Energy In California Research Articles

Technical, economic, and environmental feasibility of rice hull ash from electricity generation as a mineral additive to concrete

A circular economy based on symbiotic relationships among sectors, where the waste from one is resource to another, holds promise for cost-effective and sustainable production. This research explores such a model for the agriculture, energy, and construction sectors in California. Here, we develop new an understanding for the synergistic utilization mechanisms for rice hull, a byproduct from rice production, as a feedstock for electricity generation and rice hull ash (RHA) used as a supplementary cementitious material in concrete. A suite of methods including experimental analysis, techno-economic analysis (TEA), and life-cycle assessment (LCA) were applied to estimate the cost and environmental performance of the system. TEA results showed that the electricity price required for break even on expenses without selling RHA is $0.07/kWh, lower than the market price. As such, RHA may be available at little to no cost to concrete producers. Our experimental results showed the viability of RHA to be used as a supplementary cementitious material, meaning it can replace a portion of the cement used in concrete. LCA results showed that replacing 15% of cement with RHA in concrete can reduce carbon dioxide equivalent (CO2e) emissions by 15% while still meeting material performance targets. While the substitution rate of RHA for cement may be modest, RHA generated from California alone could mitigate 0.2% of total CO2e from the entire cement production sector in the United States and 1% in California.

Integrated economic and environmental modeling of forest biomass for renewable energy in California: Part I - Model development

Forests are a major natural resource of the state of California, where over a third of the land is forested, and provide a wide range of environmental, economic, and social benefits. Over the past decade, unprecedented drought, insect outbreaks and wildfires have resulted in large-scale tree mortality that greatly affects the forest ecosystem and poses significant threat to human health and welfare and to the environment. Forest thinning and management is considered imperative to improve forest health and resilience. Forest resources including dead and dying trees as well as the residues produced from forest thinning and timber harvesting operations could potentially be used to a greater degree than at present to generate electricity and other renewable energy to meet the increasing demand for more sustainable supplies and mitigate the risk of wildfires. However, efforts to construct new electricity generation capacity in the state at any scale over the last several decades have faced both economic and environmental challenges. As needs for alternative management approaches have become clear, opportunities have emerged for new bioenergy projects. These projects need to be effectively planned and potential economic and environmental performance carefully evaluated. Toward this purpose, an integrated framework model for lifecycle and technoeconomic assessment was developed to quantify environmental and economic impacts, initially for generating electricity using forest resources and with associated web services developed for an online application (forestdss.ucdavis.edu) that allows potential users to quickly estimate the economic and environmental performance of a potential facility at specified locations.

Life-Cycle Assessment in the LEED-CI v4 Categories of Location and Transportation (LT) and Energy and Atmosphere (EA) in California: A Case Study of Two Strategies for LEED Projects

This study aimed to identify different certification strategies for Leadership in Energy and Environmental Design Commercial Interior version 4 (LEED-CI v4) gold-certified office projects in California’s cities and to explore these certification strategies using life-cycle assessments (LCAs). The LEED-CI v4 data were divided into two groups: high- and low-achievement groups in the Location and Transportation (LT) category. The author identified two strategies for achieving the same level of certification across LEED-CI v4 projects: (1) high achievements in LT (LTHigh) and low achievements in the Energy and Atmosphere (EA) category (EALow), and (2) low achievements in the LT category (LTLow) and high achievements in EA (EAHigh). The author adopted LTHigh–EALow and LTLow–EAHigh achievements as functional units for LCA. Three alternatives were LTHigh: typical bus, EALow: gas; LTLow: typical car, EAHigh: gas; and LTLow: eco-friendly car, EAHigh: gas, where a typical bus used diesel, a typical car used natural gas, an eco-friendly car used EURO5diesel, and natural gas was used as a building’s operational energy. The ReCiPe2016 results showed that the LTHigh: typical bus, EALow: gas strategy was preferable from a short-term perspective, and the LTLow: eco-friendly car, EAHigh: gas strategy was preferable in a long-term and an infinite time perspective, while the LTLow: typical car, EAHigh: gas strategy continued to be the most environmentally damaging certification strategy for all the time horizons of the existing pollutants. Thus, it can be concluded that if there are alternative strategies for LEED certification, an analysis of their LCAs can be useful to refine the best sustainable strategy.

Zero air pollution and zero carbon from all energy at low cost and without blackouts in variable weather throughout the U.S. with 100% wind-water-solar and storage

This study analyzes 2050–2051 grid stability in the 50 U S. states and District of Columbia after their all-sector (electricity, transportation, buildings, industry) energy is transitioned to 100% clean, renewable Wind-Water-Solar (WWS) electricity and heat plus storage and demand response (thus to zero air pollution and zero carbon). Grid stability is analyzed in five regions; six isolated states (Texas, California, Florida, New York, Alaska, Hawaii); Texas interconnected with the Midwest, and the contiguous U.S. No blackouts occur, including during summer in California or winter in Texas. No batteries with over 4-h storage are needed. Concatenating 4-h batteries provides long-duration storage. Whereas transitioning more than doubles electricity use, it reduces total end-use energy demand by ∼57% versus business-as-usual (BAU), contributing to the 63 (43–79)% and 86 (77–90)% lower annual private and social (private + health + climate) energy costs, respectively, than BAU. Costs per unit energy in California, New York, and Texas are 11%, 21%, and 27% lower, respectively, and in Florida are 1.5% higher, when these states are interconnected regionally rather than islanded. Transitioning may create ∼4.7 million more permanent jobs than lost and requires only ∼0.29% and 0.55% of new U.S. land for footprint and spacing, respectively, less than the 1.3% occupied by the fossil industry today.

Techno-economic analysis of long-duration energy storage and flexible power generation technologies to support high-variable renewable energy grids

Techno-economic analysis of long-duration energy storage and flexible power generation technologies to support high-variable renewable energy grids

The curtailment paradox in the transition to high solar power systems

Summary Rising penetrations of variable renewable energy (VRE) in power systems are expected to increase the curtailment of these resources because of oversupply and operational constraints. We evaluate the effect on curtailment from various flexibility approaches, including storage, thermal generator flexibility, operating reserve eligibility rules, transmission constraints, and temporal resolution, by using a highly resolved realistic system. Results reveal two aspects of a curtailment paradox as the system evolves to higher solar penetration levels. First, thermal generator parameters, especially in restricting minimum operating levels and ramp rates, affect VRE curtailment more in mid-PV penetration levels (∼25%–40%) but much less at lower (∼20%) or higher (∼45%) PV penetration levels. Second, although allowing VRE and storage to provide operating reserve results in significant operating costs and curtailment benefits, the price suppression effect from these resources reduces incentives for PV to provide operating reserves with curtailed energy.

Adaptation Can Compound Climate Change Impacts on Energy and Water

Researchers have created a framework to trace the impacts of climate change and adaptation across energy and water systems in California.

Mitigating Curtailment and Carbon Emissions through Load Migration between Data Centers

Summary As the share of variable renewable energy (VRE) grows in the electric grid, so does the risk of curtailment. While energy storage and hydrogen production have been proposed as solutions to the curtailment problem, they often pose technological and economic challenges. Here, we analyze the potential of data center load migration for mitigating curtailment and greenhouse gas (GHG) emissions. Using historical hourly electricity generation, curtailment, and typical data center server utilization data, we simulate the effect of migrating data center workloads from the fossil-fuel-heavy PJM to the renewable-heavy CAISO. The results show that load migration within the existing data center capacity during the curtailment hours in CAISO has the potential to reduce 113–239 KtCO2e per year of GHG emissions and absorb up to 62% of the total curtailment with negative abatement costs in 2019. Our study demonstrates the overlooked role that data centers can play for VRE integration and GHG emissions mitigation.

(Invited) Catalyst Assessments and Device Incorporation in Low Temperature Electrolysis

Although electricity feedstock currently dominates hydrogen production costs in commercial electrolysis, capital cost will become a significant factor as electrochemical water splitting is directly coupled with low-cost power sources. [1,2] To minimize device costs and reach cost targets, reducing catalyst loading in proton exchange membrane-based (PEM) electrolysis will be necessary and efforts to evaluate and improve upon catalyst performance and durability will become critical. Beyond PEM-based systems, anion exchange membrane-based (AEM) electrolyzers can also reduce capital cost, with the high pH enabling non-platinum group metal (PGM) catalysts and improving the durability of system components.In these areas, efforts at the National Renewable Energy Laboratory have included developing and evaluating electrolyzer catalysts, establishing baseline performance and durability, and linking ex- and in-situ testing for commercial nanoparticles and novel materials. In PEM electrolysis, ink compositions and coating methodologies were evaluated in rotating disk electrodes, establishing best practices for screening catalysts in the oxygen evolution reaction. [3] Test factors were considered, including working electrode dissolution and catalyst delamination, and electrochemical surface area measurements adapted to differentiate between site quantity and quality. While half- and single-cell performances and durabilities do not match, higher activities translated to kinetic improvements in membrane electrode assemblies and half-cell testing was a reasonable tool for assessing relative differences between material sets. Projecting differences at the device level, however, required segregating materials based on surface composition and oxide content, and some caution is needed when using rotating disk electrodes to assess catalysts for electrolysis applications. In membrane electrode assemblies, baseline durability was evaluated when accounting for low catalyst loading and intermittent load profiles. How catalyst layers are incorporated has a significant impact on device performance and durability, and efforts have been made to translate improvements from spray coating to roll to roll coating and manufacturing appropriate processes. Various catalyst and membrane combinations have been used to assess that ability of component development and system control to limit performance loss with extended operation.In AEM electrolysis, baselines and best practices have been established in rotating disk electrodes for catalysts in the oxygen and hydrogen evolution reactions. Test factors, including electrolyte purity, conditioning protocols, and counter electrode choices were found to significantly impact measurements, and some care is needed to avoid under- or over-estimating kinetic improvements. Novel catalysts were developed for the hydrogen and oxygen evolution reactions, including low- and non-PGMs, sulfides, and metal organic frameworks, where activity improvements ex-situ generally translated to membrane electrode assemblies. [4] In in-situ testing, ionomers were varied with standard catalysts to assess the role of catalyst-ionomer interactions and supporting electrolytes in device performance.[1] H2 at Scale: Deeply Decarbonizing our Energy System. Presented at Annual Merit Review, U.S. Department of Energy; Washington, DC, June 6−10, 2016. https://www.hydrogen.energy.gov/pdfs/review16/2016_amr_h2_at_scale.pdf.[2] Denholm, P.; O’Connell, M.; Brinkman, G.; Jorgenson, J. Overgeneration from Solar Energy in California: A Field Guide to the Duck Chart; Vol. NREL/TP-6A20-65023; National Renewable Energy Laboratory: Golden, CO, 2015. http://www.nrel.gov/docs/fy16osti/65023.pdf.[3] S. M. Alia and G. C. Anderson, J. Electrochem. Soc., 166, F282 (2019).[4] S. Ghoshal, S. Zaccarine, G. C. Anderson, M. B. Martinez, K. E. Hurst, S. Pylypenko, B. S. Pivovar and S. M. Alia, ACS Applied Energy Materials, 2, 5568 (2019).

Business Groups and Advocacy Success: Insights from a Multi-venue Approach

This study applies a multi-venue approach to assess whether business groups are more likely to realize their policy preferences than citizen groups. Conceptually, it measures the advocacy success of interest groups that are involved in the various institutional venues visited during entire policy-making processes (i.e., executive, legislative, judicial and direct democracy). Empirically, it compares interest group advocacy across three different policy issues (i.e., railway infrastructure, stem cell research and promotion of renewable energy) in both pluralist California and neo-corporatist Switzerland. The findings show that, when controlling for the political system, policy issues and advocacy strategies (i.e., single- or multi-venue), business groups display higher levels of advocacy success than citizen groups.

Durability Loss Mechanisms and Sources in Proton Exchange Membrane-Based Electrolysis

In commercial electrolysis today, the cost of electricity input drives the cost of hydrogen production. As electrochemical water splitting is coupled directly with low-cost power sources, however, capital cost at lower capacity (renewable input) will be a significant factor in hydrogen cost [1,2]. While a variety of components affect electrolysis capital cost, reducing catalyst loading (several milligrams per square centimeter today) will be necessary to approach hydrogen production cost targets. Efforts have begun to address electrolyzer durability at low catalyst loading and variable load/input profiles, to: establish single-cell durability baselines for catalyst development projects; evaluate how the type and magnitude of stressor influences single-cell performance over time; and assess the ability of potential control to limit in-situ durability losses [3]. Although commercial electrolyzers are durable today, thick catalyst layers appear to mask catalyst corrosion and delay loss observations. Moreover, intermittent operation associated with renewable load profiles significantly accelerate loss compared to constant load. Performance loss has been tied to decreasing kinetics, where both catalyst layer thinning and changes to the electrode structure were observed. Cell diagnostics has been used to evaluate resistances in the catalyst layer, and changes at the catalyst layer interface may contribute to the observed loss. A variety of factors were examined as the sources of catalyst loss, including the expected dissolution rate of test profiles, the frequency of load cycling, and the ramp rate to peak load [4,5]. Testing has expanded to expected operation profiles (wind, solar) to correlate accelerated stress tests to anticipated use and device lifetime. Recently, studies have expanded into other catalyst loss mechanisms, including start-stop operation and hydrogen crossover. Lower potentials in the anode catalyst layer reduce the catalyst surface and lead to particle agglomeration and increased dissolution rates. These factors have been included to assess various stressors resulting in catalyst loss and shorter device lifetime. [1] H2 at Scale: Deeply Decarbonizing our Energy System. Presented at Annual Merit Review, U.S. Department of Energy; Washington, DC, June 6−10, 2016. https://www.hydrogen.energy.gov/pdfs/review16/2016_amr_h2_at_scale.pdf.[2] Denholm, P.; O’Connell, M.; Brinkman, G.; Jorgenson, J. Overgeneration from Solar Energy in California: A Field Guide to the Duck Chart; Vol. NREL/TP-6A20-65023; National Renewable Energy Laboratory: Golden, CO, 2015. Available at the following: http://www.nrel.gov/docs/fy16osti/65023.pdf.[3] S. M. Alia, H2@Scale: Experimental Characterization of Durability of Advanced ElectrolyzerConcepts in Dynamic Loading, 2018. https://www.hydrogen.energy.gov/pdfs/review18/tv146_alia_2018_p.pdf. [4] Cherevko, S.; Geiger, S.; Kasian, O.; Kulyk, N.; Grote, J. P.; Savan, A.; Shrestha, B. R.; Merzlikin, S.; Breitbach, B.; Ludwig, A.; Mayrhofer, K. J. J. Cat. Today 2016, 262, 170.[5] S. M. Alia and G. C. Anderson, J. Electrochem. Soc., 2019, 166, F282-F294.

Iridium and Iridium Oxide Performance in Electrolysis and Resolving Half- and Single-Cell Test Differences

In commercial electrolysis today, the cost of electricity input drives the cost of hydrogen production. Electrochemical water splitting, therefore, typically uses high catalyst loading and constant power input at high capacity. Catalyst development under these operating conditions, for cost reduction or durability improvement, are less immediate a focus. To reach hydrogen production targets, however, electrolyzers will need to be coupled directly with low-cost power sources to reduce feedstock costs. At that point, catalyst loading reductions are needed to reduce capital cost and catalyst efforts to evaluate material performance and durability become critical.[1-3] We will present efforts comparing half- and single-cells and evaluating to what extent rotating disk electrodes can be used to project membrane electrode assembly performance and durability. In rotating disk electrodes, coating technique and test parameters have a clear influence on baseline activity and the observed properties of materials. Under specific conditions, changes to these variables can shift the activity of standard catalysts by orders of magnitude. Similarly, how membrane electrode assemblies are coated, including spray temperature, ink composition, and ionomer content, has an impact on their initial performance and long-term operation. Although kinetic activities in half- and single-cell tests do not match, half-cell testing appears to be a reasonable indicator of cell performance provided that robust baselines are used. Performances between the two techniques were correlated for a variety of material types, including supported catalysts, alloys, and multicomponent materials with consistent activity trends observed. In certain cases, however, particularly for different surface types (metals, hydroxides, oxides) a disconnect was found between rotating disk electrodes and membrane electrode assemblies. Testing methodologies were explored to resolve these discrepancies and single-cell conditioning was found to incorporate aspects of half-cell durability testing. Modeling has been used to address performance differences between these surfaces, including: how surface and near-surface oxidation influences activity; and how that activity changes over time. By evaluating different catalysts and test parameters, we are looking to establish performance and durability guidelines for catalyst development efforts, and to share our perspective on how catalyst development and system controls factor into electrolysis at low loading and with intermittent operation. These tests have significant implications as electrolysis shifts toward low-cost hydrogen production coupled with renewable power inputs. [1] Alia, S. M., H2@Scale: Experimental Characterization of Durability of Advanced Electrolyzer Concepts in Dynamic Loading. Department of Energy, U. S., Ed. https://www.hydrogen.energy.gov/pdfs/review18/tv146_alia_2018_p.pdf, 2018. [2] Denholm, P.; O’Connell, M.; Brinkman, G.; Jorgenson, J. Overgeneration from Solar Energy in California: A Field Guide to the Duck Chart; Vol. NREL/TP-6A20-65023; National Renewable Energy Laboratory: Golden, CO, 2015. Available at the following: http://www.nrel.gov/docs/fy16osti/65023.pdf. [3] Alia, S. M.; Rasimick, B.; Ngo, C.; Neyerlin, K. C.; Kocha, S. S.; Pylypenko, S.; Xu, H.; Pivovar, B. S. J. Electrochem. Soc. 2016, 163, F3105−F3112.

Net-Metered Distributed Renewable Energy: A Peril for Utilities?

Electricity end-users have been increasingly generating their own electricity via rooftop solar panels. Our paper studies the implications of such “distributed renewable energy” for utility profits and social welfare under net metering that has sparked heated debates in practice. The common belief is that such type of generation significantly decreases utility profits because (i) distributed generation reduces utility’s market size, and (ii) under net metering, utilities must buy back the excess generation of their customers at a rate typically larger than their procurement cost. Based on this understanding, there have been various lobbying campaigns against the net-metered distributed solar energy. A distinctive feature of our paper is that it considers supply-side effects of distributed renewable energy on utilities by explicitly modeling the wholesale market dynamics, while also accounting for (i) and (ii). Our analysis shows that in contrast to the common belief, the presence of net-metered distributed renewable energy can strictly increase the expected profit for utilities (compared to the case with no such energy) when wholesale market dynamics are factored in. Specifically, we prove that the net-metered distributed renewable energy strictly improves the utility’s expected profit if and only if the equilibrium wholesale electricity price is sufficiently sensitive to the changes in the wholesale demand and the utility’s expected market-reliance level is above a threshold. Our numerical study uses data on distributed solar energy in California and the CAISO’s wholesale electricity market, and demonstrates that our results continue to be valid under realistic parameters.

What are You Waiting to Invest? Long-Term Investment in Grid-Connected Residential Solar Energy in California. A Real Options Analysis.

The goal of this paper is to assess the optimal choice of a household in California, United States, in terms of their decision if and when to undertake a certain investment in a residential scale, grid-connected, solar photovoltaic system, in order to obtain savings in their monthly expenditures in electricity. This irreversible option is then defined, mainly, by the initial cost of the solar PV system. For this purpose, Real Options Analysis is deployed to assess this investment opportunity for the household. This approach allows determining not only whether the investments should be undertaken or not, but also the optimal timing to do so. Results show it is optimal for a Californian household to invest in a photovoltaic system, however, some delay might be advised depending on the energy production factor of specific areas, and the expected useful life of the equipment. Furthermore, government intervention influencing subsidies and energy prices has a major effect in the length of such delay.

(Invited) H2@Scale: The Effect of Loading, Test Parameters, and Oxides on Electrolyzer-Catalyst Durability

In commercial electrolysis, the cost of electricity input drives the cost of hydrogen production. Therefore, electrolysis is typically run at high catalyst loading and constant power input over long periods of time. Lowering water-splitting hydrogen production costs to a level comparable to steam methane reformation requires: coupling electrolysis with low-cost power input (wind, solar) to reduce feedstock costs; and dropping catalyst loading to reduce the capital cost at lower capacity.[1,2] While minimal durability loss is seen in commercial electrolyzers, catalyst losses can be masked by high loading (several mg cm‒2). At low loading, however, these losses become more apparent.[3] In this study, electrolyzer durability was evaluated at low iridium-anode loading (0.1‒0.5 mg cm‒2) and with different power inputs (potentials, intermittency). Higher loading tended to delay the onset of durability losses; in contrast, a loading of 0.1 mg cmelec ‒2 resulted in incremental but immediate loss when exposed to high potential. Increasing the upper potential limit appeared to increase iridium dissolution and migration and resulted in higher performance losses. This trend was expected and iridium dissolution is anticipated to be a primary factor in electrolyzer loss at low loading.[4] Introducing cycling (square/triangle wave), however, significantly increased the rate of performance decay and was less expected from half-cell tests and even though less time was spent at elevated potential.[3] Changing the rate of potential increase (saw tooth profiles) confirmed that rapid input increases accelerated loss and may be due to localized potential spikes occurring within the catalyst layer. A variety of system control-based mitigation strategies have been evaluated for lessening durability losses when handling intermittent power sources. Several iridium catalyst types (oxides, surface areas) have been tested in half- and single-cells. Catalyst development efforts often focus on metallic- or hydroxide-based iridium structures, due to higher activity in ex-situ tests. These performance advantages, however, largely disappear in single-cell tests and may be due to surface/near-surface oxidation during conditioning protocols. Metallic/hydroxide durability losses further tend to be larger in both half- and single-cells and may be related to the kinetics of iridium metal/hydroxide/oxide dissolution. In single-cell testing, we have focused on how loading, test parameters, and catalyst type affect proton exchange membrane-based electrolyzer durability. These tests have significant implications on lowering the cost of electrolysis-based hydrogen production and on coupling electrolysis with renewable power inputs. [1] H2 at Scale: Deeply Decarbonizing our Energy System. Presented at Annual Merit Review, U.S. Department of Energy; Washington, DC, June 6−10, 2016. https://www.hydrogen.energy.gov/pdfs/review16/2016_amr_h2_at_scale.pdf. [2] Denholm, P.; O’Connell, M.; Brinkman, G.; Jorgenson, J. Overgeneration from Solar Energy in California: A Field Guide to the Duck Chart; Vol. NREL/TP-6A20-65023; National Renewable Energy Laboratory: Golden, CO, 2015. Available at the following: http://www.nrel.gov/docs/fy16osti/65023.pdf. [3] Alia, S. M.; Rasimick, B.; Ngo, C.; Neyerlin, K. C.; Kocha, S. S.; Pylypenko, S.; Xu, H.; Pivovar, B. S. J. Electrochem. Soc. 2016, 163, F3105−F3112. [4] Cherevko, S.; Geiger, S.; Kasian, O.; Kulyk, N.; Grote, J. P.; Savan, A.; Shrestha, B. R.; Merzlikin, S.; Breitbach, B.; Ludwig, A.; Mayrhofer, K. J. J. Cat. Today 2016, 262, 170.

Renewable hydrogen roadmap for transport, economy in California

Energy Independence Now (EIN), in collaboration with the Leonardo DiCaprio Foundation and the California Hydrogen Business Council (CHBC), have released a Renewable Hydrogen Roadmap. This outlines key strategies to promote ‘green’ hydrogen production that will help achieve clean energy and zero-emissions transportation in California.

The future of wind energy in California: Future projections with the Variable-Resolution CESM

Shifting wind patterns are an expected consequence of global climate change, with direct implications for wind energy production. However, wind is notoriously difficult to predict, and significant uncertainty remains in our understanding of climate change impacts on existing wind generation capacity. In this study, historical and future wind climatology and associated capacity factors at five wind turbine sites in California are examined. Historical (1980–2000) and mid-century (2030–2050) simulations were produced using the Variable-Resolution Community Earth System Model (VR-CESM) to understand how these wind generation sites are expected to be impacted by climate change. A high-resolution statistically downscaled WRF product provided by DNV GL, reanalysis datasets MERRA-2, CFSR, NARR, and observational data were used for model validation and comparison. These projections suggest that wind power generation capacity throughout the state is expected to increase during the summer, and decrease during fall and winter, based on significant changes at several wind farm sites. This study improves the characterization of uncertainty around the magnitude and variability in space and time of California's wind resources in the near future, and also enhances our understanding of the physical mechanisms related to the trends in wind resource variability. • The state-of-the-art global climate model Variable-Resolution Community Earth System Model (VR-CESM) was used. • Model validation and comparison of hub-height wind speed with industry-approved datasets. • Significant wind energy resources trend were detected at all major wind farm locations in future climate. • Analyzed synoptic-scale patterns associated with the wind energy resources change under future climate.

Low-carbon energy generates public health savings in California

Abstract. California's goal to reduce greenhouse gas (GHG) emissions to a level that is 80 % below 1990 levels by the year 2050 will require adoption of low-carbon energy sources across all economic sectors. In addition to reducing GHG emissions, shifting to fuels with lower carbon intensity will change concentrations of short-lived conventional air pollutants, including airborne particles with a diameter of less than 2.5 µm (PM2.5) and ozone (O3). Here we evaluate how business-as-usual (BAU) air pollution and public health in California will be transformed in the year 2050 through the adoption of low-carbon technologies, expanded electrification, and modified activity patterns within a low-carbon energy scenario (GHG-Step). Both the BAU and GHG-Step statewide emission scenarios were constructed using the energy–economic optimization model, CA-TIMES, that calculates the multi-sector energy portfolio that meets projected energy supply and demand at the lowest cost, while also satisfying scenario-specific GHG emissions constraints. Corresponding criteria pollutant emissions for each scenario were then spatially allocated at 4 km resolution to support air quality analysis in different regions of the state. Meteorological inputs for the year 2054 were generated under a Representative Concentration Pathway (RCP) 8.5 future climate. Annual-average PM2.5 and O3 concentrations were predicted using the modified emissions and meteorology inputs with a regional chemical transport model. In the final phase of the analysis, mortality (total deaths) and mortality rate (deaths per 100 000) were calculated using established exposure-response relationships from air pollution epidemiology combined with simulated annual-average PM2.5 and O3 exposure. Net emissions reductions across all sectors are −36 % for PM0.1 mass, −3.6 % for PM2.5 mass, −10.6 % for PM2.5 elemental carbon, −13.3 % for PM2.5 organic carbon, −13.7 % for NOx, and −27.5 % for NH3. Predicted deaths associated with air pollution in 2050 dropped by 24–26 % in California (1537–2758 avoided deaths yr−1) in the climate-friendly 2050 GHG-Step scenario, which is equivalent to a 54–56 % reduction in the air pollution mortality rate (deaths per 100 000) relative to 2010 levels. These avoided deaths have an estimated value of USD 11.4–20.4 billion yr−1 based on the present-day value of a statistical life (VSL) equal to USD 7.6 million. The costs for reducing California GHG emissions 80 % below 1990 levels by the year 2050 depend strongly on numerous external factors such as the global price of oil. Best estimates suggest that meeting an intermediate target (40 % reduction in GHG emissions by the year 2030) using a non-optimized scenario would reduce personal income by USD 4.95 billion yr−1 (−0.15 %) and lower overall state gross domestic product by USD 16.1 billion yr−1 (−0.45 %). The public health benefits described here are comparable to these cost estimates, making a compelling argument for the adoption of low-carbon energy in California, with implications for other regions in the United States and across the world.

Ecosystem management and land conservation can substantially contribute to California’s climate mitigation goals

Modeling efforts focused on future greenhouse gas (GHG) emissions from energy and other sectors in California have shown varying capacities to meet the emissions reduction targets established by the state. These efforts have not included potential reductions from changes in ecosystem management, restoration, and conservation. We examine the scale of contributions from selected activities in natural and agricultural lands and assess the degree to which these actions could help the state achieve its 2030 and 2050 climate mitigation goals under alternative implementation scenarios. By 2030, an Ambitious implementation scenario could contribute as much as 147 MMTCO2e or 17.4% of the cumulative reductions needed to meet the state's 2030 goal, greater than the individual projected contributions of four other economic sectors, including those from the industrial and agricultural sectors. On an annual basis, the Ambitious scenario could result in reductions as high as 17.9 MMTCO2e⋅y-1 or 13.4% of the state's 2030 reduction goal. Most reductions come from changes in forest management (61% of 2050 projected cumulative reductions under the Ambitious scenario), followed by reforestation (14%), avoided conversion (11%), compost amendments to grasslands (9%), and wetland and grassland restoration (5%). Implementation of a range of land-based emissions reduction activities can materially contribute to one of the most ambitious mitigation targets globally. This study provides a flexible, dynamic framework for estimating the reductions achievable through land conservation, ecological restoration, and changes in management regimes.

Can the US keep the PACE? A natural experiment in accelerating the growth of solar electricity

Growing global awareness of climate change has ushered in a new era demanding policy, financial and behavioural innovations to accelerate the transition to a clean energy economy. Dramatic price decreases in solar photovoltaics (PV) and public policy have underwritten the expansion of solar power, now accounting for the largest share of renewable energy in California and rising fast in other countries, such as Germany and Italy. Governments' efforts to expand solar generation base and integrate it into municipal, regional, and national energy systems, have spawned several programs that require rigorous policy evaluations to assess their effectiveness, costs and contribution to Paris Agreement's goals. In this study, we exploit a natural experiment in northern California to test the capacity of Property Assessed Clean Energy (PACE) to promote PV investment. PACE has been highly cost effective by more than doubling residential PV installations.