Fuel Cell Recreational Vehicles (FCRVs) are emerging as a promising sustainable alternative to conventional diesel- and gasoline-powered recreational vehicles. This paper evaluates the financial and technological aspects of FCRVs, focusing on the cost and performance of electro-mechanical subsystems such as fuel cells, hydrogen storage, and batteries. Drawing on data from peer-reviewed reports and U.S. Department of Energy projections, the analysis examines the cost evolution of these components over time and across varying production scales. Results reveal significant cost reductions, with unit costs decreasing by 75% when FCRVs are produced at 50,000 units per year compared to single-unit production in 2022. Similarly, the cost of FCRVs produced at this scale in 2050 is projected to reduce by 62%, highlighting the continued impact of economies of scale and technological advancements. The Total Cost of Ownership (TCO) analysis underscores FCRVs’ potential long-term cost advantages, primarily through reduced fuel and maintenance expenses compared to diesel RVs. Moreover, at least $1,730 in annual social carbon costs were saved per FCRV compared to diesel RVs, underscoring their environmental benefits, particularly in reducing greenhouse gas emissions when powered by green hydrogen. While initial costs remain high, ongoing innovation and supportive policy frameworks are expected to enhance the economic viability of FCRVs, positioning them as a critical component in the transition toward sustainable transportation.

Extreme heat conditions pose significant indoor survivability challenges for resource-constrained communities, which often lack access to cooling, have poorly insulated homes, and face compounding socioeconomic vulnerabilities. Moreover, concurrent power outages worsen health risks and heat-related illnesses. It is therefore crucial to develop innovative and affordable cooling approaches to protect vulnerable populations. This study assesses the efficacy of "cool rooms"- a designated space within a home equipped with passive and low-power active cooling measures to maintain safe indoor temperatures during extreme heat events and power disruptions. Using a physics-based building energy modeling approach, we evaluate the efficacy of various retrofit packages in maintaining thermal safety within the cool room under recent extreme heat conditions. The results indicate that passive measures can reduce 64% of hours with unmet standard effective temperatures, while the combination of passive and low-power active measures with built-in batteries further cuts this to 86%. Nevertheless, these strategies remain insufficient to maintain indoor thermal safety during extended outages. In contrast, integrating a solar-powered mini-split heat pump, whose technical potential was evaluated in this study, reduces indoor air temperatures below the 28 degrees C overheating threshold and significantly improves indoor habitability. The localized cool room strategy also offers potential for grid resilience by reducing peak electricity demand by up to 70% compared to whole house cooling during heat waves. The findings can inform the development of actionable heat mitigation plans and retrofit policies for residential communities with relatively low adoption of air conditioning such as warm marine climates.

To foster informed policy formulation and decision-making for the evolving energy transition and the rising demand for renewable and clean energy systems (REACES), it is imperative to establish a standardized and comprehensive Techno-Economic Analysis (TEA) method for widespread adoption. Existing TEA studies on REACES have been noted to contain significant inconsistencies and deficiencies in the economic frameworks, financial parameters, decision-making metrics, and methodological approaches. Key TEA parameters, such as balance of plant, land, and contingency cost, etc., were found underutilized, with implementation rates of only 36%, 28%, and 26%, respectively. This study addresses these critical gaps by developing a robust, comprehensive, and standardized TEA model specifically tailored to REACES. System-level macro- and micro parameters related to technical, economic, financial, and business risk were integrated. The impact of key parameters illustrated through a pilot case study emphasized that overlooking these parameters significantly skews the final decision metrics. Excluding incentives resulted in an 18% underestimation of the Levelized Cost of Energy (LCOE) and a 14% miscalculation in the Discounted Payback Period. Implementing this standardized model will enhance the accuracy, consistency, and credibility of TEA practices, enabling more precise evaluations and fostering meaningful cross-comparisons among various REACES.

Extreme heat is a major cause of weather-related deaths in the United States. To address this, a heat vulnerability index (HVI) is crucial for assessing heat risk and identifying vulnerable urban areas and populations, supporting city planning and emergency response. Current HVI studies often use Principal Component Analysis (PCA) on environmental, socioeconomic, and medical data to aggregate vulnerability indicators into a single index. However, these fixed aggregation weights struggle to adapt to different use cases, which may require varying focuses. Moreover, existing tools primarily consider outdoor heat exposure, providing an incomplete picture of actual exposure, as people spend most of their time indoors. Our research introduces an HVI web mapping tool that addresses these gaps in the literature by: (1) allowing flexible weights to adapt to different use cases, and (2) uniquely integrating both outdoor and indoor heat exposure by considering building characteristics for a more comprehensive risk assessment. We demonstrated this tool in two California cities with contrasting climates: Fresno (inland, arid, hot summers) and Oakland (temperate coastal). This HVI mapping tool provides essential decision support for policymakers and stakeholders in both short-term heat mitigation and long-term urban planning for building interventions and infrastructure development.

This work explores the concept and modeling of energy sufficiency, differentiating it from energy efficiency. Both elements are vital to rethinking established systems of production and consumption in the face of energy crises and climate change. The developing field of energy sufficiency can potentially constrain energy use within planetary resources while meeting humanity's needs. Current energy and climate models generally exclude energy sufficiency, however, or combine it with energy efficiency, obscuring its distinct benefits. Theoretical frameworks, such as avoid-shift-improve, lack clear definitions and boundaries between sufficiency and efficiency measures. This paper introduces the decentralization, right-sizing and reduction, utilization/timing and longevity, multifunctionality, substitution, and sharing (DRUMSS) framework to improve the modeling of energy sufficiency. DRUMSS provides steps for implementing sufficiency measures across demand-side sectors, identifying policy actions to achieve deep decarbonization. We present three case studies, from the United States, China, and France, to illustrate implementing the DRUMSS framework in diverse contexts.

Increasing temperature-related hazards require a collective effort to assess and enhance the thermal resilience of buildings and communities to protect occupants’ safety and minimize property or infrastructure damage. However, limited coordination across stakeholders and lack of standardized procedures for resilience assessment undermine the effectiveness of extreme temperature mitigation and adaptation strategies across the building life cycle. This review examines the current literature on resilience metrics to address thermal stress and risk due to extreme indoor environments. Stakeholders of thermal resilience include architects and engineers, occupants, property owners, real estate developers, urban planners, and policymakers. Additionally, motivations for measuring thermal resilience are emphasized, such as safeguarding occupant health and survivability, protecting property, and ensuring business continuity during extreme weather events. This review provides actionable insights and identifies future research needs for enhancing resilience through tailored metrics for stakeholders during the planning, design, construction, operation, and retrofitting phases of buildings and communities.

Designing an efficient renewable energy system is critical for achieving cost-effective energy solutions and minimizing excess generation. This study analyzes the optimization of renewable energy systems with two storage configurations: PV solar with Li-ion Batteries (PV-LIB) and PV solar with a reversible fuel cell (PV-RFC). The system maximizes renewable energy integration by optimizing component sizes to meet the buildings load demand. Results indicate that the PV-LIB system requires a smaller PV array than the PV-RFC system due to the higher roundtrip efficiency of Li-ion batteries. The PV-RFC system achieved a renewable fraction of 95.43 %, while the PV-LIB system reached 95.73 %, with 0.068 % excess energy in the PV-RFC system and none in the PV-LIB system. Monthly energy supply distribution analysis highlights the variability of PV generation and the consistent contribution of storage systems. Cost analysis reveals a levelized cost of hydrogen (LCOH) of $5.17/kg and a levelized cost of energy (LCOE) of $0.166/kWh for the PV-RFC system, compared to an LCOE of $0.071/ kWh for the PV-LIB system. The PV-LIB system is more economically viable due to lower capital costs and higher efficiency. Both systems demonstrated lower LCOE compared to local grid electricity tariffs, emphasizing their economic advantage.

We need human behavioural change to decarbonize our buildings. This requirement arises from our needs, lifestyle energy choices and interactions with buildings, and is an underexploited, yet essential demand-side opportunity for rapid and sustainable decarbonization. We propose a sufficiency-oriented approach that fosters equitable building decarbonization, while maintaining planetary boundaries.

Policy approaches to the global energy transition often focus on technology-based solutions while ignoring challenges of overall energy demand. A sufficiency-first approach aims to limit superfluous consumption while achieving wellbeing for all. This study focuses on US built environment mechanisms of sufficiency under urban land-use policy. The historical context of US exclusionary and car-oriented planning is reviewed with an order-of-magnitude assessment of the effects on greenhouse gas emissions (GHGE). Using national vehicle-miles traveled (VMT) data derived from mobile device locations (Replica) and validated here with federal data, a hypothetical scenario explores the potential for state urban land-use reforms to enable energy sufficiency. Tenth percentile-VMT (per capita) neighborhoods are defined by state: in 47 states, the typical such neighborhood has less than 33% of its housing units in structures larger than four units. Assuming each state redresses its housing shortage while matching this VMT, 31 Mt CO2e (direct GHGE) and about 38 Mt CO2e (indirect and life-cycle GHGE) would be avoided in 2033. Texas, California, and Florida have the largest absolute emissions reduction opportunity. Urban land-use reforms comprise a logical starting point for a US sufficiency agenda. Key priorities for research, data collection, and technology and policy innovation are proposed. Policy relevance International climate policy is increasingly focused on enabling people to consume less energy: not just technological ‘efficiency’ but ‘sufficiency’ is needed. However, sufficiency has seen little uptake in the US. It may be more relevant to US policymakers if related to the growing momentum for reforming land-use planning and housing policy to address the housing shortage and affordability crisis. This crisis stems in part from the US prevalence of single-family zoning and car-centric planning, rooted in a history of racial segregation; these same laws effectively mandate people to maintain more polluting lifestyles. This study estimates how much climate pollution could be avoided with state-led land-use reform. If states committed to solving the housing shortage while building new housing in neighborhoods where people can drive less, the savings could be comparable with expanding electric vehicle policies. Policymakers and practitioners can enable these reforms while supporting complementary policy goals.

High global warming potential gases ("high GWP") are the fastest growing sector of greenhouse gas emissions in the world and in California and are primarily used as refrigerant gases in refrigeration and cooling equipment. Hydrofluorocarbons (HFCs) refrigerants are the dominant type of high GWP gases with GWP values thousands of times larger than CO2 2 on a 100-year timescale. Refrigerant-grade propane ("R290") has a very low GWP (GWP = 3.3) with good thermodynamic properties and good cooling equipment performance but the flammability of any leaked refrigerant makes equipment design, handling, and maintenance critical factors to manage. This paper focuses on the potential climate benefits and costs of transitioning to R290 refrigerant in small room air conditioning (AC) units, specifically window AC, packaged terminal AC/heat pumps (PTAC/PTHP), and mini-split heat pumps. Overall climate impact for a transition to all three types of air conditioning units in the 2022-2051 timeframe is found to be from 15 to 64 million metric tons of greenhouse gas (GHG) savings in California with a cost of saved CO2eq 2 eq that ranges from $14.50 per ton of CO2eq 2 eq saved to-$50.30 per ton of CO2eq 2 eq saved (net savings) depending on whether the baseline refrigerant is R32 or R410A and depending on the relative energy efficiency for R290 units compared to baseline units.

Energy storage systems (ESSs) were introduced to overcome the risks posed by energy curtailment. In this paper, we compare the Levelized cost of storage (LCOS) for PEM Reversible Fuel Cells, Solid Oxide Fuel Cells, and Lithium-Ion Batteries in three different locations in the United States (Tucson, Seattle, and Rochester) that are characterized by different energy consumption profiles. This research examines three commercial buildings of different sizes: small, medium, and large, with three occupancy profiles: low, medium, and high energy consumption in each of the three locations. The objective is to quantify the impact of uncertain demand and uncertain financial parameters on the LCOS. The results show that all ESSs can represent an attractive alternative to energy curtailment regardless of the building size or the occupancy profile. Further, the results show that fuel cells are a better fit for demand uncertainty as they are more resilient to changes and remain attractive despite that. The uncertainty analysis showed that the minimum LCOS was $0.049/kWh, and it was for a PEM-RFC in a small building in Tucson under high energy consumption behavior. Oppositely, the maximum LCOS was $0.679/kWh, and that was for a large building in Seattle under high energy usage occupancy as well.

California has a state-wide goal of carbon neutrality by 2045. Decarbonization for disadvantaged communities (DACs) poses extra challenges due to financial, informational, language, and other barriers. This paper presents the methodology, results, and analysis of energy efficiency measures (EEMs) to save energy, reduce CO2 emission, and promote clean energy access at the district scale for two DACs in Fresno, California. The methods are broadly applicable to other neighborhoods across the U.S. 22 EEMs were identified and modelled for all residential buildings in the two DACs both individually and as packages. Results show that for energy and CO2 reduction purposes, the top performing EEM package can decrease energy use and CO2 emissions by an average of 60

These “Model Regulation Guidelines for Energy-Efficient Ceiling Fans” provide voluntary guidance for governments in developing and emerging economies that are considering a regulatory or legislative framework that requires new ceiling fans to be energy efficient. It covers products commonly used in residential and light commercial applications. The accompanying Supporting Information Annex1 describes the underlying rationale and methodologies.

With climate change leading to more frequent, more intense, and longer durations of extreme weather events such as heat waves and cold snaps, it is essential to maintain safe indoor environmental conditions for occupants during such events, which may coincide with, or even cause, power outages that expose residents to health risks. Analyzing the impacts of extreme weather events on the thermal resilience of buildings can help stakeholders (including occupants) understand the risk and inform them about mitigation and adaptation actions. Moreover, analyzing the technological, social and policy dimensions of thermal resilience is critical for climate-proofing buildings. This paper presents 10 questions that highlight the most important issues regarding the thermal resilience of buildings for occupants in the face of climate change. The proposed questions and answers aim to provide insights into current and future building thermal resilience research and applications, and more importantly to inspire new significant questions in the field.

At scale, biomass-based fuels are seen as long-term alternatives to conventional shipping fuels to reduce greenhouse gas emissions in the maritime sector. While the operational benefits of renewable methanol as a marine fuel are well-known, its cost and environmental performance depend largely on production method and geographic context. In this study, a techno-economic and environmental assessment of renewable methanol produced by gasification of forestry residues is performed. Two biorefinery systems are modeled thermody-namically for the first time, integrating several design changes to extend past work: (1) methanol synthesized by gasification of torrefied biomass while removing and storing underground a fraction of the carbon initially contained in it, and (2) integration of a polymer electrolyte membrane (PEM) electrolyzer for increased carbon efficiency via hydrogen injection into the methanol synthesis process. The chosen use case is set in California, with forest residue biomass as the feedstock and the ports of Los Angeles and Long Beach as the shipping fuel demand point. Methanol produced by both systems achieves substantial lifecycle greenhouse gas emissions savings compared to traditional shipping fuels, ranging from 38 to 165%, from biomass roadside to methanol combustion. Renewable methanol can be carbon-negative if the CO2 captured during the biomass conversion process is sequestered underground with net greenhouse gas emissions along the lifecycle amounting to-57 gCO(2)eq/MJ. While the produced methanol in both pathways is still more expensive than conventional fossil fuels, the introduction of CO(2)eq abatement incentives available in the U.S. and California could bring down minimum fuel selling prices substantially. The produced methanol can be competitive with fossil shipping fuels at credit amounts ranging from $150 to $300/tCO(2)eq, depending on the eligible credits.

Extreme heat is one of the leading causes of weather-related deaths in the U.S. Exposure to extreme heat will be exacerbated due to global climate change. It is thus crucial to design a key performance indicator, heat vulnerability index (HVI), to represent overall heat risk which can help identify susceptible regions and sub-populations in cities in the face of heatwaves. Most existing HVI tools only consider outdoor heat exposure. This paper developed an HVI web map tool incorporating both the outdoor and the indoor heat exposure, as well as population sensitivity and adaptation capability across census tracts in the city of Fresno, California. The tool can assist the planning of infrastructure and resources to reduce residents’ vulnerability to extreme heat events. (Available at https://citybes.lbl.gov/?hvi=1).

More intense heat waves are expected to occur more frequently in the twenty-first century. During severe heat waves, cooling capacity shortfall and overheating are likely to occur in residential buildings, and this will adversely affect occupant's thermal comfort and productivity. We propose a strategy of pre-cooling the house during off-peak hours to mitigate overheating during heat waves. Simulation results of a prototype single-family house show that adopting the rule-based control (RBC) of pre-cooling thermostat setpoint schedule is effective in reducing thermal discomfort, and that the efficacy of pre-cooling depends upon several building characteristics. An optimized control (OC) of the thermostat setpoint schedule was developed based on the simulation of a prototype building. A simplified yet improved RBC (IRBC) pre-cooling schedule was then extracted from the OC schedule for practical implementation at a larger scale. The effects of the RBC schedule and IRBC schedule were evaluated in the King District of Fresno, which contains 814 residential buildings. Results show that both thermostat setpoint schedules can reduce overheating effectively and that IRBC is slightly better than RBC for most buildings. The findings support the California government's recommendation on pre-cooling to mitigate overheating, which can be further improved with an optimized thermostat setpoint schedule broadcast to residents through early alert messages before a heat wave.

Long-distance road-freight transport emits a large share of Germany's greenhouse gas (GHG) emissions. A potential solution for reducing GHG emissions in this sector is to use green hydrogen in fuel cell electric vehicles (FC-HDV) and establish an accompanying hydrogen refueling station (HRS) network. In this paper, we apply an existing refueling network design model to a HDV-HRS network for Germany until 2050 based on German traffic data for heavy-duty trucks and estimate its costs. Comparing different fuel supply scenarios (pipeline vs. on-site), The on-site scenario results show a network consisting of 137 stations at a cost of 8.38 billion € per year in 2050 (0.40 € per vehicle km), while the centralized scenario with the same amount of stations shows a cheaper cost with 7.25 billion euros per year (0.35 € per vehicle km). The hydrogen cost (LCOH) varies from 5.59 €/kg (pipeline) to 6.47 €/kg (on-site) in 2050.