Probabilistic deployment pathways of scaling up distributed green hydrogen systems for urban residential communities in North America

doi:10.21203/rs.3.rs-4327177/v1

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Probabilistic deployment pathways of scaling up distributed green hydrogen systems for urban residential communities in North America

https://doi.org/10.21203/rs.3.rs-4327177/v1

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In the context of the firm and enthusiastic development of renewable-based distributed energy systems, high-profit household collaboration strategies are widely recognized as essential for scaling up decentralized green hydrogen systems in urban residential communities. Here we develop bottom-up energy models linking climate, human behavior, and community characteristics to assess the cost-effective impacts of system deployment pathways on community green hydrogen systems for 7 North American climate zones in the 2030 ~ 2050 periods. Despite lower energy costs in moderate climate zones compared to hot and cold zones, a consistent pattern in deployment pathway impacts on costs is observed across all zones. The study underscores the critical role of selecting the right deployment pathway for urban decarbonization, with potential cost discrepancies of up to 60% between optimal and suboptimal options. Furthermore, energy storage demands significantly influence energy costs, emphasizing the need to prioritize increased energy storage in pathway design.

Physical sciences/Energy science and technology/Renewable energy

Earth and environmental sciences/Climate sciences/Climate change

According to the International Energy Agency (IEA), the global energy sectors need to achieve net zero emissions by 2050 to reach the target of limiting global warming to 1.5°C in 2100¹. Currently, about one-third of global power is consumed in cities². Rapid deployment of clean energy technologies is a core pathway to achieve urban energy transition from fossil fuels to cleaner energy sources³. With surging energy demand caused by accelerating urbanization, growing evidence shows that planning large-scale plant-central renewable energy production outside the cities faces enormous pressure from technically feasible lands due to their limited renewable energy density^4,5. Thus, distributed energy systems that support integrating renewable technologies will effectively reduce external energy demand from urban residential communities, minimizing the land pressure of urban renewable energy infrastructure⁶. In addition, a large body of research supports the notion that communities with coordinated action provide critical spatial, temporal, and social pathways for energy integration to realize higher economic, environmental, and social interests of distributed energy systems^7,8. Therefore, an accelerated market introduction of decentralized energy systems into urban communities is considered a pivotal option to utilize inner-city resources for decarbonizing cities.

Distributed energy systems powered by renewable sources depend on cost-effective energy storage technologies to address the severe energy mismatch caused by high homogeneous production and demand in urban residential communities⁹, requiring high efficiency for short-term extreme energy events and high capacity for cross-seasonal energy patterns¹⁰. Growing research shows that the single battery technology as a cross-seasonal storage option may not be economically viable in long-term resilience systems due to their low energy density and high leakage rate¹¹. Green hydrogen systems, a distributed energy system with green hydrogen and battery as storage options, offer higher storage flexibility and lower storage costs, making them more suitable for long-term community sustainability¹². We consider green hydrogen systems a promising community energy solution that needs to be evaluated in detail.

Energy models are widely used to understand the impacts of energy systems on residential communities and to inform potential development directions to energy planners¹³. However, academic and policy spheres highlight concern that deep uncertainties of energy input are fundamental modelling limitations for energy models, causing inappropriate assessment and adversely impacting policy targets when ignoring modelling limitations¹⁴. Part of energy input uncertainties stems from both climate conditions and human behaviors. In future periods, energy models will confront heightened challenges associated with the evolving climate conditions that result from continuing climate change¹⁵. On the other hand, these models exhibit limited incorporation of historical data-driven methods to measure potential human behavior¹⁶. Thus, how to effectively expand input scenarios for energy models becomes core to understanding the potential fluctuations of energy input stemming from uncertainties associated with climate-human systems. The sampling method¹⁷ and generative adversarial network (GAN) method¹⁸ are adapted to generate a substantial number of energy input scenarios for modeling potential climate-human uncertainties.

Besides climate-human systems, another significant source of uncertainties emerges from the community design layer, including community compositions and renewable energy levels. Community compositions account for different residential building types and their corresponding numbers within residential communities, while renewable energy levels represent the deployment numbers of energy systems within residential communities ¹⁹. These two factors impact the diversity of energy input scenario types for energy models in the design phase, influenced by various geographical, sociological, and psychological considerations. Current studies have considered that the uncertainties of the community design layer significantly impact on the overall economic and environmental benefits of the community^20,21. Thus, energy models must integrate detailed community design layers into energy planning. However, meeting this requirement poses a dilemma for energy models, navigating the delicate equilibrium between spatial dimensions and calculating tractable. To strike balance between the diversity of household energy profiles with the robustness of urban energy planning, historical data-driven energy input scenarios²³ and city-related virtual communities²⁴ are developed.

System deployment pathways of green hydrogen systems in communities determine different household participation forms, highly affecting shared benefits and participation motivation among interconnected households²⁵. Thus, system deployment pathways are a centerpiece of understanding the full impact of green hydrogen systems on decarbonizing communities in the strategic energy planning phase. We reckon that such multiple-source uncertainties of energy models are particularly relevant for analyzing the impact on the system deployment pathways due to energy input uncertainties undoubtedly that affect the model output results of system deployment pathways. The multiple-source uncertainties in communities include climate-human uncertainties at the household level and community design uncertainties at the community level. In that context, quantifying these uncertainties into energy models presents a considerable challenge due to the complexity of multidimensional impacts. We consider that green hydrogen systems are at a nascent stage. Whether and how green hydrogen systems can expand fast enough in uncertain communities remains unclear. Thus, systematically analyzing potential expansion pathways of green hydrogen systems through high-fidelity energy models is essential to facilitate rapid deployment and unleash its potential for community energy transition.

In this article, we introduce a bottom-up energy model linking climate, human behavior, community archetypes, and energy system models, aiming to ensure cost-effective deployment pathways of green hydrogen systems for highly diverse urban residential communities. Figure 1 depicts a summary of three interconnected phases of the proposed energy model. First, we developed a multi-scale combined uncertainty approach to obtain a set of community energy production and demand profiles, including detailed household energy information with potential occurrence probability to reflect inevitable uncertainties from household and community layers. Next, we formulated three system deployment pathways based on an urban planning perspective to characterize strategies for household collaboration within the community. These pathways were merged with community energy profiles to serve as community inputs to the energy system model related to green hydrogen systems. Lastly, the robust energy system model yielded a collection of optimal system designs that reflect the cost-effective impacts of deployment pathways on green hydrogen systems under multi-source uncertainties. We extensively investigated seven North American climate zones to understand the general and overall effects of deployment pathways on community energy system design.

Multi-source uncertainty quantification of energy input scenarios at the North American scale

The IEA report points out that advanced economies need to take the lead and reach net-zero emissions earlier to buy more time for the energy transition in developing economies¹. However, the efforts undertaken by the United States and Canada in North America fall far short of what is needed to achieve net zero global energy-related carbon dioxide emissions by 2050²⁶. These developed nations need to take further action to assess the cost and availability of green hydrogen systems as "emerging" technologies for widespread commercial deployment. The United States and Canada are divided into eight building climate zones, and most of their cities are located in the previous seven climate zones. Cities within each climate zone do not exhibit significant differences in building and energy regulations. Thus, we selected one sample of cities from each climate zone to capture the typical regional energy performance. The green hydrogen systems in these cities were evaluated using an energy model.

The standard approach to obtaining dynamic energy input scenarios for energy models is to use typical urban stock community parameters, such as climate patterns, human activities, building characteristics, etc. However, this approach often overlooks the compounded uncertainty impacts from both the household and community levels. Neglecting these impacts may lead to an energy information gap between computed energy performance and reality. This study introduces multi-source uncertainties into bottom-up building energy modelling layer by layer depending on their impact pathway in the energy calculation process. Thus, we begin by quantifying the impacts of climate-human uncertainties on energy input scenarios at the household level (details about climate-human uncertainties are presented in Method).

Figure 2. shows the impact of climate-human uncertainties on energy input scenarios in 7 cities taken from climate zones 1 ~ 7. Climate and human uncertainties show a more uneven and significant effect on the energy demand side rather than on the energy production side from the median and interquartile range perspective. On the energy demand side, the annual median household energy demand exhibits a valley-shaped pattern across all climate zones, with varying interquartile ranges. Vancouver demonstrates the lowest median energy demand with a narrower interquartile range at the bottom of the valley, while Miami and Edmonton exhibit higher median energy demand values and more comprehensive interquartile ranges at the top of the valley. On the energy production side, the median annual household energy production decreases as climate zones progress backward, with a nearly uniform interquartile range. Miami and Edmonton have the highest and lowest energy production performance, respectively. The variation in urban building archetypes results in higher energy demand but similar energy production within these observed cities. The median annual energy demand of bungalows is approximately 5,000 kWh lower than that of two-story buildings, yet the annual energy production exhibits minimal variance between the two types of structures.

We then superimpose the impact of community design layer uncertainties onto the energy input scenarios at the household level using a community characteristic matrix assembled from household scale and prosumer scale (detail about community design layer uncertainties is presented in Method). The household scale represents the clustering process of average and boundary community energy scenarios from previously obtained input scenarios, while the prosumer scale denotes the labeling process of independent households as prosumers or consumers within obtained community samples. Figure 3. shows the impact of community design layer uncertainties on the energy input scenarios at the community level, depicted using the sharing level indicator. The sharing level reflects the expected potential for energy self-sufficiency of independent households within community samples.

Results show that annual median sharing levels in all community samples exhibit a ridge-shaped pattern across all climate zones. Vancouver shows the highest sharing levels at the peak of the ridge, while Miami and Edmonton exhibit lower sharing levels at the base. In addition, sharing levels within the cities show a consistent decreasing trend among the three types of community samples, with bungalow community samples exhibiting the highest sharing levels, followed by average community samples, and finally, two-story community samples. This pattern suggests that energy demand plays a dominant role in shaping sharing levels across various climate zones, regardless of energy production levels, such as the higher energy production in Miami and lower energy production in Edmonton. However, we also observed that the annual peak-sharing levels vary among cities. Despite this, the peak value in moderate climate regions is higher than in extremely hot or cold climate regions. This suggests that, within urban communities, the climate zones to which the city belongs exert a more substantial influence on sharing levels than the internal community archetypes.

Impact of system deployment pathways on levelized cost of electricity

The green hydrogen systems in North American cities were assessed using an energy model that provides all the non-dominant sets of optimal system designs for initial commercial-scale deployment via Pareto front analysis. Our analysis centers on how different deployment pathways of energy systems affect energy affordability of urban communities, measured as levelized cost of electricity (LCOE) calculated from compromise solutions of system design options for each group. The primary approach for decision-making from the Pareto front utilizes the Euclidean-distance-based method²⁵. LCOE provides a levelized present price per unit energy value, making it suitable for comparing differences in the cost of system power generation across various urban residential sectors and deployment pathways. Figure 4 shows the impact of three types of deployment pathways on potential changes in LCOE in the eight selected cities. Two key insights emerge.

First, as observed from a horizontal perspective, household distributed program (HDP) follows a small upward trend as the prosumer scale increases within an equivalent community scale in all urban community cases. In contrast, household-centralized programs (HCP) and community-centralized programs (CCP) show the opposite trend, decreasing significantly. This is due to the fact that, with more household participation, HDP faces resource congestion caused by household competition, resulting in greater costs, while HCP and CCP can fully utilize the scale effect of household cooperation to reduce costs. Additionally, the similarity in the LCOE change trend across all cities indicates that climate zones have a trivial impact on the ways in which the three deployment pathways affect LCOE, although LCOE tends to be lower in mild climate zones compared to hot or cold climate zones. Furthermore, the increased rate of LCOE in HDP has remained relatively stable as the prosumer scale increases, while the decreased rate of LCOE in HCP and CCP gradually slows down. This indicates that despite increased household participation, the increased resource congestion in HDP does not accelerate cost deterioration, while the advantages of scale economies in HCP and CCP gradually diminish.

Second, as observed from a vertical perspective, the LCOE of different community scales within each deployment pathway decreases in the order of OB, Ave, and TW community scales across all urban community cases. This reveals that urban communities with high sharing levels bring more cost advantages regardless of climate zone and deployment pathways. Additionally, in all cities except Edmonton, HDP demonstrates a greater cost advantage compared to HCP and CCP at a 20% prosumer scale under the same community scale. With a prosumer scale exceeding 40%, both HCP and CCP demonstrate a cost advantage. Notably, HCP slightly outperforms CCP in most urban community scales, with both reaching parity at a 100% prosumer scale. The subtle difference shows that consumer scale can contribute to the cost burden, which decreases as consumer scale decreases. HCP shows better cost advantage than HDP and CCP at low prosumer scale in certain cities, such as Vancouver, Las Vegas, and Houston. However, the cost benefits diminish as more households with low sharing levels join. This is attributed to the fact that consortia of households with high sharing levels can readily export energy for profit through scale effects, thus supplementing energy costs. Therefore, it can be concluded that HDP and HCP approaches are suitable for low-participation communities, while HCP and CCP are more appropriate for high-participation communities.

Analysis of system design for resilient urban community

The primary driver of LCOE is the initial capital investment derived from the optimal system design identified by the energy model. Analyzing the variations in energy design across different pathways is crucial for understanding how these pathways drive changes in LCOE from the system design perspective. Here, we now examine the impact of deployment pathways on the system design to account for our previous findings on LCOE changes. Figure 5 illustrates the potential changes in four system design parameters under three types of deployment pathways across the eight selected cities.

First, we find that the drivers of LCOE change are not the same on the same consumer scale. HDP keeps system design parameters essentially unchanged as the prosumer scale increases. This shows that the slight increase in LCOE stems from continuous external resource congestion rather than a significant change in system investment costs. In contrast, both HCP and CCP significantly expand hydrogen tanks compared to other design parameters as the prosumer scale increases. This suggests that the continuous decrease in LCOE is driven by the substantial reduction in system investment costs, as cheap hydrogen tanks replace a significant portion of batteries in energy storage as the scale increases. Therefore, it can be concluded that the hydrogen tank becomes a primary design factor in driving the scale effect of HCP and CCP.

Second, we notice that higher energy storage demands lead to a higher hydrogen storage ratio, leading to lower LCOE when comparing system design parameters at the same community scale across the three pathways. This is because the advantage of scale in hydrogen costs offsets the drawback of linear increases in battery storage costs as energy storage demand increases. In the initial phase, both HDP and HCP demonstrate higher energy storage demand compared to CCP, resulting in a higher hydrogen storage ratio and better LCOE performance. However, as the prosumer scale increases, the higher storage demand leads to an inevitable growth in the hydrogen storage ratio for both HCP and CCP. Meanwhile, the storage structure limitations of HDP result in its hydrogen storage ratio remaining nearly constant, ultimately causing it to be quickly surpassed by HCP and CCP in LCOE performance. This can be further justified by the trivial difference across different community scales within the same pathway, where the hydrogen storage ratio decreases slightly along OB, Ave, and TW due to the decrease in energy storage demand.

Current energy models typically focus on urban and national scales, overlooking the influence of local private entities such as households and communities on energy markets²⁷. However, the decentralized nature of distributed energy systems grants more agency to these entities in participating in the energy market²⁸. This oversight may result in significantly lower market participation scales than those anticipated by macro energy models, posing a risk to the achievement of energy transition targets. In this work, we built a bottom-up energy model that established links between energy systems and local urban communities, which incorporate necessary technological details related to climate, human behavior, building archetypes, and energy system characteristics. This energy model is applied to the role of system deployment pathways in developing cost-effective green hydrogen systems for diverse urban residential communities from a design and operation perspective. The evaluation results will complement critical market participation information to inform fully potential expansion pathways to energy planners.

Our study shows that differences in community sharing levels influenced by climate zones and community type significantly impact the overall value of energy costs rather than their change trend affected by deployment pathways. Energy costs are lower in moderate climate zones than in extremely hot or cold climate zones. Additionally, community samples with high sharing levels consistently exhibit lower costs relative to those with low sharing levels at the deployment pathway. These findings underscore the potential for communities characterized by high sharing levels and moderate climate zones to attain optimal energy costs.

Our study underscores the critical importance of selecting the right deployment pathway for achieving cost-effective decarbonization in urban communities, with impacts consistent across all climate zones. The cost differential between the best and worst pathways for the same community scale can be as high as 60%. A household centralized program stands out as the preferred deployment pathway for most communities, consistently driving cost reductions by harnessing scale effects. In communities with low prosumer scale, household distributed programs may demonstrate better cost advantages initially, but as prosumers increase, resource competition escalates, leading to higher energy costs. Conversely, community centralized programs are better suited for communities with high prosumer scales, where consumer scales always significantly negatively impact energy costs.

Our study shows that variances in energy storage demands across different deployment pathways serve as the principal determinant of their respective energy cost trends. In green hydrogen systems, increased energy storage demands trigger a scale effect in hydrogen storage costs, consequently mitigating system investment costs. Our findings indicate that household centralized programs exhibit higher energy storage demand than household distributed programs and community centralized programs, demonstrating greater cost advantages in most communities. This underscores the critical importance of incorporating more prosumers in the design of deployment pathways to expand energy storage demand.

There are several essential avenues for expanding upon this work. Extending our research to include future climate periods beyond 2050, such as those projected for 2050–2100 under Representative Concentration Pathway (RCP) 8.5, would offer valuable insights into the long-term performance of various system deployment pathways for green hydrogen systems¹⁵. This extended analysis would help anticipate and address the challenges posed by further worsening climate change, including ongoing shifts in climate patterns and increased frequency of extreme climate events. By examining deployment strategies across a broader range of future climate conditions, we can better understand their cost-effectiveness and resilience, ultimately informing more robust and adaptive energy transition strategies. Additionally, expanding discussions on developing green hydrogen systems to include social justice and ethical concerns is crucial, as energy policy and technology decisions impact communities in diverse ways beyond technical feasibility and cost-effectiveness²⁹. Energy inequalities arising from the energy transition can exacerbate disparities and hinder access to opportunities for specific communities within the energy market³⁰. Future studies can integrate social concerns into energy models to enhance our understanding of the deployment pathways needed to support equitable and inclusive urban energy transitions, ensuring that the benefits of green hydrogen systems are accessible to all urban communities.

Finally, the energy models in this paper can be used to expand other renewable energy sources to suit local community conditions, such as increased adoption of wind, geothermal, or biomass.

Analytical approach

This study aims to explore the impacts and implications of system deployment pathways on deploying cost-effective green hydrogen energy systems for different urban communities. Therefore, energy system design should cover all potential community energy input scenarios subject to multiple uncertainties to ensure robust and optimal outcomes. However, climate change exhibits a distinct probabilistic nature, i.e., extreme climate conditions are significantly less likely to occur than typical climate conditions. The energy input scenarios should reflect this variability in weather probabilities to ensure reasonable realism. Therefore, we use stochastic optimization to formulate and integrate the objective function into the energy model³¹. In this process, each energy scenario is treated independently, and then their results are combined based on the probability of occurrence to obtain the mathematical expectation of the outcome.

The overview of modelling multi-source uncertainties

Energy models are subject to inherent input parameter uncertainties derived from complex real-world communities. It is crucial for energy models to transparently disclose the impacts of community uncertainties on energy system inputs and provide reliable energy input scenarios for subsequent evaluation. Parameterizing the compound impacts of these uncertainties on energy input scenarios for the energy model is challenging due to the complexity of sources and the differences in their influence pathways. Thus, we distinguish the community uncertainties into two levels: climate-human uncertainties at the household level and community design layer uncertainties at the community level (Supplementary Notes 1). As a bottom-up energy model, we quantify uncertainties layer by layer from the household level to the community level and superimpose them to quantify compound impacts.

Modelling climate-human uncertainties

To parameterize the climate-human uncertainties at the household level, we distinguish climate and human systems into two treatments based on their different sources. We then associate them into compound scenarios to account for their superimposed impacts on energy input. Climate uncertainty stems from the unpredictable nature of climate period paths and their corresponding extreme weather events, leading to the loss of potential risk information on weather-dependent energy production and demand in defined climate scenarios³². Current climate change further increases uncertainty, exacerbating climate risk to energy systems due to the increasing frequency of extreme climate events and ongoing shifts in climate patterns³³. Thus, we developed a method to synthesize future representative weather datasets based on regional climate models (RCMs) data to capture potential climate uncertainty information related to weather patterns and extreme weather events (Supplementary Note 2). This method can derive an arbitrary number of stochastic hourly-resolution weather data to decrease the simulation time without destroying month-scale weather features. Thus, this method maximizes our ability to generate enough weather data to measure climate uncertainty information and then trims these data to representative weather scenario sets with occurrence probabilities, which facilitates compatibility with stochastic energy system optimization.

Human uncertainty comes from the complex stochastic nature of human behavior and their interaction with energy systems, in which the greater control freedom for the residential occupants makes the uncertainty of energy demand profiles even more significant. Deterministic occupant behavior variables not only lead to overestimating or underestimating energy demand profiles at the household level but also decrease the diversity of energy demand profiles at the community level. Thus, in human systems, we sample human-related operational information from assumed probability distributions and parameter ranges based on urban statistical data, ignoring the behavioral logic of the occupants¹⁷. We explore seven aspects of human behavior uncertainties that affect building energy demand profiles. These features encompass the full range of human-involved operational parameters in building energy simulations. Due to the aleatory nature and weak relationship of uncertainty from the approach, we specified independent probability functions and then drew random samples from these features using Latin Hypercube Sampling (Supplementary Note 3)^34,35. We specify uniform distribution as probability functions to equal probabilities of each interval in uncertainty variables because there is no explicit reason to value one probability distribution over another. Meanwhile, we extracted the boundary of these variables from the urban residential energy surveys³⁶. Every random human behavior scenario was then associated with each climate scenario to create a compound scenario pool to treat the uncertainties in both climate and humans properly.

In this study, we created eight sets of composite climate-human uncertainty scenario pools in North America (climate zones 1 ~ 7), where each scenario pool yielded a total of 50,000 household-level production and demand profiles, i.e., 50 climate scenarios and 1,000 human scenarios.

Modelling regional household benchmark buildings

Besides climate-human scenarios, an urban residential archetype is crucial in generating household energy scenarios using dynamic energy simulations. We extracted physics-based benchmark building models based on local urban information: urban building survey data and building standards of climate zones (Supplementary Note 4). In this study, we created a set of benchmark bungalows and two-story houses in each city for aggregating artificial urban communities. We combined building information modeling (BIM) and building energy modeling (BEM) to generate household energy scenarios systematically. Specifically, BIM crafts benchmark archetypes with Level of Detail-2 (LoD2), incorporating fundamental construction information such as building typologies, floors, roofs, external walls, and windows, all sourced from urban building surveys. Concurrently, BEM analyzes building energy output by associating benchmark archetypes and climate-human scenarios. This process incorporates energy characteristic factors like envelope construction, internal loads, HVAC systems, and renewable energy systems, with specifications adhering to building standards within the local climate zone. Once completed, the EnergyPlus engine executes energy simulations to analyze hourly-resolution dynamic energy performance.

Modelling community design layer uncertainties

Parameterizing uncertainties within the community design layer in bottom-up energy models entails creating detailed community models that encompass the full array of urban community features. Extracting community samples from cities to parameterize uncertainties falls into a dilemma between scenario scopes and feature completeness due to the intricate nature of urban community features. Due to the lack of boundary samples, the representative samples derived from regional-average community features may not provide complete uncertainty information for extrapolation to all urban communities. Thus, we create a set of artificial communities using community characteristic matrix: household scale and prosumer scale. The household scale quantifies uncertainties in community composition using boundary and mean urban community features, while the prosumer scale accounts for uncertainties in renewable energy using linear scale expansion. These matrix parameters define the boundary and node samples to mimic community feature information, which provides fully quantitative information on community design layer uncertainties. In this study, the community scale was assumed to be 50 households. Each community characteristic matrix for the local climate zone considered three types of household scales and five sets of prosumer scales.

The community design layer uncertainties were parameterized in two sequential processes. Initially, we clustered aggregate household energy scenarios into designed community energy scenarios. Subsequently, we assigned household roles as either prosumers or consumers within these community energy scenarios. In the first process, we translated each type of household energy scenario into corresponding shares of community energy scenarios based on household scale using k-means clustering. Subsequently, in the second step, to mitigate the impact of the direction of renewable energy penetration, we arranged households within the community in descending order of energy sharing levels. This assumed that households with higher levels of sharing were more inclined to adopt renewable energy systems. Next, we categorized households into prosumer and consumer roles based on prosumer scale. Finally, this pipeline of uncertainty propagation returned a total of 750 community energy scenarios, i.e., 50 community scenarios under per-community features. The community energy profiles of all communities were aggregated to return 15 profiles for the entire city.

Modelling system deployment pathways

From a government planning perspective, we model three system deployment pathways that coordinate households into energy community, including household distributed programs, household centralized programs, and community centralized programs³⁷. These potential community collaboration programs govern energy allocation and trades to ensure effective and equitable energy flows among households in their local communities. This requires that energy models include energy dispatch strategies and pricing mechanisms under different system deployment pathways. To distinguish the roles of households clearly in energy models, we defined intra-household layers and intra-community layers based on control logic relationships rather than physical relationships. The intra-household layers refer to energy interactions between modules within the system, while the intra-community layers refer to energy interactions between different systems. Consequently, energy dispatch strategies are present in both layers, whereas pricing mechanisms are exclusive to the intra-community layers.

We detail energy dispatch strategies using a two-stage logical framework which defines energy flow structure in intra-household layers and energy sharing structures in intra-community layers from the rational household perspective (Supplementary Note 5). In this study, our analysis of multiple deployment pathways focuses on intra-community layers that reflect collaborative solutions in local community energy markets. Thus, each deployment pathway features the same energy flow structure but differs in energy sharing structure. The energy flow structure in three deployment pathways identifies twelve operating states of the intra-household layer to manage energy flow hierarchy in system modules under varying module capacity and power states, with the goal of eliminating module interference. To exploit the storage advantages of the green hydrogen systems in large storage capacity and long timescale, we managed the battery module as a short-term energy storage option and the hydrogen module as a long-term energy storage option. Energy sharing structures are used to govern the energy trade methods between prosumers and consumers in the intra-community layer. These structures distinguish trade entities based on ownership of energy systems and trade paths based on internal energy sharing pricing. Household distributed programs describe prosumer-owned deployment pathways which specify each prosumer as an energy trade entity with a three-layer trade path. Household centralized programs describe prosumer-grouped deployment pathways which combine all prosumers as energy trade entities with a two-layer trade path. Community centralized programs describe community-owned deployment pathways that coordinate all households as energy trade entities with a one-layer trade path.

The pricing model is essential for determining energy sharing pricing between buyers and sellers in intra-community layers to facilitate energy sharing. We utilize the terms "buyers" and "sellers" to delineate household roles in the pricing model, as prosumers may adapt their behaviors to function as either sellers or buyers based on their net power profiles. We assume that all sellers have equal privilege and are equally influential participants within the energy communities, implying that all sellers should collectively determine energy sharing prices. In accordance with the basic principles of economics, disparities in demand response can result in price fluctuations. This signifies that the market price for buyers favors the grid output price, whereas the market price for sellers favors the grid input price. Thus, we use a dynamic internal pricing model that uses local feed-in tariffs to define trade prices using the production and demand ratio (SDR) of shared energy and price boundaries. Further details can be found in ref.³⁸. To maintain consistency with the time resolution of the energy model, the internal prices of the pricing model are adjusted in tandem with the hourly SDR within the boundary limitations. Moreover, the predicted time horizon of the pricing model is set to one hour ahead, with local electricity prices acting as the benchmark prices^39,40. In this study, electricity sales prices were assumed to be 70% of electricity purchase prices. Notably, we disregarded the energy price fluctuation and local government price incentives during the operating cycle of the energy model.

Outline of green hydrogen systems in urban communities

As in refs.^41,42, energy systems, long-term climate resilience systems designed for urban communities, must be considered cross-seasonal and large-capacity energy storage due to the high homogeneity of households in both energy production and demand. Compared to conventional battery storage systems⁴³, green hydrogen systems provide higher storage and operation flexibility, which can schedule multi-storage resources in the most efficient way to address uncertainty, especially during extreme energy events. Specifically, green hydrogen systems can achieve synergistic benefits from both the superior efficiency of battery storage and the high energy density and low leakage rate of hydrogen storage. From a technical perspective, the design of green hydrogen systems for urban communities must prioritize safety and portability. Safety is paramount, given the risk of hydrogen leakage and spontaneous combustion⁴⁴. Portability calls for compact equipment and installation methods that are both straightforward and minimally invasive. To meet these criteria, we have chosen photovoltaic panels as the energy production modules and paired them with lithium-ion battery packages and Liquid Organic Hydrogen Carrier (LOHC) equipment for energy storage modules (Supplementary Note 6).

Modelling design optimization for community green hydrogen systems

Design optimization in energy models involves sizing optimal system components of green hydrogen systems to inform evaluation results for metrics of interest. As discussed earlier, multi-source uncertainties should be incorporated to ensure the robustness and stability of evaluation outcomes. Scenario pools are utilized as part of stochastic optimization in design optimization, capturing compound impacts of uncertainty factors. These scenario pools comprise a set of community energy scenarios with occurrence probabilities. Once the energy input scenarios are established, design optimization maps decision space variables onto the objective space through cyclic simulation under inherent system constraints. Specifically, decision variables encompass the rated capacity of the battery package, along with the rated power and capacity of both the fuel cell and electrolyzer. Meanwhile, the objective variables consist of system affordability and independence, quantified as annual life cycle costs (LCC) and grid interaction level (GIL), respectively. In this study, the multi-objective particle swarm algorithm was used to calculate the design optimization part, as it has demonstrated effectiveness in handling multi-scenarios and multi-objectives simultaneously. To enhance the efficiency of the search process and prevent convergence to local minima, we incorporated mechanisms like self-adaptive adjustment of inertia weights⁴⁵ and wavelet mutation⁴⁶.

Formulating objective functions

The annual LCC represents the equivalent annual cost of green hydrogen systems over their lifespan in urban communities, including equivalent investment costs, equivalent operation and maintenance costs, carbon tax, and community trade costs, as formulated in Eq. (1). Notably, it is imperative to note that all the techno-economic data deployed in this study are derivatives of prevailing current social and technical conditions. The price uncertainties linked with technological upgrades and capital inflation are not considered in this study. The details of objective functions are shown in Supplementary Note 7, including each term of LCC and techno-economic data of green hydrogen systems.

$$LCC=\sum _{\forall s\in {N}_{s}}{\rho }_{s}N\left({C}_{s,inv}+{C}_{s,om}\right)CRF+\sum _{\forall n\in N}\sum _{\forall s\in {N}_{s}}{\rho }_{s}\sum _{\forall t\in T}\left({C}_{n,s,t,tax}+{C}_{n,s,t,community}\right),\forall n\in N,\forall s\in {N}_{s},\forall t\in T$$

where, n, s, and t denote the system number, expected community energy scenarios and time series; N, Ns, and T denote the total system number (prosumer number in HDP, 1 at HCP and CCP), total scenario number, and total simulation time; ρ_s is the probability of scenario s; CRF denotes the capital recovery factor; C_inv and C_om denote the initial investment cost and operation and maintenance cost per system; C_n,_s,t,_tax, and C_n,_s,_t,_community denote the carbon tax, and community interaction cost at time t in scenario s for system n.

GIL quantifies the level of independence of distributed energy systems by evaluating interactions with the power grid. The objective for urban residential communities is to minimize their interactions with the grid. This approach not only maximizes the role and benefits of communities but also helps to improve the stability of the urban power grid. This study evaluates GIL based on the amount of electricity imported from and exported to the grid, as shown in Eq. (2).

$GIL=\sum _{\forall n\in N}\sum _{\forall s\in {N}_{s}}{\rho }_{s}\sum _{\forall t\in T}\left({P}_{n,s,t,gridsell}+{P}_{n,s,t,gridbuy}\right),$ $\forall n\in N,\forall s\in {N}_{s},\forall t\in T$ (2)

where, P_n,_{s,t,gridsell t} and P_n,_s,t,gridbuy denote the amount of electricity purchased from the grid and the amount of electricity sold to the grid at time t in scenario s.

Declaration of interests

The authors declare no competing interests.

Author contributions

You Wu developed the model, performed the analysis, and wrote the paper. Lexuan Zhong supervised the study process and edited the paper.

Acknowledgements

The authors would like to express their gratitude for the partial financial support provided by the China Scholarship Council in collaboration with the University of Alberta and the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery program.

Data availability

Original data for this paper, as well as the code used for simulation and analyses, are available on Github.

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Probabilistic deployment pathways of scaling up distributed green hydrogen systems for urban residential communities in North America

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Abstract

Figures

Introduction

Results

Multi-source uncertainty quantification of energy input scenarios at the North American scale

Impact of system deployment pathways on levelized cost of electricity

Analysis of system design for resilient urban community

Discussion

Methods

Analytical approach

The overview of modelling multi-source uncertainties

Modelling climate-human uncertainties

Modelling regional household benchmark buildings

Modelling community design layer uncertainties

Modelling system deployment pathways

Outline of green hydrogen systems in urban communities

Modelling design optimization for community green hydrogen systems

Formulating objective functions

Declarations

Declaration of interests

Author contributions

Acknowledgements

Data availability

References

Additional Declarations

Supplementary Files

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