2.3.3 Transmission Considerations

Location on the transmission system and within the market are important considerations for pumped storage development in general and the Project in particular. The State of Wyoming itself has no requirement or goal to generate a certain percentage of its electricity from renewables. It is also a relatively small market compared to neighboring states like Utah and others in the Pacific Northwest region. In fact, Wyoming as a state is the largest net exporter of energy as a percentage of its energy consumption, exporting 15 times the energy it consumes. As such, existing, in-progress, and proposed transmission line projects aim to improve the ability of the State of Wyoming to deliver energy to out-of-state markets. Reliability and economic use of transmission will benefit significantly from energy storage, and pumped storage can be an exceptional value in energy storage, as previously discussed in Section 1.1.

Within the State of Wyoming, southern Wyoming represents an important crossroads of existing, planned, and proposed transmission. This allowed for consideration of a number of alternative points of interconnection and associated Project transmission line routes.

The 2011 Preliminary Permit Application, FERC No. P-14087, showed the pumped storage project connected to both the Kortes and Seminoe Reservoirs and interconnected with the existing Western Area Power Administration (WAPA) Miracle Mile-Snowy Range line at an interconnection point adjacent to Seminoe. From the interconnection point, energy from the proposed Project would transfer energy through the WAPA Miracle Mile-Snowy Range line to one of the following proposed transmission facilities: the Gateway West line via the Aeolus Substation, the Zephyr line, TransWest Express, or the Overland. The 2014 Successive Preliminary Permit Application did not propose alternatives to this original concept.

The 2013 Reclamation Phase II Report considered an interconnection at Miracle Mile Switchyard with a 230 kilovolt (kV) line and an interconnection to Aeolus Substation with 230 kV and 500 kV transmission options. Interconnection at the Miracle Mile Switchyard was considered, as this option would be the shortest transmission route, requiring only 7 miles of a single, 230 kV line. However, this interconnection would result in overloads to the existing system at 250 MW of pumping load and, therefore this interconnection point was determined to be inadequate to consider further. Interconnection at the Aeolus Substation would require more land acquisition, requiring over 30 miles of double-circuit, 230 kV line or single-circuit, 500 kV line. Both the 230 kV line and single-circuit 500 kV line options were determined to be feasible, although the 500 kV line was determined to be considerably more expensive at the time of the Phase II Report.

The 2016 Preliminary Permit Application for the Project (FERC No. P-14787) refined the interconnection options and narrowed the transmission alternatives to either the Aeolus Substation or the planned northern terminal for the TransWest Express DC line near Sinclair, Wyoming, and ruled out the other alternatives presented in the 2011 and 2014 Preliminary Permit Applications. The 2019 Successive Preliminary Permit Application was supported by a transmission screening study performed by Power Engineers, Inc. The screening study reviewed the viability of interconnecting 500, 600, and 1,000 MW Project

configuration alternatives presented in the concept study (HDR 2019) at Aeolus Substation and the planned TransWest Express Terminal. These two interconnection alternatives were presented in the Project’s PAD (Gridflex 2020). Black Canyon chose not to pursue the TransWest Express interconnection alternative due to the commercial indeterminacy of that transmission project, as well as the cost of pursuing both points of interconnection.

Preferred Interconnection Alternative

The feasibility study examined a variety of transmission alternatives, all considering Aeolus Substation as the interconnection point. Six alternatives for transmission lines from the Project location to Aeolus Substation were examined: 2 x 230 kV (2 single-circuit), 3 x 230 kV (1 single-circuit, 1 double-circuit), 2 x 345 kV (2 single-circuit), 2 x 345 kV (1 doublecircuit), 2 x 500 kV (2 single-circuit), and 2 x 500 kV (1 double-circuit). A 1 x 500 kV alternative was not examined due to feedback from the transmission provider that reliability rules would limit the capacity on that line to well below the plant-rated capacity. The 2 x 230 kV options were found to be infeasible due to energy losses in the cable, which would necessitate a larger generator to make up for the energy losses. The 345 kV options had the issue that there is no 345 kV bus at Aeolus Substation, which would necessitate a complete 345 kV switchyard to be added, significantly increasing the cost of these alternatives. The 2 x 500 kV transmission line options with interconnection at Aeolus Substation were determined to be the most technically and economically viable point of interconnection for the Project. Further engineering studies will refine the specifications of power equipment and choice of transmission line (single-circuit vs. double-circuit). The proposed transmission route can be found in Sheets 32-40 of Exhibit F.

The location of the proposed Project upper reservoir intersects with two existing WAPA transmission lines: the Miracle Mile-Snowy Range 1 115 kV line (MM-SNG-1) and the Miracle Mile-Snowy Range 2 230 kV line (MM-SNG-2), (the “WAPA transmission lines”). These lines extend past the Aeolus Substation, establishing a likely corridor for the Project’s proposed interconnection transmission line to follow. As part of Project construction, approximately 1 mile of the existing WAPA transmission lines in the area of the proposed upper reservoir will be re-routed. Two re-route concepts were investigated in 2022: (1) re-routing the WAPA transmission lines to the west of the proposed upper reservoir (Western Route); and (2) re-routing the WAPA transmission lines along the eastern edge of the proposed upper reservoir, between the reservoir wall and the Bennett Mountain access road (which forms the border of the Bennett Mountains Wilderness Study Area (WSA)) (Eastern Route). Each re-route option is less than 1 mile long. Figure 2.3-3 shows the location of the existing alignment and two WAPA transmission line re-routing alternatives.

Both WAPA transmission line re-location alternatives combine two existing transmission circuits onto a single steel monopole structure with the use of a 3-pole transmission structure at the beginning and end of each re-route. This will result in minimal impact to existing structures and the surrounding environment. The Project proposes to use Meyer pre-engineered steel poles where possible at the request of WAPA.

The Western Route includes spans of approximately 900 feet and 1,600 feet over challenging terrain, resulting in limited access to transmission towers, advanced

construction measures, and increased environmental and resource impacts. These spans would require special construction techniques include the use of helicopters for structure spotting and conductor stringing.

Based on current designs of the WAPA transmission line re-route alternatives, which designs are subject to change prior to construction, the Western Route, when compared to the Eastern Route, would result in an additional five steel monopole tower structures; 116,308 pounds of custom steel; 48 cubic yards of concrete volume; 22,129 pounds of steel rebar; 26,795 feet of conductor; 9,191 feet of optical ground wire (OPGW); and 294 feet of steel shield wire. The additional materials, weights, distances, construction activities, and required access roads would result in additional environmental and resource impacts when compared to the Eastern Route. The Eastern Route is the preferred route because it is more accessible, is located on more suitable topography, has lower estimates in the aforementioned measures, and therefore would be easier to construct and maintain over the Project lifecycle.

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