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This paper presents the application of isogeometric analysis (IGA) to the spatial discretisation of the multi-group, self-adjoint angular flux (SAAF) form of the neutron transport equation with a discrete ordinate (SN) angular discretisation. The IGA spatial discretisation is based upon non-uniform rational B-spline (NURBS) basis functions for both the test and trial functions. In addition a source iteration compatible maximum principle is used to derive the IGA spatially discretised SAAF equation. It is demonstrated that this maximum principle is mathematically equivalent to the weak form of the SAAF equation. The rate of convergence of the IGA spatial discretisation of the SAAF equation is analysed using a method of manufactured solutions (MMS) verification test case. The results of several nuclear reactor physics verification benchmark test cases are analysed. This analysis demonstrates that for higher-order basis functions, and for the same number of degrees of freedom, the FE based spatial discretisation methods are numerically less accurate than IGA methods. The difference in numerical accuracy between the IGA and FE methods is shown to be because of the higher-order continuity of NURBS basis functions within a NURBS patch as well as the preservation of both the volume and surface area throughout the solution domain within the IGA spatial discretisation. Finally, the numerical results of applying the IGA SAAF method to the OECD/NEA, seven-group, two-dimensional C5G7 quarter core nuclear reactor physics verification benchmark test case are presented. The results, from this verification benchmark test case, are shown to be in good agreement with solutions of the first-order form as well as the second-order even-parity form of the neutron transport equation for the same order of discrete ordinate (SN) angular approximation. Funding was provided by the following grants: EPSRC impact acceleration award grant reference number: EP/R511547/1, Adaptive Hierarchical Radiation Transport Methods to Meet Future Challenges in Reactor Physics (EPSRC Grant No.: EP/ J002011/1), RADIANT: A Parallel, Scalable, High Performance Radiation Transport Modelling and Simulation Framework for Reactor Physics, Nuclear Criticality Safety Assessment and Radiation Shielding Analyses (EPSRC Grant No.: EP/K503733/1)

AbstractImproving the long-term stability of perovskite solar cells is critical to the deployment of this technology. Despite the great emphasis laid on stability-related investigations, publications lack consistency in experimental procedures and parameters reported. It is therefore challenging to reproduce and compare results and thereby develop a deep understanding of degradation mechanisms. Here, we report a consensus between researchers in the field on procedures for testing perovskite solar cell stability, which are based on the International Summit on Organic Photovoltaic Stability (ISOS) protocols. We propose additional procedures to account for properties specific to PSCs such as ion redistribution under electric fields, reversible degradation and to distinguish ambient-induced degradation from other stress factors. These protocols are not intended as a replacement of the existing qualification standards, but rather they aim to unify the stability assessment and to understand failure modes. Finally, we identify key procedural information which we suggest reporting in publications to improve reproducibility and enable large data set analysis.

To continuously assess the performance of a wind turbine (WT), accurate power curve modelling is essential. Various statistical methods have been used to fit power curves to performance measurements; these are broadly classified into parametric and non‐parametric methods. In this study, three advanced non‐parametric approaches, namely: Gaussian Process (GP); Random Forest (RF); and Support Vector Machine (SVM) are assessed for WT power curve modelling. The modelled power curves are constructed using historical WT supervisory control and data acquisition, data obtained from operational three bladed pitch regulated WTs. The modelled power curve fitting performance is then compared using suitable performance, error metrics to identify the most accurate approach. It is found that a power curve based on a GP has the highest fitting accuracy, whereas the SVM approach gives poorer but acceptable results, over a restricted wind speed range. Power curves based on a GP or SVM provide smooth and continuous curves, whereas power curves based on the RF technique are neither smooth nor continuous. This study highlights the strengths and weaknesses of the proposed non‐parametric techniques to construct a robust fault detection algorithm for WTs based on power curves.

High Concentrator Photovoltaic Thermal (HCPV/T) systems produce both electrical and thermal energy and they are efficient in areas with high Direct Normal Irradiance (DNI). This paper estimates the lifecycle environmental impact of the HCPV/T 2000x system for both electrical and thermal functionalities. Process-based attributional method following the guidelines and framework of ISO 14044/40 was used to conduct the Life Cycle Assessment (LCA). The midpoint and endpoint impact categories were studied. It was found that the main hotspots are the production of the thermal energy system contributing with 50% and 55%, respectively, followed by the production of the tracking system with 29% and 32% and the operation and maintenance with 13% and 7%. The main contributor to the lifecycle environmental impact category indicators was found to be the raw materials acquisition/production and manufacturing of the thermal energy and tracking systems. The results indicate that the lifecycle environmental impact of the HCPV/T 2000x system is lower compared to fuel-based Combined Heat and Power (CHP) and non-Renewable Energy Sources (non-RES) systems.