1. Introduction
Energy plays an important role in attaining sustainable and inclusive growth both in low- and high-income countries. An increase in coverage of energy services plays a crucial role in the country’s promotion of economic growth, health improvement, poverty reduction, competitiveness enhancement, and gender balance [
1]. On the other hand, it is expected that global energy demand will continue to increase with an increase in population and the expansion of energy-dissipative economic activities [
2]. To address the high demand for energy, there is a need for clean and renewable energy technologies to mitigate climate change by reducing greenhouse gas emissions in the long term. To meet the energy needs of rural areas in an environmentally sustainable way, harvesting renewable energy in a decentralized way is one of the options that would improve their wellbeing and economic prospects for potential global investment [
3].
Around 3 billion people cook using open fires or simple stoves that burn polluting fuels such as wood, charcoal, animal dung, crop waste, coal, and kerosene [
4]. About 2.5 billion people in developing countries depend on biomass for basic energy, which includes coal and animal dung cakes since they are readily available [
5]. But in Africa, despite the availability of various energy sources, more than 80% of the total population in most countries still relies on traditional biomass as the main source of energy for cooking [
6].
Biomass energy is a large renewable source with the potential to contribute to the world’s energy needs. It contributes between 10 and 14% of the world’s primary energy, including about 3% of the world’s transport, but has the potential to contribute up to 30–40 +% in 2050, depending on the source [
7]. Many developing countries still rely on biomass energy. In Kenya, most households rely on charcoal conversion kilns, charcoal stoves, and woodlots, where it meets about 70% of Kenyans national energy requirements [
8]. Similarly, in Pakistan, traditional cooking stoves utilize 80% of the bioenergy, resulting in 64% of biomass cooking and 86% of total biomass energy in the household sector [
9].
Ethiopia has one of the world’s poorest accesses to modern energy supplies. With more than 80% of Ethiopia’s population residing in rural areas and heavily reliant on agriculture; the primary source of energy for this rural population is biomass, accounting for approximately 87% of total energy supply [
10]. However, the country has largely untapped renewable energy resources. Ethiopia has 141.8 million tons of estimated exploitable biomass potential, with a current 70.9 million tons of exploited biomass potential [
11]. The current level of electricity access is quite low in Ethiopia. In urban areas, 87% of the population has access to electricity [
12], while only 5% of the rural population has access to electricity [
13]. The annual theoretical hydro energy potential of the country was estimated at 954 TWh, out of which its geographic potential is 286 TWh [
14]. The abundance of solar energy resources is estimated to be about 5.2 kWh/m
2/day [
14,
15]. Estimation at a country level also shows the adequacy of exploitable biomass energy potential from different sources [
11].
Relying on biomass energy sources causes problems, especially household air pollution, which increases the risk of acute lower respiratory infections in children under five years old among others [
16]. Several studies have reported the effect of non-renewable energy on environmental pollution. Non-renewable energy increases environmental stress through increases in CO
2 emissions, suggesting that renewable energy is the best alternative to non-renewable energy for mitigating the level of energy-related pollution [
17,
18]. In addition, it is documented that biomass energy use exposes users to physical and psychological health challenges [
19].
Ethiopia is gradually moving forward with reducing its reliance on non-renewable energy sources and shifting power to a clean and renewable energy supply. Currently, the country’s energy demand is increasing due to its fast-growing economy and flourishing infrastructure [
10]. Thus, finding an alternative energy source and understanding determinant factors of biogas technology adoption is crucial.
Biogas is the emerging bio-energy in the rural areas of Ethiopia through biogas development, Biogas in rural households could provide a more sustainable energy source than wood fuels. Understanding its importance, Ethiopia established a national biogas program since 2007 [
20]. In Ethiopia, biogas is mainly used for cooking. Biogas can also be used to power internal combustion engines, refrigerators, or radiant heaters, yet their application is even less widespread than lighting or cooking. As a result of biogas adoption in Northern Ethiopia, the fuel wood and charcoal consumptions were significantly reduced [
21].
Understanding the importance of biogas technology, the National Biogas Policy of Ethiopia introduced and promoted the implementation of biogas technologies in rural areas. However, there is a huge burden on women and children, who spend up to 10 h a week gathering wood in rural areas [
22]. This is partly because; there is relatively low adoption of biogas technology in developing countries in general and in Ethiopia in particular. The barriers contributing to the low adoption of biogas technology as a source of energy, especially in rural areas, are not well documented [
23].
The ever-increasing demand for woody fuel and the inefficient household biomass energy utilization, which results in a huge amount of energy loss during cooking and heating, are the main causes of the subsequent degradation of woody biomass and environmental degradation in the country [
24]. This is because modern fuel devices are either unavailable or unaffordable, especially for rural and poor urban people. Hence, with the increasing cost of fuel wood, households are forced to increasingly rely on lower-quality combustible materials such as dung and crop residues. Even worse, in areas experiencing a shortage of grazing lands, most of the crop residues must be devoted to animal feeds [
25].
Ethiopia has a biomass energy potential of around 101,656.77 Tcal (equivalent to 118,125.17 GWh) from wood, crop residues, and cow dung, of which crop residues and cow dung account for 27% (14% dung and 13% residues) [
26]. The potential of dung energy potential is around 0.55% of the global biogas energy potential from available livestock manure from cattle, buffaloes, pigs, and chickens [
27]. However, the potential for biomass energy varies from place to place because of population density, household biomass sources, access to improved energy technologies, the availability of land, and common resource pools. Hence, it is imperative to study the potential of biomass energy resources, consumption patterns, and accessibility to improved energy technologies and identify the challenges and opportunities of adopting improved energy technologies, considering local contexts. Moreover, socio economic factors play a significant role in biogas adoption [
28]. On the other hand, it is documented that socioeconomic and demographic factors hinder the adoption of domestic biogas energy technologies in different parts of rural areas in Ethiopia [
29,
30]. These are not the only factors determining the adoption of modern energy technology in general, and biogas in low-income countries with huge resource scarcity and sociocultural factors is strong. However, none of the previous studies has considered Limu Kosa district, which is a cash crop-producing area with households that have the potential to afford biogas installation. This study wishes to contribute to the existing literature by analyzing the biomass potential at the local level and the determinant factors of adopting biogas technology and, hence, suggesting the sector improve adoption of the technology. Hence, understanding the potential of an area and identifying factors that determine biogas use is crucial to devising enabling policies and taking sustainable action to enhance the adoption of improved energy technologies. Thus, this study aimed at assessing the potential of biomass energy, its consumption pattern, and the challenges of adopting improved energy technologies in rural areas of Limmu Kossa woreda, Ethiopia.
4. Discussion
This study evaluated the household’s energy consumption pattern, the household’s biomass energy potential, and the situation for adoption of biogas energy technologies. The study shows that over 96% of households rely on the traditional use of biomass energy for cooking, and over 65% of them collect firewood by travelling 2–4 km. These have significant implications for the socioeconomic conditions of households and the local environment. Particularly, women who shoulder household chores are at a disadvantage and deprived of several social and economic opportunities. However, the majority of households have sufficient biomass energy resources that can be used for improved biomass energy technologies such as biogas. It has been shown that households, on average, can technically produce 1 m
3 of biogas per day from different biomass energy sources. This amount is sufficient to light a 60–100-watt bulb for 6 h, can cook three meals for a family of 5–6, replace 0.7 kg of petroleum, run a one-horsepower motor for 2 h, and generate 1.25 kWh of electricity [
38,
39]. 1 m
3 of biogas can replace 5.56 kg of firewood per day, or 2029 kg of firewood per year. Accordingly, this amount can satisfy about 70% of the household’s biomass energy demand for cooking (
Table 4). Moreover, if all the available biomass energy potential of the study area can be converted to biogas energy, it can save about 9600 tons of firewood from the study area. This indicated that biogas also reduces the increasing deforestation occurring due to heavy firewood consumption. Therefore, using the existing resource for biogas energy can reduce 69% of end-user emissions and deforestation due to firewood consumption.
The adoption of biogas technology in households would directly contribute to the attainment of different SDGs in addition to SDG 7. Biogas technology can reduce the heavy dependence of households on biomass-based energy sources by providing readily available gas for cooking, lighting, and powering elementary electric appliances with minimal emissions. The use of biogas slurry for fertilizers can improve soil nutrients, increase productivity, and contribute to SDG 2. Furthermore, in addition to increasing soil productivity, it can save households expenditure for inorganic fertilizers. This will improve food production, reduce hunger and malnutrition, and enhance sustainable agricultural practices. The substitution of firewood by biogas can reduce indoor air pollutant emissions and improve health, especially for women and children who spend a lot of time in the kitchen, thus contributing to SDG 3. Anaerobic digestion can eliminate pathogens from waste and contribute to SDG 6 by reducing the burden of wastewater discharged into water bodies and ensuring water availability for other uses. The use of biodegradable waste as a biogas energy source reduces the amount of nutrients that would have caused environmental pollution in water bodies, thus contributing to SDG 15.
Ethiopia, being an energy-deficient country, has a strong interest in the development of its abundant renewable energy resources [
40]. Moreover, it was suggested that the dire energy needs of the country can be addressed by decentralized bioenergy generation [
41]. Apart from reducing energy poverty, biogas technology has substantial economic, environmental, health, and social importance. However, adoption of biogas technologies can be affected by several factors, as indicated in our results (
Table 11). It has been shown that household gender, level of education, annual income, and distance to firewood collection were the main determinant factors for biogas adoption. Previous studies also reported family size [
42,
43], gender [
44], level of education [
45], household income [
45,
46], distance to firewood source [
47,
48], number of cattle [
49], and land holding size [
50] as main determinants for biogas technology adoption. This implies that access to biogas technology requires an overarching policy and strategy to alleviate these problems and enhance its adoption.
Our study did not show a statistically significant association between household family size and the adoption of biogas technology. A previous study also reported a mixed influence of family size on bio gas adoption [
43]. It is believed that more family members are important for the operation and maintenance of the biogas plant. However, the insignificant effect of family size on the adoption of the biogas technology in the study area might be explained by the reliance on daily laborers rather than family members. Since the study area is a cash crop producing area, the family members might engage in different activities than biogas operations. However, one of the main challenges to biogas adoption and operation is its labor costs. In particular, a biogas operation involving dung, water, and slurry collection is labor-intensive and may not be feasible in rural areas where household members have a lot of task division and responsibilities [
51].
The adoption of biogas technology can be negatively or positively affected by the gender of the head of the household. Several studies have shown that gender plays a crucial role in the adoption of biogas technology [
22,
44,
52]. Our study revealed that all the household heads of biogas adopters are male headed. This might be because men are decision-makers in economic activities in general and energy plant adoption in an area. Similarly, a previous study conducted in Ethiopia showed that male-headed households were more likely to adopt the technology than female-headed households [
22,
53,
54]. In contrast, one of the previous studies showed the significant influence of female-headed households decisions on biogas plant installation [
28]. The decision of the household to adopt biogas technology could be linked to their ability to afford the costs of its installation. Our study showed the significant effects of a household’s annual income on biogas adoption. This is supported by previous studies showing the significant association between household income and biogas technology adoption [
46,
54,
55]. This might be due to the fact that high income facilitates the adoption of biogas technology, which requires a high initial cost for the installation of biogas digesters [
56,
57,
58]. Availability and distance to fuel wood sources thus positively influence the adoption and utilization of biogas technology [
58]. The result of our study shows that the availability of firewood in nearby places had a significant effect on biogas technology adoption. Similarly, a previous study showed that adoption of biogas technology was positively correlated with the availability of firewood [
20,
28,
52]. This implies that households having access to free biomass energy collected from common sources may not be interested in paying for improved energy technologies.