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Because of its low environmental impact and high production, microalgae bio-oil has quickly become a popular renewable fuel option. The process utilizes microalgae which are readily available in nature to produce an alternative to fossil fuel. Although microalgal bio-oil production mechanisms have been previously reviewed in recent studies, comparatively few of them emphasize the significance of algal bio-oil production through all available bio-oil conversion mechanisms from microalgae. Here we review the available and common bio-oil conversion processes from microalgae, bio-oil upgrading, and the commercial aspects of its utilization. The most efficient route to bio-oil production can be identified by analysing both the biomass feedstock and the final product. For example, pyrolysis can produce high-energy bio-oil, but it also produces large amounts of char and gas. Although hydrothermal liquefaction and gasification are more complex and costly, they have the potential to produce bio-oil with greater consistency. However, the expense of using bio-oil in a commercial context is a major concern. The cost of producing bio-oil from microalgae is typically higher than that of producing conventional fossil fuels. Several factors, including cost, availability, and necessary infrastructure, contribute to the uncertainty of bio-oil’s commercial feasibility. With the constant improvements in technology and government support, however, bio-oil has the potential to emerge as a viable alternative to conventional fossil fuels.

Continual global energy scarcity and its future challenges, as well as environmental disasters, are causing global devastation. Additionally, a substantial quantity of food is being wasted regularly. Therefore, the adoption of circular bioeconomy principles and the bioconversion of wasted food appears to be both highly advantageous and urgently required. However, previous studies have placed limited emphasis on the technological progress and circular bioeconomy aspects associated with the bioconversion of wasted food. The present review thus investigates how mass-generated food waste can be used to produce valuable bioproducts through bioconversion techniques such as oleaginous metabolism, anaerobic fermentation, and solventogenesis. These techniques have attracted considerable interest due to their eco-friendly and resource-recycling capacities, as well as their efficiency and sustainability. The paper also discusses approaches to integrate biorefineries within existing economies to establish a circular bioeconomy and analyses the challenges as well as the techno-economic, environmental and life cycle scenarios of these approaches. Analysis of the techno-economic and environmental effects reveals that food waste biorefineries can be lucrative if certain pathways are maintained. The environmental impact of bioconversion methods that produce valuable bioproducts is also found to be substantially lower than that of conventional methods. Integrating bioconversion processes further improves the efficiency of the process and sustainably recovers resources. Developing a circular bioeconomy requires the adoption of a biorefinery strategy with an integrated approach.

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Perovskite solar cells (PSCs) are highly efficient and are comparatively cheaper than the large silicon crystals primarily used in solar cells. Their outstanding photovoltaic performance makes them a potential alternative to silicon solar cells. While efficiency and photovoltaic performance have been investigated in recent decades, a knowledge gap on the degradation, economic feasibility and stability of PSCs exists, and their poor stability remains a barrier to commercialization. Thus, this review aims to fill this knowledge gap by focusing on approaches to improve PSCs’ thermal and chemical stability, and their economic viability under different conditions. The structure and manufacture of PSCs are also discussed along with an economic analysis of different perovskite devices. Improvements in thermal stability can be reached by incorporating inorganic materials into the PSC. A PSC model optimized with ZnO improves chemical stability by 8% and works well under low temperatures. To make PSCs more economically feasible, certain parts like counter electrodes (CE) and hole transport materials (HTMs) can be replaced with alternative elements like carbon and inorganic HTMs, respectively. PSCs with long durability and high conversion efficiency will expand the commercial prospects for this material. To bridge the lack of knowledge, further investigation is required on the sustainability and longevity of PSCs.

The development of bio-lubricant is an immerging area of research considering the rapid depletion of petroleum reserve and environmental concern. This study aims to develop non-edible jatropha oil-based bio-lubricant and investigate the tribological properties considering commonly used piston ring-cylinder liner materials of stainless steel and cast iron due to their interaction under lubricated conditions in an internal combustion engine. The bio-lubricant was prepared by blending different percentages of vegetable oil with commercial lubricants. The tribological test was carried out using a Reo-Bicerihigh-frequency reciprocating rig (HFRR) for the duration of 6 h under standard operating conditions. Different properties of bio-lubricants were measured before and after the HFRR test using various analytical instruments. The morphology of the worn material surfaces was examined via Hitachi S-4700 FE-SEM cold field emission high resolution scanning electron microscopy (SEM). The result showed that addition of vegetable oil lubricant up to 7.5% concentration can be compared with commercial lubricant in case of wear rate and coefficient of wear as weight loss reduced significantly. Minimum change in viscosity was observed at the addition of 7.5% bio-lubricant. Surface morphology analysis confirmed less damage of metal surface when tribological analysis were performed at mixed lubricated condition.

The aim of the present study is to evaluate the thermal behavior of cylindrical modules in a thermal energy storage unit as a combined sensible and latent heat. A thermal energy storage unit is designed, fabricated, and connected to a cold and hot water supply at constant temperatures to monitor the performance of the storage unit. The thermal energy storage unit contains the cylindrical microcapsules containing paraffin waxes as a phase change material which is located inside an insulating cylinder storage tank. Water is used as a heat transfer fluid to transfer heat from a hot water reservoir to the thermal energy storage unit during the phase change material charging process and also during the discharging process water receives heat from the thermal energy storage unit. Charge tests are carried out at the constant temperature. Moreover, the effect of different inlet flow on storage unit performance is investigated. Data were analyzed using Design Expert software and regression analysis which indicated that the increase of charge inlet temperature and charge inlet flow leads to the increase of heat power, thermal performance of thermal energy storage unit, and output variables. In comparison to the heat storage system without phase change material, microcapsules phase change material can improve the heat power of the heat storage system. Also, based on the optimization process, the maximum thermal performance of 96.4% and the maximum heat power level of 1.7 kW can be achieved in the optimized condition of the charging inlet temperature of 75 °C, charging inlet flow of 1.8−4 m3/s, and discharging inlet temperature of 35 °C.

Solar energy is considered to be one of the most promising renewable and sustainable energy sources. Two key technologies such as photovoltaic and concentrated solar power are mainly used to convert solar radiation, out of which photovoltaic directly converts solar radiation into electricity, while concentrated solar power technology converts solar radiation both into heat and electricity. The key advantages of concentrated solar power technology over photovoltaic is its capability of storing heat energy which can be utilised in the absence of sunlight, overcoming the limitation of the intermittent nature of solar power. Currently, the cost for the concentrated solar power with storage is about 9.0 ¢/kWh (same as commercial photovoltaic system), which is expected to drop at ~5.0 ¢/kWh by 2030. Besides four mainstream concentrated solar power technologies, this paper reviewed the application of concentrated solar power in thermolysis, thermochemical cycle, hydrocarbon cracking, reforming and solar gasification. Based on the literature review, this study has outlined the key challenges and prospects of concentrated solar power technologies. The main challenge in thermolysis is the requirement of very high temperature, while the thermochemical cycle is inefficient. Solar thermal cracking, reforming, and gasification integrate carbonaceous fuel to produce synthesis gas and hydrogen and therefore are not emission-free. The concentrated solar power technologies require further development and cost reductions before they can be scaled up to have a meaningful impact on renewable energy targets towards 2050.