ORIGINAL ARTICLE Energy-efficient off-grid systems—review Aníbal de Almeida & Pedro Moura & Nuno Quaresma Received: 23 January 2019 /Accepted: 19 July 2019 # Springer Nature B.V. 2019 Abstract Globally, around 1.1 billion people do not have access to electricity and 84% of the population who do not have modern energy access are living in rural and remote areas of developing countries. Since the loads are far from the grid and providing the con- nection by extending from the main grid requires a high investment associated with long and costly transmission and distribution lines, addressing the problem requires innovative solutions. Therefore, off-grid microgrid sys- tems, using solar photovoltaic and storage systems, integrated with very high-efficiency lighting appliances, are a promising solution to supply energy for rural and remote location in areas which lack access to the electric grid. This paper presents an overview on the existing solar photovoltaic technologies for off-grid systems in- cluding the most recent plug and play solutions. A characterization of the most common strategies used for control, communication and metering of microgrids is presented, as well as the recent evolution of the associated component technologies. The security and protection systems used to protect the system against theft or robbery of the systems itself or energy theft in remote areas are also addressed. Additionally, a resumed characterization of the sociologic profile and motivation of people to damage off-grid systems is presented. An overview on the main off-grid appliance market evolu- tion and efficiency trends, in terms of energy efficiency, is also addressed in this paper. Finally, a set of recom- mendations to promote cost-effective systems is made, considering the market evolution path and the large growth potential of off-grid systems. There is an urgent need to reduce the total system costs, namely the soft costs of new microgrid systems in order to further accelerate the market growth, as well as widely accepted open standards to regulate and develop the market. Keywords Off-grid electricity . DC microgrids . Rural electrification . Off-grid appliances . Electricity storage . Energy efficiency Introduction There are currently 1.1 billion people worldwide living without access to energy, as presented in Fig. 1, mainly in South Asia and Sub-Saharan Africa (IEA 2017). In every region presented in Fig. 1, with exception of Sub-Saharan Africa, the population without energy access has decreased from 2000 to 2014. During this period, in Sub-Saharan Africa the population growth rate was higher than the number of people gaining access to electricity, causing an increase in the number of people without energy access. In the graphic on the left in Fig. 1, it is possible to observe the evolution of the population without access to electricity in Energy Efficiency https://doi.org/10.1007/s12053-019-09813-y A. de Almeida : P. Moura (*) : N. Quaresma Institute of Systems and Robotics, Department of Electrical and Computer Engineering, University of Coimbra, Coimbra, Portugal e-mail: pmoura@isr.uc.pt A. de Almeida e-mail: adealmeida@isr.uc.pt N. Quaresma e-mail: nquaresma@isr.uc.pt