Review of high concentration photovoltaic thermal hybrid systems for highly efficient energy cogeneration

This is the final version.Available on open access from Elsevier via the DOI in this recordConcentrated photovoltaic/thermal hybrid systems are a combination of concentrated photovoltaics and photovoltaic/thermal hybrid systems which capture waste heat for later application. Higher concentrations lead to higher energy fluxes over smaller areas which is beneficial for several reasons. Firstly, less photovoltaic material is required, instead using relatively cheap optics. This allows more efficient types of PV material to be used effectively. Secondly, the concentrated heat flux easily allows for a high outlet temperature which in turn increases the applicability. Point focused systems have experimentally achieved cogeneration efficiencies of 86.47% (excluding system losses) and concentrations of over 1000 suns, but the technology still faces challenges. The design of the cooling system must be optimised to maximise both electrical and thermal efficiency. Furthermore, the optics and cell interconnections must mitigate the effects a non-uniform focal image for high electrical efficiencies. These challenges must be faced while minimising the thermal stresses the system undergoes to ensure the system has a substantial lifetime. This review provides an in depth understanding of the challenges and function of point focused concentrated photovoltaic/thermal systems. From the literature, it is clear more focus should be put on microchannel/impinging jet hybrid cooling systems for use in dense array concentrated photovoltaic/thermal systems. More physical experimentation is needed, especially full model systems which include the output image of the optics, along with consideration to alternative cooling fluids (particularly nanofluids).Engineering and Physical Sciences Research Council (EPSRC

Optical Losses and Durability of 4-Domed Optic for Concentrator Photovoltaics

This is the author accepted manuscript.The use of optical elements to focus light onto a smaller area of semiconductor material can enhance the cost effectiveness and electrical performance. Enabling ultrahigh concentration ratios for photovoltaic systems requires an optic bonded directly to the solar cell to further concentrate and homogenise the illumination, as well as to improve the acceptance angle. For many optical materials manufacture flaws are common, and difficult to prevent. An estimation of the effective external quantum efficiency of the receiver based on the material’s transmissivity tells us the effect of added absorptivity from manufacture defects. Evaluating the module under a solar simulator under various angles yields information on how scattered light changes the optic’s concentration ability. This study suggests sapphire has higher optical losses due to its higher refractive index compared to slygard184. Thus, the need for a higher refractive index material must be considered carefully and matched with anti-reflective coatings if needed. The effective concentration of slygard-184 notably suffers when flaws are present, dropping up to 48.2%. Further, the optimum angle is difficult to predict. Minor flaws could be deemed acceptable in performance when high acceptance angles are not the primary design requirement.Engineering and Physical Sciences Research Council (EPSRC

Outdoor experimental validation for ultra-high concentrator photovoltaic with serpentine-based cooling system

This is the final version. Available from Elsevier via the DOI in this record.With demand for renewable energy growing, concentrator photovoltaic thermal hybrids have great potential. Maximising concentration ratios through the deployment of multi-stage optics can yield high power outputs from multi-junction solar cells. To prevent damaging thermal stress and to enable extraction of thermal energy, a capable cooling system is necessary. The primary objective of this study is to maximise the effective concentration ratio over a solar cell and calibrate the system to optimise the energetic and exergetic efficiencies. The capability of the serpentine-based cooling system is investigated for each concentrator optic configuration. Originality is found in the presentation of the 3-stage optic, and the use of outdoor real-world experimental data to validate a computational model. This model uses both ray tracing, heat and mass transfer simulations to enhance the understanding of system operation and enable accurate prediction of performance under various conditions. Results show focal spot shape is more important than raw optical efficiency for electrical output, making the 3-stage optic superior to the other configurations in most regards. An effective concentration of over 1200 × is achieved. Higher exergetic efficiencies are consistently found in the double serpentine configuration, though variation does not exceed ±0.3% when only changing cooling system geometry.Engineering and Physical Sciences Research CouncilSaudi Arabia Culture Bureau in the U

Indoor experimental analysis of Serpentine-Based cooling scheme for high concentration photovoltaic thermal systems

This is the final version. Available on open access from Elsevier via the DOI in this record.Data availability statement: Data will be made available on request.High concentration photovoltaic thermal hybrids are expected to play an important role in meeting growing energy demands. When approaching concentrations over 1000 suns, a cooling system is needed to maximise both the thermal and electrical performance of the multi-junction solar cell without producing excessive parasitic losses. This study develops a novel simulation model to provide an in-depth understanding of the functionality of a concentrated photovoltaic thermal hybrid system with serpentine-based cooling systems. An ultra-high concentrator photovoltaic optic irradiance profile (peak effective concentration ratio: ∼1500 suns) is considered within the simulation model, which has been validated through indoor experimentation. The effectiveness of cooling is also evaluated through maximum thermal stresses generated in the multi-junction solar cell. The double serpentine design was deemed the highest performing, primarily because of the single serpentine’s excessive pressure drop. Copper as the heat sink material yielded superior performance because of its higher thermal conductivity. The maximum total exergetic efficiency achieved by the receiver was ∼ 10.9% with this configuration. Compared to some examples in the literature this value may seem low, however, it is more accurate due to the inclusion of a specific irradiance profile. All serpentine-based cooling systems could maintain the recommended operating temperature.Engineering and Physical Sciences Research Council (EPSRC)Saudi Arabia Culture Bureau, U

Black Stork Down: Military Discourses in Bird Conservation in Malta

Tensions between Maltese hunters and bird conservation NGOs have intensified over the past decade. Conservation NGOs have become frustrated with the Maltese State for conceding to the hunter lobby and negotiating derogations from the European Union’s Bird Directive. Some NGOs have recently started to organize complex field-operations where volunteers are trained to patrol the landscape, operate drones and other surveillance technologies, detect illegalities, and lead police teams to arrest poachers. We describe the sophisticated military metaphors which conservation NGOs have developed to describe, guide and legitimize their efforts to the Maltese public and their fee-paying members. We also discuss why such groups might be inclined to adopt these metaphors. Finally, we suggest that anthropological studies of discourse could help understand delicate contexts such as this where conservation NGOs, hunting associations and the State have ended in political deadlock

Cancer Cachexia: Traditional Therapies and Novel Molecular Mechanism-Based Approaches to Treatment

The complex syndrome of cancer cachexia (CC) that occurs in 50% to 80% cancer patients has been identified as an independent predictor of shorter survival and increased risk of treatment failure and toxicity, contributing to the mortality and morbidity in this population. CC is a pathological state including a symptom cluster of loss of muscle (skeletal and visceral) and fat, manifested in the cardinal feature of emaciation, weakness affecting functional status, impaired immune system, and metabolic dysfunction. The most prominent feature of CC is its non-responsiveness to traditional treatment approaches; randomized clinical trials with appetite stimulants, 5-HT3 antagonists, nutrient supplementation, and Cox-2 inhibitors all have failed to demonstrate success in reversing the metabolic abnormalities seen in CC. Interventions based on a clear understanding of the mechanism of CC, using validated markers relevant to the underlying metabolic abnormalities implicated in CC are much needed. Although the etiopathogenesis of CC is poorly understood, studies have proposed that NFkB is upregulated in CC, modulating immune and inflammatory responses induce the cellular breakdown of muscle, resulting in sarcopenia. Several recent laboratory studies have shown that n-3 fatty acid may attenuate protein degradation, potentially by preventing NFkB accumulation in the nucleus, preventing the degradation of muscle proteins. However, clinical trials to date have produced mixed results potentially attributed to timing of interventions (end stage) and utilizing outcome markers such as weight which is confounded by hydration, cytotoxic therapies, and serum cytokines. We propose that selective targeting of proteasome activity with a standardized dose of omega-3-acid ethyl esters, administered to cancer patients diagnosed with early stage CC, in addition to a standard intervention with nutritionally adequate diet and appetite stimulants, will alter metabolic abnormalities by downregulating NFkB, preventing the breakdown of myofibrillar proteins and resulting in increasing serum protein markers, lean body mass, and functional status

Building nonparametric nn-body force fields using Gaussian process regression

Constructing a classical potential suited to simulate a given atomic system is a remarkably difficult task. This chapter presents a framework under which this problem can be tackled, based on the Bayesian construction of nonparametric force fields of a given order using Gaussian process (GP) priors. The formalism of GP regression is first reviewed, particularly in relation to its application in learning local atomic energies and forces. For accurate regression it is fundamental to incorporate prior knowledge into the GP kernel function. To this end, this chapter details how properties of smoothness, invariance and interaction order of a force field can be encoded into corresponding kernel properties. A range of kernels is then proposed, possessing all the required properties and an adjustable parameter $n$ governing the interaction order modelled. The order $n$ best suited to describe a given system can be found automatically within the Bayesian framework by maximisation of the marginal likelihood. The procedure is first tested on a toy model of known interaction and later applied to two real materials described at the DFT level of accuracy. The models automatically selected for the two materials were found to be in agreement with physical intuition. More in general, it was found that lower order (simpler) models should be chosen when the data are not sufficient to resolve more complex interactions. Low $n$ GPs can be further sped up by orders of magnitude by constructing the corresponding tabulated force field, here named "MFF".Comment: 31 pages, 11 figures, book chapte