Document mBJorrEgy880V9vxqwnXbMapk

USCA Case #24-1190 Document #2062093 Filed: 06/27/2024 Page 24 of 123 shows, the amount of electricity generated by wind facilities can quickly and significantly change. NorthWestern, however, must continue to balance at all times the electricity demands of customers with the amount of electricity supplied. This balancing is imperative; deviations between generation and customer demand of relatively tiny percentages for even a small amount of time (seconds to minutes) will lead to system instability, customer equipment damage, and blackouts. 61. During the Winter of 2023-2024, thermal generation, especially Colstrip, played a key role in helping provide reliable and affordable service. The variable cost of Colstrip was about $231MWh. Unfortunately, North Western's customers were subject to extreme market prices from NorthWestern's market contracts. As an example, market contracts cost our customers up to $9001MWh. NorthWestern purchased about $40 million of power during this 6 day critical weather period, which had wind and solar underperforming, even less than their accredited capacity. 23 Sierra Club FOIA 2025-EPA-04883 ED_018388_00000310-00024 SC_EVERSPLIT0006279