  The urgent need for decarbonization in the energy sector has led to an
increased emphasis on the integration of renewable energy sources, such as wind
and solar, into power grids. While these resources offer significant
environmental benefits, they also introduce challenges related to intermittency
and variability. Long-duration energy storage (LDES) technologies have emerged
as a very promising solution to address these challenges by storing excess
energy during periods of high generation and delivering it when demand is high
or renewable resources are scarce for a sustained amount of time. This paper
introduces a novel methodology for estimating the boundary technology cost of
LDES systems for economic viability in decarbonized energy systems. Our
methodology is applied to estimate the boundary costs in 2050 for the state of
California to achieve full retirement of gas power plants. California's
ambitious decarbonization goals and transition to a renewable energy-based
power system present an ideal context for examining the role of LDES. The
results also offer insights into the needed capacity expansion planning and the
operational contribution of LDES in the California's energy landscape, taking
into account the unique energy demand profiles and renewable resource
availability of the region. Our findings are intended to provide complementary
information to guide decision-makers, energy planners, and any other
stakeholders in making informed choices about LDES investment in the context of
a decarbonized energy future.
