**Based on the conceptualization of energy poverty, we describe these approaches in more detail but rely on approaches we can feasibly measure and monitor with the available data in Bulgaria.** As we are ultimately interested in recommending a measure of energy poverty in Bulgaria that can be operationalized for monitoring and evaluation purposes, we rely on those approaches that we can feasibly measure and monitor through household expenditure surveys and the EU-SILC (see Column 4 in Table 1). We also explore the potential of big data sources. This leaves us with the following approaches: the access-based approach, the consensual-based approach, the outcome-based approach, the big data approach, and the expenditure-based approach. Finally, we analyze the strengths and weaknesses of each of these approaches.

# 2.2. Access-Based Approach

**The most straightforward approach to measuring energy poverty is to analyze the share of the population without access to energy.** The worst form of energy poverty is not having access to energy, which has important implications for overall well-being and monetary poverty. Previous research shows a significant relationship between access to electricity, for example, and poverty rates (Asghar et al., 2022). A common approach to measuring this aspect of energy poverty is to look at the share of the population without access to certain energy services, such as electricity, natural gas, or other forms of energy. There are binary access-based approaches (e.g., having access to electricity or not) and those using a threshold (e.g., having more than 50 kWh of electricity per capita) (Nussbaumer et al., 2012). Others have constructed composite measures such as the Energy Access Index (EAI), which measures access to six essential energy services: lighting, cooking, water heating, space heating/cooling, information/communication, and mobility (Practical Action, 2010).

**Access to energy services can be measured at the extensive but also the intensive margin**<sup>**23**</sup> **and can,**

**additionally, refer to access to clean and sustainable energy.** Most measures focusing on energy access measure households' access to energy at the extensive margin, meaning that they analyze whether households have access to energy. Moreover, quality aspects in households' energy access and reliability also play a role in energy poverty (the intensive margin). Bhatia and Angelou (2015) present a multi-tier framework to analyze the quality of energy access in the case of electricity. They measure reliability (the number of disruptions per week), legality, the health and safety aspects of the available energy source, peak capacity, and duration, among other factors. Another aspect one can measure with access-based approaches to energy poverty is access to certain types of energy, such as clean energy (Ullah et al., 2021).

**Access-based measures are helpful in identifying the most deprived populations and improving energy poverty around lack of access, but they also suffer from limitations.** While access-based approaches are helpful in detecting the most deprived populations as they lack access to energy altogether, they abstract from other important aspects of energy poverty, such as variations in energy needs and preferences or the affordability and sustainability of energy services. Measures at the extensive margin also abstract from the quality and reliability of energy services.

# 2.3. Expenditure-Based Approaches

## **The discussion on how to best measure energy poverty does not stop with the type of approach one should best use but extends to questions around how to best construct each metric within a given**

> 23 By extensive margin, we refer to having access to energy or not (a binary description). By intensive margin, we refer to various characteristics of energy poverty related to its quality and reliability. For example, how many hours per day the household receive electricity, the number of blackouts per month, etc. This is more difficult to quantify.

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