**1. Introduction**

Energy plays a pivotal role in the social, economic and cultural development of any population [1]. Energy from carriers (e.g., electricity) is converted via end-use technology (e.g., televisions, mobile phones, bulbs and mechanical fans) into useful household energy services (e.g., entertainment, communication, lighting and space cooling). Energy also supports income-generating activities including construction, agriculture and manufacturing. This is especially relevant for developing nations, who have been shown to exhibit a much larger increase in the Human Development Index (HDI) for a corresponding increase in energy consumption per capita, compared to developed nations [2]. However, it is estimated that almost 800 million people lack any access to electricity, with approximately 550 million of them living in Sub-Saharan Africa [3]. Transitioning these people from traditional sources of energy (biomass and waste) to accessing modern energy such as that provided by electricity poses a major challenge. The importance of this challenge is encapsulated by the United Nation's (UN) Sustainable Development Goal (SDG) 7, which calls for universal access to affordable, sustainable, reliable and modern energy by 2030. There has been significant progress towards the goals of SDG7 at the country level in developing regions, with countries such as Kenya, Uganda and Sudan making the most progress, even though the current pace of global efforts has so far been insufficient [3].

While there is no single definition of energy poverty, it has been referred to as a lack of access to modern energy services [4] and a deficiency in the consumption of energy required to meet basic human needs [5–7]. Reddy [8] (p. 44) captures the multi-dimensional nature of energy poverty by defining it as "the absence of sufficient choice in accessing adequate, affordable, reliable, high-quality, safe and environmentally benign energy services to support economic and human development". This recognition of the multi-dimensional nature of energy poverty (and therefore access) helped shape development of the Multi-Tier Framework (MTF) formulated by the World Bank's Energy Sector Management Program (ESMAP) designed to provide a measurement framework for measuring energy access [9], although it does focus mainly on electricity. The MTF has been referred to as providing the most sophisticated energy measurement metric [10], and measures seven attributes of capacity, availability, reliability, quality, affordability, legality, and health and safety, an approach that takes into account the various factors that influence a household's ability to access energy. It also recognizes that energy access is not a binary 'have or have-not' condition, but rather that households can exist at varying levels of access depending on socioeconomic factors and other circumstances dictated by the seven attributes listed earlier. The levels of energy (electricity) access described in the MTF are referred to as 'tiers' and vary from Tier 0 (no access) to the highest level of access, which is Tier 5. Moving up these tiers can be seen as climbing up the so-called 'energy ladder'. A visual representation of the MTF, showing the various tiers, is shown in Figure 1, a matrix for measuring access to household electricity supply, and Figure 2, a matrix for measuring access to household electricity services.

For decades, rural electrification in developing regions has primarily been achieved via grid extension, and this is still integral to rural electrification policies in many parts of the developing world [11–13]. However, grid extension has been much slower than anticipated in many regions [12,14], and a key barrier to it is that it is not profitable for utilities to invest the capital required to deliver electricity to rural communities with relatively low patterns of consumption [15,16]. In the meantime, decentralized options such as solar home systems (SHSs) have proven to be popular for electrifying households and other small users due to their falling prices and renewable power source; in Kenya, more than 30% of off-grid households have a solar PV product at home [17].

A typical SHS consists of a PV module typically placed on a rooftop to capture sunlight, a battery for storing energy, and end-use appliances which provide energy services. Capacities of SHS can range from 10 to 200 W [18]. However, the typical SHSs used in rural Sub-Saharan Africa are in the 10–100 range [19,20]. While the upfront costs of SHSs, at up to \$400 for an 80 W system [21], can act as a barrier to entry for many of the poor rural households, the introduction of Pay-As-You-Go (PAYG) service has helped improve its uptake. This is achieved by providing the SHS as a service, with the households making small, regular payments to access the service over an agreed time period, after which they own the SHS [22,23]. Companies such as M-KOPA and Bboxx in Kenya have successfully integrated mobile payment technologies with their SHS services, providing their customers with the convenience of making payments using their mobile phones, and increasing the flexibility of the amounts they pay and the payment intervals [24,25].

Multiple studies have shown that households moving from Tier 0 (i.e., unelectrified) to using SHS (typically Tiers 1 and 2) have seen an improvement in their quality of life [26–28]. SHS use has been linked to health benefits, as it displaces household use of kerosene and candles which expose users to a range of health risks including burns, child poisoning due to inadvertent consumption of fuels, and a variety of conditions linked to indoor air pollution from fine particulate matter, sulphur and nitric oxides. The most common use for SHSs is the improved lighting service it provides compared to kerosene or candles [29] with educational improvements for children who use the light to read and do homework as a key outcome [26,30]. SHS use has also reduced the need for household members to travel long distances for charging their mobile phones [31].


**Figure 1.** Multi-tier matrix for measuring access to household electricity supply (source: [9]).


**Figure 2.** Multi-tier matrix for measuring access to household electricity services (source: [9]).

Access to, and initial consumption of electricity has been shown to lead to increases in consumption over time, as users purchase more appliances (if affordable) [32]. This is in line with the study by Opiyo [33], which demonstrated that rural households in Kenya, upon realising the socioeconomic benefits of their basic electricity access from SHS, began to desire more high-powered appliances such as televisions and cooling fans. However, some researchers, such as Lee et al. [34] and Stojanovski et al. [20], have observed that while rural households purchased these appliances to benefit from the services they provide, they could not be accommodated by their SHSs due to their relatively small energy capacity, and hence these appliances were unusable. Hence, despite their broad appeal, there are questions surrounding home solar products and the energy services they are able to provide to rural households. There is a paucity of research designed to explore the nature of the energy services home solar products provide to rural communities in the developing world and especially the views and aspirations of households regarding access to energy services. For example, do households feel that they may become 'trapped' into what they see as an 'inferior' source of energy? In this paper, the results of a household energy survey conducted across two locations in Nigeria are used to provide an empirically based analysis of SHS use in rural households and how those households view such systems vis-à-vis alternatives such as an extension of the grid supply. In particular, the research aims were to:

