Three Mile Island is a nuclear power station in Pennsylvania. In September 2024, its owner, Constellation, announced that it signed an agreement with Microsoft whereby:
- Constellation would refurbish and bring online the 837 MW TMI-1 reactor at a cost of $1.6 billion by 2028.1 The reactor was taken offline in 2019 due to adverse economic conditions.
- The reactor will operate until at least 2054
- Microsoft has agreed to a twenty-year power purchase agreement.
Microsoft’s official announcement about this is here: Accelerating the addition of carbon-free energy: An update on progress.
A layperson’s description of this power purchase agreement is described in For Now, There’s Only One Good Way to Power AI - The Atlantic:
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Microsoft will buy enough carbon-free nuclear energy from the facility to match the power that several of its data centers draw from the grid, a company spokesperson told me over email.
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Microsoft will use the refurbished Three Mile Island to offset, rather than supply, its data centers’ electricity consumption suggests that the facilities will likely continue to rely on fossil fuels for some time2
Microsoft has committed to buy the power coming out of the plant and resell it to local markets to offset the power it uses in its own data centers (which can be anywhere in the country or world) which may rely on carbon-emitting power production. This effectively allows the utility company (Constellation) to not have to worry about losing money for selling expensive nuclear power instead of cheap gas-fired power, because Microsoft is effectively paying others to use carbon-free nuclear when they would have otherwise not.