Heat pump (HP) is one of the most energy efficient tools for address heating and possibly cooling needs in buildings. Growing environmental concerns over conventional HP refrigerants, chlorofluorocarbons (CFCs), and hydrofluorocarbons (HFCs) have forced legislators and researchers to look for alternatives. As such, carbon dioxide (R744/CO2) has come to light due to its low global warming potential (GWP) and zero ozone depleting characteristics. Even though CO2 is environmentally benign, the performance of CO2 HP has been of concern since its inception. To improve the performance of CO2 HP, research has been playing a pivotal role in developing functional designs of heat exchangers, expansion devices, and compressors to suit the CO2 transcritical cycle. Different CO2 HP cycles coupled with auxiliary components, hybrid systems, and refrigerant mixtures along with advanced control strategies have been applied and tested. This paper presents a complete overview of the most recent developments of transcritical CO2 HPs, their components, and applications.

A novel porous three dimensional (3D) hierarchical graphene-beaded carbon nanofibers with incorporated Ni nanoparticles (G/CNFs-Ni) were used for the first time as cost-effective counter electrode for dye-sensitized solar cells (DSCs). G/CNFs-Ni was synthesized by electrospinning G/PAN/Ni(AcAc)2 precursor nanofibers, followed by carbonization and activation. The introduction of graphene nanosheets and Ni nanoparticles in CNF networks significantly increased the cells' stability and decreased the charge-transfer resistance at the interface between electrolyte and counter electrode, leading to the high electrocatalytic activity/efficiency for triiodide reduction. The G/CNFs-Ni composite counter electrodes possessed larger capacitance than that of Pt counter electrodes due to larger specific surface area, leading to significantly higher electrocatalytic activity/efficiency for triiodide reduction at the interface between electrolyte and counter electrode. The dye-sensitized solar cells (DSCs) fabricated using G/CNF-Ni composite as counter electrodes were tested at 100 mW/cm 2 AM 1.5 illumination. The G/CNFs-Ni composite exhibited an overall power conversion efficiency of 7.14 % as compared to 7.59 % for reference platinum (Pt) counter electrodes.

A perovskite solar cell in the inverted configuration was modeled and simulated to investigate the impact of the cathode work function on the cell performance. The model utilized the drift-diffusion current equations, coupled with Poisson’s equation and continuity equations to determine the J-V characteristics, the band diagram, and the external quantum efficiencies. It was found the power conversion efficiency (PCE) tended to decrease with the increasing work functions of the metal cathode. The device using low work function metal Ca delivered the best PCE of 16.7%, whereas the one with high work function Au possessed the lowest PCE of 0.3%. These results were in a close agreement with experiments in literature. Photovoltaic parameters (FF, Jsc, and Voc) showed the same tendency and were responsible for the PCE. The band diagram revealed the formation of Schottky barrier was the main reason for the reduction in Voc, and the external quantum efficiency spectrum showed the adverse effect of the Schottky barrier on the charge extraction.

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Solar photovoltaic (PV) technology has matured to become a technically viable large scale source of sustainable energy. Understanding the rooftop PV potential is critical for utility planning, accommodating grid capacity, deploying financing schemes and formulating future adaptive energy policies. The NIWE (National Institute of Wind Energy) under MNRE (Ministry of New and Renewable Energy) is an esteemed institute dedicated to Indian wind and solar renewable energy generation and monitoring. The SRRA (Solar Radiation and Resource Assessment) is a division under NIWE that is responsible for solar energy monitoring throughout India. They have created the Solar Radiation Map of India using high quality, ground measured solar data. This asks the question, whether it is possible to get a quick estimate of a solar installation. Thus, the paper explains the problems in the field of solar potential measurement and the deployment of a calculator in a mobile front platform. The mobile app would quickly and effortlessly give a rough estimate on what a solar installation could save in power consumption costs.