The Potential Related to Microgeneration of Renewable Energy in Urban Spaces and Its Impact on Urban Planning

Abstract

This research aims to explore the potential of renewable energy sources in urban planning, focusing on microgeneration technologies, through a structured literature review. A systematic review was conducted using the PRISMA method, encompassing the identification, selection, eligibility, and analysis of studies related to renewable energy microgeneration in urban environments. The findings emphasize key areas such as policy development, energy security, and future scenario projections, with a particular focus on solar energy generation. The review highlights the importance of robust regulatory frameworks and monitoring systems for effectively managing prosumers and ensuring equitable energy distribution. Key challenges identified include the intermittency of renewable energy sources, regulatory complexities, monitoring systems, prosumer management, energy sizing risks, and the lifecycle of microgeneration technologies. The research accentuates the need for outstanding collaboration between academia, industry, and urban planners to accelerate the adoption and implementation of renewable energy solutions. The main conclusion is that such collaboration is essential for addressing challenges, driving innovation, and contributing to the development of sustainable urban energy systems.

1. Introduction

Urban planning is essential when studying urban centers [1,2]. Continuous urban development often leaves some population needs unmet or worsened, especially during rain or power outages. A long-term urban planning instrument that has the function of guiding the occupation and development of urban territory in cities is the Municipal Master Plan [3].

Although the Municipal Master Plan aids urban development, it lacks specific legislation [4,5,6]. One of its objectives is to address challenges related to climate change [7,8]. It is important to identify and share guidelines that address local climate issues, since the Municipal Master Plan does not often receive due attention in urban policies [7]. Thus, identifying practical urban planning actions already in use can help enhance urban policies [9].

In addition to actions that address the need for urban planning, the issue of energy transition in cities must be addressed in the Master Plan since, according to the International Renewable Energy Agency (IRENA), it has the transformation of a global energy system heavily dependent on fossil fuels to one with zero emissions as a main focus [10]. As a result, in recent years, actions have been emerging, mainly in advanced economies, to ensure energy transition [11,12].

Regarding energy transition and resource utilization, the concepts of minigeneration and microgeneration of energy are increasingly applied. While minigeneration is generally understood to occur between 5 kW and 1 MW, there is no universal standard for microgeneration [13]. The absence of standardized legislation allows for variability in defining this range. For instance, in Brazil, microgeneration is defined as up to 75 kW, in Portugal, it ranges from 700 W to 30 kW, and other countries adopt up to 100 kW [14,15]. Microgeneration makes use of technologies that are highly efficient and use less amounts of fuel, such as thermal pumps, combining heat and power [16]. The study also considers that renewable energy sources can be used, such as solar energy panels, wind turbines, and biomass [16].

Regarding energy sources, it is necessary to evaluate each one individually center. Each source has unique characteristics trade-offs, and meteorological and application conditions must be considered in each implementation scenario to achieve optimal results [17,18]. Additionally, different types of microgeneration can be used concurrently. This diversity, whether in geography or technology type, can help generate sufficient energy to meet demand [19]. It can also help balance the unpredictability and climatic limitations of renewable sources by considering the timing of their applications. The most suitable technology will depend on the specific context and scale of the application [20].

To foster urban planning initiatives and microgeneration of renewable energy in urban environments, it is necessary to understand their potential impact on achieving Sustainable Development Goals (SDGs) 7 (Clean and Sustainable Energy) and 11 (Sustainable Cities and Communities). By encouraging self-generation, cities can not only produce clean energy, but also become more sustainable [21]. Sustainable strategies must be built to enhance energy security and ensure socioeconomic well-being, which requires understanding the dynamics of energy generation and consumption across different spatial and temporal dimensions [22]. Bear in mind that understanding and illustrating how discussions around this topic are unfolding can assist municipal authorities in gaining insights and incorporating new ideas into their urban plans.

With the purpose of focusing the review on the context of urban planning and microgeneration of renewable energy, this paper aims to answer the following questions addressed (QAs):

• QA1—which technologies for microgeneration of renewable energy are applicable to urban spaces?
• QA2—what are the main focuses addressed in research related to the combination of microgeneration technologies with potential for installation in urban spaces?
• QA3—how do studies discuss the role of prosumers in the context of urban planning as part of strategies for energy issues?
• QA4—what strategies do researchers propose for dealing with the reuse of urban waste in sustainable energy microgeneration through microgeneration?
• QA5—what microgeneration energy solutions are suggested to address specific social issues in the urban context?
• QA6—how can community urban spaces contribute to the expansion of widespread use of microgeneration of energy?

Thus, the purpose of this paper is to conduct a rigorous structured literature review within the context of urban planning and microgeneration of renewable energy, with a focus on their intrinsic characteristics and facilitating a detailed analysis of energy microgeneration. The remainder of this paper is organized as follows: Section 2 presents the methodology to make a Systematic Literature Review (SLR). Section 3 describes the application of PRISMA Protocol. Section 4 provides the discussion with regard to the responses and, as documented, present the six research questions addressed, and Section 5 concludes the review, including the research implications for future work.

2. Methodology

To achieve this goal, this study conducts an SLR focused on the potential of renewable energy microgeneration in urban contexts. Six questions were formulated to guide the analysis, and the research was conducted using a scientific database to evaluate them.

The PRISMA method was applied in four stages: Identification, Selection, Eligibility, and Outcomes [23]. This method structured the publication base and ensured a transparent and comprehensive review process, as recommended by Page et al. [24]. Following the PRISMA stages, responses to the initial research questions were evaluated, and the main findings are presented in Figure 1.

3. Results

3.1. Identification

For the identification stage, the SCOPUS database was selected to carry out the bibliographic survey, as described in

Table 1. Article search mechanism adopted in the planning stage.

Focused Terms	Searched Content
Searched Database	SCOPUS
Applied searching method	PRISMA
Keywords Searched within	“Titles”, “Keywords”, “Abstracts”
Main Research	“Urban planning”, “Microgeneration”, “Microgrid”, “Renewable energy”
Type of Articles	Journal/conference research papers, review papers/paper in-press

. The set of keywords to carry out the systematic review of the topic was: “urban planning and (Microgeneration and renewable energy)”.

Table 1, the initial list of research questions that was used to explore articles related to urban planning and microgeneration of renewable energy is presented. Using these parameters, 29, 9, and 84 publications were found using Scopus search tools, respectively (as shown in Figure 2).

The PRISMA protocol [25], was utilized to build a base with several articles and understand how urban planning can promote energy microgeneration. The objective of this research is to prepare a review on urban planning and microgeneration of renewable energy, considering their intrinsic characteristics, and addressing technologies that can bring better returns in terms of energy. The results of this review serve as a basis for analyzes of energy microgeneration in urban planning. The proposed process is presented in Figure 2, in addition to illustrating the findings of each step.

3.2. Selection Process

This stage began with 1997, the year in which the Kyoto protocol was created. This was created at the 3rd Conference of the Parties (COP), and considered one of the main global agreements related to reducing gas emissions into the atmosphere [26]. Addressing the issue of gases, it also became a milestone for promoting renewable energy [26]. In addition to this parameter, publications that were repeated were considered as exclusion criteria.

Based on this, when applying the exclusion criteria of the 94 publications found at the end of the identification stage, 92 publications dealing particularly with urban planning and microgeneration of renewable energy were obtained between 1997 and 2023 (as shown in Figure 2).

3.3. Eligibility

The eligibility stage aims to identify which publications are associated with the topic of urban planning and microgeneration of renewable energy. Publications that do not address this topic should be disregarded. Therefore, the following points were considered as exclusion criteria from the eligibility stage:

• The publication goes off topic;
• It does not address urban planning;
• It does not address microgeneration;
• It does not take place in an urban environment.

Thereby, articles that were not directly related to the topics of the defined research domains were excluded. As a result of the effort, when applying the exclusion criteria of the eligibility stage of the 92 publications, 40 publications deal particularly with urban planning and microgeneration of renewable energy (Figure 2).

3.4. Outcomes

In the findings stage, utilizing the PRISMA method, it was possible to create a database of publications on the topic. Through this, it is possible to carry out various analyzes and identify points, such as the main authors and which are the main journals. All selected publications were registered in a file.

Following these steps, a database of articles about urban planning and microgeneration of renewable energy was created, which triggered a set of evidence, with highlights represented in

Table 2. Research on renewable energy micro-generation in urban planning from 1997 to 2023.

	Energy Policies	Energy Security	Scenario Construction
Solar	4 [27,28,29,30]	10 [27,28,29,30,31,32,33,34,35,36]	17 [27,28,29,30,32,33,34,35,36,37,38,39,40,41,42,43,44]
Wind	0	3 [32,33,45]	4 [32,33,45,46]
Biomass	1 [30]	2 [30,47]	2 [30,47]
Other Renewable Energy	2 [27,48]	11 [27,32,33,36,47,49,50,51,52,53,54]	15 [27,32,33,36,41,46,47,48,49,50,51,52,53,54,55]

, and more in Appendix A, in

Table A1. Works on renewable energy micro-generation in urban planning found through the period of 1997–2023.

Article	Micro-generation				Urban Planning			Impact Fator|Cite Score
	Solar	Wind	Biomass	Other Energy	Energy Policies	Energy Security	Scenario Construction
[48]				x	x		x	11.7|18.4
[31]	x					x		12|17.2
[56]							x	-|8.6
[27]	x			x	x	x	x	10.4|19.1
[28]	x				x	x	x	1.7|3.6
[29]	x				x	x	x	-|-
[37]	x						x	7.4|11.3
[38]	x						x	8|8.4
[39]	x						x	2|4.4
[40]	x						x	6.7|-
[45]		x				x	x	11.1|18.5
[49]				x		x	x	15.9|26.3
[57]						x	x	-|-
[58]						x	x	11.2|21.1
[32]	x	x		x		x	x	4.9|4.2
[59]						x	x	-|3.3
[41]	x			x			x	-|-
[42]							x	-|-
[43]	x						x	4.9|-
[33]	x	x		x		x	x	-|-
[34]	x					x	x	1.971|2.4
[35]	x					x	x	4.2|8.5
[46]	x	x		x			x	-|-
[60]					x	x	x	5.8|5.5
[36]	x			x		x	x	15.9|26.3
[50]				x		x	x	6|10.8
[51]				x			x	3.2|3.7
[52]				x			x	2.8|5.7
[53]				x			x	11.4|16.7
[30]	x		x		x	x	x	12|17.2
[61]					x		x	11.2|21.1
[47]			x	x		x	x	6.7|11.8
[54]				x		x	x	7.4|12.2
[44]	x						x	2.2|7
[55]				x			x	5.6|10
[63]							x	12|17.2
[64]							x	-|2.4
[65]						x		-|-
[66]							x	|0.9
[67]								-|-

The ‘x’ in the table indicates that the article addresses the theme corresponding to the column, while the ‘-’ means that the article does not have or does not provide the Impact Factor or CiteScore of the journal in which it was published.

.

With those articles and their subjects of research found, it was also possible to classify them according to three main themes about microgeneration and urban planning: Energy Policies, Energy Security, and Scenario Construction. For the first one, Energy Policies, it explores the subsidies, incentives, and different strategies applied by the government and other official entities applying energy with diverse characteristics and sources [48]. To define Energy Security, as highlighted by Bertheau [31], it is necessary to analyze the availability of renewable energy to the population, with potential to supply enough energy to their daily usage routine, being reliable, affordable, and operationally safe for customers. Regarding Scenario Construction, it is relatable with the example of different properties in terms of location, their possibility of using different energies, and how to visualize and manage them through data [56].

The number of publications in relation to the year, represented by Figure 3, demonstrates that, even considering the beginning of the time interval in 1997, it was only in 2007 that the first publication on the topic occurred.

One of the significant observations made during the execution of this work was the frequency with which certain topics were addressed in the analyzed publications. Regarding the 40 selected publications, the frequency with which each topic was addressed is highlighted, as shown in

Table 3. Distribution of research topics in selected publications on energy and sustainability, 1997–2023.

Research Topics	Number of Occurrences
Solar	18
Wind	4
Biomass	2
Other Energy	15
Energy policies	7
Energy security	20
Scenario construction	37
SDGs	8

.

Table 2 does not include the SDGs, as it is a broad concept and lacks detail on how to implement them. However, there is a clear concern in relating the SDGs to urban planning, highlighting the need to integrate them into development strategies.

From a survey of publications, one can identify parameters that enhance the understanding of the current state of microgeneration in renewable energy. This approach aims to develop new strategies and explore legal instruments that may not have been addressed in previous studies. Additionally, considering the replication of research in this field, along with environmental factors such as climate, population density, and topography, is crucial. This will facilitate a risk-free comparative analysis of the results obtained.

4. Discussion

In this section, the main findings from the systematic analysis using the PRISMA method will be discussed. The focus is on the characteristics of renewable energy sources and elements that promote microgeneration in urban environments, such as microgrids and urban planning. Current legislation was also reviewed to identify technical gaps that could enhance sustainable urban planning and support the SDG 7 and 11.

The analysis revealed that, beyond solar energy, other renewable sources like wind, hydro, biogas, waste, and biofuels have significant potential for urban microgeneration. However, their effective implementation depends on advances in planning. The potential for using solid waste in buildings as a renewable source was noted, though the technology is not yet mature enough for widespread use.

Additionally, studies on energy policies and security have shown that short- and medium-term policies impact municipal energy plans, as seen in the work of Brandoni [27]. Cansino [28], explored the effects of increased solar plant production on local activities, while Teles da Silva, Dutra, and Guimarães [29] focused on strategies to strengthen Brazil’s national energy policy. These studies highlight the need to align energy policies with urban planning for sustainable development.

Drawing on an extensive review of the literature, we have synthesized the responses and, as documented, present the six research questions addressed, as follows.

4.1. Answer QA1

With regard to the technologies of microgeneration utilizing renewable energies that might be applicable to urban spaces, the authors specifically address the microgeneration technologies of solar, wind, and biomass energy, highlighting them as the most prevalent in urban areas. In addition, they mention other sources in lesser proportions, such as hydro, waste, biogas, and biofuels. Despite the predominance of solar, wind, and biomass sources, hydro and waste sources also present significant potential for urban microgeneration. These sources, still underutilized, have a substantial volume that can be further explored, thus increasing their applicability in urban spaces.

Heusinger et al. [37] evaluated the adaptation of the UCRC-Solar photovoltaic energy balance model to rooftop scenarios. The study was conducted in Braunschweig, Germany, demonstrating that the model accurately predicts module temperatures and energy production, with the potential to integrate climate models and energy simulations. Singh [38] generated rough estimates of the solar photovoltaic potential on city rooftops. The analysis was performed in 13 cities in India, estimating approximately 17.8 GWp of technical rooftop solar energy potential, useful for planning renewable energy scenarios and expanding generation capacity.

Kc Chen and Kien Pham [39] determined the development and knowledge flows of dye-sensitized solar cells, analyzing 132 patents of dye-sensitized solar cells (DSSCs) in the USA, Japan, Germany, and Taiwan, highlighting the role of Japan in the flow of technological knowledge, with implications for strengthening the green energy industry. Gagliano et al. [40] developed a solar energy planning system to predict the potential of solar photovoltaic energy, using a GIS to identify available rooftop areas in urban environments across Europe, demonstrating the potential of solar systems to optimize energy efficiency and integrate renewable energy on an urban scale.

Regarding the issue of wind energy, especially those dealing with energy security and scenario construction, Zhou [45] identified the ideal design of a building that can allow the collection of maximum wind power, this on a micro scale, in low-rise residential buildings. The study found that the “composite prism” building shape optimizes wind energy capture in low-cost residential buildings, successfully tested in a residential project in Pingtan, China. Boroomandnia, Rismanchi and Wu [49] analyze the technical aspects and estimated capacity of micro-scale urban hydro systems (UMHS) in urban infrastructures. They highlight that these systems harness excess energy from water and sewage networks, as well as gravitational energy from water stored in high-rise buildings, focusing on economic feasibility, water savings, load peak reduction, and optimization through simulation tools.

Alhamwi et al. [57] presents an open GIS-based platform for optimizing the costs of flexibility and operation options in urban areas, with a focus on the city of Oldenburg, Germany, demonstrating that investment in local storage and renewable energy generation can reduce the overall system costs and increase urban self-sufficiency. Another article, Alhamwi et al. [58] performed the integration of GIS techniques to calculate the ideal size, location, and operation of electricity battery storage. The analysis was conducted in the city of Oldenburg, demonstrating that investment in battery storage and renewable energy can reduce costs and increase self-sufficiency, while highlighting that a completely off-grid city is not economically or technically feasible.

Zhu [32] sought to satisfy the demand for energy in urban areas through the planning and construction of a distributed energy network. This approach was implemented in the Sino-German Eco-Park in Qingdao, China, demonstrating that the network, combining renewable sources and cogeneration units, can optimize energy use, improve efficiency, and provide sustainable solutions for industrial parks and cities. Tkác [59] demonstrated the importance of urban energy models, indicating that the Efficiency Electric Power Grid Circles (EEPGC) model can promote sustainable development by integrating self-sufficient micro-urban structures, reducing energy losses, and decentralizing energy generation. Lee and Blyden [41] deepened the proposals previously presented for a balanced Distributed Generation strategy. The research provides a global perspective on microgrids, highlighting their benefits, such as increased efficiency and grid resilience, while addressing the technical and economic challenges related to their integration and operation.

Luo et al. [42] make a description of the concepts and technical advantages and disadvantages of distributed production, micro and smart electrical grids, as well as their relationships. The study, focused on the Tiandong County in China, demonstrates that the implementation of these technologies can address the local energy crisis, promote the use of renewable energy, and improve the efficiency of the electrical system. Palmas et al. [43] presented a new concept for regional planning for the Cagliari, Italy, identifying suitable areas for settlements and micro-renewable energy technologies. The methodology integrates energy potential and environmental criteria into urban planning, promoting sustainable development and the incorporation of renewable technologies into land use.

One of those questions, related to technologies for renewable energy microgeneration applicable in urban spaces is addressed in varied methods according to different authors. For instance, a great number of them consider solar, wind, and biomass energy as the most prevalent in urban areas. But it also mentioned other sources in lesser proportions, such as hydro, waste, biogas, and biofuels. Although these types of technologies and energy application are explored in different perspectives by the authors, there is a common sense that those technologies are underutilized, and they have potential to be more explored and provide greater outcomes.

Alhamwi et al. [57] presents an open GIS-based platform for optimizing the costs of flexibility and operation options in urban areas. Zhu et al. [32] sought to satisfy the demand for energy in urban areas through the planning and construction of a distributed energy network. Luo et al. [42] description of the concepts and technical advantages and disadvantages of distributed production, micro and smart electrical grids, as well as their relationships. Palmas et al. [43] presented a new concept for regional planning.

4.2. Answer QA2

The main focuses addressed in research related to the combination of microgeneration technologies with potential for installation in urban spaces is observed that analyzed articles highlight the use of a high percentage of microgeneration technologies in order to help reduce ${\mathrm{CO}}_2$ emissions, mitigating their impacts in urban centers, in addition to improving the efficiency of the energy sector and reducing operational costs. Brandoni et al. [27] considered various technologies, such as solar, internal combustion engines (ICE), micro-combined heat and power technologies, Stirling engines, and fuel cells, aiming for efficiency superior to traditional systems, using EnergyPlan software, a tool developed by the Sustainable Energy Planning Group of Aalborg University, which has been widely used to analyze the integration of intermittent renewable energy technologies based on a variety of parameters in the simulation process.

Zhu et al. [32] discussed the expansion to a new model that includes energy optimization and utilization, defining limits and optimizing the structural space of urban planning, aiming for a sustainable and friendly energy solution. They propose multi-energy integration as a promising direction for the development of future energy systems evolving from a purely distributed system to an intelligent system combining energy and information, enabling coordinated control of the flow through the combination of multiple renewable technologies, microgrid technology, and information technology.

Bracco et al. [33] addressed the challenge of finding the best sizing and combination of available technologies for each location, considering their specific properties. They proposed a decision model for energy production planning in a smart grid that powers a smart district, specifically considering wind turbines, photovoltaic plants, micro-cogeneration turbines, boilers, and connection to the electrical grid, integrating the modeling of the distribution network using the DIgSILENT Power Factory 2017 software to minimize the problem of energy losses in the simulation of generation expansion, together with HOMER software, which, according to the authors, has been applied in the energy planning of municipal energy systems within the electricity market.

Lee and Blyden [41] highlighted the solar thermal storage platform, capable of reaching high temperatures and providing long-duration storage, as a promising solution to improve the efficiency of microgrids in small communities or urban areas, for this purpose, it brings together a body of state-of-the-art research in this field, including distributed generation, microgrid value propositions, power electronics applications, economic issues, microgrid operation and control, microgrid clusters, and issues of protection and communication.

Gasparovic et al. [34] explored the integration of RES in two case study communities in an urban agglomeration to provide optimal conditions to satisfy a part of the electrical loads, and with the aim of managing local energy production, this study was carried out using H2RES energy planning software, and resulted in the need for storage due to the surplus generated by the software with respect to photovoltaic production.

Yan, Abbes, and Francois [35] sought to develop an easy-to-use tool for an Energy Management and Operational Planning System, sing Artificial Neural Networks (ANNs), with the aim of measuring the next day’s predictability through a learning process based on real-time data collection via smart meters, sensors, and meteorological data. Scarlatache et al. [46] analyzed the impact of hybrid energy systems (HESs) considering different types of renewable energy sources to determine the optimal solution, using HOMER to ensure high system efficiency, increasing reliability at the lowest possible cost.

4.3. Answer QA3

Considering the options for energy sources, to respond to QA3, which discusses research on the role of prosumers in the context of urban planning as part of strategies for energy issues, it is observed that these can be utilized by consumers in various ways, including combining them in multiple manners. These combinations would help both in the generation of energy by microgenerations and in their management, considering their specificities.

From the perspective of the authors, the combination of these energy sources is important not only for energy generation, but also for storage strategies, allowing consumers to generate and store excess energy for future use or even sell it to utilities or energy sector entities. Another relevant issue is the untapped potential, such as the scenario of using more than one type of energy to consider local seasonality. In this sense, the exploitation of energy sources such as hydro, waste, and biofuels could be utilized for these proposals. In the urban planning scenario, the use of more than one energy source, considering the most available and abundant in each context, would allow consumers to produce and consume their own energy, promoting greater autonomy and energy efficiency.

Alvarado et al. [60], which describes the importance of promoting urban planning and renewable energy production and consumption policies without limiting the expansion of production, analyzed the relationship between urban concentration, utilization of different patterns of energy consumption, and economic output, highlighting how economic development levels influence these dynamics in 110 countries during 1971 and 2017. With that analysis, authors were able to suggest that countries with higher levels of economic development, have more favorable conditions for adopting microgeneration technologies, with infrastructure that makes it easier to implement small-scale renewable energy systems for consumers. On the other hand, in less developed countries, urbanization was commonly associated with higher non-renewable energy consumption and limiting the capacity of investing in solutions such as microgeneration.

Although having those differences, the authors suggest that the consumption of renewable energy had positive effects and outcomes in most countries and with all income levels. Also, it is proposed that countries should invest and promote mechanisms to develop conscientious urbanization, and policy makers should stimulate renewable energies sources to reduce polluting gasses and help energy transition.

Related to the question prosumers and their roles in the context of urban planning as part of strategies for energy issues, it is observed that these can be utilized by consumers in distinct manners, including combining them in multiple configurations. These configurations could be strategically organized to both provide and generate energy, when necessary, furthermore, managing its resources considering the particularity of each region that these technologies are being implemented, their instability in some cases and changeable conditions. That way, one could obtain the most efficient and greater outcome for energy and availability.

According to Tkac [59], an EEPGC model was developed, utilizing case studies in Slovakia and Taiwan, focused on energy distribution via connections among micro-urban structures, their onsite renewable resources, and the perception of micro-urban structures as decentralized energy carriers, that could function as separated units, but could be interconnected network-wise. With that perception, units would be able to optimize resource management and energy distribution if consumers want to. From this perspective, the authors also indicate that, besides the possibility of energy units supporting other structures, neighbor villages and grids directly, individuals should be able to apply renewable energy sources to their houses and even save energy to utilize it in other applications or energy units.

Adil and Ko [36] gather analysis on social dynamics of decentralized energy systems focusing on distributed generation, microgrids, and smart microgrids, to draw insights for their integration in urban planning and policy, with particular reference to climate change mitigation and adaptation planning, emphasizing the interactions between energy infrastructure and urban dynamics. According to the authors, one major contributor to these energy systems are consumers, utilizing principles of collaboration and community in energy transitions, given in a way of co-providers of energy, with local governments and planners incentives, and highlights the possibility and the arrangement of combining different sources of renewable energies in households, not only solar that are majorly applied, but also other sources, such as wind and biomass to the framework.

Bracco et al. [33] proposed a decision model with mathematical modeling and computer simulations, applied to a neighborhood in Savona, Italy, for the planning of the energy production in a smart grid feeding in a smart district considering wind turbines, photovoltaic plants, cogeneration micro-turbines, boilers and a connection to the electrical grid, to consider and try to guarantee an electrical demand in each time interval while the decisions related to installation have to be considered for the whole lifetime of generation units.

Aiming not only to reduce carbon emissions, but also to improve the energy autonomy and flexibility of the system, prosumers would be acting as optimizers for the framework, since they could be adapting to the consumption needs, variability of renewable energy and determining the best combination of sources. Additionally, helping decision makers to select the best method for investments in different urban scenarios.

Luo et al. [42] utilizes a theoretical and computational model, according to Baise Tiandong County case study, describes advantages and disadvantages of the distributed generation, micro and smart power grid, as well as their relationships considering their combination, and how it affects energy management and outcome. In that model, it was considered a smart grid consisting of power stations, plug-in vehicles, local power grids, and renewable energy sources, such as wind and solar, generators, and home users. They also considered the feasibility of applying wind and photovoltaic power generation in different areas of Tiandong.

From their perspective, prosumers would contribute to the supply of energy additionally, promoting a more decentralized, flexible and resilient system, suggesting that implementing these technologies not only optimize energy consumption and reduces losses, but also allows one to participate in a more interconnected and efficient energy grid, increasing the sustainability of the urban electricity system, making easier the alignment of smart cities needs and energy transition.

4.4. Answer QA4

This is based on the papers showing that there are some, but few, initiatives to make use of urban waste for sustainable energy micro-generation. One of them is Van Leeuwen, Cappon, and Keesman [50], who present a renewable energy model developed to balance sustainable electricity generation and residential consumption in Amsterdam, simulating electrical self-sufficiency in an isolated system, without connections to the electric grid. The study focuses on biomass, omitting conventional storage options, and uses data with a temporal resolution of one hour, running the model on a daily basis to analyze the interseasonal contribution of biological waste. The selected technologies include photovoltaic solar panels, internal wind turbines, and Biomass Gasification Fuel Cells, organized into four modules to calculate the production of solar, wind, and bioelectricity, in addition to daily residential consumption.

The study by Chrispim, Schol, and Nolasco [48] presents a strategy focused on the reuse of wastewater using microalgae, anaerobic digestion and co-digestion in treatment plants adapted to maximize biogas production. It addresses the challenges in biogas recovery, reviewing technologies that enhance its production and considering local conditions that influences implementation. It analyzes recent techniques, presenting examples in developing countries and suggesting strategies to facilitate energy recovery in megacities. The focus of the study is on analyzing the interactions between energy recovery and the local context to support public policies and promote energy sustainability in large cities.

Deng et al. [51] argue that third-generation biofuel production using algae is an economically promising alternative compared to other renewable sources. Algae, when cultivated in nutrient-rich environments, can accumulate nutrients and heavy metals from wastewater, making them a versatile option. By producing renewable biofuels such as biohydrogen, improving water quality, and due to their richness in carbohydrates, proteins, and vitamins, they can be used as food and raw material for animals. However, technical challenges in the cultivation and harvesting of algae hinder industrial-scale production.

The main contribution of the article by Nematian and Farzi [52] was to utilize a linear programming model for deterministic optimization; fuzzy linear programming is applied to six renewable energy sources and nuclear energy to meet different electrical demands. The model is validated through a case study in Iran, divided into eastern and western sections, with distinct energy potentials.

Wang et al. [53] demonstrates the capacity for waste treatment and energy recovery at the lowest economic and environmental cost with a platform, which is based on the NEXUS concept for energy, water and waste systems analyzed. Three categories of waste (wastewater, municipal solid waste, and agricultural waste) are tested for thermochemical and biological treatment. To demonstrate this, a case study was conducted in Ghana, in sub-Saharan Africa, where the biogas generated from waste treatment stands out as a promising source of renewable energy. Furthermore, simulations with optimization models offer new perspectives for designing sustainable value chains, emphasizing the analysis and integration of the system.

Finally, Arteconi et al. [30] investigate the potential energy savings of a detailed local energy policy. They analyze initiatives in the energy sector to increase efficiency and reduce carbon emissions, based on energy planning for five urban areas in Italy with about fifty thousand inhabitants. Various initiatives were considered, including combined heat and power generation, electricity from renewable sources, thermal insulation of buildings, and micro-combined heat and power in the residential sector. The study evaluates primary energy reduction and greenhouse gas (GHG) emissions, along with a feasibility analysis for investment profitability. It highlights the public sector for its role in leading change and reducing administrative expenses. The results presented indicate that local policies significantly contribute to emission reduction targets.

4.5. Answer QA5

Microgeneration solutions are usually limited to the most frequently used and predominant energy sources in urban environments, such as solar, wind and biomass energy. These solutions often suggest various ways of combining these sources, as illustrated by their application in island scenarios. The use of these energy sources is particularly common in urban settings due to their application and the availability of resources. Another point noted to help ensure that generation takes place effectively was to consider the scale of these sources in the context of urban environments.

Regarding the articles, we identified that Adil and Ko [36] made an interdisciplinary analysis of the co-evolving technical and social dynamics of energy technologies through a critical review. In this work, he evaluated the points to bring about systemic and paradigmatic change in local energy infrastructure, since the impact of physical urban forms on energy consumption efficiency was being considered, ignoring how the dynamics of new energy technologies and the associated social responses. Although no direct practical effects were observed, the study highlights key areas where energy infrastructure could be optimized, improving efficiency and promoting the integration of renewable technologies. These changes could bring long-term benefits, such as reducing energy consumption, highlighting new sources of clean energy and improving social acceptance of new energy systems.

The study by Arteconi et al. [30] provides an overview of energy policies that can include the use of municipal waste as one of many renewable energy sources. While it does not yield direct practical results, the work develops widely applicable criteria for assessing the contribution of local energy policies to reducing greenhouse gas (GHG) emissions, and suggests that these policies could bring substantial benefits, such as enhanced energy efficiency and resilience, reduced waste, and contributions to clean energy production. It also emphasizes the potential to replicate these strategies in other urban areas facing similar challenges related to waste management and energy supply, which could help lower GHG emissions and facilitate the shift toward renewable energy sources. While the study does not identify a specific location, its focus underscores the relevance of these approaches to a variety of urban contexts dealing with energy and waste issues.

In addition, the exploitation of less utilized sources, such as waste, can prove advantageous. Urban centers produce a substantial volume of waste, which is still little exploited for microgeneration purposes. Incorporating waste as a potential energy source in urban microgeneration could increase sustainability and resource efficiency.

4.6. Answer QA6

Urban spaces can contribute to the expansion of microgeneration by serving as energy sources and combining them with other energy sources. Waste can be a viable candidate for microgeneration due to the large quantities produced daily in urban centers that are not properly managed. In addition to recycling methods and the proper disposal of waste, which are addressed by the Brazilian National Solid Waste Policy and associated management, manufacturers, importers, distributors and, above all, consumers and producers, could use waste not only for microgeneration, but also for large-scale applicability and expansion.

In this sense, the article by Mena and Yang and Zacharis [61] proposes a new business model that considers multiple interested parties to develop a framework for the investment of third parties and a future flexible electricity market in community microgrids, it is made up of two stages: firstly, through the participation of investors who can operationalize these investments in systems made up of multiple sources of community energy, and secondly, with the participation of consumers, producers, and prosumers who can minimize the daily costs of the systems, maximizing the benefits for the stakeholders. In this way, a proposal has been identified that can help contribute to the expansion of the use of microgeneration. However, we have identified that before adopting any action, some care should be taken before implementing it in this context.

4.7. Assessing the Viability and Challenges of Renewable Energy Technologies in Urban Environments

The literature identifies three main sources that discuss both the technical feasibility and practical challenges of implementing urban renewable energy projects. Solar power stands out as a well-established technology with multiple suppliers, making it an appealing option for urban areas, due to its quick scalability and adaptability. Solar installations can be effectively integrated into diverse urban spaces, such as rooftops, parking lots, and stadiums, providing flexibility in location and seamless integration with existing infrastructure. However, practical challenges include potential efficiency losses caused by shading, limited space, and variations in sunlight throughout the day and year. Additionally, there are concerns about equipment lifecycle, the pace of technological obsolescence, and the complexities of performing maintenance while ensuring consistent efficiency.

Wind energy is gaining traction in urban areas through mini-turbines and micro-wind generators, specifically designed to suit the unique challenges of these environments. Some of these smaller-scale turbines have already been commercialized, and are being installed in diverse urban locations such as rooftops, open spaces, and other areas where traditional, large-scale turbines would not be feasible. These turbines offer the advantage of generating renewable energy in areas with limited space or where larger turbines could disrupt the urban landscape. Nevertheless, their implementation is not without challenges. The mechanical vibrations generated by the turbines can lead to wear and tear on surrounding buildings and structures, posing potential long-term maintenance issues. Additionally, concerns related to noise pollution, visual impact, and disruption to local wildlife, particularly birds and bats, have been raised. The aesthetic impact of wind turbines can also be a significant issue in areas with dense urban development or where tourism is a key economic driver, as their presence might be deemed undesirable or intrusive. Despite these obstacles, mini-turbines offer an intriguing solution for urban energy generation, but careful consideration of these factors is essential to their successful integration.

Biomass also offers opportunities and challenges in urban environments. One possible use could be to use the biomass generated in urban areas to generate gas to meet their energy demand. One possibility identified is the use of gas boilers that run on methane produced from landfill waste. Another option is to install boilers on the outskirts of urban areas to produce energy. However, biomass in urban areas faces unique challenges, particularly in storage. Urban spaces, especially those with limited land or poorly planned infrastructure, may struggle to find suitable locations for biomass storage without creating hazards or inefficiencies. Moreover, when using biomass in urban areas some challenges have been identified mainly when it involves the storage, handling and management of biomass, as there are some associated risks. Among the events involving waste management, we highlight that biomass collection often occurs intermittently, as well as public health concerns such as the spread of diseases, which can be exacerbated by poorly managed waste.

In addition to technical feasibility, practical challenges must be addressed to implement these technologies effectively. For example, solar panels can require a significant initial investment and long payback periods, which can prevent their wide adoption in economically diverse urban areas. Biomass systems face challenges related to how it is collected, processed, and stored safely in urban environments, as well as logistical challenges and health risks. Moreover, integrating these technologies into existing urban infrastructure requires careful planning to ensure compatibility with local power grids, building codes, and regulatory standards. Another challenge is the intermittency of renewable energy sources, such as solar and wind, which may necessitate energy storage solutions to ensure a continuous power supply during periods without sunlight or wind. Addressing these challenges will require innovative approaches, such as hybrid systems that combine different renewable sources, along with energy storage solutions to mitigate intermittency and improve reliability.

4.8. Gaps in the Systematic Literature Review

Gaps have been identified in the literature concerning the integration of microgeneration technologies in urban spaces, particularly in addressing intermittency and energy management challenges. Intermittency, caused by the variable nature of renewable energy sources such as solar and wind, has been recognized as a significant barrier to ensuring a reliable and consistent energy supply in urban environments. Although hybrid systems combining different renewable sources can mitigate some of these issues, the papers does not discuss that, nor monitoring of these hybrid configurations of renewable sources. The effective monitoring of energy output and system reliability has been highlighted as strategic, but is insufficiently explored. Similarly, the topic of energy sizing has not been adequately addressed, especially regarding regulation, control, and the management of new installations. The need for monitoring to prevent accidents, control prosumer activities, and ensure safe energy production has been acknowledged, yet gaps remain in the supervision of independent generation systems. Concerns have also been raised about the possibility of Jevons’ paradox [62], where improved energy efficiency may paradoxically lead to increased energy consumption, undermining sustainability efforts.

In the area of solid waste management, gaps in addressing the life cycle of renewable energy technologies, particularly solar panels, have been identified. As the use of solar panels in urban areas increases, concerns about their eventual disposal and the potential accumulation of waste in landfills has been raised. Limited discussion has been found in the literature regarding the environmental impacts of solar panel disposal, the need for recycling policies, and the exploration of new waste management strategies. Furthermore, while decarbonization efforts for cities are gaining attention, the development of policy frameworks to achieve net-zero emissions in urban areas have been found lacking. Insufficient focus has been placed on urban decarbonization strategies that align with Sustainable Development Goals (SDGs) 7 and 11. These gaps underscore the need for comprehensive regulatory measures, monitoring systems, and waste management strategies to fully harness the potential of renewable microgeneration in achieving urban sustainability goals.

To summarize this stage, we present a graphic outline in which the representation of research on renewable energy microgeneration in urban planning is based on a literature review. The intersections between urban planning and renewable energy sources are emphasized by intensity, while gaps indicate topics not addressed in the review; Figure 4.

5. Conclusions

The study revealed that discussions on policy, energy security, and future scenario projections were focal points, with a particular emphasis on the development of scenarios related to solar energy generation. In contrast, discussions on wind energy and biomass within the context of urban planning were scarce or non-existent. From a qualitative perspective, gaps should be highlighted, such as the intermittency of primary energy sources, the lifecycle of devices such as solar panels, the scaling of energy production by prosumers, and strategies to promote carbon neutrality goals in urban areas. These issues should be more extensively addressed within the framework of urban planning.

Moreover, robust regulatory frameworks and monitoring systems are essential for effectively managing prosumers and ensuring equitable energy distribution. Collaboration between academia and society should also be encouraged, potentially through committees involving members of the scientific community and industry leaders. Additionally, lifecycle management and recycling of renewable technologies must be prioritized to minimize environmental impacts, supporting the transition to net-zero emissions and fostering a sustainable urban energy landscape.

In conclusion, we propose that fostering collaboration between academia, industry, and urban planners is necessary to accelerate the development and implementation of renewable energy sources and innovations in urban contexts. Future research should focus on a deeper exploration of the technical feasibility and additional challenges associated with achieving net-zero carbon emissions in urban areas.