Macro-energy systems analysis of technology options for decarbonizing California's electricity system
Keywords: Energy Resources Engineering.

California is the fifth largest economy in the world and has ambitious climate goals to reach a carbon neutral economy by 2045. In recognizing the importance of decarbonizing the electricity grid in reaching its economy-wide decarbonization goals, California implemented Senate Bill 100 (SB100), which requires a 100% clean energy grid by 2045. So far, California has made remarkable progress in decarbonizing it's electricity grid by retiring coal power plants and investing in solar PV and onshore wind resources. There is no doubt that variable renewable resources will likely be the mainstays of California's future energy grid. However, balancing daily and seasonal energy needs in a grid with high shares of intermittent resources will be a challenge that requires additional technology options. As California looks forward to meeting its SB100 goals, a deeper look into a broader technology base will be needed to ensure cost-effective and reliable decarbonization of the grid. This dissertation provides an assessment of three different technology options (clean firm resources, long duration storage, and flexible load) for California to reach a net-zero carbon grid consistent with its SB100 goals by using a detailed capacity expansion and economic dispatch model. Firm resources can operate at any time of the year and for as long as needed to maintain electricity system reliability. Including low-carbon, firm dispatchable resources in energy systems provide a significantly more cost-effective pathway for California to meet its climate goals and prevent overbuilding of intermittent renewable and energy storage resources to maintain reliability year-long. Furthermore, including such resources provides less uncertainty for future energy systems costs across varying technology cost estimates, weather patterns, and operational constraints. Low- and zero-carbon firm technologies include high variable cost, low capital cost, and highly flexible generating technologies such as biogas or hydrogen combustion turbines, low or zero variable cost and capital-intensive resources such as nuclear and geothermal, as well as intermediate sources like natural gas plants with carbon capture and sequestration (CCS). In assessing the role of nuclear, natural gas plants with carbon capture and sequestration (CCS), and combustion of zero-carbon fuels in California's decarbonized electricity systems, the analysis shows that individually, each of these technologies delivers similar cost reductions relative to a system without significant shares of clean firm resources. Additionally, because each technology occupies a distinctive functional niche in the electricity system and provides incremental value to a zero-carbon system, having all of these technologies available results in the lowest cost generation system, reducing system costs by up to 10% over having just one type. The analysis highlights the benefits of an expansive range of technology options to meet emissions reductions goals for the power sector while maintaining operational reliability and affordability. Long duration energy storage has also been spotlighted as another technology that can help smooth seasonal intermittency of variable renewable resources. While not as effective as clean firm resources, long duration storage resources, when operated synergistically with short duration storage resources, can reduce system costs significantly by decreasing the necessary generation capacity by up to a factor of three and avoiding excess investment in solar PV and short duration storage, the primary system cost drivers. The results also show a positive correlation between the utilization of short and long duration energy storage resources: when long duration storage is affordable, it enables the efficient operation of short duration storage; conversely, when long duration storage is expensive, short duration storage is forced into an imperfect substitution of long duration storage resources. 5 $/kWh is identified as a general benchmark for the energy cost of long duration storage in order to facilitate the ideal synergistic operation of short and long duration storage. Finally, from the demand-side perspective, the potential for flexible load to contribute to California's decarbonization is assessed. The analysis finds that the value of flexible load in a decarbonized California system ranges significantly, from 1% to 40% reduction of total system cost relative to the scenario without any flexible load depending on the parameters allowed for flexible load operation. In grids with little to no dispatchable resources, flexible load largely saves costs not by displacing generation resources but by displacing energy storage. However, system cost savings from any level of flexible load that is modeled within this analysis cannot achieve as much cost savings as having clean firm resources such as natural gas with carbon capture and storage. Furthermore, the value of flexible load decreases in scenarios with clean firm resources as the need to balance supply and demand decreases with a dispatchable and reliable source of generation available. The dissertation informs the continuously evolving California policy landscape, and provides insight for policy makers and technology developers as they assess a range of technology options and future pathways to decarbonizing the electricity sector. Understanding the role and value of various technologies can directly inform California policy makers on prioritizing pathways and technologies of least regret for decarbonization, anticipating and preparing for changes to the market required to sustain the evolving electricity system, and overall ensuring a reliable, affordable, and smooth transition to a decarbonized grid. As a leader in climate policy and action, California's policies and pathway choices will likely inspire action globally as well, further underscoring the importance of the results of this dissertation