Recent publications

Note: if you have difficulty accessing one of these papers, please contact skurtz@ucmerced.edu.

• Zabir Mahmud and Sarah Kurtz, “Effect of Solar Mounting Configurations on California Zero-Carbon Grid", IEEE 50th Photovoltaic Specialists Conference (PVSC), 2023. On line           

  The effects of PV-panel tilt and tracking on California's zero-carbon grid were modeled and compared for multiple target years from 2030 to 2045, and for a range of cost assumptions. It was found that using south-facing tilt in the candidate solar projects significantly reduces the annual solar curtailment in 2045. Tilted panels can decrease the total system cost and average annual cost of delivered solar electricity over time, if technological advancement can lower the cost for tilting. 

• Mariela Colombo and Sarah Kurtz, “Oxy-Fuel Combustion: A Threat or an Opportunity for Solar?", IEEE 50th Photovoltaic Specialists Conference (PVSC), 2023. On line           

  The impacts of introducing an oxy-fuel combustion resource in California's energy grid are evaluated. To do so, we use RESOLVE, a capacity expansion model, to predict the energy grid mix for 2030 to 2045. Our results indicate that the model chooses to build the oxy-combustion resource when it is available at relatively low costs. While the introduction of oxy-fuel combustion, even at limited scale, reduces the selected operational capacity of solar PV and lithium-ion batteries, it substantially reduces the curtailment of the solar that is installed. Far from being a threat, this reduction could be an opportunity for solar to continue with robust growth, retaining its economic and environmental value even when the procurement of storage might otherwise limit its adoption rate.

• Farzan ZareAfifi and Sarah Kurtz, “Powering the Future: Electric Vehicle Charging Profile Impact on California's Future Energy Storage Needs", 2023 North American Power Symposium, 2023. On line           

  This research explores the impact of various light-duty electric vehicle (EV) charging profiles on energy storage requirements in California. It was shown that daytime charging could halve the need for storage required to meet the light-duty EV charging load, but it would be at the expense of needing more non-residential charging infrastructure. Interestingly, utilizing longer-duration storage, particularly 8-hour storage, could offer a solution, i.e., reducing the impact of different load patterns and potentially decreasing the need for extensive public charging infrastructure investments. 

• Mariela Colombo and Sarah Kurtz, "Value of long-duration energy storage and oxy-combustion in renewables-driven grids", 2023 North American Power Symposium, 2023. On line
  In this paper, the combination of 100-h LDES and oxy-combustion was studied and found to allow for a reduction in the overall capacity expansion needed in grids with high renewable energy penetration. Combined, they can compensate short-and long-duration supply and demand imbalances, while reducing curtailment and ensuring a reliable supply.

• Farzan ZareAfifi, Zabir Mahmud and Sarah Kurtz, “Diurnal, physics-based strategy for computationally efficient capacity-expansion optimizations for solar-dominated grids", Energy, Vol. 279, 128206, 2023. On line             

  This study introduces a new technique called Critical Time Step for capacity-expansion modeling in renewable energy-driven grids. The technique focuses on specific critical times during the day, resulting in a balance between accuracy and computational complexity. The technique is evaluated using three weather years and shows high accuracy in predicting power and energy expansion for a solar-dominated grid. Although there is some underestimation of capacity expansion, the technique correlates well with hourly simulations. The highest error occurs in storage power buildout but remains within 10% relative to 1-hour resolution simulations for the studied case.

• Zabir Mahmud, Kenji Shiraishi, Mahmoud Y. Abido, Pedro Andres Sanchez-Perez, and Sarah R Kurtz, “Hierarchical approach to evaluating storage requirements for renewable-energy-driven grids" iScience, Vol. 26(1), 105900, Jan. 2023. Open access
  In this study, using a hierarchical-storage approach we quantified how many fewer times wind-driven grids cycle the storage compared with solar-driven grids, as well as how winter-dominant wind generation and latitude-tilt solar may reduce the need for seasonal storage. Also, higher discharge rates are required for energy storage products that cycle most frequently.  

• Farzan ZareAfifi and Sarah Kurtz, “Analytical analysis of stationary Li-ion-battery storage-system efficiency on a large scale" IEEE Vehicle Power and Propulsion Conference (VPPC), 2022. On line 
  In this study, the efficiency of the energy storage plants in U.S. was calculated based on U.S. Energy Information Administration (EIA) data. We conclude that newer plants show higher efficiencies, and in the case of experiencing an average of one cycle per day, the newer plants show efficiencies of almost 90%. Also, we see a lower efficiency for plants cycled less than five times per month. The efficiency is observed to be between 80% and 90% for most batteries experiencing more than five full cycles each month.

• Zabir Mahmud and Sarah Kurtz, “Impact of EV Charging Schedule on Storage Requirements for a Renewable-driven Grid in California" IEEE Vehicle Power and Propulsion Conference (VPPC), 2022. On line 
  This paper considers daytime and nighttime EV charging profiles assuming the anticipated number of EVs and investigates the impact on different types of storage in a renewable-driven grid in California. A hierarchical-storage technique is used to understand the role of different charging profiles on the minimum number of cycles and size of energy storage required in a zero-carbon grid, showing the strong benefits of daytime charging.

• P.A. Sánchez-Pérez, Martin Staadecker, Julia Szinai, Sarah Kurtz, Patricia Hidalgo-Gonzalez, "Effect of modeled time horizon on quantifying the need for long-duration storage" Applied Energy, 2022 Article
  Capacity expansion modeling using SWITCH for Western North America. Examines the effect of increasing the number of allowed consecutive days of energy arbitrage on the selection of storage by the optimization model. Longer duration storage is selected when time horizons are increased, and decreases overbuild of renewables by up to 10%. Seasonal storage is deployed when CapEx cost is reduced to $1.3/kWh. 
   
• Russell K. Jones and Sarah Kurtz, “Optimizing the Configuration of Photovoltaic Plants to Minimize the Need for Storage" IEEE Journal of Photovoltaics, 2022. Open access
  Simple cost and engergy balance modeling of PV + storage in isolation shows that high tilt PV plants have the potential to reduce required storage capacity by optimizing winter generation, resulting in substantially reduced overall system costs.
   
• F. ZareAfifi, D. Baerwaldt, S. Hour, Y. H. Xie and S. Kurtz, “Performance investigation of batteries supporting solar power in U.S." 49th Photovoltaic Specialists Conference, 2022. 10.1109/PVSC48317.2022.9938520
  Data from the EIA are compiled and analyzed to quantify the real-world efficiencies of utility-scale batteries. Batteries that are cycled frequently typically show average efficiencies of about 85%. Batteries that cycle less than about 5 times per month often exhibit lower efficiencies. There is a slight trend toward higher efficiencies for batteries installed more recently.
   

• Sánchez-Pérez, P. A., et al. "Effect of Time Resolution on Capacity Expansion Modeling to Quantify Value of Long-Duration Energy Storage." 2022 IEEE Electrical Energy Storage Application and Technologies Conference (EESAT). IEEE, 2022.
  We formulated a capacity expansion problem for the California region using three different temporal resolutions. We obtained that decreasing the model complexity by using fewer time points yielded different configurations and utilization of LDES technologies.

• Z. Mahmud, K. Shiraishi, M. Abido, D. Millstein, P. Sanchez, and S. Kurtz, “Geographical variability of summer- and winter-dominant onshore wind"Journal of Renewable and Sustainable Energy, Volume 14, 023303, 2022. Open access
  Analyzes the generation from existing California wind plants and simulates potential onshore wind resource for the whole state using a metric that reflects the relative wind resource in winter. Results indicate that the seasonality of the wind can vary for very small spatial difference with more than half of California showing stronger wind resource in the winter compared with the summer despite the current observation of the opposite trend. 
   
• R. Shan, J. Reagan, S. Castellanos, S. Kurtz, and N. Kittner. "Evaluating emerging long-duration energy storage technologies" Renewable and Sustainable Energy Reviews,
  Volume 159, 2022. Article 
  An overview of energy storage technologies currently on the market or under commercial development.Technologies are compared on the basis of capital cost, land footprint, and equivalent efficiency, including idle losses for long duration storage.
   
• M. Abido, Z. Mahmud, P. Sanchez, and S. Kurtz, “Seasonal Challenges for a California renewable-energy-driven grid" iScience, 2021. Open access
  Studies various scenarios for applying a 100% renewable energy grid using six years (2015–2020) of historical demand and scaled-up solar and wind generation. The most challenging months for energy storage will always be in the winter when both solar and wind resources are scarce due to California winds being summer dominant. Depending on the exact power mix and scale of buildout, the peak challenging month can be shifted from March to January, and an increase of 30% in generating capacity can halve total storage needed.

• Kittner, N., Castellanos, S., Hidalgo-Gonzalez, P., Kammen, D. M., & Kurtz, S. (2021). Cross-sector storage and modeling needed for deep decarbonization. Joule, 5(10), 2529-2534. Article 
  Establishes a classification of energy storage as distinguishing between power to power (such as a battery) and cross-sectional storage, in which the form of stored energy can have alternate uses. For example, liquid hydrogen can be used for electricity generation, fuel for trasnportation, or for other industrial uses, providing for more flexible energy systems. Further discusses the role of a hypothetical Strategic Energy Rserve, analogous to the current Strategic Petroleium Reserve maintained by the the Us, in a deeply decarbonized system, as well as the impact on cross-sector approaches on the commercialization of seasonal energy storage.
   
• M. Abido, K. Shiraishi, P. Sanchez, R. Jones, Z. Mahmud, S. Castellanos, N. Kittner, D. Kammen, and S. Kurtz, “Seasonal Challenges for a Zero-Carbon Grid in California" 48th Photovoltaic Specialists Conference, 2021.PDF Presentation
  Uses historical demand and generation data from CAISO to model a future zero-carbon solar dominated grid and identify the times mostly likely to result in shortages of stored energy. Discusses how effectively these challenge points can be shifted based on the amount of solar overbuild vs increased storage resources, vs the inclusion of on-shore and off-shore wind generation.
   
• A. Leilaeioun, R. Jones, R. Sinton, and S. Kurtz, “Demand Shifting as a Profitable Strategy for Solar Plant Operators" 48th Photovoltaic Specialists Conference, 2021. PDF Article
  Uses historical CAISO data to examine the potential economic impact of Load Shifting/Demand Shifting, where energy intensive activities are preferentially conducted during times when energy production is highest, on both costs to consumers and the profitability of solar plant operation. Shifting leads to both lower peak prices for consumers, and higher prices during the middle of the day, incentivizing solar plant operation.
   
• S. Kurtz, N. Kittner, S. Castellanos, P. Hidalgo-Gonzalez, and D. Kammen, “For Cleaner, Greener Power, Expand the Definition of "Batteries"" Issues in Science and Technology, 2021. Article 
  Argues for the inclusion of long duration energy storage into invesment plans, as opposed to an overly narrow focus on carbon capture technology for existing generation systems. In light of the advancements made in the fields of renewable generation and energy storage and continuously declining costs, it is too early to commit to a path based on present day costs. Furthermore, there is a common misconception that energy storage is just a scaled up version of batteries in laptops and vehicles, when in reality it covers a broad spectrum of various technologies in different stages of development.

Related Publications: These are not direct results of our project, but are foundational to its formation, or otherwise closely related to it.

• N. M. Haegel and S. R. Kurtz, "Global Progress Toward Renewable Electricity: Tracking the Role of Solar," in IEEE Journal of Photovoltaics, vol. 11, no. 6, pp. 1335-1342, Nov. 2021, doi: 10.1109/JPHOTOV.2021.3104149. Article 
  Collects data from multiple sources tracking in differening ways and present it in a unified fashion. Examines solar power as proportion of total global electricy produced (about 3% currently), as well as proportion of installed electric capacity and expansion. Also distinguishes between PV systems and CSP (Concentrated Solar Power) system, with the rapid growth in PV after 1999 making it the overwhelmingly dominant factor. 

• S. Kurtz, “Accelerating Growth of Solar Energy" The Bridge, p. 98, 2020.
• P.A. Sanchez-Perez and S. Kurtz, “California's Vision for Reaching Zero-Carbon Emissions" Proc. of the 47th IEEE PVSC, 2020. Preprint
• R. Bailey, P.A. Sanchez-Perez, Z. Mahmud, and S. Kurtz, “Methodology for Quantifying Value of Storage Toward Reaching 100% Renewable Electricity" Proc. of the 47th IEEE PVSC, 2020. Preprint

• P.A. Sanchez-Perez and S. Kurtz, “Capacity Factor Analysis of US PV System Reliability and Performance" IEEE Journal of PV, 2020.