Hydropower is an important renewable energy resource worldwide. However, its development is accompanied with environmental and social drawbacks. Issues of degradation of the environment and climate change can negatively impact hydropower generation. A sustainable hydropower project is possible, but needs proper planning and careful system design to manage the challenges. Well-planned hydropower projects can contribute to supply sustainable energy. An up-to-date knowledge is necessary for energy planners, investors, and other stakeholders to make informed decisions concerning hydropower projects. This is basically a review paper. Apart from using expert knowledge, the authors have also consulted extensively from journals, conference papers, reports, and some documents to get secondary information on the subject. The paper has reviewed the world energy scenario and how hydropower fits in as the solution to the global sustainable energy challenge. Issues of hydropower resource availability, technology, environment and climate change have been also discussed. Hydropower is sensitive to the state of environment, and climate change. With global climate change, though globally the potential is stated to slightly increase, some countries will experience a decrease in potential with increased risks. Adaptation measures are required to sustainably generate hydropower. These are also discussed in the paper.

The importance of renewable energy such as small hydropower for sustainable power generation in relation to its capacity to contribute towards alleviating acute shortage of rural electricity supply in the sub-Saharan African region has been discussed. A relatively comprehensive small hydropower technology review has been presented. Rural electricity supply scenario in the region has been presented and, in general, the region has very low electricity access levels coupled with various challenges. Small hydropower technology has been discussed as one of the promising decentralised power generation system for rural electricity supply in the region. Despite challenges in data acquisition, this paper has shown that the SSA has significant hydropower resources, but the level of installation is very low. Challenges hampering SHP technology development in the region have been identified and discussed, such as those concerning technology, climate change, finance, and policy. This is basically a paper where the authors consulted a wide range of literature including journals, conference proceedings, and reports as well as expert knowledge in the area. It is hoped that this paper contributes to the information base on SHP technology which is quite lacking in the region.

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The most common type of energy used is firewood. In some Sub Saharan countries, up to 90% of total energy use is from firewood. The consumption of wood fuel is in some countries as high as twice the sustainable yield, something that has led to environ-mental degradation due to deforestation and scarci-ty of firewood. The use of fossil fuels such as kerosene and LPG for cooking is expensive. Solar energy is a non-consumptive and non-polluting fuel. It can help alleviate the problem of insecurity of cooking energy, which is the major domestic energy requirement. Several attempts have been made to introduce solar cookers in different coun-tries and have achieved variable successes. There are still critical issues yet to be resolved in order to make that technology acceptable for wider dissemi-nation. They include getting the most appropriate types of solar cookers for specific locations, opti-mum size/capacity, types of materials to be used, optimal design and affordable cost. In an attempt to resolve these issues, a comprehensive study involv-ing theoretical review, development work, experi-mental testing and evaluation of solar cookers was conducted for several years on six different types of solar cookers. The cookers are the ‘SunStove’ box cooker, wooden box cooker, panel cooker, reflector cooker with unpolished aluminium reflectors, reflec-tor cooker with polished aluminium reflectors and reflector cooker with glass mirror reflectors. This paper presents the results of the study. Results obtained indicate that many of the cookers could be used to cook food for households in areas with medium and high insolation, with appropriate selec-tion of the type and specification of the cookers. The specification should be based on the measured inso-lation data of the location indication of the direct and diffuse components. As a guiding tool, reflector cookers offer best comparative performance in areas with longest durations of clear sky (greatest direct beam), panel and collector cookers under moderate cloudy conditions and box cookers under very cloudy conditions.

The hydropower resources have become an attractive means of generating electricity to the off-grid network, especially in rural areas. This article assesses the small, mini and large hydropower resources and identified to reach 5.3 GW for electricity generation in Tanzania. The technology development discussed comprises of hydro turbine manufacturers, classification and turbine selection. The barriers presented include the presence of sediment in the hydropower reservoirs, financial viability, policy and regulatory issues related to hydropower development. This reviewed article serves the investors and policymakers to understand the status of hydropower resources in Tanzania.

Lack of access to clean energy for cooking and heating applications is one of the challenges faced by households in developing countries. Solar cooking is one of the solutions, but suffers low adoption and utilization due to various challenges including technical limitation. This study investigated initiatives on improving the technical viability of parabolic dish solar system used for direct cooking by focusing on the receiver. Three receiver prototypes namely; Insulated, Oil-filled and Air-filled, all incorporated with a base circular ring, were constructed and their performance was compared experimentally with the conventional receiver. The maximum temperature inside cooking vessels were 154 °C, 99 °C, 141 °C and 128 °C while standardized stagnation temperature and first figure of merit (F1) were found to be 159 °C, 100 °C, 154 °C and 109 °C; and 0.26, 0.15, 0.54 and 0.17, for systems with insulated receiver, oil-filled receiver, air-filled receiver, and conventional receiver, respectively. The second figure of merit (F2), overall heat loss factor, heat exchange factor and optical efficiency were determined as 0.36, 0.15, 0.14 and 0.33; 59.7 W/m2 K, 28.6 W/m2 K, 20.49 W/m2 K and 73.4 W/m2 K; 0.18, 0.75, 0.69 and 0.23; 25%, 4%, 4% and 17%. The study found that the cooking system with Insulated Receiver gave more merits and was established as the best.

An experimental study on the performance of calcium chloride-ammonia adsorption system is described. A single bed water cooled condenser adsorption refrigerator prototype, which utilises calcium chloride-ammonia pair has been developed and tested in the laboratory. Experiments have been conducted for desorption temperatures of 100 °C with desorption time varying from 1 to 4 hours. An electric tape heater and a timer were used to perform the experiments. The adsorption temperature profile, adsorption rate and prototype performance have been analysed and discussed. The tested heating and desorption temperature of 100 °C and heating and desorption time of 1 to 4 hours was able to create a cooling effect of the cold chamber of the prototype of between -0.8 to 8.3 °C, which is adequate for vaccine storage requirement of 2 to 8 °C. The estimated Coefficient of Performance of the system ranges between 0.025 and 0. 076.

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