Renewable Energy Generation Technologies for Decarbonizing Urban Vertical Buildings: A Path towards Net Zero

Abstract

Greenhouse gas (GHG) emissions, especially CO₂, represent a global concern. Among those responsible for CO₂ emissions, buildings stand out due to the consumption of energy from fossil fuels. In this sense, initiatives for the decarbonization of buildings and construction tends to contribute to the achievement of the target defined in the Paris Agreement of limiting the increase in global temperature to 1.5 degrees Celsius above pre-industrial levels, as well as in achieving the Sustainable Development Goals (SDG) and of the Triple Bottom Line (TBL). This article aimed to identify renewable energy generation technologies that can be applied in urban vertical constructions, contributing to the reduction of carbon emissions in the atmosphere. To this end, the following methodology was adopted: a survey of the Conferences of the Parties on climate change; identification of European Union Legislative Directives for the decarbonization of buildings; and a literature review to identify research that deals with renewable energy generation technologies that can be adopted in buildings. The results indicated that there seems to be a correlation between the growth in the number of articles that deal with the topic of decarbonizing buildings and the increase in world concerns about global warming. A hybrid microgrid proposal, combining different sources of renewable energy such as solar photovoltaic, wind, biomass, micro-hydroelectric, and others for vertical buildings with more than five floors, is presented as viable to achieve zero emissions in these buildings, contributing to future research, that can carry out quantitative analyses and feasibility studies, as well as for experiments and applications in existing buildings and the projects of new vertical constructions.

1. Introduction

The speed and impact of climate change are a global concern, as they pose serious risks to life on planet Earth. Among the causes of such changes, the emission of greenhouse gases (GHG) stands out, such as CO₂, responsible for global warming. Thus, the topic has been addressed over the years in national and international forums, the most representative being the United Nations Conference on Climate Change, which has resulted in agreements to try and limit global warming. In this sense, the Paris Agreement brought the need to seek efforts to limit the increase in temperature to 1.5 degrees Celsius above pre-industrial levels [1].

In this context, the growth of cities brings with it an increase in the demand for buildings and, consequently, a greater consumption of energy, which if it comes from non-renewable sources, contributes to the generation of CO₂. According to Zarco-Soto et al. (2021) [2], more than half of the world’s population lives in cities, and in some places, this number is even higher, such as in Europe. In 2021, buildings and the construction industry accounted for about 37 percent of global [3] CO₂ emissions.

Thus, the challenges for achieving decarbonization and net zero carbon emissions in urban areas are great. This emphasizes the need for an integrated approach to implementing renewable energy projects that consider not only technical aspects but also social, economic, and environmental aspects [4].

Among the possible solutions, the use of Nature-based Solutions (NBS) stands out, which involves multiple measures based on land use management options that consider the restoration, protection, and sustainable management of ecosystems [5]. As indicated by Makvandi et al. (2023) [6], the growth of urban areas generates changes in land use and land cover, as well as heat islands, due to reduced natural ventilation, increased urban heat, and air pollution problems. To mitigate these impacts, strategies have been proposed, such as the growth of urban green space with shading and blue spaces (ponds, rivers, swamps) which have the potential to absorb heat. Anderson et al. (2022) [7], in turn, study the use of green infrastructure based on nature in urban areas, from four areas of application: green roofs, green walls, urban vegetation and forestry, and systems of urban agriculture, to reduce the impact of atmospheric warming, among other benefits. It should be noted that the NBS represents one of the possible initiatives in pursuit of decarbonization and can work in parallel with other measures, such as encouraging the use of renewable technologies.

In addition, recent research shows the use of Artificial Intelligence (AI) applied in Intelligent Systems to forecast renewable energy production to optimize proposed projects, in which Elsheikh et al. [8] and Al-qaness et al. [9] use, respectively, the Artificial Neural Network (ANN) applied to solar energy and wind energy.

Furthermore, Alhawsawi et al. [10] presents a comprehensive theoretical modeling and performance analysis of a solar dish/Stirling-powered single effect distillation system (SDSPSEDS) for the combined tri-production of electricity, heat, and freshwater, thus proving that the hybrid SDSPSEDS is an efficient system to produce energy and water in rural areas without running water or electricity. There is also a review article, presented by Elsheikh [11], which discussed the applications of bistable morphing composites in addition to dealing with applications of artificial intelligence techniques to optimize the design of bitable structures and predict their response under different actuation schemes.

As noted in the 2022 Global Status Report for Buildings and Construction [3], the COVID-2019 pandemic has resulted in a drop in demand for buildings as well as workplace closures due to lockdowns to contain the spread of the virus, resulting in a drop in CO₂ emissions. In 2021, activities in the civil construction sector returned to pre-pandemic levels, energy consumption in buildings grew with the return to face-to-face activities, and in emerging economies, there was an increase in the use of fossil fuels in buildings. As a result, CO₂ emissions from building operations reached an all-time high of around 10 GtCO₂ (billion tons of CO₂) [3].

In this way, the implementation of actions with the objective of making buildings capable of producing and consuming renewable energy, becoming a prosumer, can contribute to their decarbonization, as well as show adherence to the Sustainable Development Goals (SDG), in particular, objectives 7, 9, 11, 12, and 13 and their targets, as summarized in the

Table 1. Adherence to the Sustainable Development Goals (SDG).

SDGs	Adherence
7. Affordable and clean energy - Ensure access to affordable, reliable, sustainable, and modern energy for all [12]	Contribute to increasing the share of renewable energies in the global energy matrix (target 7.2).
9. Industry, innovation, and infrastructure - Build resilient infrastructure, promote inclusive and sustainable industrialization, and foster innovation [12]	Contribute to the development of quality, reliable, sustainable, and resilient infrastructure (target 9.1).
11. Sustainable Cities and Communities - Make cities and human settlements inclusive, safe, resilient, and sustainable [12]	Contribute to the reduction of the adverse per capita environmental impact of cities, including by paying special attention to air quality (target 11.6).
12. Responsible consumption and production - Ensure sustainable consumption and production patterns [12]	Contribute to the achievement of sustainable management of natural resources (target 12.2).
13. Climate action – Take urgent action to combat climate change and its impacts [12]	Contribute to the integration of climate change measures into national policies, strategies, and planning (target 13.2).

Source: Authors, 2023.

.

This work aims to identify renewable energy generation technologies that can be applied in vertical constructions (e.g., buildings with more than five floors), contributing to the reduction of carbon emissions in the atmosphere. With this, it is intended to answer the following research question: how to contribute to the reduction of carbon emissions in the atmosphere with the production of renewable energy generated from different sources in vertical urban constructions.

Therefore, in addition to this introduction, the article is organized as follows: Section 2 presents the proposed methodology adopted to achieve the proposed objective; Section 3 discusses the results obtained with the application of the methodology; Section 4 brings the discussion; and Section 5 presents the conclusions about the obtained findings.

2. Materials and Methods

Society has been concerned about climate issues and how humanity can contribute to reducing the emission of greenhouse gases (GHG). Thus, to answer the research question, three steps were adopted, according to the methodological scheme shown in Figure 1. Initially, a survey was carried out of world events promoted by the United Nations, whose main topic under discussion was climate change in the world. Such events resulted in agreements between the countries involved for carrying out short and medium-term actions to reduce the environmental impacts caused by the world’s population. Then, specific European Union (EU) legislative initiatives were identified to encourage the transition to zero emissions in buildings.

Following this, a literature review was carried out in order to locate research that deals with renewable energy generation technologies applicable to urban buildings. Finally, to assist in the ideation and construction of a theoretical proposal, it was verified which of these selected studies had technologies that adhered to the theme proposed by this work. This way, this paper was supported by critical reviews [13] to provide an interpretive analysis of the key features of renewable energy, prosumers, and microgeneration technologies.

Bibliographic Search

In order to identify renewable energy generation technologies that allow their use in urban vertical buildings, this was searched for in March 2023, through a Brazilian government tool, the CAPES portal (https://www.periodicos.capes.gov.br/, accessed on 15 February 2023), which covers approximately 122 databases (such as Web of Science, Cinahl, Scopus, and Pubmed), with the search string building AND (prosumer OR (“renewable energy” AND (solar OR hydro OR wind OR sewage))) AND (“carbon credit” OR decarbonization) for the period 2013 to 2023, for peer-reviewed articles. An amount of 115 (one hundred and fifteen) publications were located, from which those whose impact factor of the journal was greater than zero were selected, thus totaling 49 (forty-nine) publications, which were distributed in the timeline according to

Table 2. Distribution of publications by year.

Publication Year	Total	Total Selected	Publication Year	Total	Total Selected
2014	1	1	2015	0	0
2016	2	2	2017	5	4
2018	3	2	2019	4	1
2020	15	4	2021	30	8
2022	44	23	2023	11	4

Source: Authors, 2023.

.

Then, the selected articles [14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62] were analyzed to obtain information on the technologies used in the research that are applicable in urban vertical buildings, and that can, in a combined way, be used to make this type of building self-sufficient in energy, making it a prosumer, that is, a consumer of renewable energy that produces the energy needed for its use [63].

3. Results

In 1995, the first Conference of the Parties—United Nations on Climate Change (COP’s) [64]—was held in Berlin/Germany, and since then, participating countries have tried to annually establish more energetic actions in relation to the reduction of greenhouse gas emissions. Below, in

Table 3. Milestones of the United Nations Climate Change Conferences (COP’s).

Year	Name	Local	Definitions
1995	COP 1	Berlin, Germany	First conference, in which it tried to establish a consensus among the participating countries to take more energetic actions in relation to the reduction of the emission of greenhouse gases.
1997	COP 3	Kyoto, Japan	Defined the Kyoto Protocol, which established targets for reducing greenhouse gas emissions in relation to the year 1990 that should be achieved between 2008 and 2012 for some countries; for example: (i) for most industrialized countries and some Central European economies: 6-8% reduction; (ii) for the European Union and Japan: 7 to 8% reduction; and (iii) for the United States: 7% reduction.
2001	COP 6-2	Bonn, Germany	The United States rejected the Kyoto Protocol and attended the COP as an observer. Ways of generating carbon credits were defined.
2005	COP 11	Montreal, Canada	It marked the entry into force of the Kyoto Protocol and defined an agreement to extend the Protocol after 2012 with greater targets for reducing greenhouse gas emissions.
2012	COP 18	Doha, Qatar	A second period, from 2012 to 2020, was proposed for the Kyoto Protocol, defining new limits for global CO2 emissions.
2015	COP 21	Paris, France	Defined the Paris Agreement in which it establishes measures to reduce climate change from 2020.
2021	COP 26	Glasgow, UK	The Paris rulebook was completed, making the Paris Agreement operational. A limit of 1.5 degrees of average temperature increase was defined as a goal for the decade.

Source: Authors, 2023.

, some milestones and definitions that occurred over the years are presented.

As indicated in Table 3 at COP 26, the Paris Agreement became operational, as well as the 1.5-degree average temperature increase limit that had been agreed upon in 2015, set as a goal for the decade, which has led the signatory nations to adopt more energetic measures to reduce CO₂ emissions, including those aimed at zero emissions in buildings.

In addition, the European Union has defined, through legislative directives, changes in legislation to increase the use of renewable energies in buildings. Some of these directives, which were extracted from the European Union law portal [65], are highlighted in

Table 4. Directive of the European Parliament and of the Council on the use of renewable energies in buildings.

Directive	Alias	Objective
Directive 2002/91/EC of the European Parliament and of the Council of 16 December 2002 on the energy performance of buildings.	EU 2002	Promote the improvement of the energy performance of buildings in the Community, taking into account external climatic conditions and local conditions, as well as requirements in terms of indoor climate and economic profitability [66].
Directive 2010/31/EU of the European Parliament and of the Council of 19 May 2010 on the energy performance of buildings (recast).	EU 2010	Promote the improvement of the energy performance of buildings in the Union, taking into account external climatic conditions and local conditions, as well as requirements in terms of indoor climate and cost-effectiveness [67].
Directive (EU) 2018/844 of the European Parliament and of the Council of 30 May 2018 amending Directive 2010/31/EU on the energy performance of buildings and Directive 2012/27/EU on energy efficiency.	EU 2018	Develop a sustainable, competitive, safe, and decarbonized energy system. The Energy Union and the 2030 Energy and Climate Action Framework set out ambitious Union commitments to further reduce greenhouse gas emissions (by at least 40% by 2030 compared to 1990 levels), increase the share of renewable energy consumption, achieve energy savings in line with the level of ambitions of the Union, and increase Europe’s energy security, competitiveness, and sustainability [68].

Source: Authors, 2023.

and together with the agreements listed in Table 3, a timeline is consolidated as is shown in Figure 2.

According to Uche et al. (2022) [69], it is intended that from 2020, new buildings (residential and commercial) in Europe will have almost zero energy, and new rules will try to promote the decarbonization of the construction sector by 2050, which requires the implementation of energy transition strategies. A new Directive is being prepared with the aim of limiting the use of fossil fuels for heating and a new energy classification for buildings must be updated according to the age of the building.

Corti et al. (2020) [70], in turn, points out that the review carried out in 2018 (Directive 2018/844) introduced changes with the aim of accelerating the profitable renovation of existing buildings, with the vision of a decarbonized building stock by 2050 and the mobilization of investments.

Figure 2 illustrates, in a timeline, the main milestones of the Conference of the Parties—United Nations on Climate Change (COP’s) and the evolution of legislative directives of the European Union (EU) to date.

This way, following the methodology described in Section 2, it was verified that, as shown in Table 2, there was an increase in the number of publications on the subject from the year 2020 onwards. Consonance with the advance of global concerns about climate change, evidenced in Table 3, and initiatives seeking to decarbonize buildings, such as the European Union directives, are detailed in Table 4. Such findings were consolidated in the timeline shown in Figure 3.

In order to adhere to the scope of analysis of the theme proposed in this work, of the 49 (forty-nine) articles consulted (

Table 5. Information extracted from selected publications. Legend: Biomass; Green Hydrogen; Hydro; Solar; Wind.

Title	Informations	Adherent	Technology
A review of approaches to low-carbon transition of high-rise residential buildings in China.	Review article that investigated efforts to transition low-carbon buildings in China, highlighting potential solutions to increase energy efficiency, self-sufficiency, and system resilience.	Yes	S  W
Assessment of the renewable energy generation towards net-zero energy buildings: A review.	The article presented a review of issues related to buildings with zero energy consumption (NZEB), bringing the diagram that indicates that NZEBs reduce energy use through two strategies: reducing the need for energy use in buildings by using energy efficiency measures and adopting renewable energy technologies to meet remaining energy needs.	Yes	B  S  W
Assessment of the visual impact of offshore wind farms.	The article evaluated the visual impact caused by offshore wind farms (OWFs) and the acceptability of these parks by the community impacted by their implementation.	No	-
Challenges and opportunities in decarbonizing the U.S. energy system.	The article assessed the opportunities and challenges that the United States will have to achieve a 100% carbon-free power generation system in 2035 and an economy with zero net greenhouse gas emissions in 2050.	No	-
Climate change adaptation with energy resilience in energy districts—A state-of-the-art review.	This article reviewed energy resilience in multi-energy district systems in relation to reliability, robustness, and flexibility, indicating, among other points, compensation solutions during the planning, design, and energy operation phases in low-impact events and high-probability, and high-impact, low-probability events.	No	-
Contestation, contingency, and justice in the Nordic low-carbon energy transition.	This article discusses the energy transition of the five Nordic countries (Denmark, Finland, Sweden, Norway, and Iceland) to reach the “fossil free” target by 2050.	No	-
Decarbonization and its discontents: a critical energy justice perspective on four low-carbon transitions.	This research examined the normative perspective for four low-carbon transition policies in Europe with a critical view of fairness (distribution, procedural, global, and vulnerability).	No	-
Decarbonizing power systems: A critical review of the role of energy storage.	This article documented a system-level review of over 100 studies to highlight key findings about the role of Energy Storage Systems (ESSs) and highlight research gaps. It was found that (i) most decarbonization studies do not consider ambitious emission targets; (ii) carbon reduction strongly depends on local contexts; and (iii) from a technological point of view, duration and capital cost are the main factors in assessing the viability of each ESS technology.	No	-
Decarbonizing residential building energy: A cost-effective approach.	This article evaluated, in 2016, the microeconomic principles of energy decarbonization solutions with the use of renewable energy for residential buildings, bringing light to the effective cost of decarbonization.	Yes	S
Decarbonizing rural residential buildings in cold climates: A techno-economic analysis of heating electrification.	This article discussed the economic viability of using renewable electrification for heating systems in rural homes in the United States. The research concluded that electrification is an economically viable decarbonization method for cold climates.	Yes	S
Design of an exhaust air energy recovery wind turbine generator for energy conservation in commercial buildings.	The research proposed the use of wind turbines to generate renewable energy from the wind flow generated by the cooling tower or exhaust air in commercial buildings. The study proved to be promising and applicable because the discharged air is strong, consistent, and predictable, in addition to having wide applicability in the market.	Yes	W
Design optimization of a novel cryo-polygeneration demonstrator developed in Singapore—Techno-economic feasibility study for a cooling dominated tropical climate.	The article discusses a case study with real application, in an urban district of Singapore, of a decentralized polygeneration system to solve the ambient cooling demand in a tropical location that requires the application of this solution throughout the year.	No	-
Determining cost-optimal approaches for managing excess renewable electricity in decarbonized electricity systems.	This study investigated which technologies should be used to capture the excess production of renewable energy, verifying how much of this energy could remain unused in order to minimize the cost of a zero carbon electricity system, in addition to seeking the characteristics that determine the effectiveness for the reduction of this cost.	No	-
Electricity Generation Through Water Supply Pipes in High Rise Buildings.	The study was inspired by the gravitational force that drives water energy, which can be explored and extracted for use by means of mini-hydro turbines. In tall buildings, suspended tanks are a precious source of water energy due to the high water head. This piped water has enough energy to drive a micro hydroelectric turbine, which can produce electricity. The reason for the study is to develop a cheaper way to generate this electricity.	Yes	H
Energy infrastructure transitions with PV and EV combined systems using techno-economic analyses for decarbonization in cities.	This study investigated the potential of applying the Solar Electric Vehicle (SolarEV) concept in the city with five cases in Korea (four cities and one province), evaluating the energy, economic, and environmental performances. The results indicated that the potential for SolarEV city development in residential buildings is high.	No	-
Energy pile-based ground source heat pump system with seasonal solar energy storage.	This study considered a solution for residential high-rise domestic hot water heating/cooling and preheating demands considering different soil conditions and climate conditions dominated by heating across China.	Yes	S
Evaluating business models for microgrids: Interactions of technology and policy.	The article starts from the issue of decentralization of the electrical grid, a concern of policy makers, in which a business model for a decentralization mode—microgrids—is analyzed and the savings for a self-supply of electricity and thermal energy are quantified. A tool based on the Distributed Energy Resources Customer Adoption Model (DER-CAM) modeling structure is adopted, being applied in Southern California to three types of microgrids. The article concludes that in all microgrids, natural gas generators supply most of the local electrical and thermal energy, in relation to the use of renewable energies, especially due to the attractive price of natural gas. However, policy makers can act, on the one hand, by stimulating the expansion of the deployment of microgrids aimed at reducing the emission of greenhouse gases; on the other hand, they can discover that the stimulus for the use of Distributed Energy Resources (DER) of zero emission can confront the prevalence of microgrids powered by natural gas (which is not zero carbon), making it necessary to think of a policy that stimulates micro-resources and DER, and affects the price of carbon.	No	-
Evaluating metal constraints for photovoltaics: Perspectives from China’s PV development	The article estimates the future demand for metal from the Chinese solar photovoltaic industry, which is intensive in ore, in view of the trends in the photovoltaic industry regarding the demand for decarbonization of the mix and energy by 2050.	No	-
Exploring the link between the EU emissions trading system and net-zero emission neighbourhoods	The article starts from the context of the EU emissions trading system, investigating how the integrated development of the European heating and electricity system is influenced by net zero emission neighborhoods that offset their own carbon emissions with local renewable energy.	No	-
Feasibility study of China’s electric power sector transition to zero emissions by 2050.	The study explored the feasibility of China achieving, in 2050, the transition to zero emissions in the electricity sector. The simulation used solar and wind energy as primary sources and the simulation results indicated that it would be possible to achieve this goal by including a set of balancing technologies replacing the need for battery storage.	No	-
Flexibility index and decreasing the costs in energy systems with high share of renewable energy.	The study uses a modeling that generates different scenarios in order to show how each energy use flexibility option influences the economically viable generation capabilities of renewable energy sources, storage technologies, and demand responses to reach a certain energy share of renewable energy in the total energy consumed.	No	-
Heat and electric vehicle flexibility in the European power system: A case study of Norwegian energy communities.	The article studies how the short-term interaction between buildings (heating), electric vehicles, and the central energy system affects the long-term energy decarbonization path. It uses a stochastic linear programming model for a Norwegian case study. It tests the hypothesis that it is more economical to decarbonize when the central power system is coordinated with building heating systems and electric vehicle charging. It concludes that for the decarbonization plans of the European energy sector until 2060, the growth in the supply of non-electric heat for buildings in Norway is attractive.	No	-
How can green building certification systems cope with the era of climate emergency and pandemics?	This article discusses the metrics used to rank a green building, as well as sheds light on adding new criteria to existing green building certification programs. The satisfactory analyses in this article were not pleased that the green energy input in a so-called green building may not be so green depending on where and how this green energy is consumed in the building, further assessing that solutions against global warming fall short of the Paris agreement targets by almost 45% in terms of decarbonization efforts.	No	-
Hydrogen production from the WindFloat Atlantic offshore wind farm: A techno-economic analysis.	The article studied the feasibility of producing green hydrogen from surplus wind energy generated due to the incompatibility between the instant supply of this energy and its demand. It adopts the WindFloat Atlantic offshore wind farm and the electricity market in Portugal as a case study.	No	-
Impact of sector coupling on the market value of renewable energies—A model-based scenario analysis.	The article considers that flexibility in the European electricity sector with greater interconnection with other energy sources such as renewables, leading to a coupling in the sector, can contribute to a low carbon economy. It applies a model, analyzing three flexibility options: intelligent charging of electric vehicles, decentralized heat pumps in buildings, and multivalent district heating networks.	No	-
Implementation of a solar-biomass system for multi-family houses: Towards 100% renewable energy utilization.	The study evaluates the decarbonisation potential of a renewable energy system based on solar thermal collectors, a biomass boiler, and an innovative hybrid heat pump concept to meet the heating, cooling, and domestic hot water needs of residential buildings. The study is applied in three cities (Madrid, Berlin, and Helsinki), which represent different European climates.	Yes	B  S
Inefficient Building Electrification Will Require Massive Buildout of Renewable Energy and Seasonal Energy Storage.	The study evaluates the degree of seasonality in the consumption of buildings in the United States and how this seasonality should be considered in the electrification of these buildings by renewable energy.	Yes	S  W
Measurements and analysis of a solar-assisted city bus with a diesel engine.	This work investigated a new attempt to develop a hybrid photovoltaic solar electric system for electricity production in a heavy-duty diesel-powered city bus. It has been observed that nearly 21% of the total electricity demand of the city bus is provided by solar hybrid photovoltaic systems, which can save the annual diesel consumption 630 L and also reduce 1.6 tons of greenhouse gas emissions. It was then concluded that photovoltaic technology suitable for automotive applications would improve the world’s fuel economy and could also produce a clean environment in the near future.	No	-
Micro hydro power generation from water supply system in high rise buildings using pump as turbines.	The article investigates the feasibility and performance of pumps (turbine)—PAT—used in a water supply system for electricity generation. In the research process, a PAT was selected by empirical equations for a typical tall building. After selection, CFD simulations and laboratory tests were performed to study the performance of the selected PAT. Simulated and measured results show that the selected PAT is viable for power generation and water load reduction.	Yes	H
Moving the system boundaries in decarbonization of large islands.	The article presents an energy planning model through the creation of different decarbonization scenarios for island systems. It adopts the island of Sardinia in Italy as a case study.	No	-
Optimization of hydrogen-producing sustainable island microgrids.	The paper works with the development of clean, powered, and driven hybrid microgrids to span hydrogen and electricity loads across three energy stressed islands in eastern Canada. Elements of solar, wind, fuel cells, fuel, and electricity storage are incorporated.	No	-
Performance assessment of a solar-assisted absorption-compression system for both heating and cooling.	The paper proposes a solar-assisted absorption compression system for heating and cooling residential buildings. Four operating modes are proposed: solar assisted heating, solar assisted cooling, vapor compression heating, and vapor compression cooling.	No	-
Positive energy district stakeholder perceptions and measures for energy vulnerability mitigation.	Starting from the assertion that in order to promote urban decarbonization, by 2025, 100 Positive Energy Districts (PEDs) will be created in Europe, i.e., urban residential areas with high energy efficiency, powered entirely by renewable sources, the article seeks to contribute with the debate about energy vulnerability in urban areas of European smart cities, focusing on the perceptions of key stakeholders.	No	-
Power-to-gas: Decarbonization of the European electricity system with synthetic methane.	The study analyzes how combinations of carbon pricing and synthetic natural gas in the form of methane, from green energy to gas conversions, followed by methanation using captured CO2 emissions, can provide transitions towards the deep decarbonization of energy systems.	No	-
Power-to-heat for renewable energy integration: A review of technologies, modeling approaches, and flexibility potentials.	The article carries out a literature review in order to evaluate a greater integration of renewable energies for heat generation (residential heating), in search of a reduction in the use of fossil fuels and an increase in decarbonization.	No	-
Pricing the deep peak regulation service of coal-fired power plants to promote renewable energy integration.	This research proposed a pricing mechanism for the deep peak regulation service (DPR) and proved that this mechanism meets the requirements of compatibility of incentives and individual rationality. For this, a unit compromise case based on the actual generation structure and load curves of a southern Chinese province was constructed to quantitatively study the mechanism.	No	-
Profitability of commercial and industrial photovoltaics and battery projects in South-East-Asia.	The article develops a model to carry out technical–economic evaluations of photovoltaic (solar energy) and battery storage projects. The study is carried out in three developing countries in Southeast Asia focusing on three different sectors (Textiles, Consumer Goods, and Electronics).	No	-
Rapid rise of decarbonization potentials of photovoltaics plus electric vehicles in residential houses over commercial districts.	In this study, technical–economic analyzes were performed on rooftop PV systems integrated with stand-alone batteries or EVs in residential and commercial districts in Japan from 2020 to 2040. It was found that rooftop PV systems in 2020 are already competitive with existing energy in these systems. “Photovoltaic (PV) + electric vehicle (EV)” systems in homes have been found to rapidly increase their economic advantage over commercial districts due to the larger roof space and the greater number of available vehicles, also showing that power sharing energy has significantly improved the potential for decarbonisation.	No	-
Sites exploring prioritisation of offshore wind energy potential and mapping for wind farms installation: Iranian islands case studies.	In this paper, a time series method was designed, tested, and developed to better understand and manage the offshore wind (OW) potential and the mapping of the decision-making process of the Iranian islands. Furthermore, the time series method was applied to the energy source generated based on the OW speed used in the Iranian islands. Exploration results have shown that Iranian islands such as the Kharg, Siri, and Abu Musa islands have attractive Offshore Wind Power (OWE) potentials for Offshore Wind Turbine Installations (OWTGs).	No	-
Sources of opposition to renewable energy projects in the United States.	The article assesses the barriers to the development of public renewable energy supply projects in the USA, in order to better understand the obstacles to the decarbonization of the American economy.	No	-
State-of-the-art sustainable approaches for deeper decarbonization in Europe—An endowment to climate neutral vision.	The study analyzes effective decarbonisation strategies in the European context. For this purpose, initially, the influence of several factors such as population size, economic growth, energy intensity, emission intensity, innovation, accessibility, and time are considered in this context. It then presents a qualitative analysis considering decarbonization in the heating sector; proposes sustainable approaches and practices that promote a carbon sink in sectors such as construction, energy, industry, and transport; the roles of digitization in decarbonization are explored and their inherent challenges; and it also looks at various decarbonization policies that can guide government action to transition to a climate-neutral society.	Yes	B  G  S  W
The effects of CCUS combined with renewable energy penetration under the carbon peak by an SD-CGE model: Evidence from China.	The study builds a systems dynamics model to show the industrial and macro impacts of policies for the application of technology for capturing, using, and storing carbon, based on different scenarios, assessing the social, environmental, and economic effects. The case study is China.	No	-
The impact of policy actions and future energy prices on the cost-optimal development of the energy system in Norway and Sweden.	The study applies a stochastic model, considering the short-term uncertainty in electricity supply and the flexibility of hydroelectric reservoirs, to analyze the effects of policy actions on energy systems in Norway and Sweden, from a social welfare perspective.	No	-
The need for holistic enterprise control assessment methods for the future electricity grid.	This work reviewed existing trends in the evolution of the electrical network given the change caused by the incentive to decarbonization and consequent change in the energy generation infrastructure.	No	-
Ultrahigh-efficiency solar energy harvesting via a non-concentrating evacuated aerogel flat-plate solar collector.	This article studied the application of an airgel to improve the performance of the solar energy collector when the inlet temperature is greater than 120 ºC. A 20% performance improvement was verified in the collector prototype with the application of airgel, bringing important advances in research with a view to increasing decarbonization for residential buildings.	Yes	S
What makes them believe in the low-carbon energy transition? Exploring corporate perceptions of the credibility of climate policy mixes.	This article analyzed the credibility of climate policies as a factor in achieving the goals outlined by the Paris Agreement. The responses of 390 companies regarding the case of the German company Energiewende in 2014 were analyzed, using a linear regression model to detect the perception of companies about the credibility of energy policies.	No	-
Where is the most feasible, economical, and green wind energy? Evidence from high-resolution potential mapping in China.	This study estimated the feasibility of deploying wind farms in China, deployed on land or sea, to achieve the country’s planned decarbonization by 2030.	No	-
Winding down the wind power curtailment in China: What made the difference?	This article analyzed the impact of China’s energy transition because of the reduction in wind energy production over time, from 17% in 2016 to 4% in 2019.	No	-
Zero air pollution and zero carbon from all energy at low cost and without blackouts in variable weather throughout the U.S. with 100% wind-water-solar and storage.	The article analyzed the energy stability of 50 US states in the scenario of energy transition to 100% renewable energy, using wind, solar, and hydropower sources, in addition to the use of a storage battery of up to 4 h. The article also studied the impact of this energy transition on employment and energy consumption.	No	-

Source: Authors, 2023.

), 37 (thirty-seven) were discarded for not dealing with technologies for renewable energy generation with potential application in vertical buildings. In this way, it was verified that 12 (twelve) articles adhere to the proposal of the present work and are detailed in

Table 6. Existing technologies applicable in urban vertical buildings. The colors of the initial letters help to associate technologies (Table 6) and researched works (Table 5).

Technology	Papers	Authors
Biomass	3	Ahmed et al. [25], Madurai et al. [19] and Palomba et al. [36]
Green Hydrogen	1	Madurai et al. [19]
Hydro	2	Du et al. [62] and Suman et al. [61]
Solar	9	Ahmed et al. [25], Buonocore et al. [33], Gao et al. [51], Ma, Fan and Liu [56], Madurai et al. [19], Padovani et al. [26], Palomba et al. [36], Timmons et al. [28] and Wang et al. [38]
Wind	5	Ahmed et al. [25], Buonocore et al. [33], Chong et al. [35], Madurai et al. [19] and Wang et al. [38]

Source: Authors, 2023.

.

Based on these results, in the next section, we discuss the theoretical possibilities of the combined use of existing technologies.

4. Discussion

The analysis of the results obtained in this work indicates that concerns about climate change resulted in agreements between signatory countries of the Convention of the Parties (COP’s) to act on an emergency basis in view of the need to limit global warming to the levels defined in the Paris Agreement. This can be illustrated at COP 26 when the Paris Agreement became operational and adopted the target of limiting the average temperature increase to 1.5 degrees Celsius, a major challenge.

Faced with the representativeness of buildings and the construction industry in global CO₂ emissions, which represent about 37% of these emissions, the European Union promoted legislative directives with the aim of achieving zero emissions in buildings and decarbonizing the housing stock in a few decades. As already mentioned, such initiatives tend to contribute to the Sustainable Development Goals, as can be seen in Table 1.

In this scenario, the bibliographic survey carried out in this article indicated that there seems to be a correlation between the number of publications that deal with the decarbonization of buildings, the urgency of limiting global warming as agreed in the COP’s on climate change and the evolution of the European Union Directives for zero-emission in buildings. Figure 3 illustrates that in 2022, there was an increase in the number of publications with this theme compared to previous years. Table 6, in turn, indicates that of the 12 selected articles, 75% were published from the year 2020 onwards, and in 2018, there was a review of the European Union Directives and in 2021, the Paris Agreement became operational.

In this way, each technology highlighted in the previous section has characteristics, as detailed below, that can be theoretically used to jointly make vertical urban buildings producers/consumers (prosumers) of renewable energy.

• Biomass: Energy from biomass is usually obtained by burning biogas or solid biomass, which is a biological material derived from living organisms such as wood, agricultural waste, and dried manure [71];
• Green Hydrogen: Green Hydrogen is hydrogen produced from low-carbon or carbon-free energy sources [72];
• Hydro: Energy produced through the movement of a turbine caused by the passage of water [62];
• Solar: Energy produced by capturing solar radiation [36];
• Wind: Energy produced through the movement caused by the force of the wind, being recognized as one of the most abundant natural resources of electricity [73].

Due to their physical characteristics, vertical urban buildings have limited space to accommodate certain types of technology in isolation, such as a possible installation of solar panels on top of these buildings. In this way, building a hybrid microgrid combining such renewable technologies can prove to be viable and help society to reduce carbonization levels, in addition to achieving some sustainable development goals, as seen in the introduction. The theoretical proposal for the association of these technologies is diagrammed in Figure 4, whose strategies are detailed below:

• Solar panels installed on the roof of the building to capture existing solar radiation;
• Adapted mini wind turbines that can capture the force of the wind on top of buildings, as suggested by Liew et al. [73], to capture the wind generated by passing cars on a highway and discussed by Kumar and Prakash [74] that proposed a review paper to analyze micro wind turbines on high-rise buildings;
• Mini hydro turbines adapted to capture the force of the displacement of water (hot or cold) from the upper tank to the housing units;
• Bio digestion process with Biomass composed of food waste from housing units and the use of sewage treatment produced by the units;
• Water heating from the biodigester combustion process;
• Carrying out hydrolysis to generate green hydrogen from energy generated by the private power generation microgrid;
• Distribution of surplus energy produced for the Public Energy System.

Therefore, the practical use of these combined technologies can be feasible for existing buildings and planned for new constructions. As indicated in the EU Directives, the improvement of the energy performance of buildings depends on external climatic conditions and local conditions, as well as requirements in terms of indoor climate and profitability. In addition to these conditions, in existing buildings, decarbonization through the combined use of renewable sources will depend on the pre-existing structure, which may require greater or lesser investments. This difficulty can be eliminated in the case of new buildings, due to the possibility of including in their projects the requirements for the implementation of a hybrid microgrid. This path towards decarbonization will help achieve the SDG targets, create a broad network of prosumers, reduce energy costs, and improve the environment.

Through the mapping of actions, norms, and studies (Table 3, Table 4 and Table 5, respectively), the qualitative analysis of the theoretical proposal discussed by this research could contribute as a basis to help society in the construction and modernization of vertical urban buildings. In addition, they bring light to governments to think about tax incentives that allow society to improve business models, focusing on low carbon emissions and the use of clean energy, as suggested by recent research [37,58].

5. Conclusions

We believe that improving air quality and achieving energetic efficiency in vertical buildings are essential for reaching the Triple Bottom Line (TBL, which may be described as financial, social, and environmental initiatives for working together) and contributing to the 9th Sustainable Development Goal (e.g., SDG 9). Thus, one way to achieve this is by investing in sustainable infrastructure and innovative technologies.

In this way, initiatives to decarbonize buildings and constructions that were responsible in 2021 for approximately 37% of global CO₂ emissions may contribute to the development of resilient and sustainable infrastructures, as determined in target 9.1 of SDG 9. In addition, the production of renewable energy in vertical buildings, with the installation of infrastructure for photovoltaic solar energy generation, such as the canopy top, generating solar energy on top of buildings; wind energy; biomass energy; geothermal energy; mini hydroelectric; and others, makes it possible to act as a prosumer and reduce the amount spent on energy consumption for heating, cooling, lighting, and other applications.

Thus, to achieve the objective of identifying renewable energy generation technologies that can be applied in vertical constructions, this study mapped the state of the art in terms of innovative renewable energy generation technologies, performing an analysis of the potential application of these technologies in urban vertical buildings. For instance, modern microgrid technologies can help reduce consumption and carbon emissions, while vertical building designs can promote the efficient use of resources. In addition to the environmental benefits, implementing sustainable practices can also improve social equity and economic prosperity, which are crucial components of the TBL framework.

Furthermore, renewable energy-based microgrids can enable buildings in large urban centers to function as weather stations, allowing that the temperature, atmospheric pressure, humidity sensors, and other climate variables can be integrated into the microgrid control system, allowing weather data to be collected and used to predict and manage the building’s energy demand. By considering the specific weather conditions of the area where the building is located, it is possible to develop more efficient and resilient energy systems, as well as contribute to monitoring and predicting the weather in the city. This process could include computer modeling to understand the microclimate during extreme weather events [75,76,77].

The high concentration of individuals in large cities seems to be inevitable. Nevertheless, reducing carbon emissions in the atmosphere is mandatory by applying the production of renewable energy generated from different sources. By investing in sustainable infrastructure and adopting energy-efficient practices, businesses can contribute to the achievement of SDGs 9 and 11 while improving their TBL performance. Furthermore, prioritizing the social and environmental impacts of business operations can help create long-term value and foster positive relationships with stakeholders. Ultimately, achieving TBL and promoting sustainability requires a holistic approach that considers social, environmental, and financial considerations.

However, it is necessary to advance the studies and technical feasibility of technologies in buildings, aiming to effectively contribute to environmental sustainability, with the use of quantitative data to develop mathematical models applied to renewable energy systems, which was not achieved by this study, in view of scope limitations. In future perspectives, the creation of a laboratory for simulation and experimentation of micro production of renewable energies in vertical buildings is suggested, evaluating which technologies present the viability of joint application, including the study of other technologies not presented in this work, which can replace technologies from non-renewable sources and contribute to the reduction of carbon emissions into the atmosphere.