The Building Decarbonization in High-Density Cities: Challenges and Solutions

With the development of urbanization and industrialization, environmental issues have become increasingly prominent. The building sector accounts for 28% of carbon emissions from operational energy and building-related energy accounts for 40% of global carbon emissions (including construction), growing at a rate of 2–3% annually [1]. Against this backdrop, there is a growing interest worldwide in decarbonizing the building sector [2,3]. Worldwide, many researches have conducted on the decarbonization efforts in the building sector [4–6].

During the transformative period of building decarbonization, various challenges have emerged across several key areas, including technical, economic, policy, and public engagement aspects [7–11]. From a technical standpoint, current building energy codes in countries such as Denmark, France, England, Switzerland, and Sweden have been found inadequate for driving the required decarbonization of the building sector [12]. Economically, uncertainties regarding the costs and benefits associated with low-carbon building technologies create significant barriers, particularly for existing building owners contemplating decarbonization renovations [13,14]. On the policy front, the development of tailored policies that align with decarbonization goals is critical, yet remains a complex challenge [15,16]. Fostering public engagement through effective collaboration among stakeholders and the public is crucial to achieving meaningful progress.

Building decarbonization in high-density cities faces unique and prominent challenges due to the compact land use inherent in such urban environments. In recent years, the rapid urbanization has led to the proliferation of high-density cities worldwide. High plot ratios and dense high-rise buildings are among the main characteristics of these high-density urban areas [17]. Although cities cover only 2% of the world's land area, the people living in them consume 75% of the resources used by humans [18]. Consequently, decarbonizing buildings in high-density urban areas will face challenges such as high energy consumption per unit area of land [19]. Worsening the situation is the mutual shading between city buildings and the reduced potential for on-site photovoltaic (PV) [20,21] and small wind turbine installations [22], as buildings block each other, making decarbonization significantly more difficult from the perspective of past research experience [23,24]. Mid-floor apartments in multi-tenant high-rise blocks have been categorized as hard to decarbonize buildings by the UK's Local Government Association [25]. Moreover, previous cases of carbon-free building practice projects have been mainly conducted in low-rise buildings [26–34]. Therefore, decarbonizing buildings in high-density urban areas not only presents numerous challenges but also lacks systematic experiential guidance for its implementation.

The increasing demand for building decarbonization and the challenges of decarbonizing buildings in high-density cities have motivated this review. Compared to existing reviews on similar topics [7,8,24,35–37], the key gaps addressed in this work include:

• Summarizing recent zero-carbon building (ZCB) case studies and analyzing the technologies utilized.

• The distinct difficulties and obstacles encountered in the decarbonization of buildings in high-density cities have been highlighted.

• A feasible decarbonization solution for buildings in high-density cities has been proposed, based on the decarbonization experiences of buildings in high-density urban areas reported worldwide and the design experience accumulated by the research team of the authors.

The remainder of the paper is organized as follows: Sec. 2 introduces the review methods. Existing practices in achieving building decarbonization are described in Sec. 3. Challenges on the CO₂ emission cut in high-density cities are explained in Sec. 4, followed by the promising solutions in Sec. 5, and a discussion is presented in Sec. 6, a conclusion is Sec. 7.

The references for this work mainly come from literature retrieved from four major databases: ScienceDirect, Web of Science, Scopus, and Google Scholar. The literature retrieval process was as follows:

• The initial literature search was conducted using the keywords “zero-carbon building,” “building decarbonization,” and “zero-energy building.” However, due to the overwhelming number of papers related to these topics (see Fig. 1), we specifically focused on papers published within the past 5 years N ≈ 1500, as well as papers from any publication period that defined by Web of Science as a highly cited paper N = 263;

• We then conducted a rapid review of the paper titles and abstracts to identify studies that are most relevant to the theme of this article N = 105;

• Carefully selected papers closely related to the themes of high-density cities and high-rise buildings, as well as those reporting on completed zero-carbon building projects;

• In addition to the literature, this article refers to standards for building energy efficiency and carbon reduction, and building decarbonization development reports.

Various regulations and policies have been adopted by countries around the world to promote the development of building decarbonization [4]. China has implemented standards for nearly zero-energy buildings and standards for building energy conservation and renewable energy utilization, supporting pilot projects for building decarbonization nationwide that include comprehensive retrofits of existing buildings and the adoption of new energy-efficient technologies in new buildings. In the United States, legislation by state and local governments plays a crucial role, with California having the strictest energy conservation standards [38]. The state leads in mandates that require all newly built residential buildings with three floors or less must have solar panels installed, unless the building is in the shade or the roof is too narrow. And governments in China and the US force's specific function or types of buildings to participate in building energy grading and labeling [39].

In addition to China and the United States, Japan is promoting zero-carbon communities and cities plan through government subsidies and energy management initiatives [40]. Canada targets carbon neutrality by 2050, using the national building code (NBC) to evaluate building energy performance [41]. Sweden plans zero net greenhouse gas (GHG) emissions in the building sector by 2045, with an 85% reduction in domestic emissions from 1990 levels [42]. Germany seeks to halve 2018 CO₂ levels by 2030 and achieve a nearly carbon-neutral building stock by 2050 through energy efficiency and renewable energy [43]. The UK aims for net-zero building sector emissions by 2050, with regulations cutting new home emissions by 30% in 2022 and a 75% reduction planned by 2025 [44].

Table 1 summarizes the targets and technical regulations for building decarbonization across different countries. These measures reflect a global collective effort to reduce carbon emissions from the building sector. Despite the variations in strategies and frameworks, the unified goal of achieving substantial emissions reductions in the building sector remains a priority around the world.

After years of development in building energy conservation technology, it is now relatively easy to find engineering cases of nearly zero-energy buildings. As the decarbonization of buildings progresses further, zero-carbon buildings are gradually becoming a research focus. However, the existing literature contains few reports on zero-carbon buildings that have already been completed and are in use. The authors have collected some engineering practice data on zero-carbon buildings, which are summarized in Table 2.

Many pioneers have explored the topic of zero-carbon buildings [51,52], but most literature in this field began to emerge around the period of 2010–2012 (see the diamond-shaped line of Fig. 1). A zero-carbon building needs to have zero-carbon emissions over its entire lifecycle of use [38]. The zero-carbon buildings constructed around 2010 were mostly a result of pioneering explorations into the concept of zero-carbon buildings, requiring substantial technological layering or inherently low energy consumption to achieve their goals. This process often involved using high-performance insulation materials, optimizing building orientation for maximum solar gain, and incorporating advanced energy-efficient technologies. The zero-carbon buildings reported in the literature [50] are evaluated based on the carbon emission factors of local electricity in the year of construction, using surplus electricity generated by their on-site photovoltaic systems and wind turbines as a carbon sink to offset remaining carbon emissions, which is inconsistent with the design of most contemporary zero-carbon buildings [33,34]. Despite this, they laid important groundwork for future zero-carbon designs by demonstrating the feasibility associated with on-site energy generation.

With the rapid development of energy-efficient and renewable energy technologies in buildings, recent zero-carbon buildings are increasingly consistent with the characteristics of typical residential or office buildings in cities. Advances in materials, smarter building management systems, and the integration of local renewable energy sources such as solar panels and wind turbines have facilitated this shift to mainstream adoption. In one completed project [21], the focus is on the use of an energy management system that intelligently balances supply and demand dynamically. In addition to the projects summarized in Table 2, many studies focused on zero-carbon renovation plans with real buildings as the object of study [53–55].

According to Table 2, which shows the specific carbon reduction technologies used in completed zero-carbon building projects, these technologies are mapped to the four stages of zero-carbon building construction (see Fig. 2). The process begins with reducing hidden carbon emissions using green or recyclable building materials, followed by lowering energy consumption through building renovation and equipment performance improvements. Subsequently, carbon emissions are minimized through electrification and the supply of clean energy, with remaining emissions offset through methods such as greenery, carbon capture, or carbon trading. For the decarbonization of existing buildings that do not involve demolition, the focus should be on reducing operational carbon emissions to zero. Additionally, it is worth noting that regardless of climate zone or building type, the zero-carbon building technologies implemented in completed projects have all chosen to embrace photovoltaic technology.

In addition to common challenges like financial support and public willingness, building decarbonization in high-density urban areas also faces unique challenges due to their geographical characteristics. According to the latest “Net Zero 2050: global energy industry action guide” and “2050 energy zero carbon emission roadmap report” issued by the International Energy Agency (IEA), deep electrification + renewable energy can achieve 75% of the carbon reduction goal [56]. However, buildings are generally taller in high-density urban areas, and the roof area is relatively small compared to the total building area (as shown in Fig. 3(b)). Therefore, the potential for on-site PV to reduce operational carbon emissions is limited.

Figure 4 displays the calculated results for the proportion of rooftop photovoltaic energy generation to the total building energy consumption for various types of buildings across six climatic zones in China, with the increase in the number of building floors. It's a straightforward metric that indicates the degree of energy self-sufficiency a building can achieve through the installation of PV systems. The unit area energy consumption for different types of buildings is selected from “Building Energy Conservation and Renewable Energy Utilization” in China [45]. The method for calculating photovoltaic electricity generation is adopted from literature [57]. Solar radiation data are averaged from NASA [58] and the Global Solar Atlas database [59]. The details on the energy consumption intensity of different buildings and the calculation method for photovoltaic power generation are provided in  Appendix.

As illustrated in Fig. 4, for a three-story building, the annual photovoltaic electricity generation to annual energy consumption for cooling, heating, and lighting ratio for large office buildings in different climate zones ranges from 164% to 391%, and for hospital buildings, it ranges from 52% to 108%. For the 18-story building, this value has already decreased to 27–65% for office buildings and 8–18% for hospital buildings. If the actual usage of the building, including elevators and hot water consumption, is considered, this value would decrease further.

Apart from the data on the contribution of photovoltaics to building energy consumption calculated in this study, a feasibility analysis study of PV use in high-rise buildings in Hong Kong showed that for a typical 30-story high-rise residential building in Hong Kong, covering the building's roof and available façades with PV panels could only cover 16.6% of its annual energy consumption [60]. In contrast, Ref. [61] conducted a feasibility of achieving net-zero energy performance in high-rise buildings using solar energy, which shows the allowed building height is 5–6 floors while the energy use intensity is 75 kWh/m²·y.

On another note, in fact, in the operational period, environmental factors such as temperature, wind speed, and daylighting outside the building that varies with building height as well as operational requirements such as intensive use of elevators will also affect the overall energy consumption of the building. An analytical study of 700 different height buildings in the UK showed that when building heights increase from 5 floors or less to 21 floors or more, the average intensities of electricity and fossil fuel usage will increase by 137% and 42%. Subsequently, the average operational carbon emissions also increase by more than 100% [19]. Furthermore, more steel and concrete, these building materials will generate more carbon emissions during manufacturing, transportation, maintenance, and disposal processes. This makes the decarbonization of buildings in high-density urban areas appear more challenging.

This results in a significant residual carbon emission in high-density urban areas that needs to be mitigated using other technologies. There is a substantial gap in carbon emissions that needs to be filled. If energy-saving technologies are used to reduce the energy consumption of buildings, this is clearly not an economical method, as any addition of technology incurs costs [62]. The difference in investment between 100 kWh/m² and 80 kWh/m² is just one-seventh compared to improving this further to 50 kWh/m². There are diminishing returns in reaching for a higher target [25]. Looking at the subsidies and engineering practices of housing and construction departments from various regions in China, the incremental cost of ultra-low energy buildings is about 30% of the unit construction cost of buildings in China. For zero-carbon building design, the incremental cost is even higher, but there are currently few quantitative statistics due to limited practice. Achieving zero-carbon building in high-density cities is not easy under current technical level.

In summary, the most pronounced challenge faced in the decarbonization of buildings in densely populated urban areas is the high energy consumption resulting from the compact use of land, alongside the corresponding issue of limited installation space for solar energy collection due to shading by adjacent buildings. This combination of factors makes it increasingly difficult to offset carbon emissions through on-site renewable energy generation alone. Overall, the issues underscore the need for comprehensive, innovative strategies to tackle urban building decarbonization.

As shown in Fig. 5, grid-interactive efficient buildings play a crucial role in building decarbonization by optimizing energy use and reducing carbon emissions [63]. On one hand, a considerable body of research has established that the construction of a clean electricity grid requires a substantial number of flexible resources to provide a stable power input [64]. Buildings contain a significant number of adjustable loads and can offer low-cost flexible resources to the clean electricity grid, thus accelerating the construction process toward a 100% clean energy grid, which in turn supports the decarbonization of buildings. On the other hand, effective interaction between buildings and the electrical grid can help buildings utilize their own renewable energy production capacity [65].

Renewable energy is significantly affected by seasonal changes, day and night cycles, and weather conditions [66], resulting in significant fluctuations and intermittency. This also does not align with the timing and intensity of energy demand in buildings. Among this, daily mismatch between renewable energy generation capacity and building energy demand accounts for 30–50% varies depending on different types of buildings [67]. At this point, flexibility regulation of building loads can provide economically favorable energy flexibility. In comparison, the utilization cost of building heating load flexibility is only 0.024–0.035 €/kWh (equal 0.026–0.038 $/kWh) [68]. For a more specific example, considering the current price of lithium batteries and assuming an average annual cycle count of 500, with a battery life of 9 years, the cost to store 1 kWh of electricity is approximately 0.67 CNY/kWh (equal 0.093 $/kWh). In contrast, the off-peak electricity rates in China are about 0.2–0.3 CNY/kWh (equal 0.028–0.041 $/kWh), with peak rates ranging from 0.6 CNY/kWh to 0.9 CNY/kWh (equal 0.083–0.013 $/kWh). It is crucial that adjusting the building's energy consumption timeline to coordinate renewable energy fluctuations and building user demand [69].

The building loads, such as air conditioning, hot water, lighting, cleaning, and cooking, all possess the potential for energy flexibility adjustments [70]. For air conditioning loads, an investigation shown the existing potential of commercial and residential air-conditioning systems to provide demand response across Australia, which shows the National Electricity Market could be reduced by up to 5.8% or 1.2 GW with the time of day at which the peak occurs delayed by approximately 2 h [71]. Besides, the suitable management of the air conditioning load has the feasibility of utilizing 100% on-site photovoltaic energy supply for air-conditioning energy consumption [72]. In addition, as electric vehicles become more and more popular among consumers, if the charging time of electric vehicles is controlled and their energy storage characteristics are fully utilized to integrate them into the entire system for scheduling [73], it can effectively improve the economic efficiency of the system by alleviating the negative impact of their charging power on the system [74]. Electric vehicles can provide buildings with usable batteries [75], while buildings can provide charging power for cars and electric vehicles further enhance building energy flexibility by acting as both consumers and suppliers of electricity [76]. This can significantly reduce the additional energy storage capacity and investment required by the system, and achieve synergy in the consumption of self-renewable energy sources.

Installing photovoltaics on the building roof and facade is a great choice as it can save transmission losses and reduce roof temperatures in the summer, thereby saving air-conditioning energy. In recent years, many studies have evaluated the potential for installing photovoltaics on urban building facades [77]. At the policy level, net-zero energy building standards in Europe and China require a certain proportion of photovoltaics to be installed in buildings. In addition, the development of flexible perovskite components [78], allows buildings to choose different colors of photovoltaic installation on more structures, which is more in line with the design aesthetics of owners and architects.

However, the authors team's extensive experience in the design and engineering practice of many nearly zero-energy buildings in China shows that many building owners tend to choose the self-use and grid-connected use mode of surplus electricity due to convenience and easy management. This mode is also widely chosen by homeowners in California [79]. Although at the initial design phase, the annual PV power generation can offset the estimated total energy consumption of the building, practical challenges such as mismatching and various uncertainties in equipment utilization [80,81] may hinder efficient usage. Due to the mismatch in timing between building loads and renewable energy production capacities, the self-use rate of a single building's household photovoltaic system cannot exceed 40%, while that of a multi-story residential building is only about 18% [82]. When renewable energy sources such as solar and wind generate excess energy beyond the current demand, this surplus energy need to be stored in battery or other energy storage systems for later use and the consequent an increase of approximately 1 h rated power generation of electrochemical energy storage will result in a high initial investment increment [83]. In addition, electrochemical energy storage only has a few thousand charge–discharge cycles [84] and need to be replaced after approximately 8 years [85]. With good interaction with the grid, shifting the timing of energy use in buildings through the grid's demand response commands can significantly increase the consumption of building on-site photovoltaic output [65]. Developing the efficient building energy consumption prediction models [86,87] and data-driven energy management systems [88] will greatly assist in this process.

The role of a clean grid in building decarbonization accounts for as much as 74% [89]. It is necessary to fully leverage the previously overlooked positive interaction between buildings and the electrical grid, enabling buildings to assist in the operation of the public electric grid [89]. Furthermore, the quantification of flexible resources within buildings and the technological approach to coordinating with grid demand response commands, as well as policy support, are all still underdeveloped [90]. And, most of the existing demand response comes from non-automated (i.e., manual) peak load reductions, and although this investment is beneficial for building owners and residents, sometimes there is a lack of awareness of the expected cost-effectiveness of the investment. A minimal hardware approach to heat pump and smart-grid interactivity is crucial for alleviating the issues [91].

The connection of microgrids interactive with buildings has a very small share. According to the information available, microgrids currently serve less than 1% [92].

Meanwhile, energy cooperation between buildings has created numerous opportunities for collaboration among groups of buildings, as external green power inputs are crucial for building decarbonization [93]. By leveraging temporal differences in energy consumption patterns across buildings with varying functions and configuring hybrid building clusters with complementary solar and wind systems, it is possible to optimize energy systems and storage capacities, thereby enhancing the overall utilization of renewable energy [94,95].

Buildings in city centers and suburban areas can collaborate effectively. While the space for PV installations is limited in high-density urban areas, suburban buildings with extensive low-rise roofs fully equipped with PV panels frequently produce electricity well beyond their own consumption needs. A study surveyed the potential for rooftop-mounted PV installations with an installed capacity of 66 GW, which could supply 70–80% of the total energy consumption of Nanjing city [96]. Thus, to facilitate the provision of clean energy to buildings in high-density urban areas, it may be beneficial to consider partnerships with suburban buildings. Such collaboration could allow for the reliable transmission of PV-generated electricity from suburban areas to urban centers as shown in Fig. 6. This approach would not only offer suburban buildings an additional revenue stream through the sale of electricity but also contribute significantly to the decarbonization efforts within the building sector. But the investment methods and implementation plans related to this strategy still require further meticulous research.

Additionally, buildings can share energy usage data with each other and adjust energy usage collaboratively, which helps balance the energy usage discrepancies between buildings and reduces power fluctuations [97]. In typical cases, residential and commercial buildings have different energy consumption time series, with residential electricity loads mainly concentrated in the evenings and early mornings [98], while commercial buildings have peak electricity loads during the daytime. Specific to application implementation, smart control systems can be installed in commercial buildings to flexibly adjust energy usage based on demand, minimizing energy waste and addressing energy supply-demand mismatch. The surplus energy generated during the daytime in residential buildings can be used to meet the peak electricity demand in commercial buildings, reducing the need for energy storage devices.

The carbon emissions during the construction phase of buildings account for 10–30% of their entire life cycle emission [99], as shown in Fig. 7, with the majority coming from concrete and steel production [100]. In 2021, China produced 2.38 billion tons of cement, 51 million tons of glass, and 25.2 million tons of steel [101]. The carbon emissions from glass production are only 2.2% of those from cement production. Building material manufacturing accounts for over 80% of energy use of construction [102].

The carbon emissions from concrete production come from two sources: 55–70% from the decomposition of carbonate, and 25–40% from fuel combustion during production, with other emissions accounting for about 4–7% [103]. Using clean energy for cement clinker calcination and wet material drying, as well as replacing limestone raw materials with gel materials and calcium silicate, could greatly reduce carbon emissions from cement production.

Researchers worldwide are exploring the best sustainable and alternative materials for concrete and cement to minimize or achieve complete decarbonization. Correspondingly, some interesting and forward-looking sustainable and zero-carbon concrete and carbon-negative concrete solutions have been developed [104,105]. In addition, high-strength wood and transparent wood can also be used to meet the needs of modern architecture. As technology advances, zero-carbon and even negative-carbon building materials are increasingly becoming mature technologies for application.

The carbon reduction role of greenery is often overlooked in the pathways for building decarbonization. Table 3 lists the carbon sequestration capabilities of various trees, shrubs, and grasses. For trees, the value is −22.5 kgCO₂/m², and for dense shrubs, it is −5.125 kgCO₂/m². Although its carbon sink intensity is on a smaller scale [107] compared to the life cycle CO₂ emissions intensity of buildings per unit area. Merely relying on a few square meters of greenery around buildings indeed plays a minimal role in offsetting carbon over the building's entire lifecycle, and considering the use of water, electricity, and fertilizers in the cultivation process, the potential carbon sink of plants might be further reduced. However, suburban ecosystems can provide significant carbon reduction effects.

A systematic study on the changes in Chinese terrestrial ecosystem carbon sinks and their role in offsetting energy CO₂ emissions showed that current Chinese terrestrial ecosystem carbon sinks can offset 15.3–16.0% of current CO₂ emissions [108]. The United Nations Framework Convention on Climate Change defines carbon sinks as “processes, activities or mechanisms that remove carbon dioxide from the atmosphere”[109]. Green plants can bring good carbon reduction benefits because photosynthesis releases oxygen, absorbs atmospheric carbon dioxide, and fixes it in vegetation and soil, thus reducing atmospheric carbon dioxide concentration. The purpose of saying this is to express that building decarbonization does not need every building to achieve 100% net-zero carbon. Because plants will help offset the remaining parts of decarbonization that have very low marginal benefits.

Not only that, urban green corridors, green roofs, urban tree canopies, and permeable pavements, as well as other forms of green infrastructure, primarily offer various climate-related benefits, such as indirectly reducing building carbon emissions by lowering the urban heat island effect. However, the indirect effects of vegetation on building decarbonization cannot be accurately quantified; for instance, the reduced HVAC energy consumption due to the shading effect of trees surrounding buildings has yet to be precisely evaluated. In summary, urban greening and exurban forest ecosystems are an indispensable aspect of building decarbonization that should not be overlooked.

Drawing from several decades of experience in building energy conservation [24], it has been observed that strategies such as enhancing the thermal performance of building envelope, heat pump, and employing renewable energy sources (refer to Fig. 8, plan A) significantly contribute to reducing energy consumption, improving energy efficiency, and minimizing carbon emissions during the operational phase of buildings. However, as discussed in this review study, for high-density urban buildings, additional measures are necessary to achieve decarbonization. In such urban areas, the decarbonization of buildings is hindered by both the high energy intensity per unit of land use and the constrained availability of on-site renewable energy sources.

Under these circumstances, transcending the traditional boundaries of building performance optimization and adopting a collaborative perspective in its role within public utilities seem to be a prudent choice. Wang et al. [110] highlighted that future buildings, as active components of larger districts, need to be more intricately linked with public utilities and ecosystems, playing a more proactive role. This entails the coordination of buildings with clean power grids and additional infrastructures, capitalizing on the advancement of zero-carbon or even negative-carbon building materials. Furthermore, it includes the retention of specific carbon emissions that provide substantial marginal abatement benefits, which can subsequently be compensated by the carbon sequestration capabilities of green plant sinks (see in Fig. 8, plan B).

For buildings utilizing clean energy, merely waiting for the development of a clean electricity grid and relying solely on the input of green electricity can be costly. This passive approach does not harness the full potential of current technologies and may lead to higher overall costs due to inefficiencies and missed opportunities for energy optimization [111]. On the other hand, adequate flexibility is necessary for the power system to ensure safe and efficient utilization [112], otherwise, it may increase the comprehensive cost of energy utilization by four times [113]. Leveraging the regulatory capacity of buildings to actively engage with both the grid and the demand side presents a more proactive strategy.

Buildings to play a proactive role within a broader scope significantly aid in achieving decarbonization in high-density urban areas. However, there are still some issues to be resolved in this process, such as incentivizing users and deploying infrastructure like microgrids [92]. Encouraging constructors to adopt innovative low-carbon building materials [114] and scientifically integrating feasible greenery [115] into the building's carbon sequestration strategy are essential steps forward in aligning with current building decarbonization standards [106].

This study primarily discusses the technical feasibility of building decarbonization in high-density urban areas and does not cover policy formulation or the analysis of the driving forces of various stakeholders. Building decarbonization in high-density cities is very challenging, especially since self-generated photovoltaic power generation technologies, such as rooftop solar panels, are not effective in reducing carbon emissions for high-rise buildings. Despite the considerable difficulties associated with decarbonizing buildings in high-density urban areas, adopting new perspectives and leveraging the role of buildings in public infrastructure, and viewing the decarbonization of the building sector through a lens of synergistic development with other parts of the city can aid in decarbonizing buildings in high-density urban areas. It's time to change our mindset and embrace a collaborative perspective toward building decarbonization.

This work was supported by “Pioneer” and “Leading Goose” R&D Program of Zhejiang (Grant No. 2023C03152). We would like to thank the good research infrastructures provided by the Zhejiang International Science and Technology Cooperation Base of Green Building and Low-Carbon City sponsored by the Department of Science and Technology of Zhejiang Province.

G.L. proposed the topic of the perspective, conducted the literature review, led the drafting of the manuscript, and designed the figures; Z.Z. discussed and revised the manuscript; K.Z. supervised the manuscript and contributed to the literature review; J.G. supervised and provided resources for the manuscript. All authors have approved the final version of the manuscript.

There are no conflicts of interest.

The datasets generated and supporting the findings of this article are obtainable from the corresponding author upon reasonable request.

In 2021, the Chinese government issued GB 55015-2021 [45], “General Specifications for Building Energy Conservation and Renewable Energy Utilization,” which sets energy consumption standards for new public buildings. The specific data are shown in Table 4.

where $Isolar$ is the total solar radiation on the plane of the PV panels, $SPV$ is the installation area of the PV panels, which is taken as 80% of the roof area. $ηmodule$ is the power generation efficiency of the PV panels under standard conditions, here assumed to be 21% based on the efficiency of advanced, mature products available in the market. $ηloss$ represents the losses in PV power generation, including inverter losses, power transmission losses, dust losses, etc., and is taken as 0.8 [57].