علم اقتصاد انرژی خانگی در مناطق روستایی اتیوپی: تجزیه و تحلیل هزینه - منفعت از انرژی بیوگاز

Limited success in promoting improved energy sources, such as biogas, in rural areas of developing countries has been partly blamed on insufficient understanding of household energy use patterns. In this study, we assess the costs of energy generation from major energy sources (firewood and dung) in rural Ethiopia, as well as the economic potential of biogas as an alternative in addressing both energy and food security challenges. Results show that households in rural areas largely collect their own fuel, with female household members being mainly responsible for the chore. By investing in biogas plants, households could save time and energy, and have a supply of slurry that can be used as fertilizer in agricultural production. A cost-benefit analysis of biogas plants yields positive net present values for households collecting their own energy sources. Even higher net present values are obtained for households purchasing all of their energy needs; these households stand to gain significantly from the financial benefits of energy cost savings with biogas technology. Results are highly dependent on slurry being effectively used as a source of fertilizer and on the price of the replaced energy source. Thus the promotion of slurry use as fertilizer must be an integral part of a successful biogas programme. Another important issue is that at present, biogas plants are highly subsidized and thus the above conditions hold under the assumptions of subsidies. When analysed without subsidies, indicators are still positive, yet amortisation periods are significantly longer and close to the depreciation point, so that investment risks increase.

Africa's energy challenges have been described as major and severe despite the existence of great energy potentials on the continent [1], [2], [3] and [4]. Access to modern energy systems remains a challenge in Sub-Saharan Africa despite reserves of petroleum, natural gas and coal, which in 1990 accounted for nearly 2%, 3% and 1% of world reserves respectively, and the potential of hydro-, solar and geothermal energy sources [4]. Consequently, biomass, consisting of firewood, charcoal, dung and crop residues, remains the main source of energy in Sub-Saharan Africa [1], [2] and [3]. The current widespread and inefficient use of biomass energy has implications on the environment, human health and food security [5], [6] and [7]. Deaths from acute respiratory infections as a result of indoor air pollution have been estimated at around 1.3 million annually, which is higher than malaria deaths and almost half of HIV/AIDS deaths [8]. Women and children are the most affected as their exposure to indoor air pollution is higher than that of men [2] and [5]. Air pollution also contributes to greenhouse gases (GHGs) leading to climate change [5]. High demand for firewood (and its charcoal form) in urban areas has been linked to increased deforestation [9]. Household productivity is affected by the reallocation of time and labour from yield bearing activities to the collection of biomass energy [10]. Households also lose productive time due to ill health [5]. Biomass combustion in general and dung and crop residue combustion in particular amount to nutrient export from agricultural land [11]. Like other Sub-Saharan countries, Ethiopia is highly dependent on biomass for energy; households in rural areas are almost completely dependent on biomass for their energy needs [12]. Firewood is becoming scarce in Ethiopia where increasing population pressure, land degradation, deforestation and loss of soil nutrients continue to worsen both food security and the energy crisis [13] and [14]. With the increasing shortage of firewood, households are turning to dung and crop residues for energy. This new reliance further contributes to environmental, human health and food security problems. Consequently, there is a need to jointly address energy and food security challenges [15] and [16]. The lack of success in promoting cleaner and improved energy sources in Sub-Saharan Africa is partly due to the limited understanding of household energy use patterns [17]. Relatively few studies have focused on household energy use in Africa [18]. Biogas offers a technically feasible energy alternative in rural areas and helps mitigate some of the consequences of extensive biomass energy use [19] and [20]. Ethiopia, where the technology has been promoted since 1979 to kerb the energy crisis, has, according to the UNDP/World Bank Energy Management Assistance Program (ESMAP), a biogas potential of up to two million family units [21]. A feasibility study carried out by Eshete et al. (2006) revealed that of Ethiopia's 600–700 domestic biogas plants, about 60% have stopped functioning due to water and dung shortages, technical problems, abandonment and loss of interest [12]. A similar trend was observed by Ethiopian Energy Authority (EEA) [21]. Despite past failures the country has recently set up a multiple stakeholder driven biogas programme implemented by the National Biogas Programme Ethiopia (NBPE) to develop a viable and sustainable commercial biogas sector [22]. One of the earlier studies on biogas in Ethiopia has been conducted by Seyoum (1988) [23]. A more recent study undertaken by Renwick et al. in 2007 also deals with the financial performance of biogas plants in Sub-Saharan Africa as a whole, including, but not solely focused on, Ethiopia [24]. We follow the conclusions of their research which propose further studies examining market segmentation with respect to different potential target household types. Therefore, the main objective of the study is to provide a detailed analysis across different segments of the potential target groups and plant types. In particular, we segment the potential demand situations for biogas plants in three energy source scenarios, namely for households purchasing firewood, collecting firewood, and collecting dung. In a sensitivity analysis, we differentiate households according to their income. We also discuss two different sizes of biogas plants with 4 m3 and 6 m3 fermenter volume. As the majority of potential target households live in rural areas with agriculture as their main economic activity, we have a closer look at the potential linkages between agriculture and biogas plants by computing the fertilizer value of slurry as a by-product in the process.

The study results indicate that most rural households collect their own firewood and dung. Thus, blanket valuation of own collected energy sources using market prices may fail to represent the actual cost of energy use for rural households. Female household members, aged 18–59, constitute the main labour group responsible for energy source collection and management. The same category of labour is largely engaged in agricultural production and as such, opportunity costs of energy source collection are reflected in the alternative contribution of the respective labour to agricultural production. However, due to overall low agricultural productivity, the marginal productivity of labour is very low for rural labour leading to low shadow prices of own collected energy sources compared with purchased and other improved energy sources. This partly explains rural households' preference of own produced energy sources. With the additional opportunity costs of dung in its fertilizer value, the shadow price of own collected dung is comparable to the price of purchased firewood. However, low shadow prices of own collected energy sources leave biogas unable to compete unless heavily subsidized. While biogas is attractive under the present subsidy scheme, this attractiveness is reduced when subsidies are removed. From the cost-benefit assessment of the biogas plant, investing households stand to benefit mainly through slurry use as fertilizer, saved energy expenditure in traditional cooking and lighting energy sources and the associated labour savings. Consequently, profitability highly depends on slurry use as a source of fertilizer and on the price of replaced energy sources. Returns to biogas investment are highest for households which invest in biogas to replace purchased firewood. This factor also makes biogas attractive to this section of rural households as benefits are financially recovered through energy cost savings. The results are highly sensitive to both actual, market-based price and opportunity costs of replaced energy sources. Another limit to the economic attractiveness of plants is the absence of a biogas injera stove, which would have the potential to enhance the use of biogas plants thereby raising benefits which accrue at the household level.