1.7 Conclusion

development times, modularity, and flexibility of location. However, BESS have substantial disadvantages as compared to the Project:

• Higher cost at longer durations of storage (duration will be increasingly important as renewable energy penetration increases); • Significantly shorter useful life (10 to 20 years, depending on cycling); • Degradation of storage capacity and efficiency through use (resulting in a higher fixed operations and maintenance [O&M] cost for augmentation); • Environmental impacts from mining of battery materials and the lack of methods for recycling spent battery cells; • Future supply risks associated with competition for materials (lithium and other materials) and policy considerations (e.g., reliance on raw materials and manufacturing in China). Evidence of this risk is seen in recent industry studies showing a slowdown in battery price decline due to rising commodity prices and reduced production; and • An inability to supply inertia to the grid.

Exhibit D includes an analysis (Estimated Annual Value of Project Power) using lithiumion as a benchmark for comparison to illustrate how and why the Project represents a lower, long-term, long-duration cost of storage than utility-scale batteries when viewed through the energy or megawatt hours (MWh) lens.

New battery technologies, hydrogen-based systems, and mechanical systems (rail energy storage and systems that lift and lower concrete blocks) are at the demonstration or research and development stage and do not represent commercially available alternatives to the Project.

Compressed air energy storage (CAES) is the only other long-duration energy storage technology with an established track record, but this technology requires very specific and rare geology. The CAES technology available today requires the combustion of natural gas, a source of greenhouse gases. A CAES project in Utah is being developed for the only known “Gulf Coast” style domal-quality salt formation in the western United States. There are no known active proposals for CAES projects in Wyoming.

BESS are the most likely alternative to the Project in terms of addressing utility and market needs for a distributed storage solution in the emerging low-carbon market. However, the advantages of pumped storage, where it can be built, make the Project an exceptional opportunity for meeting the needs of Wyoming and the greater regional energy market.

There are currently no proposed projects that could provide the same benefit to optimizing regional diversity of renewable energy siting and existing and new transmission in the region. Therefore, no other pumped storage project in Wyoming is a viable generation alternative to the Project.