NorthWestern : Energy joins the Western Energy Imbalance Market

Butte, Mont. - June 25, 2021 - NorthWestern Energy is now participating in the Western Energy Imbalance Market, operated by California Independent System Operator. The Western EIM is a real-time, within-hour energy market serving 10 states.

Since its launch in 2014, the Western EIM has been using advanced technology to find and deliver the lowest-cost energy to utilities.

NorthWestern Energy's participation in the Western Energy Imbalance Market will provide the company's Montana customers with economically efficient energy to resolve imbalances and variations in load and generation on our Montana system.

This achievement is the result of more than two and half years of preparation, data analysis and technology integration with NorthWestern Energy's system by NorthWestern Energy personnel. The last 18 months were complicated by safety precautions during the COVID-19 pandemic.

'We appreciate the flexibility of our team, including new team members hired in the past 18 months, and the assistance and guidance of the CAISO staff, which made this milestone possible,' said NorthWestern Energy Vice President Transmission Mike Cashell. 'This represents a significant change in the way we balance the system using advanced tools.'

NorthWestern Energy is now a member of the Southwest Power Pool Regional Transmission Organization for its South Dakota electric operations and the California Independent System Operator Western EIM for its Montana electric operations.

'NorthWestern Energy supports an incremental approach to energy markets in the West and has pursued the Western EIM because clear benefits exist for our customers,' said NorthWestern Energy Vice President Supply/Montana Government Affairs John Hines. 'Participating in the Western EIM will provide our customers access to cost effective energy and a market for our excess energy from intermittent generation sources when it is not required to serve our customers.'

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About NorthWestern Energy (Nasdaq: NWE)

NorthWestern provides electricity and / or natural gas to approximately 743,000 customers in Montana, South Dakota, and Nebraska. We have generated and distributed electricity in South Dakota and distributed natural gas in South Dakota and Nebraska since 1923 and have generated and distributed electricity and distributed natural gas in Montana since 2002. More information on NorthWestern is available on the company's website at www.northwesternenergy.com.

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