As renewable energy production is intermittent, its application creates uncertainty in the level of supply. As a result, integrating an energy storage system (ESS) into renewable energy systems could be an effective strategy to provide energy systems with economic, technical, and environmental benefits. Compressed Air Energy Storage (CAES) has been realized in a variety of ways over the past decades. As a mechanical energy storage system, CAES has demonstrated its clear potential amongst all energy storage systems in terms of clean storage medium, high lifetime scalability, low self-discharge, long discharge times, relatively low capital costs, and high durability. However, its main drawbacks are its long response time, low depth of discharge, and low roundtrip efficiency (RTE). This paper provides a comprehensive review of CAES concepts and compressed air storage (CAS) options, indicating their individual strengths and weaknesses. In addition, the paper provides a comprehensive reference for planning and integrating different types of CAES into energy systems. Finally, the limitations and future perspectives of CAES are discussed.

Solar energy has been one of the accessible and affordable renewable energy technologies for the last few decades. Photovoltaics and solar thermal collectors are mature technologies to harness solar energy. However, the efficiency of photovoltaics decays at increased operating temperatures, and solar thermal collectors suffer from low exergy. Furthermore, along with several financial, structural, technical and socio-cultural barriers, the limited shadow-free space on building rooftops has significantly affected the adoption of solar energy. Thus, Photovoltaic Thermal (PVT) collectors that combine the advantages of photovoltaic cells and solar thermal collector into a single system have been developed. This study gives an extensive review of different PVT systems for residential applications, their performance indicators, progress, limitations and research opportunities. The literature review indicated that PVT systems used air, water, bi-fluids, nanofluids, refrigerants and phase-change material as the cooling medium and are sometimes integrated with heat pumps and seasonal energy storage. The overall efficiency of a PVT system reached up to 81% depending upon the system design and environmental conditions, and there is generally a trade-off between thermal and electrical efficiency. The review also highlights future research prospects in areas such as materials for PVT collector design, long-term reliability experiments, multi-objective design optimisation, techno-exergo-economics and photovoltaic recycling.

The literature presents a review of the current application of lean and green practices and highlights the context, barriers, drivers, tools, and critical success factors and tools for the integration of lean and green practices within the Sub-Saharan African (SSA) manufacturing industry. In addition, the current state, gaps in the existing literature, and future perspectives on the current challenges of the industry have been suggested for the integration of both paradigm and sustainability of the industry. Integration of lean-green provides means to addressing issues faced by manufacturing industries for improved competitiveness. This study demonstrates that the application of lean and green practice is critical to be identified and applied within the region through the analysis of research papers published in both operational and sustainability journals. The findings of this review indicate that the synergy of lean and green practices is an effective initiative for resolving the operational and sustainability challenges of the manufacturing industry within SSA. To achieve operational excellence and mitigate environmental concerns, industries must implement the right tools and consider the critical success factors. By applying appropriate tools and models, the SSA region can address the current challenges and achieve a reduction in cost significantly.