The goal of this review is to offer an all-encompassing evaluation of an integrated solar energy system within the framework of solar energy utilization. This holistic assessment encompasses photovoltaic technologies, solar thermal systems, and energy storage solutions, providing a comprehensive understanding of their interplay and significance. It emphasizes the importance of solar energy as a renewable resource and its role in addressing global energy demand and mitigating climate change. The review highlights the significance of advancements in various solar energy technologies, focusing on their environmental benefits, including greenhouse gas emissions reduction and air and water pollution mitigation. It explores the evolution of photovoltaic technologies, categorizing them into first-, second-, and third-generation photovoltaic cells, and discusses the applications of solar thermal systems such as water heaters, air heaters, and concentrators. The paper examines key advancements in energy storage solutions for solar energy, including battery-based systems, pumped hydro storage, thermal storage, and emerging technologies. It references recent published literature to present findings on energy payback time, carbon footprint, and performance metrics. Challenges to widespread adoption are discussed, including cost and economic viability, intermittency, environmental impacts, and grid integration. Strategies to overcome these challenges, such as cost reduction, policy support, energy storage integration, and sustainable practices, are presented based on published literature. By bridging gaps in existing literature, this comprehensive resource aims to equip researchers, policymakers, and industry professionals with insights into forging a sustainable and renewable energy future.

Plastics, integral to various human activities, have led to a surge in production, posing substantial challenges in waste management. The persistent non-biodegradability of plastics, taking over a century to decompose, necessitates exploration into technologies for their conversion into sustainable fuels. Pyrolysis, an oxygen-free thermal decomposition process, emerges as a promising avenue for producing liquid fuels from plastic waste. This study's primary objective is to create and validate an Aspen Plus simulation model, enabling techno-economic evaluation and sensitivity analysis of pyrolysis for converting waste plastics into liquid fuels. Critical parameters-temperature, retention time, and particle size-are examined for their impact on product yield and quality. The methodology involves model development, validation, and subsequent simulations with various waste plastic types under different pyrolysis conditions. Experimental investigation using waste high-density polyethylene (HDPE) in an auger reactor yielded an oil yield of 61.29%, char yield of 10.98%, and syngas yield of 27.73% at 525 °C. Post-validation against this data, the model explored four plastic types, revealing significant influences of plastic type and reactor temperature on product yields. Polystyrene (PS) at 500 °C produced the highest oil content at 83.69%, with temperature affecting yield before secondary cracking. Techno-economic evaluation for a pyrolysis plant processing 10,000 tons of waste HDPE annually indicated a minimum selling price (MSP) of $302.50/ton, a net present value (NPV) of $12,594,659.7, and a 1.03-year payback period. This study provides crucial insights for designing an economically viable and sustainable pyrolysis process, guiding further research and industrial implementation.

Strict emission regulations and demand for better fuel economy are driving forces for finding advanced engines that will be able to replace the conventional internal combustion engines in the near future. Homogeneous charge compression ignition (HCCI) engines use a different combustion technique; there are no spark plugs or injectors to assist the combustion. Instead, when the mixtures reach chemical activation energy, combustion auto-ignites in multiple spots. The main objective of this review paper is to study the engine performance and emission characteristics of HCCI engines operating in various conditions. Additionally, the impact of different fuels and additives on HCCI engine performance is also evaluated. The study also introduces a potential guideline to improve engine performance and emission characteristics. Compared to conventional compression ignition and spark ignition combustion methods, the HCCI combustion mode is noticeably faster and also provides better thermal efficiency. Although a wide range of fuels including alternative and renewable fuels can be used in the HCCI mode, there are some limitation/challenges, such as combustion limited operating range, phase control, high level of noise, cold start, preparation of homogeneous charge, etc. In conclusion, the HCCI combustion mode can be achieved in existing spark ignition (SI) engines with minor adjustments, and it results in lower oxides of nitrogen (NO_x) and soot emissions, with practically a similar performance as that of SI combustion. Further improvements are required to permit extensive use of the HCCI mode in future.