Ecological Benefit Optimization and Design of Rural Residential Roofs Based on the “Dual Carbon” Goal

Abstract

With the continuous advancement of urbanization, rural areas are facing increasingly severe environmental pollution, excessive energy consumption, and high carbonization resulting from both daily living and production activities. This study, which is aligned with the low-carbon objectives of “carbon sequestration increase and emissions reduction”, explores the optimization strategies for ecological benefits through the combined application of rooftop photovoltaics and rooftop greening in rural residences. Three design approaches are proposed for integrating rooftop photovoltaics with green roofing: singular arrangement, distributed arrangement, and combined arrangement. Using PVsyst (7.4.7) software, this study simulates the effects of roof inclination, system output, and installation formats on the performance of photovoltaic systems, providing a comprehensive analysis of carbon reduction benefits in ecological rooftop construction. A rural area in East China was selected as a sample for adaptive exploration of ecological roof applications. The results of our research indicate that the optimal tilt angle for rooftop photovoltaic (PV) installations in the sample rural area is 17°. Based on simulations combining the region’s annual solar path and the solar parameters on the winter solstice, the minimum spacing for PV arrays is calculated to be 1.925 m. The carbon reduction benefits of the three arrangement methods are ranked, from highest to lowest, as follows: combined arrangement $14530.470{\mathrm{t}\mathrm{C}\mathrm{O}}_{2\mathrm{e}}$ > singular arrangement $11950.761{\mathrm{t}\mathrm{C}\mathrm{O}}_{2\mathrm{e}}$ > distributed arrangement $7444.819{\mathrm{t}\mathrm{C}\mathrm{O}}_{2\mathrm{e}}$. The integrated design of rooftop PV systems and green roofing not only meets the energy demands of buildings but also significantly reduces their carbon footprint, achieving the dual objectives of energy conservation and sustainable development. Therefore, the combined application of rooftop PV systems and green roofing in rural spaces can provide data support and strategic guidance for advancing green transformation and ecological civilization in East China, offering significant practical value for promoting low-carbon rural development.

1. Introduction

In response to the ecological crisis driven by severe climate change, a global “low-carbon revolution” has emerged. As China advances its rural revitalization strategy and rural living standards improve, carbon emissions from production and consumption processes have become a primary obstacle to sustainable ecological development in rural areas [1]. Under the “dual carbon” framework, meeting the high standards of rural living quality and fulfilling the need for a better rural life are essential for advancing the transition to net-zero carbon development in rural regions. Consequently, rural environmental construction must follow low-carbon principles, transitioning towards a compact, efficient, and sustainable model of development.

East China, located at the economic center of the country, has a strong foundation for rural development. Compared to other regions in China, East China’s rural areas are more advanced in terms of mechanization, modernization, and economic development, with a steadily increasing trend in total carbon emissions from production and daily living, particularly in sectors like electricity and coal production [2,3]. The rural areas of East China face significant challenges, including high energy consumption in industrial development and difficulties in structural adjustment. With the accelerated pace of industrialization and urbanization, rural areas have become sites for industrial relocation, and for the development of township industries and services, particularly for high-energy, high-carbon manufacturing industries [4]. As the rural revitalization strategy advances, infrastructure construction, including that of roads, logistics, water supply, electricity, and communications, has rapidly expanded in rural areas, leading to the conversion of extensive farmland into construction land, thus weakening the regional carbon sequestration capacity [5]. Additionally, the use of high-energy materials and energy inputs in infrastructure projects has further increased carbon emissions, resulting in low energy utilization efficiency and high carbon emissions in rural areas. East China possesses rich historical sites and cultural heritage, with a diverse landscape including mountains, hills, and plains, providing favorable conditions for agricultural production and ecological tourism. However, in current rural production and living activities, traditional energy sources still dominate, primarily relying on fossil fuels and coal, resulting in low energy efficiency and increased greenhouse gas emissions. This situation imposes both economic and technical pressures on energy transition. Therefore, promoting low-carbon sustainable development in East China’s rural areas is crucial for improving the rural ecological environment, advancing the green transformation of rural energy, and optimizing the allocation of urban and rural resources to achieve high-quality rural development.

The building sector is one of the main areas of energy consumption and carbon emissions in China. Rural residences, a unique architectural form in China’s countryside, play a crucial role in advancing green, low-carbon, and sustainable development in rural architecture through the application of green energy-saving technologies. Currently, domestic and international research on ecological roofs focuses primarily on green roofing [6], solar thermal systems [7], and rainwater harvesting [8], with limited studies integrating solar photovoltaics and ecological roofs to advance the “dual carbon” goals [9,10]. Rural rooftops hold substantial potential for solar power generation, especially in sunny regions [11]. Green roofs not only enhance aesthetics but also offer ecological benefits, such as mitigating urban heat islands, improving air quality, and increasing biodiversity [12,13]. Zhang Shanfeng et al. propose that roof plants, growing media, and associated structures help intercept, absorb, retain, and purify rainwater, establishing a “near-natural” water management process [14]. Green roofs contribute to the cooling of urban areas, reducing the urban heat island effect [15,16], and provide stable insulation, thus reducing building energy consumption [17,18]. In renewable energy utilization, solar photovoltaic (PV) panels can reduce building energy consumption, playing a positive role in energy conservation and carbon reduction. In the design of distributed rooftop systems, the scientific arrangement of PV arrays is critical, including factors such as an installation angle and array spacing [19,20]. The proper configuration and arrangement of PV arrays are essential for ensuring efficiency and long-term stability. By combining these two technologies, the shading effect of PV panels and the cooling effect from plant transpiration can enhance the efficiency and functionality of both systems [21]. The integration of PV systems and green roofing offers multiple benefits. Green roofs can reduce rooftop surface temperatures through plant transpiration, thereby increasing PV panel efficiency [22,23] and improving building insulation. Together, they maximize rooftop space usage, enhancing spatial efficiency, energy savings, and ecological benefits [24,25]. Rural residential buildings in East China typically have spacious rooftops, offering substantial potential for resource development. Therefore, utilizing existing spatial resources to maximize ecological benefits under the “dual carbon” goals is highly feasible.

The above studies indicate that integrating PV systems with green roofing can achieve complementary effects. The green layer reduces the operating temperature of PV panels, thereby enhancing power generation efficiency, while also minimizing rainwater runoff, aiding in water resource management [26,27]. This design provides multifunctionality for rural buildings, not only meeting energy demands but also enhancing ecological resilience and sustainability [28,29]. However, despite the numerous advantages of this integrated design, the technical complexity and initial investment costs remain significant challenges [16,30]. Based on this, the present study explores an integrated design scheme combining rooftop PV and green systems in rural areas, evaluating its economic and ecological benefits, and proposing directions for future research. Focusing on a rural village in East China as a case study, the research optimizes the energy-saving and landscape effects of ecological roofs, developing a carbon emissions calculation model for these systems. This provides a basis for improving the energy consumption and carbon emissions accounting system in rural building sectors.

2. Materials and Methods

This study focuses on an integrated design of PV and green roofing systems for rural residential buildings in East China. It comprehensively considers multiple factors, including the climatic conditions, spatial layout, plant selection, soil substrate, and ecological benefits of rural residential rooftops. By conducting a thorough analysis of the energy-saving and low-carbon effects of ecological roofs, the study aims to ensure the synergistic functionality of the PV and green roofing systems, contributing positively to environmental protection and sustainable development. This research involves optimizing design schemes and adjusting system parameters to maximize low-carbon emissions and high carbon sequestration benefits in rural spaces, enhancing the efficiency, sustainability, and eco-friendliness of the system [31]. The overall framework of the study is shown in Figure 1.

2.1. Selection and Design of Rooftop Photovoltaic System

The classification of PV rooftop designs is primarily based on the geometric characteristics, materials, and functions of the roof [32,33]. When designing and installing a PV rooftop, it is essential to consider factors such as the roof’s material, structure, area, orientation, shading, waterproofing, and load-bearing capacity [34]. Understanding the specific roof type aids in selecting the appropriate installation method and optimizing the performance of the PV system to ensure safety, photoelectric conversion efficiency, and aesthetic integration [35,36]. In East China, common rooftop types are broadly categorized into flat roofs, sloped roofs, color steel tile roofs, and uniquely shaped roofs, as shown in Figure 2. Among these, flat roofs are the most widely used for PV installations due to their smooth surface and minimal slope of less than 5 degrees. The primary advantage of flat roofs is the flexibility they offer in adjusting the optimal tilt angle based on actual needs to maximize power generation [37]. Sloped roofs, with inclines typically ranging from 15 to 45 degrees, come in various forms, such as single-slope, double-slope, and four-slope roofs. Sloped roofs facilitate self-cleaning and drainage for PV modules, allowing for uniform distribution of PV components and optimal use of rooftop space [38]. Color steel tile roofs are most common in modern commercial and industrial buildings, characterized by their lightweight and corrosion-resistant materials, making them suitable for PV installation [39]. Roofs with unique shapes, such as arched, conical, and irregular designs, require more specialized layout and installation methods for PV modules. Such roofs often utilize translucent PV components for skylight applications, necessitating tailored design plans and professional construction techniques. While these have high aesthetic value, the increased translucency typically results in lower power-generation efficiency [40]. Each type of PV rooftop design has its own distinct characteristics, which are suitable for different building types and functional needs. In PV system design, installation methods and layout are selected based on the specific roof configuration.

2.1.1. Selection of Rooftop Photovoltaic Panels

The primary function of PV panels is to convert solar energy into electrical energy, serving as the core component of a solar power-generation system [41]. PV panels are mainly classified into monocrystalline silicon, polycrystalline silicon, and amorphous silicon thin-film panels. When selecting PV panels, factors such as application scenarios, actual roof conditions, photoelectric conversion efficiency, and material lifespan should be considered. Monocrystalline silicon panels are suitable for scenarios with high photoelectric conversion demands, polycrystalline silicon panels are cost-effective for budget-sensitive buildings, while amorphous silicon thin-film panels are ideal for diverse installation sites and situations with special spatial constraints [42].

Common crystalline silicon panels are available in blue, black, and various other colors. Monocrystalline silicon panels are typically black, with surfaces treated to create microstructures that significantly absorb light. This structure allows the light on the silicon surface to be repeatedly reflected and absorbed, providing excellent light-trapping properties and greatly enhancing the photoelectric conversion efficiency of the panels [43]. Polycrystalline silicon panels usually appear in a brighter blue due to their multi-grain crystal structure, where varying crystal orientations cause internal light scattering, resulting in a unique color effect. Adding pigments or using structures with specific optical properties in polycrystalline silicon materials can achieve different colors, allowing better integration with surrounding environments [44]. Amorphous silicon thin-film panels commonly feature blue-gray or dark blue tones, and thus are less vivid than monocrystalline and polycrystalline panels. Due to the material’s ability to absorb most of the visible-light spectrum, its optical properties dictate a particular color of reflected light [45].

In this study, monocrystalline silicon PV panels are selected for the sample case, primarily because East China has abundant solar resources, and monocrystalline silicon panels offer high photoelectric conversion efficiency. They can achieve maximum power output on limited rooftop space and perform well under low-light conditions [46], making them suitable for East China’s variable weather. Additionally, monocrystalline silicon panels have a long lifespan and stable performance, making them ideal for the long-term development needs of rural environments. The choice of rooftop PV panels directly affects the system’s actual power generation efficiency and economic benefits, necessitating a design based on site conditions, sunlight levels, tilt angle, and shading. This selection process is critical for assessing actual power output and system performance, as show in

Table 1. Classification of solar photovoltaic panels.

Battery Type	Solar Panel Classification		Functional Features	Incident Light Power	Common Dimensions	Photoelectric Conversion Efficiency
Crystalline Silicon Solar Cell		Monocrystalline	1. High photoelectric conversion efficiency 2. Long lifespan 3. High production cost	305 w	1956 × 992 ×50 mm	13–18%
		Polycrystalline	1. Manufactured using casting methods, resulting in lower production costs 2. Slightly lower photoelectric conversion efficiency	300 w	1970 × 990 × 50 mm	11–17%
		Amorphous Thin Film	1. Good flexibility, lightweight, and can be bent 2. Low photoelectric conversion efficiency 3. Suitable for special installation conditions	43.2 w	1200 × 600 ×3 mm	6–10%

.

2.1.2. Calculation of Tilt Angle and Spacing for Rooftop Photovoltaic Panels

The tilt angle of a PV panel refers to the angle between the panel’s surface and the ground plane [9]. In rooftop PV system design, the tilt angle of PV panels determines the efficiency with which the panels capture solar radiation. The optimal tilt angle allows the panels to receive maximum solar irradiance, thereby enhancing the overall photoelectric conversion efficiency of the system [47]. This study employs the PV system design and performance simulation software PVsyst to conduct a simulation analysis of various tilt angles in PV system case models. Through various factors such as geographic location, climate data, solar radiation, and installation site characteristics, the panels’ suitability and efficiency for specific regions are verified, thereby generating a meteorological model tailored to the specific location. Further customized design and simulation are conducted to select appropriate PV modules and simulate the power generation performance of the solar system under different conditions, assessing the reliability and power generation benefits of the solar PV system in the sample region.

According to the requirements of the Design Code for Photovoltaic Power Stations, the spacing of PV arrays must ensure that there is no mutual shading between arrays from 9:00 to 15:00 (local solar time) throughout the year [48]. On the winter solstice, when the solar altitude angle is at its lowest for the year, the spacing between PV arrays is set to ensure that the rear arrays are not shaded by the front ones, thus maintaining power generation efficiency.

First, the optimal installation tilt angle for the PV modules is determined $\mathsf{\theta }$. Based on the shading conditions of the PV modules, the spacing between PV arrays, denoted as D, is adjusted. The front-to-back spacing between arrays can be expressed by the following formula:

$$\mathrm{D}=\mathrm{h}·\cos \mathsf{\theta }+\mathrm{h}·\sin \mathsf{\theta }·\cot \mathsf{\alpha }·\cot \mathsf{\beta }$$

(1)

where $\mathsf{\alpha }$ is the solar altitude angle; $\mathsf{\beta }$ is the solar azimuth angle; d₁ represents the distance between the vertical projection of the rear edge of the front PV array to the front edge of the subsequent PV array on the horizontal plane; d₂ is the vertical projection of the front PV array on the horizontal plane; and D is the spacing between two adjacent PV arrays.

Secondly, the spacing of PV arrays is adjusted based on the shading conditions of the PV modules. The required number of PV modules is determined, and the array layout is optimized to minimize power generation losses caused by shading. The calculation diagram of the PV panel tilt angle and array spacing is shown in Figure 3.

2.1.3. Integrated Design of Solar Photovoltaic System and Green Roofing

Based on the sample region, this study’s ecological rooftop system is designed primarily for two types of roof surfaces: flat roofs and sloped roofs. The integration of the PV system and greenery is classified into three specific arrangement types:

(a) Singular arrangement: This involves arranging PV components neatly across the entire roof area, typically using a uniform orientation and tilt angle. The layout of PV panels is relatively simple, with high technical maturity; solar panels are usually placed directly at the planned rooftop locations. This method is suitable for rooftops with regular spaces and minimal obstructions.

(b) Distributed arrangement: In this setup, solar PV panels and green roofing are positioned on separate sections of the roof, dividing and combining rooftop areas. This allows for flexible design of the proportion of PV panels and green roofing area based on actual needs, avoiding mutual interference. It requires detailed analysis and planning to ensure optimal use of each section, increasing implementation complexity.

(c) Combined arrangement: This approach involves installing solar PV panels across the entire roof area, with low-growing vegetation planted beneath the panels. It fully utilizes the rooftop area for multifunctional purposes, maximizing the green roof and solar PV design area. This setup helps absorb rainwater, reduces the pressure on drainage systems caused by runoff, and filters airborne pollutants. Regular maintenance of both PV panels and vegetation is necessary to ensure proper operation and healthy growth.

In an integrated ecological roof design, a small green balcony can be built on the sunny side under the eaves. This not only improves the microclimate both indoors and outdoors but also enhances the aesthetic appeal of the residential environment. When designing a green balcony, considerations should include its orientation, size, load-bearing capacity, plant species, and the specific preferences of residents. The orientation of the balcony affects plant growth, as different species have varying light requirements. A south-facing balcony is suitable for sun-loving plants, while a north-facing balcony should feature shade-tolerant plants [49]. According to the national Building Area Calculation Standards, the horizontal projection area of balconies should not exceed 12 m² for residences with a floor area of 90 m² or less, 15 m² for residences between 90 m² and 140 m², or 18 m² for residences larger than 140 m² [50]. The soil substrate on the balcony should be adequately thickened, with a planting soil depth of no less than 0.5 m. When selecting plant species, it is recommended to consider the preferences of residents and choose evergreen or seasonally variable groundcover plants or small shrubs with aesthetic appeal and carbon sequestration potential. Based on the three arrangement types, a design diagram for an integrated ecological roof with PV systems and greenery on flat and sloped roofs is shown in Figure 4.

2.2. Introduction to the Sample Site

The experimental sample site is located in Renshou Town (with geographic coordinates 115°21′–115°31′ E and 28°50′–28°58′ N), Jing’an County, Yichun City, Jiangxi Province. Jiangxi Province borders Zhejiang, Fujian, and Guangdong Provinces, and its unique geographic location positions it as the hinterland of the Yangtze River Delta, the Pearl River Delta, and the West Coast Economic Zone. Jing’an County is one of China’s first “Two Mountains” innovation bases, and this study uses the ancient village of Leijia in Renshou Town as a case for simulation analysis. Leijia Village has a long history and rich cultural heritage, with traditional residential buildings in the typical “Four Waters Return to the Hall” style of Jiangnan architecture. Most buildings are constructed from brick and wood, featuring unique rural elements such as nameless ancestral houses, ancient wells, and old camphor trees, which together create a distinctive rural landscape. The sample area has a planned area of 85,100 m², with 149 planned buildings primarily featuring sloped and flat roofs, covering an approximate building footprint of 9278 m². The site receives abundant sunlight throughout the year, with moderate rainfall, and has favorable solar resources that present potential for development, as shown in Figure 5.

Our experiment involves designing low-carbon ecological roofs for the village, incorporating both solar PV systems and green roofing to achieve functional and spatial integration on the rooftops. Different roof design methods are simulated to calculate and compare carbon reduction effects, ultimately determining the most suitable ecological roof design for Leijia Village.

2.3. Calculation Setup for Carbon Sequestration Effects of Ecological Roofs

This study aims to assess the carbon sequestration effects of the modified ecological roofs. This assessment includes the carbon compensation generated by the solar PV system and the rooftop greening. The carbon emissions calculation area is based on the rooftop area of Leijia Village buildings as the functional unit, with carbon emissions measured accordingly. The system measurement boundary primarily focuses on the operational phase of the ecological roof, specifically from the completion of the ecological roof through the operation of the green roofing and solar PV systems until the end of their service life. During this period, the carbon compensation of the system is calculated; plants absorb carbon dioxide through photosynthesis, and the solar PV panels utilize renewable energy, reducing reliance on traditional energy sources and lowering carbon emissions. Throughout the entire operational cycle, these systems will continuously contribute positive carbon reduction benefits to the environment.

2.3.1. Calculation of Carbon Sequestration Effects from Green Roofing

The carbon sequestration in the green roofing component primarily consists of plant carbon sequestration and soil carbon sequestration. In the sample village, traditional residential roofs typically have a certain slope, and the environmental conditions limit the types of plants that can be grown on the roofs, generally favoring low-growing grass species with shallow substrates (typically less than 15 cm). The carbon storage capacity of the vegetation can vary with growth rates, often showing rapid growth within the first three years [51]. The organic carbon content in the soil is determined by the balance between the input of organic matter, such as biological residues, and the loss of organic material primarily through microbial decomposition in the soil [52].

The calculation formula can be expressed as follows:

$${\mathrm{C}}_{\mathrm{o}\mathrm{p}}=\left({\mathrm{S}}_1{\mathrm{E}}_1-{\mathrm{S}}_0{\mathrm{E}}_0\right)·\mathrm{T}+\left({\mathrm{D}}_1{\mathrm{P}}_1-{\mathrm{D}}_0{\mathrm{P}}_0\right){\mathrm{C}}_{\mathrm{I}}·\mathrm{T}$$

(2)

where ${\mathrm{C}}_{\mathrm{o}\mathrm{p}}$ represents the carbon compensation generated by the rooftop green roofing (${\mathrm{t}\mathrm{C}\mathrm{O}}_{2\mathrm{e}}$); ${\mathrm{S}}_1$ is the green area resulting from the construction of the ecological roof; ${\mathrm{S}}_0$ is the original green area on the roof; ${\mathrm{E}}_1$ is the annual carbon sequestration of vegetation after the construction of the ecological roof; ${\mathrm{E}}_0$ is the original carbon sequestration of rooftop vegetation; ${\mathrm{D}}_1$ is the soil area after the construction of the ecological roof; ${\mathrm{D}}_0$ is the original soil area on the roof; ${\mathrm{P}}_1$ is the soil depth after the construction of the ecological roof; ${\mathrm{P}}_0$ is the original soil depth; and $\mathrm{T}$ is the lifespan of the ecological roof construction.

2.3.2. Calculation of Carbon Sequestration Effects from Rooftop Solar Photovoltaic Systems

Solar PV panels do not directly produce carbon dioxide emissions during power generation. Instead, they convert solar energy into electrical energy, thereby reducing the carbon emissions associated with the combustion of fossil fuels for electricity generation. According to the carbon emission coefficients specified in the Building Carbon Emission Calculation Standards [53], the calculation of carbon dioxide emissions generated during the operational phase of the rooftop PV system involves the total power generation of the PV system and the carbon emission factor of the electrical grid (i.e., the amount of carbon emissions per kilowatt-hour of electricity produced).

The calculation formula can be expressed as follows:

$${\mathrm{C}}_{\mathrm{O}\mathrm{S}}=\left[\sum _{\mathrm{a}=1}^{\mathrm{n}}\mathrm{P}{\left(1-\mathsf{\lambda }\right)}^{\mathrm{a}-1}\right]{\mathrm{F}}_{\mathrm{e}}{\displaystyle \frac{\mathrm{T}}{\mathrm{n}}}$$

(3)

where ${\mathrm{C}}_{\mathrm{o}\mathrm{s}}$ represents the carbon compensation generated by the rooftop solar PV installation (${\mathrm{t}\mathrm{C}\mathrm{O}}_{2\mathrm{e}}$); $\mathrm{a}$ represents the number of years for which the rooftop solar PV system is operational; ${\mathrm{F}}_{\mathrm{e}}$ is the carbon emission factor for solar PV power generation in the region; $\mathrm{n}$ is the lifespan of the rooftop solar PV system; $\mathrm{P}$ is the power output of the ecological rooftop PV system; and $\mathsf{\lambda }$ is the annual degradation rate of the rooftop solar PV system’s power generation, set at 1% [9].

3. Results

Through the area calculation of the ecological roof in Leijia Village, the total rooftop building area is approximately 9278 m², which is divided into flat roofs and sloped roofs. The calculations indicate that the flat roof area is about 2674 m², while the sloped roof area is approximately 6604 m². Using the PV system simulation design software PVsyst, the optimal tilt angle for the PV system is calculated. Different tilt angles affect the amount of solar radiation received by PV modules, thereby impacting power generation efficiency. By importing detailed sample parameters of the PV modules and geographical information of the site, the simulation analysis determines that the optimal tilt angle range for the PV array in this area is between 17° and 21°. Within this range, the annual total solar radiation received by the rooftop PV system is maximized, and simulation analyses are conducted for each value within this range in the model. Generally, a smaller tilt angle is preferable for the PV panels, as it reduces the amount of cable support material required, simplifies the installation process, and enhances the wind resistance of the support structure, thereby increasing the installation capacity. Consequently, the optimal tilt angle $\mathsf{\theta }$ for the PV array in the sample area is set at 17°, with the PVsyst software used for sunlight parameter simulation analysis, as shown in Figure 6.

Based on the three arrangement types of the ecological roofs, we calculate the carbon sequestration efficiency for each arrangement. The average annual sunlight hours for the region are 1637 h, combined with data from the carbon emission calculation standards, indicating that the carbon emission factor for the East China power grid is $0.7035{\mathrm{K}}_{\mathrm{g}}{\mathrm{C}\mathrm{O}}_{2\mathrm{e}}·{\left(\mathrm{K}\mathrm{W}·\mathrm{h}\right)}^{-1}$ [54]. Using PVsyst software, the simulation results show that the system output energy for the three types of PV panels, in descending order, is as follows: monocrystalline silicon panels > polycrystalline silicon panels > amorphous thin-film panels. Additionally, the photoelectric conversion efficiency for different ratios of PV panels to rooftop area, also in descending order, is monocrystalline silicon panels > polycrystalline silicon panels > amorphous thin-film panels, as presented in Figure 7 and Figure 8.

In this case study, monocrystalline silicon PV panels with high photoelectric conversion efficiency are selected for the ecological roof in Leijia Village. The dimensions of the modules are 1956 mm × 992 mm × 50 mm, with an average peak power of 305 W. Based on the solar parameters for the winter solstice in this region (

Table 2. Solar parameters for the winter solstice in the sample area.

Time	Hour Angle (ω)	Solar Altitude Angle (α)	Solar Azimuth Angle (β)	Solar Declination
AM 09:00	−45°	29°	−47°	−23.5°
PM 15:00	45°	15°	52°	−23.5°

), when the tilt angle of the PV array is set to the optimal angle of 17°, the minimum spacing without shadow interference between the front and rear of the array at 9 AM on the winter solstice is D = 1.217 m. At 3 PM, the minimum spacing is 1.925 m. The minimum spacing for the PV array should be taken as the maximum value, D = 1.925 m.

According to the calculation of the carbon sequestration benefits of green roofing, the amount of carbon transferred from the atmospheric reservoir to the vegetation and soil carbon reservoirs by rooftop plants is 9.54 ${\mathrm{K}}_{\mathrm{g}}{\mathrm{C}\mathrm{O}}_2·{\mathrm{m}}^{-2}·{\mathrm{a}}^{-1}$ [55]. Since the soil selected for the construction of rural rooftops is local soil, it can better adapt to the local climate and ecological conditions, resulting in a carbon sequestration amount of $3.89 {\mathrm{K}}_{\mathrm{g}}/{\mathrm{m}}^2$ [56]. Based on the three design forms of ecological roofs mentioned above, the study combines the energy-saving benefits of the PV system with the carbon sequestration capacity of the green roofing to simulate the three design approaches. Given that the safe operational lifespan of the PV panels is 25 years, the growth cycle of the plants is also considered over a 25-year period to ensure that the greening portion continues to provide ecological benefits throughout the operational life of the PV system. A comparison of the ecological benefits of the three different roof distribution forms is shown in

Table 3. Comparison of ecological benefits for three different ecological roof arrangement forms.

Arrangement Method	PV Module Type	PV Device to Roof Area Ratio	Green Roof Area Ratio	PV System Carbon Reduction (CO₂)	Vegetation Carbon Sequestration (CO₂)	Carbon Sequestration Summary of Rooftop Photovoltaics and Green Roofing (CO₂)
Single Arrangement	Monocrystalline	100%	0%	11,950.761 t	366.906 t	12,317.667 t
Distributed Arrangement	Polycrystalline	50%	50%	5971.512 t	1473.307 t	7444.819 t
Combined Arrangement	Amorphous Thin-Film	100%	100%	11,950.761 t	2579.709 t	14,530.470 t

.

(a) Single arrangement: The roof is equipped solely with monocrystalline silicon PV modules, allowing for the installation of 2391 panels, covering an area of 4639 m². The carbon reduction achieved by the small green balcony portion over its service life is 366.906${\mathrm{t}\mathrm{C}\mathrm{O}}_{2\mathrm{e}}$. The carbon emissions reduction achieved over its operational lifespan is 12317.667${\mathrm{t}\mathrm{C}\mathrm{O}}_{2\mathrm{e}}$.

(b) Combined arrangement: The roof features a combination of monocrystalline silicon PV modules and low-growing grass species planted beneath them. Taking a PV system to vegetation ratio of 1:1 as an example, together, the PV modules and vegetation can reduce carbon emissions by 7444.819${\mathrm{t}\mathrm{C}\mathrm{O}}_{2\mathrm{e}}$.

(c) Distributed arrangement: The entire rooftop area of 9278 m² is planted with low-growing grass species, while monocrystalline silicon PV modules are installed over an area of 4639 m², adhering to optimal tilt angles and spacing. The carbon reduction achieved by the ecological green roofing portion is 2212.803${\mathrm{t}\mathrm{C}\mathrm{O}}_{2\mathrm{e}}$, and when combined with the small green balcony, the total carbon reduction over the entire operational lifespan amounts to 14530.470${\mathrm{t}\mathrm{C}\mathrm{O}}_{2\mathrm{e}}$.

Under the three different arrangement types, the carbon compensation potential generated by the modified ecological roof in Leijia Village, from highest to lowest, is as follows: (combined arrangement $14530.470{\mathrm{t}\mathrm{C}\mathrm{O}}_{2\mathrm{e}}$) > (single arrangement $12317.667{\mathrm{t}\mathrm{C}\mathrm{O}}_{2\mathrm{e}}$) > (distributed arrangement $7444.819{\mathrm{t}\mathrm{C}\mathrm{O}}_{2\mathrm{e}}$).

4. Discussion

Rural areas often have ample rooftop space and abundant natural resources; however, challenges remain in terms of energy acquisition and environmental management. The integrated design of ecological roofs in rural areas, combining PV systems with green landscaping, presents a viable solution for sustainable development in rural environments [57]. This approach not only provides clean energy for rural buildings but also enhances the ecological environment of rural spaces. Our analysis indicates that the larger the proportion of PV module area to the total roof area, the greater the energy benefits generated. Among the three types of PV panels, monocrystalline silicon panels exhibit the highest system output and photoelectric conversion efficiency. Based on our results, the carbon reduction benefits of the roof arrangements are ranked as follows: combined arrangement $14530.470{\mathrm{t}\mathrm{C}\mathrm{O}}_{2\mathrm{e}}$ > singular arrangement $11950.761{\mathrm{t}\mathrm{C}\mathrm{O}}_{2\mathrm{e}}$ > distributed arrangement $7444.819{\mathrm{t}\mathrm{C}\mathrm{O}}_{2\mathrm{e}}$. Different arrangements impact carbon dioxide CO₂ reduction to varying degrees, with the combined arrangement offering the highest carbon reduction potential, while the singular arrangement provides the smallest reduction potential. The combined arrangement demonstrates significant advantages in terms of carbon reduction by synergizing and integrating multiple resources, resulting in additional reduction effects. While the singular arrangement features mature technology, it is relatively simple and lacks the synergistic benefits of integrating diverse resource technologies. The distributed arrangement links various components but lacks strong interconnectivity. The direct carbon reduction benefits of solar PV panels, due to their photoelectric conversion, are significantly greater than the carbon sequestration capability of green roofing. Consequently, PV systems are more effective when it comes to reducing energy consumption and carbon emissions. However, the environmental benefits of green roofing in other aspects should not be overlooked. While PV systems provide direct carbon reduction through clean energy output, green roofing indirectly contributes to carbon reduction by enhancing landscape and ecological functionality, further promoting the sustainability of the entire building. Both rural rooftop PV systems and green roofing have unique advantages in terms of carbon sink benefits. The combined application of these technologies should be optimized to fully leverage their respective strengths and enhance overall benefits, contributing positively to climate change mitigation. The three arrangement methods are not limited to rural areas. The combined arrangement can also be applied to large-scale, integrated industrial zones or urban environments, where sufficient resources and scale support the coordinated and integrated application of various components, achieving maximum carbon reduction. The singular arrangement is suitable for small areas or specific industries with abundant solar resources, meeting local energy demands while reducing carbon emissions. The distributed arrangement, as a simple and decentralized energy-saving and emission-reduction measure, can be applied to scattered residential buildings or small-scale agricultural production activities. These arrangement methods provide important references for addressing climate change and formulating carbon reduction strategies. By selecting the appropriate carbon reduction approach based on site-specific resources, technology, and economic conditions, a win–win situation for both economic and environmental benefits can be achieved.

In the experimental setup for the ecological roofs of residential buildings in Leijia Village, green roofing serves as an important complementary component to the rural green space system. Green roofs effectively absorb and retain precipitation, reducing rooftop rainwater runoff and mitigating soil erosion risks, thus helping to maintain soil stability. Additionally, the green roofing layer can filter pollutants from rainwater. By absorbing carbon dioxide and harmful gases from the atmosphere, rooftop vegetation transforms and stores carbon as organic matter while releasing oxygen, fulfilling a “carbon sink” function. The vegetative layer on green roofs can absorb, decompose, and amend dust, bacteria, and other harmful gases in the environment, improving air quality in rural areas, especially during peak farming seasons when air pollution from activities like straw burning becomes an issue. Green roofs also provide insulation, with diverse plantings that create a thermal barrier for rural buildings, reducing heat transfer and indirectly lowering energy consumption-related carbon emissions. This helps to regulate the microclimate and maintain ecological stability. For plant selection on green roofs, native species are recommended to establish a composite landscape structure suitable for rooftop ecological conditions, enhancing the coherence of rural green spaces. Plants should be chosen with specific growth conditions in mind, favoring species adapted to rooftop environments with high carbon sequestration potential, such as groundcover plants (e.g., mint, verbena, sedum, and mossy saxifrage). These plants are suitable for rooftop growth, as their shallow roots reduce the amount of structural stress on the roof, lower roof temperatures, prevent soil erosion, and provide aesthetic greening effects [58]. Green roofing differs from ground-level greening, and when selecting plants, it is essential to consider seasonal blooming and visual appeal to enhance ecological diversity and aesthetic value. A suitable soil substrate provides essential moisture, nutrients, and support for the plants, ensuring healthy root growth. Studies indicate that local natural soil, sludge-based medium, and waste-construction medium demonstrate superior carbon sequestration compared to other substrates, with local natural soil exhibiting the highest sequestration capacity [59]. Therefore, local natural soil should be prioritized in construction to maximize the environmental benefits of green roofs and avoid the carbon emissions associated with transportation.

Through careful design and effective management of green roofing, its functions can complement the power generation benefits of PV systems within ecological roofs. When it comes to the design of ecological roofs for rural residences, the synergy between the solar PV system and green roofing can yield greater ecological benefits. Additionally, rooftop vegetation enhances the power output of solar PV panels by reducing rooftop temperatures, which in turn improves the panels’ power generation efficiency. The transpiration of plants lowers the temperature of the PV panels, thereby increasing their conversion efficiency, while the shading effect of the panels protects the plants from direct sunlight, reducing water evaporation and the risk of drought. This design contributes to the overall sustainability and efficiency of the system [60]. The integrated design of combined rooftop PV systems and green roofing offers numerous advantages, but also presents certain limitations. To maximize the solar radiation absorption of the PV panels, the panels must be installed at a specific tilt angle. Since the green vegetation is planted beneath the PV panels, the vertical distance between the panels and the green roof varies, potentially leading to uneven temperature distribution within the vegetation. Some areas may experience excessively high or low temperatures, which can adversely affect plant growth. The shading provided by the PV panels reduces direct rainfall impact on the soil, enhancing its water retention capacity. However, this may also result in uneven soil moisture distribution, affecting the normal activity and nutrient absorption of plant root systems. Although the vegetation mainly consists of low-growing grass species, the growth of these plants could potentially obstruct sunlight from reaching the PV panels, thereby reducing their power generation efficiency. On the other hand, installing PV panels at a higher height to mitigate this issue could increase installation costs and impose additional safety challenges. Therefore, careful consideration must be given to the distance between the PV panels and the vegetation to strike a balance between efficiency and practicality.

It is important to note that when constructing ecological roofs for rural residences, installing PV modules on flat roofs is relatively straightforward. However, flat roofs tend to have lower drainage efficiency compared to sloped roofs, and high temperatures in summer can lead to excessively elevated internal temperatures [61]. Sloped roofs typically offer greater aesthetic appeal and can blend well with the building’s exterior. They can be tilted at an appropriate angle based on site conditions to better capture solar radiation. It is important to note that when transforming ecological roofs, a well-designed drainage system must also be constructed to ensure that excess moisture is quickly removed after rainfall, preventing water accumulation that could lead to plant death and roof damage. The design of ecological roofs should fully consider ecological and safety aspects while also focusing on the overall effect of coordination and integration between the building and its surrounding environment. Without altering the original architectural style, the aesthetic appeal of the PV roof can be enhanced by incorporating a diverse range of plant species to create a visually impactful design [62]. Combining the ecological aesthetic benefits of green roofing with the economic benefits of the PV system can better promote the realization of economic, ecological, and social benefits.

The integrated design of rooftop photovoltaics and green roofing shows significant advantages over traditional rural rooftops in terms of energy efficiency and carbon footprint. It not only improves energy utilization efficiency and reduces dependence on conventional energy sources but also significantly lowers building carbon emissions by combining green vegetation with photovoltaic technology. In modern construction, opting for ecological roofs has become an essential choice for sustainable development. Compared to traditional rooftops, ecological roofs require a higher initial investment. However, in the long run, energy savings and policy subsidies can significantly reduce overall costs, decrease electricity expenses in rural areas, increase residents’ income, and improve their quality of life.

5. Conclusions

The design of ecological roofs in rural areas must take into account factors such as climate conditions and geographical environment to ensure the stable and efficient operation of solar PV systems and green roofing. This study uses Leijia Village in East China as a case study, guided by the design goals of enhancing carbon sequestration and ecological improvement through the transformation of rural residential landscapes. Our research explores methods for improving rural ecological roofs based on the concept of low-carbon construction by integrating solar PV systems with green roofing, and examines three arrangement types: single arrangement, distributed arrangement, and combined arrangement, assessing their respective carbon sequestration effects. The results indicate that all three arrangement types effectively enhance regional environmental quality and mitigate energy consumption, with the carbon compensation capabilities ranked from highest to lowest as follows: combined arrangement $14530.470{\mathrm{t}\mathrm{C}\mathrm{O}}_{2\mathrm{e}}$) > (single arrangement $11950.761{\mathrm{t}\mathrm{C}\mathrm{O}}_{2\mathrm{e}}$) > (distributed arrangement $7444.819{\mathrm{t}\mathrm{C}\mathrm{O}}_{2\mathrm{e}}$). Rooftop photovoltaic systems possess high efficiency in terms of their carbon reduction and significant economic benefits, making them well suited for areas with abundant sunlight and moderate building density. In contrast, green roofing, with its multiple environmental benefits, is particularly effective in high-temperature regions and areas with high building energy consumption. A scientifically and rationally integrated application of these two technologies can achieve effective carbon reduction on a larger scale.

The integrated design of solar PV systems and green roofing for rural residences is one of the important directions for the future sustainable development of rural architecture. Ecological roofs in rural areas effectively conserve land resources, enhance usable building space, increase green space, improve regional carbon sequestration capacity, and address ecological environmental issues. This design not only facilitates the promotion of green energy but also enhances the ecological environment and quality of life in rural regions. This research provides theoretical references and practical insights for the sustainable development of buildings and environments in rural areas, offering new ideas and methods for optimizing building energy efficiency, improving ecological environments, and promoting rural sustainability. However, it is important to note that the sample in this study may not fully represent the diversity of rural communities and may not comprehensively reflect community characteristics. The unique and constrained nature of the sample site may also affect the analysis of experimental data in assessing the carbon sequestration benefits of ecological roofs. Therefore, conducting large-scale, regional-level carbon sequestration calculations based on rural ecological roofs will be a continued focus of this research.