Energy Poverty and Its Indicators: A Multidimensional Framework from Literature

Abstract

People aim for thermal comfort inside their homes. However, this is not achievable for everyone due to several factors, such as low income, poor building envelope, expensive technology, and increased energy costs, thus leading to energy poverty. This work gathers studies regarding energy poverty and its indicators, identified by different authors and considering different regions, techno-economic, governmental, and political considerations. It was observed that renewable energy sources are a good investment in the long term but require a high initial investment. Government policy measures should be applied to mitigate the costs, especially given the increasing requirement for clean energy use in new buildings. There are still many barriers to overcoming energy poverty, and the variables for action are numerous. The best solution passes through the assessment of adequate technological solutions with economic incentives from the government for the most vulnerable individuals that should be identified by region and economic power. Energy poverty is a multidimensional problem that depends on individual characteristics such as households’ income, specific energy needs, and available technologies, as well as external factors such as energy prices, climatic conditions, and energy access. The majority of energy indicators are directly related to economic aspects, whereas social or environmental considerations are only indirectly accounted for.

1. Introduction

Energy poverty deeply affects the quality of life and, subsequently, the well-being of individuals. The concept of energy poverty is associated with three main aspects, i.e., the lack of thermal comfort in buildings, low family incomes, and high energy costs. Combined, all these aspects lead the inhabitants to prioritize their essential/basic needs over thermal comfort. Due to its multidimensionality, energy poverty requires the analysis of specific factors in different contexts [1].

Thermal comfort can be defined as the mental state of an individual expressing satisfaction with the surrounding thermal environment. Thermal comfort is determined through a subjective assessment, whereas a person wearing a normal amount of clothing feels neither too cold nor too hot, given a set of thermal conditions.

Indoor thermal comfort plays an important role because people spend a significant share of their time indoors. Thus, in residential buildings’ spaces, air quality needs to be ensured. Most thermal comfort indices include human factors, i.e., aspects such as the metabolic rate and clothing insulation, and environmental factors, i.e., air temperature, air velocity, radiant mean temperature, and air humidity [2,3].

The environment actively contributes to thermal comfort; it is essential to study the building’s orientation, geometry, and insulation materials, as well as the shading zones and ventilation affecting thermal comfort and building energy needs [4,5,6].

The inability to invest in and acquire climatization equipment is not only a matter of comfort. A properly climatized building provides protection against drastic climate conditions for both the winter and summer seasons, a factor of utmost importance to the well-being of susceptible individuals, particularly the elderly [7,8]. Additionally, the building’s ventilation is essential for air renewal and the removal of contaminants that cause health problems [9]. Active ventilation systems also contribute to energy efficiency while controlling energy consumption with the adoption of constructive measures and adjusted ventilation strategies [10].

Part of the problem is related to the inability to keep dwellings effectively warm during the winter [1,11]. Another problem is related to the building stock conditions. There is a considerable share of the population living in buildings that were built in the 1960s–1970s. Those buildings have poor insulation, or even worse, have a leaking roof, moist walls and basements, as well as decay in window frames or floors [12,13]. In the literature, several authors used surveys to identify potential thermal comfort problems within a societal parameterization corresponding to energy poverty [11,14,15,16]. In a particular study, it was concluded that about 74% of all respondents considered their dwelling “cold” during the winter, whereas a percentage of 24% pondered their houses “too hot” during the summer. Only 1% reported that their dwellings provide thermal comfort. The majority of the respondents (more than 80%) also felt the need to significantly increase energy consumption to maintain adequate indoor temperatures, which represents an increase in energy costs [1,17].

In the building sector, the absence of insulation and good-quality construction materials contribute to energy poverty, whereas active technology energy systems are often lacking or not well enough adjusted to produce the energy required in a specific context [1,18]. Nonetheless, the adjustment of active energy systems is dependent on the climate conditions [8,15,19], insulation thickness, building envelope [13], and whether the energy production technologies are centralized or not [20].

The combination of low income levels and the prevailing energy expenses requires that the selected technological alternatives to overcome energy poverty must reduce the economic burden on families and guarantee thermal comfort while improving energy efficiency and integrating affordable renewable energy conversion solutions [15,21]. Thus, the energy, economic, and social vectors are the main aspects contributing to energy poverty. The consecutive increase in energy prices, the low incomes, and the resulting lack of population purchasing power, combined with poor housing conditions, have aggravated the impacts of energy poverty. The model presented in Figure 1 defines the most relevant energy poverty vectors [13].

Numerical simulation tools and software allow the study of different technological combinations and, therefore, improve and/or optimize the operating parameters for a specific case study, i.e., a building with a certain geometry, envelope, ventilation conditions, occupation, and energy requirements, to predict its performance and the respective cost [16,21]. The numerical studies have been conducted in the literature for the assessment of energy needs, thermal comfort, equipment performance, and ventilation settings [22] in several applications, from universities [23] to schools [24], supermarkets [25], cinemas [26], hospitals [27,28,29], and residences [11].

It is impossible to talk about energy poverty without relating it to current affairs, namely climate change and the need to find eco-efficient alternatives to fossil fuels. In this sense, the scientific community and the governments of the most developed countries have been progressively discussing the depletion of natural resources and the consequent increase in their costs, as well as the need to reduce CO₂ emissions and use cleaner energy instead of fossil-fuelled energy conversion systems, which significantly contribute to environmental quality deterioration [30]. The most agreeable solution to support the adoption of renewable and eco-friendly technologies is the application of subsidies [30] and policies that promote the efficient use of energy, specifically those focused on low-carbon intensity energy production and waste use and management. Most of these proposals are associated with regulations and agreements such as the Paris Accord in 2016 and the European Green Deal policy of the European Union (EU) [31].

In this regard, every year, the United Nations Climate Change Conference (COP) organizes a conference where critical decisions are taken following global climate objectives, government strategies, and other important stakeholders involved. For instance, the outcomes from the last two editions, COP27 carried out in 2022 (Egypt) and COP28 carried out in 2023 (Dubai), did not achieve much success on the strategy definition to mitigate the increase in temperature, and no agreement was reached on phasing out fossil fuel use.

The main objective is to present a multidimensional framework about the energy poverty status quo and the current energy poverty indicators referred to in the literature, considering content analysis as a methodology. The relevance of this research is associated with the great impact of energy poverty in the emerging Society 5.0. As previously stated, energy poverty is a multidimensional problem caused by a combination of factors such as low-income, high-energy expenses, and poor energy efficiency in buildings. A set of indicators related to energy poverty has been proposed and applied to a specific situation. In this view, this paper aims to contribute to the awareness of energy poverty at an international level by identifying and presenting several energy poverty indicators that could be adapted to different socio-economic contexts. This statement is intended to analyse how people’s thermal comfort can be affected, study the implementation of technological solutions capable of providing the energy needs of residential buildings at the most effective cost, and provide good practices for making housing more efficient.

This paper is organized into the following five main sections: After a brief background is provided in Section 1, the research methodology is presented in Section 2. Details about the literature process and its meta-analyses are disclosed. In Section 3, the current state of energy poverty and its indicators are discussed and based on content analysis. Section 4 gathers the most relevant aspects associated with energy poverty, considering its relationship with thermal comfort as well as the role of technology and policies in reducing energy poverty. Section 5 refers to the main conclusions and the study limitations.

2. Research Methodology

From the methodological point of view, a literature review and a content analysis were carried out. Scientific evidence can be reported and analysed by using different review methods, and the type of review to be conducted depends on the proposed research goal, approach, and scope. Nevertheless, all review methods aim to summarize the available information and provide context or background about a topic of interest [32].

The literature review conducted in this study is more narrative than structured, and, thus, it cannot be considered systematic. Qualitative content analysis is a methodology employed in research for systematically and methodically analysing qualitative data. This approach entails the scrutiny of textual materials or other qualitative data sources to uncover recurring patterns, underlying themes, and significant interpretations.

2.1. Literature Review and Content Analysis

The performed literature review was based on the use of published resources collected from specific databases, namely Research Gate, Scopus, and Web of Science. The search for published studies on the topic was comprehensive but not exhaustive. The search process was conducted considering the combination of main referable keywords [“Energy Poverty”] AND [“Thermal Comfort”] AND [“Energy and Buildings”] considering the title, abstract, and indexed keywords (TITLE-ABS-KEY). To allow a general perspective of developed works in this field of knowledge, no filter or exclusion criteria were considered. However, only studies after the year 2001 were considered.

The sample considered in the study was based on a set of 115 technical documents from indexed and peer-reviewed journals (82%), international conference papers (12%), book chapters (3%), and technical reports (3%). A total of 49% of the included studies correspond to the first quartile (Q1). These data can be depicted in Figure 2, which presents the distribution of publications by type of document and by quartile.

A brief analysis was carried out regarding the scientific field of the collected publications (Figure 3). The majority of the publications (a share of 35%) were indexed in the field of “Energy and Buildings”, followed by “Thermal Comfort” (20%) and “Technological Solution Combination” (5%). “Energy Poverty” was identified in only 5% of the searched publications in scientific fields, highlighting the gap in the literature on this topic.

From a methodological perspective, the analysis involved examining the content of textual data within the collection of documents. This process included tallying and contrasting predetermined indexed terms, which were then followed by their corresponding interpretations.

The keyword frequency within the data can offer valuable insights into their usage and the surrounding context, facilitating the recognition of potential similarities or discrepancies. The results of this analysis were documented through descriptive summaries and displayed in tables located in both Section 3 and Section 4.

2.2. Research Question Definition

To accomplish the objectives, a main research question (RQ) and sub-questions were proposed (

Table 1. Research questions and sub-questions considered in the study.

Main RQ	sRQ
RQ: How do technology, socioeconomic aspects, local climate conditions, and policies influence the definition of energy poverty indicators?	sRQ 1.1: What are the most relevant energy poverty indicators applied nowadays?
	sRQ 1.2: How is energy poverty perceived in different contexts, and what is its relationship with thermal comfort?
	sRQ 1.3: What is the role of technology in reducing energy poverty?
	sRQ 1.4: What is the impact of the policy framework in the combat of energy poverty?

). The main RQ aims to understand the following: “How do technology, socio-economic aspects, local climate conditions, and policies influence the definition of energy poverty indicators?”.

This RQ was defined to identify how technology solutions, socioeconomic aspects, local climate conditions, and policies influence energy poverty and the definition of energy poverty metrics. Most of the research in the literature is focused on characterizing energy poverty for a specific context, i.e., region or country, whereas the present study pretends to provide an overview of energy poverty indicators and their relationship with technology and societal aspects.

Taking into account the main research question, three sub-questions (sRQ) were also identified to support the study. The first sub-question (sRQ1.1) is related to the most important contribution of this research, i.e., identify relevant energy poverty indicators. The second sub-question (sRQ1.2) regards the energy poverty concept itself and how it is perceived in different social, economic, and geographic contexts.

The third sub-question (sRQ1.3) is to understand the role of technology in reducing energy poverty and, lastly, to understand the impact of policy frameworks in combating energy poverty (sRQ1.4). An interpretative analysis was carried out to reach the answers to the research questions.

2.3. Bibliometric Analysis of Energy Poverty

Based on the selected set of documents, a bibliometric analysis was performed. The free software VOSviewer^® (version 1.6.18) was used to generate the co-occurrence bibliometric maps. The maps represent a network based on the association of indexed keywords (Figure 4). Based on co-occurrence maps, the following four main clusters were identified: (1) energy poverty; (2) household energy; (3) energy use; and (4) economic analysis. The cluster of different types of energy poverty has a great level of association with energy policy and energy efficiency.

The cluster “energy poverties” has several ramifications related to energy efficiency, but mostly with the energy policy. The implementation of regulations contributes to higher levels of energy security and guarantees access to energy, even in rural areas [8,33,34]. The integration of highly efficient energy measures plays an important role in energy poverty reduction because some of those plans do not entail significant investment but decrease energy consumption (e.g., window reinforcement, insulation, shading, blinds, or heat recovery systems) [35,36,37].

The cluster of “household energy” has links with energy resources, energy services, and techno-economic resource scarcity. Despite their feasibility and capacity to suppress energy needs, several technologies have higher specific costs, which limits the range of possibilities for families with lower economic resources [18,21,38].

Both “energy use” and “economic analysis” clusters have several shared links. Both are associated with several indexes (e.g., human development index or multidimensional index). Sustainable development is related to energy planning, technological maturity, the energy market’s reliability, and alternative energies.

According to the literature, incorporating clean and renewable energy-driven technologies in the building sector has the potential to overcome energy poverty. However, this scenario will only be possible when heat and electricity storage are affordable [39,40].

3. Energy Poverty and Its Indicators

The analysis was conducted through a literature review and the respective content analysis. Content analysis is a widely used qualitative research technique to correlate concepts within some given qualitative data [41]. In this section, different energy poverty concepts are studied, and an overview of the topic is provided.

3.1. Concept of Energy Poverty

Energy requirements have been rising in recent years due to the escalating dependence of human efforts on technological advancements, leading to an increase in energy consumption that comes with a high cost. Society has recognized the energy dependence of household appliances, especially their energy consumption. As a result, new concerns have arisen about occupational health and well-being [14].

Although there is no universal definition of energy poverty, recent studies have increasingly emphasized the importance of interpreting it as a multidimensional concept. Energy poverty has been defined as a “situation where a household cannot meet its domestic energy needs due to a combination of three factors: low income, high energy costs, and poor energy efficiency in buildings” [42].

Lately, the volatility of energy market prices and the concerns related to housing thermal comfort have contributed to worsening this situation. Both inappropriate indoor temperatures and low air quality result in inadequate comfort and sanitary conditions, leading to health problems and higher mortality rates [43]. When talking about energy poverty, several aspects need to be considered, and they must be analysed in a specific context due to the socio-economic status, the weather and climate conditions, the management of the energy distribution grid, and other criteria. All these aspects create a unique niche, which results in a distinct parameterization in terms of energy poverty characterization [44].

Table 2. Concepts and criteria associated with energy poverty assessment.

Authors	Concept/Criteria	Description
[45]	Affordability and energy prices	Regarding the capability of final energy consumers to pay for the consumed energy, energy may be too expensive for a significant share of the population/community. High energy costs when compared to household income can lead to energy poverty, as families may be forced to spend a disproportionate amount of their income on energy. Expenses higher than 50% spent on energy services can indicate energy poverty.
[46]	Grid connection assess	It is related to the ability to access electricity services. This aspect is particularly relevant in rural or isolated areas where electrification is unfeasible. Furthermore, in those locations, the frequency and length of power interruptions affect the reliability of the electricity supply.
[47]	Grid connection assess	The lack of access to electricity services, heating, or cooking appliances is characteristic of energy poverty. A great share of the population in developing countries still rely on traditional and inefficient energy sources like firewood for heating and cooking.
[48]	Reliability and quality of energy services	Energy poverty is not only related to the availability of energy but also to its reliability and quality. Poor service quality, recurrent power outages, and voltage fluctuations can contribute to energy poverty. Energy reliability is more than a suppression of basic energy needs; it also enables economic activities and stabilizes the energy supply grids, which can affect productivity. The lack of infrastructure and technological development represents a barrier to accessing energy services. Remote communities face challenges in the implementation of energy infrastructure (this aspect is also related to energy access).
[49]	Thermal comfort and health impact	The use of conventional energy sources or outdated heating methods can have severe health implications. Indoor air pollution from these sources contributes to respiratory diseases, with a notable impact on children.
[44]	Environmental sustainability	Dependence on non-renewable or fossil fuel energy sources can contribute to environmental degradation and climate change. Sustainable energy solutions are crucial for addressing energy poverty in the long term. The use of sustainable energy sources and technologies such as solar thermal systems and photovoltaic (PV) panels integrated with the energy mix can lead to a decrease in energy bills for all energy consumers.
[50]	Policy and governance	Effective policies and structural legislation for energy management are crucial in tackling the issue of energy poverty. Insufficient regulatory structures, instances of corruption, and political instability have the potential to block endeavours aimed at enhancing energy accessibility.
		Global energy justice emphasizes the need for a fair distribution of energy resources and benefits on a global scale. It necessitates the mitigation of inequalities in energy provision between advanced and developing regions.

summarizes the main aspects discussed in the literature regarding the criteria typically associated with energy poverty assessment.

These concepts and criteria can be considered individually or simultaneously to provide a comprehensive understanding of energy poverty in a specific region or country. Most studies take into account the dwellings’ low energy efficiency, high domestic appliance energy consumption, and high energy prices as decisive aspects when addressing the energy poverty problem [43]. In this context, several reasons for energy poverty have been disclosed, such as low incomes [1,8,13,16,51,52,53,54,55,56,57], poor building insulation and low-quality construction materials [51,58,59], and non-rational energy use [51,53,60]. As the price of electricity increases, energy consumption represents a substantial burden on the household budget.

Thus, many families cannot afford enough energy to provide their comfort at a reasonable cost. Over the years, this has proven to be a major difficulty because energy consumption has increased and government subsidies are not enough to deal with the actual demand.

According to [61], factors associated with energy consumption include built area, energy envelope, quantity and type of appliances, the existence of ventilation systems, occupation, and building use profile. The increase in energy consumption of household appliances and electronics is an evident circumstance. Although specific devices, such as refrigerators and washing machines, have improved in efficiency due to mandated standards, the rise in the quantity of electrical appliances has negated these efficiency improvements. Another contribution to the energy poverty occurrence is the old building stock [6,11,14,62,63,64,65] and lack of insulation conditions [13]. Old building stock refers to existing buildings that were constructed with outdated construction methods, using materials with poor insulation properties and inefficient ventilation.

Poor insulation, inefficient heating and cooling, and single-glass windows result in higher energy consumption and increased costs [6]. To address this issue, the majority of research refers to retrofitting measures such as enhancing insulation to minimize energy waste, implementing energy-efficient technologies, or enhancing heating and ventilation systems with more energy-efficient alternatives. Additionally, incorporating renewable energy resources such as photovoltaic panels can diminish reliance on traditional energy sources. In 2021, around 75% of the building stock in the European Union was considered to be energy inefficient, while 90% of these buildings are expected to still be standing in 2050. Older dwellings with construction dates preceding the 1980s are especially problematic and are classified with poor energy labels. Their constructive solution involved the use of poor insulation materials like stone, bricks, and cement. However, the vast majority of the residential building stock consists of these older dwellings, and these situations are aggravated in countries with severe climates. These lead to inadequate indoor air conditions and, therefore, to a deficit of minimum thermal comfort conditions [11].

Extreme climatic conditions [15,18,19,64,65,66] and climate changes have a great impact on people vulnerable to energy poverty [6,13,56,67,68,69]. Groups experiencing social vulnerability not only possess limited economic means, as previously mentioned, but also bear the brunt of climate-related effects to a significant degree. The rise in temperature variations due to climate change has served to worsen issues like energy deprivation and the subsequent rise in mortality rates, particularly among the elderly demographic.

Since energy poverty is an intrinsic issue, it is eminently a political problem, given the difficulties in accessing quality housing and the high costs of electricity. The problem has been dealt with within the context of the energy transition, which is based on the urgency of renovating buildings with a view to energy efficiency, energy self-sufficiency of buildings, and cost savings. This is an important step towards reducing greenhouse gas emissions and promoting the well-being of vulnerable people [7,51,55,56,57,65].

3.2. Energy Poverty Assessment Worldwide

In South Africa, where poverty conditions are even more severe, energy poverty is vastly amplified. In [55], causes such as households’ energy demands, cultural factors, illiteracy, income poverty, security concerns, health hazards, premature death, domestic fire, and drudgery in households are identified. Also, there are frequently reported problems, such as the fact that cooking is done with wood-burning cookers placed on the floor of the house, which creates unsafe situations.

Another similar case is in India [70] and Brazil [71]. Both studies show empirical results that indicate the prevalence of extensive energy poverty in India and Brazil, respectively, especially in rural areas where households rely on traditional biofuels such as dung cake, firewood, and agricultural waste subproducts.

There is a direct proportionality between income level and energy poverty, implying that in predominantly agrarian societies like India, access to modern energy services remains an ambition for the poorest population in the foreseeable future.

In the case of the United States of America (USA), Ref. [57] states that the USA has not formally recognized energy poverty as a problem distinct from general poverty at the federal level. In the absence of federal recognition of energy poverty, states have implemented low-income energy assistance programs. As a result, 51% of all funding to address high energy burdens comes from utility-funded bills and energy efficiency support. However, the evidence suggests that the economic and financial insufficiencies, high energy burden, and demographic characteristics of a “vulnerable household” underlie the cause of energy poverty.

In addition, the study [72] found a positive correlation between industrial CO₂ emissions and green obligations based on an approach relating oil price fluctuations to industrial CO₂ emissions in the USA, which could jeopardize the commitment to carbon neutrality by 2050. As a consequence, the government of the USA will have to take measures by investing in cleaner and more sustainable energy sources.

In [73], the authors present a study based on the energy consumption problem in older households in Japan. It was observed that older households consume more energy than younger households. This issue is quite relevant in Japan, since 30.0% of the Japanese population was 65 years of age or older in 2017, and this rate is expected to increase to 38.4% by 2065, which is expected to be the highest in the world. In Japan, the rate of households with members aged 65 and above has increased, as has the rate of individuals aged 65 in the poverty group, according to the Organization for Economic Cooperation and Development. Both the elderly population and vulnerable households, such as single parents with dependent children and individuals living alone, exhibit greater susceptibility to the escalation in living expenses, which encompasses increased energy costs. Besides the population aging, in Japan, both the increase in energy costs and the intensification of energy use are growing [74].

The world is experiencing climate change that will directly interfere with energy needs. For example, Cyprus is estimated to experience a gradual and relatively strong warming of about 3.5 to 7 °C for the period from 2070 to 2099, mostly in regions where, nowadays, the maximum temperatures reach values above 40 °C in July and August. Finland is experiencing a significant impact on temperature increases, and average temperatures are expected to rise by approximately 2 °C. Average temperatures in Greece have increased by 2.2 °C. Israel has a hot desert climate, and it has experienced many heat waves in recent years, where the maximum temperature reached 48.9 °C. Slovakia is located in central Europe and is considered a country subjected to high risk from the impacts of climate change. Average temperatures may increase by at least 2 °C in urban areas and 0.5 °C in rural areas. Spain is another country with wide climatic variability, and the increase in average temperatures corresponds to 2 °C in winter and 3 °C in summer every 30 years [63].

Typically, Europe has rigorous winters and has increasingly experienced a gross increase in the cost of energy. In 2021, 7% of the European population was not able to have their home warm enough. In Figure 5, the most affected countries are Bulgaria [75], where one in four people (23.7%) have been affected by energy poverty, followed by Lithuania (22.5%) and Cyprus (19.4%). On the other hand, there are countries with low energy poverty rates, namely Switzerland (0.2%) and Norway (0.8%). Unfortunately, southern European countries have a higher rate of people who cannot heat their homes. Also, it is expected that the following years will bring even more catastrophic results for these countries [76].

In [51], the social and spatial patterns of household energy deprivation across Europe are presented, which are highly variable geographically. The data provided an insightful overview regarding the geographical extent of energy poverty in the EU, which was generated by a subjective measure, i.e., “inability to keep the house warm”. This metric can be combined with more objective data on the shares of each country’s population facing housing burdens.

Some South European countries have been pointed out as the most vulnerable countries in the European Union regarding this issue [60]. In Mediterranean countries, most residential buildings are old, and the used construction materials are thermally inefficient [11,62]. The use of masonry stone, wooden roofs, and floors was predominant in older buildings [35], a very different scenario from nowadays, since reinforced concrete-bearing structures are the most common current practice. These differences justify the poor energy performance, mostly before the implementation of building energy performance regulations. Some regions are hot in the summer and cold in the winter, with greatly inefficient housing buildings and a huge insulation deficit. Thus, researchers [14,77] worked on vulnerable zone mapping to identify the neediest Portuguese regions. In [36,78], the authors did the same mapping for Greece and Italy, respectively. There is still noticeable resistance to the adoption of measures to reduce energy dependence [16].

Finland, despite its cold climate, is among the nations where society excels at keeping its home warm. Indeed, Finland ranks as the third-most sustainable country globally, known for its approach of raising public awareness rather than mandating regulations to enforce compliance. Finland’s objective is to achieve carbon neutrality by the year 2035, establishing itself as a pioneer in the field with significant progress in developing solutions that assist businesses in optimizing emissions and attaining carbon neutrality.

However, a study by [79] demonstrated that the advancement in the economy as quantified by Gross Domestic Product (GDP) poses a considerable threat to the durability of the environment in the long run; therefore, one of the proposed strategies is the adoption of policies that encourage the establishment of a circular economy.

In countries with the world’s fastest-growing emerging economies, known as “MINT” countries (Mexico, Indonesia, Nigeria, and Turkey), high CO₂ emissions, rising energy prices, and rapid depletion of energy resources are evident. Moreover, economic volatility, environmental pollution, and inefficiency in energy use are inherent factors in these nations, thus necessitating prompt allocation of resources towards sustainable energy. It is imperative to assess the societal response to the integration of eco-friendly energy generation technologies. To this end, implementing strict environmental measures and legislation, studying the most convenient and favourable energy source for each country, encouraging the population to take out loans, and promoting industries that opt for more sustainable solutions are key measures to minimize emissions [80].

In sum, the poor quality of buildings, especially regarding thermal insulation, contributes to the lack of thermal comfort during both the winter and summer seasons [15]. The lack of subsidies supporting part of the acquisition and maintenance costs of energy production and ventilation systems, as well as the high energy prices considering society’s standard of living, make them unreachable to many households. Appealing to the population to invest in technological solutions without presenting an estimation of the economic and energy savings [16,53], without an incentive or reformulation of energy strategies [8,13], will not change their mentalities. Sareen et al. (2020) [54] present comparative studies between European countries that show that a change in legislation and the creation of incentives can be a starting point to overcome the energy poverty paradigm.

3.3. Energy Poverty Indicators

In this section, an overview of energy poverty indicators is presented based on the information from the literature analysis. This section aims to answer the second sub-research question, i.e., “What are the most relevant energy poverty indicators applied nowadays?”.

Policymakers, organizations, and researchers working in the energy sector often consider a combination of indicators to assess the nature and extent of energy poverty and to develop effective strategies for its addressing [81,82]. In 2018, the European Energy Poverty Observatory (EPOV) started to report data on energy poverty through figures collected from several databases, such as the European Union Statistics on Income and Living Conditions (EU-SILC) and Household Budget Survey (HBS) [13,60]. At present, several indicators are employed for the examination and evaluation of energy poverty, relying on household income and spending, while others are founded on self-reported household circumstances [83], which can be both ‘subjective’ and ‘objective’ as they can refer to [36]:

• Inability to keep home adequately warm;
• Arrears on utility bills;
• Deficiencies like leaking roofs, damp walls, or rot in window frames or floors.

Table 3. Synthesis of energy poverty indicators.

Indicator	Meaning	Applied Country	Authors
Low Income–High Cost (LIHC)	Identify low-income households living in inefficient dwellings as fuel-poor, and a self-reported subjective index	UK, France, Germany, Austria, Spain, and Italy	[13,19,34,45,50,84,85]
Measure Energy Poverty (MEP)	It is based on the LIHC. It works by determining a threshold beyond which energy services are considered unaffordable.	Belgium	[86]
High Share of Energy Expenditure in Income (HSEEI)	Proportion of households whose share of energy expenditure in income is more than twice the national median share, based on HBS data.	Finland, Spain, Sweden, Portugal, Greece, Germany, and Hungary	[13,16,45,46,50,60]
Minimum Income Standard Indicator (MIS)	Subsidized acquisition of heating equipment and subsidized energy during the winter season (during the cold).	Portugal, Germany, Italy, and Spain	[13,34,45,50,53]
After-Fuel-Cost Poverty Indicator (AFCP)	It identifies households that are in income poverty and whose situation is worsened by fuel costs.	France	[13,84]
EU-Statistics on Income and Living Conditions (SILC) data or the Ten-Percent Rule (TPR)	Arrears on utility bills, based on self-reported experiences of limited access to energy services; Calculates the ratio between income and energy costs, where energy costs should not exceed 10% of household income.	UK, Portugal, Spain, Japan, France, Germany, Greece, China, and Ecuador	[13,16,44,50,60,73,74,84,87]
Low Absolute Energy Expenditure (LAEE)	Share of households whose absolute energy expenditure is below half the national median, based on household income and/or energy expenditure data. Example: Housing Budget Survey (HBS) data.	Portugal and Spain	[16,60]
EU-SILC	The percentage of dwellings unable to keep the environment adequately warm.	Greece, Belgium, and the EU	[13,44,60]
BRE Domestic Energy Model (BREDEM)	The modeling tool, using data from the English Housing Survey (EHS), is applied to calculate the threshold of the median modeled bill, avoiding energy costs related to unheated spaces.	UK	[60]
Hidden Energy Poverty (HEP)	Households with an energy expenditure lower than 50% of the national median are also considered to be in energy poverty.	Belgium	[60,86]
Perceived Energy Poverty (PEP)	It is a subjective indicator and concerns the perception of households as regards their ability to pay their energy bill.	Belgium	[86]
Stochastic Model of Energy Poverty	Energy consumption is modeled as a variable for assessing energy poverty.	Greece	[88]
Energy PHEBUS *	A simplified approach by income and the French energy performance label DPE (Diagnostic Performance Energetic).	France	[60]
European Fuel Poverty and Energy Efficiency (EPEE)	It uses three indicators from the SILC dataset (‘ability to pay to keep one’s home adequately warm’, ‘leaking roofs, damp walls/floors/foundations, or rot on windows/floors’, ‘arrears on utility bills’).	Belgium, Spain, France, Italy, and the UK	[51]
EU-SILC (structural)	The house has a leaking roof, damp walls/floors/foundations, and rot in the window frames.	EU and Ireland	[44]
EU-SILC (economic)	Inability to pay utility bills on time.	EU and Ireland	[44]
Multidimensional Energy Poverty Index (MEPI)	Assess the multidimensional nature of energy poverty through the lens of the energy services delivered to a household, such as lighting, communication, and thermal comfort.	Brazil	[71]

* PHEBUS is an international cooperative research program that provides data for validating computer codes dedicated to the analysis of severe accidents and their calculation results.

presents several indicators and their definitions, as well as countries where indicators to quantify energy poverty have already been applied and analysed and the respective authors that mention their application.

4. Energy Poverty: A Multidimensional Analysis

Recent studies have converged around the necessity of understanding energy poverty as a complex issue with various dimensions. It is imperative not to oversimplify the concept of energy poverty by focusing solely on a restricted set of indicators. The gaps in research on energy poverty have underscored the importance of taking into account numerous viewpoints, many of which are structural in nature. These include the arrangements of energy supply systems and appliances that contribute to the well-being of building occupants. Hence, it is crucial to grasp the correlation between energy poverty and thermal comfort, as well as the significance of policies and technological advancements in reducing energy poverty.

4.1. Energy Poverty and Thermal Comfort

In this section, the literature is analysed taking into consideration the sub-research question, “How is energy poverty perceived in different contexts and what is its relationship with thermal comfort?”. The dwelling’s main function is to provide shelter and safety. Dwellings are constructed with the primary purpose of shielding inhabitants from environmental elements and potential dangers. Following the fulfilment of essential survival needs, individuals typically tend to pursue enhanced habitation settings, exemplified by the quest for optimal thermal comfort.

Thermal comfort can be assessed through subjective and quantitative methods [89]. The approaches to assessing spatial thermal comfort can therefore be divided between steady-state assessment models and adaptive thermal comfort models. Regarding subjective and steady-state models, Fanger’s theory states that if the incoming energy plus the metabolic rates are equal to the sum of the outgoing energy fluxes, a comfortable situation is reached, resulting in a Predicted Mean Vote (PMV) of 0. If the outgoing energy is greater than the incoming energy, a sensation of coldness will occur, resulting in a negative PMV. A positive PMV is attained when the total incoming energy surpasses the outgoing energy, leading to a perception of warmth. The PMV results are scaled from −3 (cold) to +3 (hot), and 0 represents a sensation of thermal comfort. To provide an insight into how people experience the PMV score, the Predicted Percentage of Dissatisfied (PPD) was developed. This PPD is directly linked to the PMV. At a PMV of 0, the PPD shows that 5% of people will still be uncomfortable. A building performs well if 10% of people are dissatisfied, resulting in a PMV of ±0.5. The PMV should not exceed ±0.7, resulting in a PPD of 15%. For subjective evaluation, questionnaires can be used to identify the influence of the outside environment. Regarding the objective assessment, it can be based on field measurements and numerical simulations performed to calculate the PMV that is presented in ISO 7730 based on Fanger’s index [90].

Numerical models allow the study of the thermal variables through a simpler approach and to test actions to mitigate thermal discomfort, including methods able to predict and assess thermal comfort. Numerical models have also been implemented as an important tool for optimizing thermal comfort while testing ventilation parameters [91]. This information can be used to maintain low energy consumption values.

Adaptive thermal comfort models are covered by other authors [6] and by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) [92] as a solution. A building serves as a barrier between an interior area and its external surroundings. Nevertheless, in numerous cases, this function proves to be insufficient, requiring the adjustment or regulation of the interior thermal conditions. Occupants within a building have the ability to employ various methods to change their thermal sensation. Some authors [93] studied the thermal comfort of disabled people in healthcare buildings and their strategies to feel more comfortable, such as the amount and type of clothing used, the use of hot or cold beverages, and adapting the activities (metabolic rate) whenever possible.

People can make use of natural ventilation to have some control over the indoor environment. Opening a window in the afternoon during the summer, particularly when the temperature is lower outside, serves to lower the temperature within the house. Additionally, the introduction of fresh outdoor air reduces the concentration of CO₂ and other harmful substances, thereby enhancing the general air quality and influencing the indoor environment [59]. Thus, the type of technology adopted and the way the ventilated air is distributed [22,94,95] have an impact on thermal comfort, thermal sensation, and the spread of pollutants and particles [96].

Depending on the climate, the methods previously referred to may not be enough, being necessary active systems that consume energy. In 2020, 27% of the final energy consumption in Europe occurred in households, with the majority of that energy, about 63%, being used for space heating [97].

The assessment of thermal comfort is an indicator of energy poverty since people who struggle to keep their homes comfortable may be at risk of energy poverty. Several studies have been performed regarding thermal comfort. The study in [98] was focused on the assessment of thermal comfort in Mediterranean buildings. It was possible to verify that people struggled to maintain indoor thermal conditions due to poor building conditions in Spain. The authors in [11] also noted that the poor building conditions affected the ability to provide thermal comfort. Their study was performed in the Portuguese context, showing that a significant percentage of time over the year was spent in discomfort during inhabited periods, from 78% to 100%.

A work published in [99] studied the ability of social housing in Chile to maintain thermal comfort. The authors concluded that one-third of the participants were not capable of keeping their home comfortable for at least 80% of the time, and more than a fifth were incapable of doing so 65% of the time, even when they used the cheapest source of fuel. The authors in [100] examined a decision-making process concerning thermal comfort and energy efficiency optimization for smart windows in Brazil. The authors aimed to implement a naturally ventilated control system in conjunction with various window types to reduce energy usage without compromising thermal comfort. Thus, the literature identifies thermal comfort as a goal to achieve while overcoming energy poverty.

Energy efficiency is getting more attention, and the studies not only emphasize energy poverty reduction but also reducing energy consumption [52,63]. To change the current paradigm, it is essential to implement tactics aimed at enhancing the energy efficiency of passive structures and dynamic systems, thus playing a crucial role in diminishing the carbon footprint towards a more pristine, environmentally friendly, and enduring realm of technologies [101]. Low-carbon building emerges as a key objective in contemporary times, playing a central role in meeting worldwide carbon emission targets.

Consequently, there exists a prevailing tendency to promote the shift from conventional building practices towards a sustainable and low-carbon emission framework. These buildings are specifically designed with the concept of sustainable development, which is seamlessly integrated throughout the building project, construction, and use [95]. Implementing more efficient technologies is a great starting point for reducing energy poverty as well as the CO₂ emissions that threaten living conditions.

Thus, there is an important gap that should be addressed, i.e., how do technology, socioeconomic aspects, regional climate conditions, and policies influence thermal comfort, and how do energy poverty indexes reflect those asymmetries? The rise in energy prices has become an ongoing challenge for societies worldwide, particularly affecting those who are economically vulnerable. Addressing the impact of energy poverty goes beyond social consideration; it also encompasses repercussions on public health and the economy. Developed countries have tackled this challenge by employing diverse strategies to pinpoint households experiencing energy poverty. However, defining energy poverty is not a one-size-fits-all approach, which can hinder effective action.

Considering the diverse array of factors influencing energy poverty, the identification of appropriate intervention points proves to be a challenging endeavor. This intricacy is further heightened by the variability observed within a single nation, where disparate climatic conditions and varying levels of energy resource accessibility exist. The viability of renewable energy outlets as a potential remedy is contingent upon resource availability within distinct geographical areas. Additionally, there is an initial investment cost that could be a barrier for households that are already financially fragile.

Hence, the main goals for the future involve the identification of energy poverty on a regional scale, alongside the acknowledgment of the principal factors that contribute to it, the alignment of suitable technologies or construction strategies with the specific context of each region, and the development of carefully crafted policies and incentives that promote the adoption of the suggested solutions.

4.2. Technology’s Role in Reducing Energy Poverty

The objective of this section is to understand the following question: “What is the role of technology and policies in reducing energy poverty?”, which is the third sub-research question under study. Different technologies are employed to alleviate energy poverty, particularly in the context of enhancing affordable and cost-effective energy services.

The integration of efficient energy supply solutions into old stock buildings requires higher levels of investment due to the need to replace energy-intensive construction materials and invest in more sustainable insulation options [77]. Otherwise, the thermal losses of buildings outweigh the nexus between energy efficiency and investment rationalization. The embodied energy of conventional buildings is high due to the employment of energy-intensive construction materials and traditional construction practices. Thus, moving to an energy-efficient heat and cooling technology, as well as an eco-friendly building material, can result in noteworthy energy savings and CO₂ emission reductions [59]. Other efficiency measures can include improving the ceiling, walls, or floor insulation and upgrading space heating or water heating equipment.

To overcome energy building problems, most countries have employed regulations to incentivize the installation of renewable and/or efficient energy production systems. However, older energy-inefficient buildings, particularly those located in historical or emblematic places or even those whose characteristics need to be preserved, represent a large fraction of the construction [58]. Most of them are inhabited by an aging population with low incomes and, therefore, are incapable of affording to heat their homes with the installation of renewable energy systems or heat pumps due to their purchasing costs [53]. Thus, the correct technology selection and adequate energy system sizing depend on the energy needs, building characteristics, and climate conditions.

Nevertheless, most efficient technologies entail complex installation and operation requirements, which cannot be technically accomplished without fundamental changes to buildings. This is a reality not only applied to developing countries but also to several worldwide economies due to the increase in energy costs verified after the COVID-19 pandemic and the Ukraine–Russia conflict.

4.2.1. Integration of Renewable Energy Technologies

Renewable energy technologies, mainly solar energy, have been identified as the most cost-effective technologies to provide energy in the building sector and, therefore, combat energy poverty. Solar energy is considered the top source of renewable energy in terms of installation and maintenance expenses as well as lifespan [102].

Solar thermal systems can be classified into distinct categories according to their performance and range of applications [103], considering different factors of combination, namely, occupancy rate, internal thermal load gains, envelope renovation, and the efficiency of the heating system [40,62]. Optimizing solar thermal systems [104] is also studied to reduce their integration impact; for instance, solar thermal systems and heat pumps for domestic hot water networks [105] or solar systems for water heating [40]. Thermo-economic optimization of solar thermal systems for residential building applications allows reducing the specific cost of these systems [106]. The implementation of solar thermal systems has been investigated in several geographical areas, each characterized by distinct climatic conditions and diverse economic priorities influencing their utilization. The optimal configuration of this system allows for a reduction in electricity demand and consequent economic savings [107]. Thus, the effectiveness of the energy transition depends on governmental policies and incentives to subsidize technology adaptation [108,109].

The installation of PV panels and battery storage systems in low-income settlements can contribute to limiting energy poverty, creating employment opportunities, and achieving the milestone set for the energy transition [110].

A significant reduction in the consumption of non-renewable primary energy can be achieved by using PV systems, despite the unattractive acquisition and installation costs [39,111]. A considerable and continuing drop in purchasing costs of PV components has been observed since 2018, mostly due to the technical progress associated with advances in semiconductor physics but also due to scale effects in industrial production [112]. Effectively, in existing buildings, it is feasible to specify the energy expenditure by utilizing sustainable sources, specifically those that incorporate PV panels [113]. Through economic feasibility studies using simulation models [103] and given the average consumption of the building, it is possible to size and design a suitable technological solution that is not overestimated [114,115].

A study on the potential use of PV panels has revealed a potential reduction in the need to purchase energy by 15% [52]. Nevertheless, this value has the potential to escalate through the utilization of energy storage solutions, given that 79% of the overall photovoltaic electricity produced exceeded the immediate requirements. It is imperative, therefore, to promote the integration of Battery Energy Storage Systems (BESS) in conjunction with photovoltaic energy, along with other sustainable energy sources capable of generating power outside of sunlight hours [52].

A great challenge regards the estimation of the cost-effectiveness of these system installations. The cost benefits can be estimated through models able to predict the annual energy savings as well as the payback period [107,116,117]. Since one of the energy poverty vectors is high energy demand and/or price, building energy reduction can provide an important opportunity to reach energy efficiency. To meet space heating needs, systems that use solar energy as an input can have a thermal storage system as a backup. The solution starts with knowing how to store thermal energy based on phase-change materials (PCM) or thermochemical materials (TCM) [118].

Additionally, these materials contribute to the building’s thermal inertia, maintaining small temperature differences between the indoor air temperature and the internal surface. This effect allows for reducing temperature fluctuations and decreasing the peak load due to their high latent heat storage capacity [119].

Small and micro-scale biomass energy production systems have been considered for residential applications. Biomass-fuelled domestic boilers have emerged as a good alternative to conventional systems to heat residential buildings, such as oil radiators or diesel boilers [37,120,121]. Nevertheless, it is important to mention that the recent events have negatively impacted the price of solid biomass, from logs to wood chips or pellets.

The relatively recent concept of Renewable Energy Communities (REC) allows the production of decentralized energy based on clean energy technologies at low prices. The REC makes it possible for companies, local agents, public entities, or citizens to group up to produce energy from renewable sources and then consume, store, or sell energy to third parties. In addition, it is also possible to share locally the produced renewable energy (e.g., district heating). Community-based energy grids offer a feasible and efficient strategy for combating energy poverty and have the potential to serve as a substitute system for the social energy tariff. This enables the economic support of disadvantaged households in managing energy costs. The social energy tariff is an automatic mechanism that provides a discount on the electricity bills of financially disadvantaged households without incentivizing any improvements in the efficiency or energy output of appliances, residences, or the overall energy infrastructure [122].

A study by [123] supports that the use of renewable energy improves environmental quality and promotes the fulfilment of the Sustainable Development Goals (SDG). They point out that electricity generated from nuclear energy is one of the best options because it is reliable, safe, and has low pollutant emissions. The authors also pointed out that, with the price of fossil fuels, nuclear energy satisfies energy supply needs and reduces dependence on imported fuels.

Integrating renewable energy technologies contributes to reducing energy poverty by promoting energy-efficient and renewable-power solutions, which results in better living standards, economic growth, and sustainability. Systems powered by renewable energy sources, such as PV or solar thermal systems for heating and cooling, further reduce dependence on expensive and polluting fossil fuels.

4.2.2. Energy-Efficient Appliance Installation

An additional technological aspect that holds significant importance is the installation of energy-efficient appliances, which plays a critical role in mitigating energy poverty. The implementation of energy efficiency measures serves as enduring remedies that shield households from fluctuations in prices, reduce environmental impacts, and result in financial savings [46].

Energy-efficient appliances: Using light-emitting diode (LED) bulbs and compact fluorescent lamps (CFL) is advisable due to their lower energy consumption compared to traditional incandescent bulbs; incorporating electric or gas cookers specifically designed for efficiency can be effective in diminishing energy usage within households.

Heating, ventilating, and air conditioning (HVAC) systems uphold stable temperature and humidity levels to ensure high-quality living environments within structures. By effectively managing thermal comfort and indoor air quality, HVAC systems have the potential to lower energy consumption. The incorporation of smart control mechanisms enables seamless grid interaction, load management, and energy expenditure reduction [124]. Modern, energy-efficient HVAC systems reduce energy consumption, lowering utility bills for households and businesses. This makes energy more affordable and accessible.

Energy storage solutions: The use of batteries, encompassing progress in cost-effective and expandable energy storage, facilitates the retention of surplus energy produced during peak hours for utilization in times of diminished energy generation, thus surmounting the variability of renewable energy sources. Additionally, monitoring systems empower enhanced oversight of energy use, invoicing, and surveillance, fostering energy efficiency and mitigating waste [125]. All these strategies necessitate financial mechanisms and policy assistance for the implementation of these technologies to combat energy poverty.

An important parameter that can be used to measure the effectiveness of energy generation corresponds to the energy-specific cost. This indicator can be estimated as the specific investment cost or the specific cost of energy produced for each technology. In this analysis, the specific cost was determined when energy is produced by using biomass boilers, solar PV panels, and heat pumps. On average, higher costs per produced amount of energy are determined for solar technologies reaching 30 EUR/MWh.

When determining the costs per installed capacity, heat pumps represent the highest value (about 890 EUR/kWh). These indicators are a valuable measure to analyze the nexus between energy efficiency and the money spent to install and operate these technological alternatives. For instance, costs for biomass boilers differ a lot. In the case of small-scale systems (around 200 kW), the specific costs can differ even five times from 100 EUR/kWh to almost 500 EUR/kWh. The main reason for such variance is the use of diverse biomass technologies (wood chip boilers or wood pellet boilers) [108,116,126,127].

4.3. Policy Framework in the Combat of Energy Poverty

In this section, an analysis was performed to answer the last research question, i.e., “What is the role of policies in reducing energy poverty?”. As already stated, energy poverty is also a political problem that should be addressed globally and locally with adjusted policy frameworks.

Energy poverty was absent in some countries from any policy framework until 2010, when the social energy tariff emerged due to the severe economic crisis [13]. The lack of research on regional and national scales has hindered analysts and policymakers from creating more effective energy and building policy suggestions that account for various climates, types of buildings, and patterns of consumption [14].

Recommendations for crafting policies and strategies to address energy poverty should encompass socio-economic and cultural aspects. This involves evaluating the susceptibility to energy poverty through both quantitative and qualitative means, as well as incorporating socio-economic factors [1,18].

Efforts to address energy poverty should primarily prioritize securing funding for enhancing residential properties, with a particular emphasis on assisting low-income families. However, the decision-making processes at the national level are shaped by the guidelines and criteria set by the European Union. Nevertheless, the actual environment displays a diverse range of characteristics, thus necessitating energy poverty strategies to account for the unique and fluctuating factors of the particular location, region, and country being assessed [1,128]. Policies and strategies related to building rehabilitation are fundamental to:

• Improve the global energy efficiency of the buildings.
• Enhance the potential of renewable energy sources to decrease vulnerability to higher energy costs while increasing energy consumption with less environmental impact [14].

This type of policy should be prioritized over the current use of social energy tariffs for vulnerable consumers to support utility bill payments, as it provides a long-term solution. Central and local governments play a crucial role in underpinning energy efficiency measures, facilitating the decrease in energy use while upholding satisfactory levels of building energy efficiency and thermal comfort [63,129].

Policies should include renovation strategies, specifically passive methods aimed at diminishing energy consumption, highlighting the necessity for renewable energy sources to meet energy demands. The enhancement and upkeep of buildings are crucial investments that can enhance environmental, economic, and societal dimensions, thereby fortifying the architectural legacy, which in turn contributes to enhancing the populace’s quality of life. Implementation of passive renovation strategies has the potential to cut occupants’ energy requirements by around fifty percent in terms of heating needs.

Reviews have been conducted on key national policies and measures examining energy poverty in Europe, such as Cyprus, Lithuania, Spain, Portugal, and Bulgaria. Some nations exhibit different degrees of advancement in their research endeavours, with the levels of participation among these five countries being deemed pertinent for this examination. The European Union persistently formulates interdisciplinary strategies, exemplified by the utilization of directives, including financial support to facilitate initiatives at the domestic level within each member state [8]. Figure 6 summarizes the types of measures already adopted and their respective forms of action.

As for consumer protection, Directives 2009/72/EC and 2009/73/EC argue that safeguarding vulnerable consumers entails guaranteeing their ability to meet their energy expenses while maintaining an uninterrupted provision of energy during crucial periods. This involves safeguarding vulnerable consumers in the realm of electricity bill payments, as well as implementing broader initiatives within the social welfare framework and prohibiting disconnections during critical times [8,13,75].

Directive 2012/27/EU [60], European Fuel Poverty and Energy Efficiency (EPEE) project [51], Integrated Action Plans for Disadvantaged Communities (IAPDC) and Energy Efficiency (EE) [13], were examples of plans and programs created to target vulnerable families, and the National Energy and Climate (PNEC) Plan for 2030, in addition to identifying vulnerable groups, promoted new long-term strategies and looked for mechanisms using the integration of renewable energies [13].

In relation to financial interpositions, the emphasis lies on offering assistance to individuals with low incomes by granting a subsidy for heating and hot water expenses in accordance with various statutes and legal provisions. Vulnerable consumers are to be protected through the “provision of social security benefits” to ensure the continued supply of electricity and gas [8,13].

In the EUA, the “fuel project” was implemented, focusing on home weatherization and energy conservation; in addition, funds were allowed for fuel voucher programs. Also, the Low-Income Home Energy Assistance Program (LIHEAP) offers financial support to low-income households to mitigate the burden of high energy costs. The Wellness Action Plan (WAP) is the largest and longest-running federally funded residential energy efficiency program, which provides eligible low-income households with the opportunity to permanently reduce costly energy bills through cost-effective energy efficiency upgrades [57].

Energy-saving measures and Renewable Energy Systems (RES) integration are focusing on energy efficiency and RES promotion. Available schemes encompass enhancements in residential energy efficiency alongside the encouragement of renewable technologies, notably solar power. Vulnerable consumers frequently benefit from augmented funding, while support is also extended to biomass, biogas, and geothermal energy [8,13].

It is also important to note that providing information, raising public awareness, and providing information for improved energy efficiency in dwellings are the most underrepresented topics. The closest approximation can be found in the Directive (EU) 2018/844 for the energy performance of buildings, which states that when outlining national actions to contribute to energy poverty alleviation in their renovation strategies, member states have the right to set out what they consider relevant actions [8,13].

The European Domestic Energy Poverty Index (EDEPI) considers all the causes of domestic energy poverty included in the recast of the Internal Market in Electricity Directive [122]. The three most relevant aspects are (1) low income, (2) high energy expenditure, and (3) poor energy efficiency. The directive recommends that each member state take into account all aspects when establishing indicators for measuring energy poverty. EDEPI also encompasses the quality of dwellings, such as damp walls and rot in window frames, in addition to the inability to maintain suitable warmth in winter and coolness in summer.

It is essential to bridge theoretical concepts with practical political practices to combat energy poverty by establishing evidence-driven policies. Establishing a transparent and flexible framework for assessing the interplay of policy tools is crucial for the formulation and assessment of measures designed to alleviate energy poverty. By implementing policies that tackle income disparities and providing access to clean energy sources, countries can progress towards mitigating energy poverty.

Governmental incentives are targeted at the advancement of efficiency and technical capabilities in particular energy sectors. Consequently, policymakers are required to transition their focus from a purely technical standpoint to addressing social, political, and cultural obstacles.

Thus, policies to combat energy poverty depend on context, implementation, and local conditions. One of the most common policies is direct financial support to reduce the cost of energy for low-income households through energy subsidies. This allows for improved energy affordability. Another important policy is the adoption of social tariffs, which usually apply to low-income households [130]. However, both policies may not address issues like energy inefficiency, and, as a consequence, the cost might be shifted to other consumers. Governments also promote energy efficiency programs, i.e., initiatives improving energy efficiency, such as insulation, efficient appliances, and better heating systems. This includes plans to increase access to renewable energy sources, such as solar panels and off-grid solutions. Combining short-term measures with long-term solutions such as energy efficiency and renewable energy access tends to be the most effective way of addressing energy poverty sustainably [131]. These policies have been addressed all over the world, as well as in European countries.

An interesting work on assessing the energy efficiency mechanisms and energy poverty alleviation based on environmental regulation policy measures concludes that policies focusing on biomass use, energy production diversification, and regional energy databases are crucial for effectively combating energy poverty [132].

Non-governmental organizations and community initiatives also play a crucial role in combating energy poverty. Those actions include raising awareness about the challenges of energy poverty and the benefits of sustainable energy solutions; promoting energy efficiency measures and providing training on energy-saving practices; implementing renewable energy projects in off-grid areas; and providing clean and reliable energy sources to communities [133,134].

Some energy poverty programs identify vulnerable people anonymously for statistical purposes and to analyze the severity of energy poverty. However, respondents have to give consent to answer some questions, namely individual lifestyle factors, social and community networks, living and working conditions, and general socio-economic, cultural, and environmental conditions. These programs use local organizations or non-governmental organizations to find legible individuals to join this study in order to make the research trustworthy [131,135].

Table 4. Barriers to reducing energy poverty [81].

Dimension	Examples
Technical	Lack of high-quality equipment and/or standards and certifications; Difficulty in providing maintenance; Difficulty sitting projects/conducting resource assessments; Logistical problems, including transport and installation; Conducting proper environmental impact assessments; Constrained manufacturing capacity.
Economic and financial	Lack of capital; Electricity tariffs; Failure to include externalities in energy prices; Unfavorable power purchase agreements; Underinvestment in electricity infrastructure; Difficulty procuring financing; Long project lead times; Comparatively lower rates of return on investment.
Political and institutional	Political instability; Poor institutional capacity; Fragmentation in energy policymaking and integration obstacles; Lack of information; Corruption; Political patronage; Commitment to fossil fuels and/or subsidies for licensing.
Social and cultural	Local opposition and protests; Unfamiliarity and lack of knowledge; Theft and vandalism; Unrealistic expectations; Donor-driven priorities and aid dependency.

presents many of the barriers to be overcome in the fight against energy poverty, as suggested by the review presented in [81].

Technical barriers are one of the most critical issues in reducing energy poverty. Ensuring the reliability and maintenance of energy systems is challenging, particularly in rural areas, where the lack of existing infrastructure makes it difficult to deliver energy services. Solutions like solar systems and other decentralized technologies can bypass the need for extensive infrastructure. The initial capital investment, including power systems, grid extensions, and renewable energy installations, is considerable. The lack of financial literacy in society makes it difficult to access low-interest loans to install HVAC systems.

The key to mitigating energy poverty and its consequences is to promote education and culturally rational energy use. General society should be better informed to implement cleaner technologies, and it should be more aware and proactive in changing behaviour with a more sustainable mindset. There is also a need for the government to facilitate public and private initiatives, promoting collaboration between industry, academia, and the government to develop energy solutions [136].

5. Final Considerations and Conclusions

Energy poverty has been shown by several authors to be a problem on a global scale. Part of the issue is the result of inadequate salaries in comparison to the energy costs, compounded by the aging infrastructure that was established at a time when adherence to minimum certification standards was not obligatory. This is further exacerbated by the utilization of suboptimal or less advanced building materials due to limited options during that period. On the other hand, the specific policies and climate conditions of a country or region must be analysed prior to building construction, as energy needs depend on the geographical position and insolation conditions. These are the considerations to respond to the research question, “How do technology, socio-economic aspects, local climate conditions, and policies influence energy poverty and their respective indicators?”. Based on the literature content analysis, there are several mature technological solutions available in the markets to mitigate energy poverty and the consequent lack of thermal comfort, with reasonable specific costs, but the low financial income of families makes their acquisition and installation difficult.

Climate change has caused a great impact on the weather patterns in several regions worldwide, making the identification of building energy requirements to ensure thermal comfort unpredictable. Energy poverty was initially associated with the inability to heat homes during the winter season. However, with the increase in global temperatures, energy poverty now encompasses cooling needs. Many authors recommend the mapping and identification of vulnerable areas, as well as the study of improvements at the level of the economic possibility of society, for example, in the type of air conditioning technology adopted and insulation used in relation to the type of building under study.

In part, technological measures are suggested to meet the energy needs and at the same time end up being economically compensated to the individual, such as being clean, sustainable, and coming from renewable sources, such as solar energy, namely solar collectors and solar panels, geothermal energy, biomass, wind energy, or rather, finding a solution capable of combining technologies to meet the maximum needs. However, the initial cost may be less economical; however, studies prove that the adoption of these technologies has been recovering over time.

On the other hand, these technology adoption measures can be exempted from government policy measures that help the individual make the initial investment. Furthermore, it is argued that this technology adoption exemption should be made for a clean and environmentally friendly solution, as well as appropriate to the application and region/area of incorporation.

However, this investment is not taken for granted by the whole society. It is notorious for great social inequality, namely salary inequality, and many are those who cannot pay the bills at the end of the month. In this sense, measures that protect the most vulnerable are necessary, along with tariffs and voucher supports capable of financially helping those cases, at least in periods of economic crisis.

Another solution for the most vulnerable is perhaps not through financial help but through flexibility, i.e., preventing the cutting-off of electricity or gas in more critical economic moments. Energy poverty is worsening year by year, with measures being established and even an obligation to adopt clean, renewable technology solutions in new buildings. Society is failing to the extent that it resists the adoption of technologies due to cultural factors or vulnerability, even if this vulnerability comes from wallets. Governments are failing with the measures they adopt, as what they establish is badly balanced against the needs of society. Wages stay the same or go up, but costs go up.

Many authors refer to qualitative and quantitative indicators of energy poverty, which helps to take action in the face of what is happening in the various countries and regions under analysis. Based on this analysis, there are still many barriers to overcome to overcome energy poverty, and the reality of the countries varies greatly from one to another.

This study points out a solution related to the promotion of economic and financial governmental incentives, taking into account the local climate conditions in the region where economic power and geographical reality are determining factors to simulate the need for providing aid to individual dwellings so they can warm them in winter and cool them down in summer. Technological combinations are available in the market that are capable of meeting the needs in a cost-effective way and, at the same time, contributing to the reduction of energy dependence, such as efficient HVAC equipment and systems using renewable energy sources (e.g., PV systems).

Many countries have limited studies and policies regarding energy poverty. The multiplicity of existing climates and the multitude of technical and economic variables are decisive in defining the concept of energy poverty and identifying metrics for its quantification. In conclusion, measuring energy poverty is a multidimensional problem that depends on the individual characteristics of households (income, specific energy needs, and available technologies) as well as external factors (such as energy prices, climatic conditions, and energy distribution infrastructure). Consequently, a range of indicators have been developed to measure energy poverty. The majority of these indicators are directly linked to the economic aspects; social or environmental considerations are only indirectly taken into account (such as the relationship between energy efficiency, income, and energy consumption). The environmental aspect is encompassed by only a limited number of composite indicators that have been developed to measure energy poverty. With a view to the future, it would be useful to streamline a set of countries and study the similarities and the possible categorization of similar energy poverty metrics to be applied to those countries.