Renewable Energies in the Built Environment

1. Introduction

The attention to environmental sustainability and energy has progressively increased in recent years, driven by the global energy crisis and mounting climate change concerns. These fundamental challenges, combined with the COVID-19 pandemic, have transformed the worldwide energy situation, impacting energy security, climate response, and lifestyles (e.g., smart working, home–school, online shopping). Our built environment is undergoing a metamorphosis, driven by the need for sustainable development and energy efficiency. This revolution brings with it an opportunity to reimagine and redefine the way we harness and utilize energy. This situation opens new possibilities for the energy retrofit of buildings, as well as for the adaptive reuse of existing buildings, asking for a conscious use of passive and active systems.

In this context, the idea of sustainable transition arose, defined as “[…] long-term, multidimensional, and fundamental transformation processed through which established socio-technical systems shift to more sustainable alternatives” [1]. Inside it, the energy transition asks for the replacement of fossil fuels with low or zero-carbon energy sources, such as renewable energy sources (RESs) like active solar energy, wind technologies, biomass and bioenergy, geothermal energy, hydropower, and ocean energy.

The energy transition is suggested at the international level to face the effects of climate changes and global warming through the “decarbonization” of the energy system, especially for building, transportation, and industrial sectors. Several policies have been developed internationally for decreasing greenhouse gas (GHG) emissions and for improving the energy efficiency of the built environment, with a particular emphasis on the design, construction, operation, and integration of RESs. For example, the Sustainable Development Goals (SDGs) adopted at the international level aim at reaching a sustainable development balancing social, economic, and environmental aspects [2]. Key goals supporting RES integration include Goal 7 “Affordable and clean energy” that boosts energy efficiency and renewable energy production in the infrastructural sector; Goal 11 “Sustainable cities and communities” advancing sustainable urbanization through green infrastructure and RES integrated housing; and Goal 13 “Climate action” supporting fossil-free adoption [3]. Specific legislative frameworks have been developed in Europe, the United States, Asia, and Australia.

RES development has reached advanced solutions, both on technological and building integration issues. Special attention is devoted to the evolving area of solar energy technologies, as they are shaping a new paradigm in architectural and urban design. This includes both pioneering works on module design, photovoltaics, or solar thermal integration in retrofitted buildings to foster the harmonious coexistence of esthetic appeal, technologic development, and energy production [4]. In this direction, the study of practical applications and tests of energy, esthetic, and sustainable performances (e.g., life cycle assessment, building and landscape integration, grid connection, energy communities) of groundbreaking photovoltaic (PV) and solar thermal (ST) systems is an important field to be investigated. At the same time, solar energies’ potential applied in the built environment is also deeply studied, including a comparison of traditional and innovative evaluation potential methods [5,6]. In line with this, the potential of Building Information Modeling (BIM) to aid the integration of solar technologies into the design and construction processes deserves further exploration, both for implementing the visual appearance and for calculating the energy production from the early design to the construction phase [7]. Also, the policy environment influencing their implementation is scrutinized, shedding light on how these policies can further propel the adoption of renewable energy in the built environment [8].

Presently, special attention is given to wind energy technologies, considering wind farms, landscape integration, visibility mapping, policy, and acceptability issues. The integration of wind technologies is studied mainly at the territorial level for offshore and wind farms in natural areas, while the integration of wind technologies in the built environment, especially in heritage or sensitive contexts, is less studied due to the presence of strict regulation constraints. Applications and studies in this direction can demonstrate the feasibility of these systems, showing good and wrong practices.

Furthermore, the integration of ground source heat pumps in existing buildings requires adequate design and construction to overcome administrative and technical problems. This topic is less studied in the literature, delineating problems and opportunities for energy production [9]. Finally, hydropower and ocean energy integration in the built environment or in existing landscapes is rarely addressed [10].

At the intersection of built environment and RES lies the challenge of balancing conservation and innovation, especially when it comes to cultural heritage [9]. In addition, the uncritical application of RESs in the built environment could generate serious conservation issues, especially in culturally significant built environments and heritage-built environments as well as in protected landscapes. Here, it can compromise heritage values, biodiversity, traditional visual appearance, and materiality. Here, RES integration presents a delicate interplay of tradition and modernity, requiring a balance between heritage preservation and energy production with the support of clear rules, policies, criteria, and heritage-compatible technologies [11]. Furthermore, the acceptability (and acceptance) of these technologies, especially of solar and wind systems, deserves to be deeply analyzed for the presence of technical, economic, informative, and legislative barriers [9]. Furthermore, the importance of the energy efficiency of the built environment requires a focus on energy auditing and simulation [12]. These tools enable the efficient use of energy resources for improving the sustainability in the built environment [13].

2. Contributions

According to this background, the Special Issue on “Renewable Energies in the Built Environment” aims at presenting a holistic view of the opportunities and challenges associated with integrating renewable energy into the fabric of our built environment. The development of these technologies from planning, design and construction perspectives has been investigated. This Special Issue provides a platform for thought-provoking discussions, innovative ideas, and the sharing of best practices, heralding a sustainable future for our cities and communities. Its scope spans across several domains of research—engineering, architecture, urban planning, environmental sciences, policymaking, finance, and heritage conservation—aiming to foster innovative and sustainable solutions to energy use in the context of the built environment.

Through various studies, innovative approaches have been revealed to optimize energy consumption, reduce environmental impacts, and foster energy self-sufficiency. Research areas include the following:

• Building components, where emerging technologies in RES integration are analyzed (e.g., innovative PV technologies, such as tensioned membranes and agrivoltaics building envelopes).
• Building applications, with a particular focus on historic and protected buildings.
• Urban areas, discussing energy communities, renewable energy company development and RES applications at the large scale.

Complementing these technological advances, Yu et al. provide a comprehensive bibliometric analysis of research trends in low-carbon rural areas through systematic examination of 583 papers published between 2013 and 2023. Their findings demonstrate the evolution of rural carbon emission research through three distinct stages: from initial conceptual development (2003–2010) to technical implementation (2011–2018), and finally to the current deepening stage focused on comprehensive carbon reduction strategies. The study reveals that while rural carbon emissions have gained increasing global attention, research remains concentrated in China, the United States, and the United Kingdom, with limited cross-regional collaboration. The authors make an important contribution by identifying critical research gaps and proposing future directions, including the need for standardized emission inventories, multi-scale statistical methods, and region-specific reduction pathways that balance environmental goals with economic development. Their analysis provides valuable guidance for researchers and policymakers working to develop effective, locally adapted solutions for rural carbon emission challenges.

2.1. Building Components

Milošević, Marchwiński and Lucchi examine PV-integrated hyperbolic paraboloid membranes to optimize their design, minimizing strain and enhancing energy efficiency. A major technical hurdle lies in managing the substantial strains caused by external forces, which can negatively impact both the PV system’s efficiency and the structural stability of the membrane. While current design methods focus on stress and deflection, overall strain behavior is often overlooked. Thus, the study evaluates the impact of load types, geometry, material properties, and patterning direction using the Finite Element Method (FEM) with Sofistik software 2023. The results show that wind loads induce higher strains than snow loads, larger structures and increased curvature amplify strain, and diagonal patterning helps reduce it. High tensile-strength materials and optimized prestress further mitigate strain, while edge type has minimal influence. The findings provide design guidelines to improve the structural performance and efficiency of PV-integrated tensioned membranes in sustainable construction.

Zhang, Chen, Gasparri and Lucchi present an innovative agrivoltaics building envelope (ABE) system that integrates thin-film photovoltaics with hydroponic vertical farming in a modular design approach. The system incorporates transparent thin-film PV glass modules alongside low-E glass modules in a “checkerboard” pattern, achieving PV conversion efficiencies of 18% while maintaining 20–30% transparency to support plant growth. The modular design employs recycled aluminum frames as primary structural support, offering both sustainability benefits and flexibility for new construction or retrofitting applications. Their experimental investigation demonstrates that this integrated approach can generate approximately 80–100 W/m² under standard test conditions while providing adequate natural light transmission for agricultural modules through multiple pathways: diffused light through semi-transparent PV panels, direct sunlight through clear glass sections, and reflected light from adjacent surfaces. The system’s adaptable tilt angles (5° to 20° C) and ventilation cavities (65–100 mm) help optimize both energy generation and growing conditions while managing heat accumulation. This research represents a significant advance in multi-functional building envelope technology, demonstrating how careful integration of renewable energy and food production systems can enhance building sustainability while maintaining architectural flexibility.

2.2. Building Applications

Han, Qu, Wu, Su, Qiu and Zhang examine the spatial patterns of carbon emissions and differentiated peak paths at the county level in Shandong Province, China. Through a comprehensive analysis utilizing principal component analysis and k-means clustering, they identify five key driving factors of carbon peak: green transformation, urbanization, industrial construction, energy consumption, and environmental constraints. Their findings reveal distinct spatial patterns characterized by an east–west gradient, with higher emissions concentrated in coastal areas. The study identifies five cluster areas with different carbon peak characteristics: agricultural transformation pending areas, low-carbon lagging areas, industrial transformation areas, low-carbon potential areas, and low-carbon demonstration areas. Each cluster represents different stages of development and faces unique challenges in achieving carbon peak targets. The research demonstrates how county-level analysis can provide valuable insights for formulating targeted low-carbon development strategies, highlighting the importance of considering local conditions and development stages when designing carbon reduction policies. Their findings underscore the critical role that county-level regions play in achieving China’s carbon neutrality objectives while revealing the complex interplay between economic development, industrial structure, and environmental constraints at the local level.

Xie et al. examine passive energy conservation strategies for traditional dwellings in the Peking area through a systematic investigation combining field experiments and numerical simulations. Their findings demonstrate that optimizing building envelope components can significantly reduce energy consumption, including an up to 744.68 kWh reduction through optimal wall thickness of 800 mm, 2514.58 kWh through roof insulation of 15 mm thickness, and 1997 kWh through external wall insulation of 50 mm thickness. Additionally, installing photovoltaic tiles achieved annual electricity generation of 12,057 kWh while reducing CO₂ emissions by approximately 6631.35 kg annually. This comprehensive analysis provides valuable guidance for retrofitting traditional brick dwellings to improve energy efficiency while preserving architectural heritage, with implications for similar building types across northern China.

Ziozas et al. analyzed the potential for renewable energy application and design direction from the perspective of energy consumption analysis of an Italian cultural heritage building. They utilized a dynamic simulation tool named INTEMA.building to simulate the energy-saving retrofit performance of a cultural heritage building in Italy. Their findings demonstrated that by renovating the building envelope, applying the PV panels, using ground-source heat pumps, and installing LED lighting systems, the project can reduce the primary energy demand by 30.49%, the final energy demand by 36.74%, and the net electricity demand by 8.72%. These included a 48% reduction in natural gas consumption due to the using of a ground-source heat pump and a 22.8% reduction in electricity demand attributed to PV applications in the case of a cultural heritage building in Italy.

2.3. Urban Areas

At the urban level, studies focus on protected areas, such as high-value natural and architectural marine landscapes, rural areas, or new urban developments. Romano, Baiani and Mancini explores the opportunities and challenges of integrating renewable energy into the built environment, focusing on less than 3000 residential buildings on Procida, a small island in southern Italy. Through territorial, urban, historical, structural, and environmental analyses, it develops a classification system using in-house software to assess building conditions and propose intervention scenarios. These scenarios combine technological and environmental upgrades (e.g., improved building envelopes and bioclimatic strategies) with energy retrofitting measures like system replacements and solar panel installations. The findings highlight strategies for enhancing building performance and achieving self-sufficiency energy. With a different approach, Abouaiana and Battisti examine rural energy consumption in Egypt. They explore its relationship with the built environment and socio-economic factors, also assessing the feasibility of PV systems. Using analytical, field, and statistical methods, the research focuses on a typical agricultural village in the Delta region, evaluating its built environment, building types, and socio-economic conditions. They discovered that rooftop PV panels could generate substantial energy, but they remain financially unviable under current regulations. Thus, the research offers policy recommendations for rural energy transition. In addition, Ahern et al. proposed an Electrical Water Heater Aggregation (EWHA) scheme with wind energy for fuel-poor households in Ireland, using electricity generated from surplus wind-generated electricity to provide domestic hot water (GHW) to address the hot water supply issues of fuel-poor families. They assessed the feasibility and cost-effectiveness of the solution using a developed wind-generated electricity allocation model and calculated that the scheme can meet the needs of poor users, providing a full tank of hot water every three weeks, while reducing 33 Mkg CO₂ annually. It is expected to save Ireland about EUR 4 million in carbon costs by 2030, increasing to EUR 11 million by 2050.

Another key topic of interest is Renewable Energy Communities (RECs), which enable collective RES generation by actively involving citizens in the energy transition. The primary goals of RECs are to maximize energy sharing among members and optimize RES use by reducing supply-demand imbalances. One strategy to align energy demand and supply in RECs is the use of Thermal Energy Storage (TES) systems that, through power-to-heat technology, offer a cost-effective and versatile solution compared to battery storage. Brunelli et al. examine the role of TES in RECs through a bibliometric analysis focused on TES applications in buildings and districts. The research reveals that TES and REC studies have gained momentum in recent years, particularly in Europe, due to energy efficiency goals and European directives. Despite the increasing interest, the findings highlight a lack of direct focus on TES in the existing literature on RECs, while energy storage is generally discussed within broader RES studies. However, terms like “district heating”, “smart grid”, and “micro grid” suggest a potential overlap in collective self-consumption research, which includes thermal energy. The merging of these keywords points to potential future research in applying TES technologies to RECs, particularly in Europe, where research on both topics is concentrated. In addition, another key topic of interest that has been studied is the development trends of the renewable energy industry. Osiichuk conducted a comparative analysis of the financial conditions of renewable energy companies and conventional energy companies in the European Union and explored the factors affecting the relationship between energy price fluctuations, financial conditions, and the external financing needs of renewable energy companies. The research shows that the financial conditions of renewable energy companies are currently improving, and the return on assets generated by them is significantly higher than that of their peers in conventional energy companies. He also pointed out that the biggest challenge for the operating performance of renewable energy companies may lie in the restrictive revenue cap, price regulation, and the exposure of renewable energy companies to spot market price fluctuations, in addition the cumbersome permit system. He also proposed that the development of the renewable energy industry could be promoted by increasing the prices of renewable energy and relying on market pricing mechanisms.

3. Conclusions

These studies highlight the transformative potential of RES systems in positioning the built environment as a key driver of global energy transition. Throughout this Special Issue, we have seen how technological innovations must be supported by effective policies to achieve widespread adoption of RES. The research presented demonstrates significant advances in several critical areas: the optimization of building components for RES integration, particularly in innovative PV technologies; the successful implementation of renewable systems in various building types, including historically sensitive structures; and the emergence of energy communities as a model for collective renewable energy generation and management at the urban scale.

Moving forward, several priorities emerge for future research and development. Economic feasibility remains a crucial consideration, particularly in developing regions and heritage contexts. System integration challenges persist, especially regarding the harmonious incorporation of renewable technologies into existing built environments. Public engagement and acceptance continue to be vital factors in successful implementation. These challenges underscore the necessity of maintaining a multidisciplinary approach that combines technical expertise with social, economic, and cultural considerations.

The findings presented in this Special Issue provide a strong foundation for advancing the integration of renewable energies in the built environment. They also emphasize the critical importance of collaboration across disciplines—from engineering and architecture to urban planning and heritage conservation—in developing sustainable solutions that meet both energy needs and broader societal goals.