The latest version of Idaho Power’s 2019 integrated resource plan calls for completely exiting the coal-fired Jim Bridger plant by 2030, four years earlier than called for in the plan's initial version filed last year with the Idaho PUC.

The change came after Idaho Power staff manually fine-tuned the top portfolios to fit even better with the utility’s needs. The first version of the IRP exclusively relied on computer-generated portfolios using a long-term capacity expansion model [IPC-E-19-19]. However, Idaho Power staff determined that the portfolios, which were optimized for the entire WECC region, could be further refined to better fit the utility’s needs.

Idaho Power analysts used the four top WECC-optimized portfolios to produce another 20 portfolios for the amended IRP, which was filed Jan. 31 with the PUC.

The main variable in the new portfolios was the date Idaho Power would exit from the Jim Bridger coal-fired power plant.

“We found that as we moved those dates earlier...the cost of each portfolio was driven down further,” Kresta Davis-Butts, Idaho Power’s senior manager of resource planning and operations hydrology, told Clearing Up. “So, we really focused on [exit] dates.”

It did not come as much of a surprise to Davis-Butts that accelerating Idaho Power’s exit from a coal plant would drive down portfolio costs.

“Those coal resources within the portfolio are expensive resources. So, as we keep them on longer, what results is a higher cost portfolio,” she said. “By finding earlier [exit] dates that still assure that we are meeting planning margins, then we found the cost of those portfolios are driven down further.”

The amended IRP’s preferred portfolio has the earliest Jim Bridger exit dates allowed by the modeling parameters—Unit 1 in 2022, Unit 2 in 2026, Unit 3 in 2028 and Unit 4 in 2030. The portfolio is based on an adjusted version of Platts 2018 Henry Hub natural gas price forecast and includes the 500-kV Boardman-to-Hemingway transmission line, which is expected to come online in 2026.

It also assumes high carbon costs beginning in 2022 under a federal program. The projected carbon cost curve, which is based on a projection in the California Energy Commission’s 2017 Integrated Energy Policy Report, rises from about $30 per ton of carbon dioxide in 2022 to nearly $110/ton in 2030.

Under those conditions, the plan charts a course for Idaho Power to exit its entire 1,026 MW coal-fired fleet by 2030. It exited North Valmy’s 127 MW Unit 1 at the end of 2019, and plans to exit its 10 percent share (58 MW) of the Boardman coal-fired plant by the end of 2020. It would exit its 177 MW share of Jim Bridger Unit 1 in 2022, exit North Valmy’s 133 MW Unit 2 in 2025, followed by Jim Bridger Unit 2 in 2026, Unit 3 in 2028 and Unit 4 in 2030.

To make up for the capacity loss, the plan calls for adding 120 MW of solar in 2022 that Idaho Power already has that under contract with Jackson Solar. The original IRP had called for 220 MW, which would have included a 100 MW additional development, dubbed Franklin Solar. However, following initial talks with the developer, the utility opted in December to not pursue Franklin Solar.

The preferred portfolio calls for 40 MW of solar and 30 MW of battery storage in 2029. The next year, it calls for 300 MW of natural gas. In all, the portfolio calls for 411 MW of natural gas, 300 MW of wind, 1,160 MW of solar, 80 MW of battery storage and 30 MW of demand response.

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Contributing Editor

Dan has covered stories from Seattle to Tbilisi; spent time with the AP, Everett Daily Herald and Christian Science Monitor; and was twice a member of a team nominated for a Pulitzer Prize. He and his wife have three young children and live in Seattle.