**1. Introduction**

Despite enhanced efforts to increase energy access in sub-Saharan Africa (SSA) and an estimated overall investment of over \$1.4 bn for off-grid electrification in the global South [1], the number of people without access to electricity in the region has remained largely unchanged [2]. This means that around 600 million people still lack access to energy in SSA. Over 80% of the people without electricity access living in rural areas [3]. Decentralised renewable energy (RE) systems such as solar PV mini-grids (MGs) are considered to be central solutions to enhance access to clean energy in rural SSA [4] and are estimated to provide connections to 75% of the rural SSA population in a universal energy access scenario by 2030. This scenario translates into roughly 100 to 120 million additional MG household connections, or around 350,000 MGs to be implemented within the next decade [3]. Consequently, questions related to the planning and implementation of RE MGs and their sustainability dimensions have gained substantial public and academic interest [5,6] resulting in two conflicting major overall findings. The first is that RE MGs have the potential to significantly contribute to the achievement of the Sustainable Development Goals (SDGs) in rural SSA. The second is that they face substantial sustainability

**Citation:** Stritzke, S.; Jain, P. The Sustainability of Decentralised Renewable Energy Projects in Developing Countries: Learning Lessons from Zambia. *Energies* **2021**, *14*, 3757. https://doi.org/10.3390/ en14133757

Academic Editors: Michal Bernard Pietrzak and Bartlomiej Iglinski

Received: 28 May 2021 Accepted: 17 June 2021 Published: 23 June 2021

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challenges which hamper their widespread adoption and market-take-off [7] in many rural areas. Hence, the significant capital investment and scaling of RE systems that might cease operation if operation expenses permanently exceed revenues and maintenance costs is a substantial long-term threat to enhance energy access in the Global South.

To assess opportunities to scale the implementation of RE mini-grids to achieve the UN Sustainable Development Goals including clean and reliable energy access for all by 2030, a systematic understanding of the specific sustainability challenges of RE MGs is required to enhance implementation strategies for sustainable off-grid solutions. Previous learning lessons and insights gained during the implementation and operation of RE minigrids that have been implemented in a developmental context are of pivotal significance in this context but are often performed in silos, either focusing on technical—or financial or socio-cultural aspects of MG implementation or operation.

The goal of this article is to examine factors and their interdependencies that determine the sustainability of decentralised off-grid systems in a developing context from a multi-disciplinary perspective. Based on a comprehensive data analysis, the study aims to extract key learning lessons and strategic recommendations for scaling MG implementation through an interdisciplinary review process that integrates the three interrelated dimensions of MG implementation. These include the technical design, MG finance and economics as well the end-user perspective in the community context.

A systematic analysis of RE mini-grid case studies published between 2010 and 2020, the evaluation of over 1200 community surveys performed in Uganda and Zambia and a longitudinal, in-depth evaluation of two solar PV mini-grid projects in Zambia are the basis of this research. The analysis aims to provide detailed insights on the technical and economic challenges for MG systems and suggests technical, financial and operational solutions to address them in the context of scalability of decentralised energy solutions.

The analysis is guided by three research questions which also structured the research approach: First, how can sustainability of RE MGs be defined and which dimensions need to be taken into consideration when assessing the sustainability of a RE mini-grid? Secondly, what determines or influences the longer-term sustainability of MGs in a rural developmental context and which learning lessons can be derived from previous cases? Thirdly, which strategic implications can be generated from such an analysis for the scaling of RE mini-grid projects? The study aims to derive specific approaches for sustainable MG planning and implementation approaches in developing contexts.

This article is structured into five main sections. The overview of the discussion about the sustainability of RE MGs and the related dimensions in the following section will lead to the presentation of the methods applied to answer the research questions in section three which are a comprehensive literature review on MG sustainability, community surveys to understand the consumer perspective and an in-depth analysis of two case studies from solar PV MGs in Zambia. The findings for each approach, which will be presented in section four will be contextualised and discussed in section five under the aspect of implications for MG project development and operation as well as the scaling of MGs in SSA. The final section six summarizes key conclusions for a way forward to enhance the sustainability of MGs in developing countries.

The study is mainly focused on a rural sub-Saharan African context but includes findings from other regional developmental settings in Asia and Southern America. The data generated from the Zambian case study evaluation and the scale-up implications are mainly focused on solar PV mini-grids. However, the findings also bear implications for other types of RE MGs such as hydro MGs which have a substantial potential to achieve SDG 7 [8–10] and hybrid MGs as well, which however display different system-economics than solar PV MGs [11,12].

### **2. Background & Hypothesis: The Sustainability of RE Mini-Grids in a Rural African Context**
