Worldwide, over 1.1 billion people have no access to electricity. The consequences for the affected people include health hazards from fuels used for lighting, limits to learning when it gets dark, a short productive day and high expenditures on lighting alternatives. Since 85% of affected people live in rural areas in developing countries, increasing access to electricity through grid supply is logistically and financially challenging. As a potential solution to this issue off-grid solar chargers have been gaining popularity. This technology is under continuous development to achieve lower costs, faster battery charge and more electricity generation to prolong light hours. This review contains a comprehensive analysis of possible improvements to solar lights and the role solar PV concentrators can play in it. It aims to provide the reader with a critical comparison of existing solar PV concentrators and to consider the advantages and drawbacks if applied to portable solar systems used in developing countries. From this review, static nonimaging concentrators have been identified as best suited since they are easy to operate and maintain and have shown high reliability. A detailed comparison of existing static nonimaging concentrators is presented in this work and their suitability for being deployed in portable solar systems in developing countries is evaluated. It concludes that the existing designs need adjustment if to be used for this purpose. Thus, novel concentrator designs for portable solar systems for developing countries are needed to facilitate more off-grid solar power generation. It is the aim therefore of this review to stimulate more research in this field.

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.Vehicular safety applications have much significance in preventing road accidents and fatalities. Among others, cellular networks have been under investigation for the procurement of these applications subject to stringent requirements for latency, transmission parameters, and successful delivery of messages. Earlier contributions have studied utilization of Long-Term Evolution (LTE) under single cell, Friis radio, or simplified higher layer. In this paper, we study the utilization of LTE under multicell and multipath fading environment and introduce the use of adaptive awareness range. Then, we propose an algorithm that uses the concept of quality of service (QoS) class identifiers (QCIs) along with dynamic adaptive awareness range. Furthermore, we investigate the impact of background traffic on the proposed algorithm. Finally, we utilize medium access control (MAC) layer elements in order to fulfill vehicular application requirements through extensive system-level simulations. The results show that, by using an awareness range of up to 250 m, the LTE system is capable of fulfilling the safety application requirements for up to 10 beacons/s with 150 vehicles in an area of 2 × 2 km 2 . The urban vehicular radio environment has a significant impact and decreases the probability for end-toend delay to be ≤100 ms from 93%-97% to 76%-78% compared to the Friis radio environment. The proposed algorithm reduces the amount of vehicular application traffic from 21 Mbps to 13 Mbps, while improving the probability of end-to-end delay being ≤100 ms by 20%. Lastly, use of MAC layer control elements brings the processing of messages towards the edge of network increasing capacity of the system by about 50%.