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• Smaller/lighter materials which dominate retrofit are poorly characterised in datasets. • Materials are poorly named, described, or are absent in LCA datasets. • LCA for retrofit may not yield reliable information for design decisions. • Embodied energy coefficients may be more reliable than embodied carbon ones. • Reporting only carbon could lead to externalisation of impacts, not avoidance. Low energy domestic retrofit consumes materials, such as insulation, membranes and glazing, with smaller quantities of structural timber, steel or concrete, which have associated embodied impacts from resource extraction, manufacture and end-of-life treatments. In retrofit design, coefficients for material embodied impacts vary widely between sources and can lead to different results in a life cycle energy or carbon analysis, and perhaps different material choices in retrofit implementation. This paper considers how and why results differ between sources, and whether such data is suitable for making climate-beneficial design decisions. Embodied energy and carbon coefficients for 18 key retrofit materials were obtained from two widely used LCA databases and their similarity was quantified. The data collected illustrates that 70% embodied energy and embodied carbon data is within 20%, but that 30% of data was more than 20% different. Consistency of product naming and the absence in the datasets of key retrofit materials are factors identified contributing to variation, and present real constraints in practice. Furthermore, this exercise showed that embodied impacts for the types of materials most prominent in retrofits are less-well characterised than other major construction materials, and presents another layer of uncertainty. The data showed embodied energy was more consistent between sources than embodied carbon. This raises doubts about the predominant use of embodied carbon over energy for such analyses and establishes that a focus on embodied carbon over embodied energy has less power to reduce greenhouse gas emissions than considering both metrics together. It is concluded that obtaining such data with confidence is challenging and requires expertise in LCA, and is therefore unlikely to be accessible to most retrofit designers. Datasets need to be more complete and offer higher confidence to ensure delivery of high quality and meaningful results for climate-beneficial design decisions. [ABSTRACT FROM AUTHOR]

• Transient and steady-state thermal-electrical behaviour has been analysed by using MATLAB and COMSOL. • The operating temperature variable from 25 to 80 °C and CR = 500x is considered in this study. • The steady-state cell temperature occurs at 78.4 °C within the 30 s, at DNI = 1000 W/m2 and T amb = 25 °C. • Cell temperature and cell conversion efficiency are affected by the changes of parameters for T amb , h conv , DNI and AM. The cell efficiency of a solar CPV system can be enhanced by the dissipation of the thermal load from the receiver assembly. The performance of the solar cell is influenced by the incident light and cell operating temperature. In this study, a triple-junction solar cell, under a concentration ratio of 500x and cell dynamic efficiency, is considered for a wide range of operating temperatures (25-80 °C). The key purpose of this work is to simulate both transient and steady-state operating conditions, based on the temperature-dependent conversion efficiency. In this study, a transient model has been developed using COMSOL Multiphysics®. A live-link technique of COMSOL with MATLAB® is used to couple of successive thermal and electrical steady-state models for a fixed timestep. The performance behaviour of electrical parameters J sc , V oc , P , FF and P max are investigated. The results show that a dynamical efficiency, compared with constant efficiency and integrated error, was approximately 12%. The cell cycle steady-state temperature occurs at a maximum cell temperature of 78.4 °C within 30 s at the convective heat transfer coefficient h conv = 1400 W/m2 K and 500x of concentration ratio. Thus, steady-state cell temperature and time to reach it significantly dependence on the values of the environmental parameters of DNI , AM and T amb. Therefore, we can determine the thermal response of h conv to keep the value of T cell ≤ 80 °C. [ABSTRACT FROM AUTHOR]

• Thermal load and the approaches of prediction/measuring solar cell temperature is presented. • An overview of development on the technology of solar CPV receiver is presented. • The reliability of HCPV solar cells is highly effects on the lifespan of the entire system. • Performance characterisation of solar CPV receiver assembly is described. • Highlighted on the development of triple-junction solar cells compound. The performance behaviour of solar concentrating photovoltaic (CPV) is an important element for the design and development of solar devices and system. A CPV receiver assembly consists of layers of solar cell materials and some the receivers equipped with heat exchanger, used to dissipate heat and prevent the cells from overheating. CPV receiver have better conversion efficiency than non-concentrating devices and could, therefore, make a greater contribution to renewable energy sources. However, there is a trade-off between efficiency and cost for non-concentrated (conventional PV) systems and CPV. The performance behaviour of CPV at various environmental operating conditions needed for the accurate estimation of the energy yield from a CPV over its lifetime. Besides, a better understanding of the CPV device performance is necessary to continually improve system efficiency. The paper is also highlight on thermal effects and the effective thermal management of concentrating photovoltaic assemblies, in which changeable with environmental conditions. Moreover, numerical and experimental studies related to the thermal performance behaviour of HCPV receiver assembly are analysed. Thus, these investigations are significant to understand the operating behaviour, in turn, that leads to improving the design of CPV receivers. [ABSTRACT FROM AUTHOR]

A simplified transient model for fixed-bed reactors was extended to account for the heat sink effect of the phase change material diluent in the Fischer-Tropsch reactor energy balance. The resulting model was found to accurately approximate the more rigorous two-dimensional model with significantly less computational requirements even at the hotspot, where the reactor enthalpy balance is most sensitive. As anticipated, the presence of the encapsulated phase change material in the reactor induced thermal inertia, thereby restricting the temperature ramp rate in the reactor to acceptably safe operational limits for the catalyst. Although there was a reduction in both the CH4 and C5+ productivity, the reduction in CH4 production was up to four times that of the C5+ at the same coolant temperature. [ABSTRACT FROM AUTHOR]

The influence of the incident spectral irradiance on the electrical and thermal behaviour of triple-junction solar cells has been investigated. A spectral dependent electrical model has been developed to calculate the electric characteristics and quantify the heat power of a multijunction solar cell. A three-dimensional finite element analysis is also used to predict the solar cell’s operating temperature and cooling requirements for a range of ambient temperatures. The combination of these models improves the prediction accuracy of the electrical and thermal behaviour of triple-junction solar cells. The convective heat transfer coefficient between the back-plate and ambient air was found to be the significant parameter in achieving high electrical efficiency. These data are important for the electrical and thermal optimisation of concentrating photovoltaic systems under real conditions. The objective of this work is to quantify the temperature and cooling requirements of multijunction solar cells under variable solar spectra and ambient temperatures. It is shown that single cell configurations with a solar cell area of 1 cm 2 can be cooled passively for concentration ratios of up to 500× with a heat sink thermal resistance below 1.63 K/W, however for high ambient temperatures (greater than 40 °C), a thermal resistance less than 1.4 K/W is needed to keep the solar cell operating within safe operating conditions. [ABSTRACT FROM AUTHOR]

Abstract: Concentrating technology is long established in the field of solar thermal applications. However, there is still scope for improvement due to innovation in design, materials and manufacturing methods. The optical efficiency of a solar concentrator depends largely on the geometry of the concentrator profile. This paper evaluates the optical performance of a static 3-D Elliptical Hyperboloid Concentrator (EHC) using ray tracing software. Ray tracing has been used extensively to calculate the optical efficiency of the static 3-D EHC. Performance parameters such as effective concentration ratio, optical efficiency and geometric concentration ratio are also evaluated for different aspect ratios of the elliptical profile. Optimization of the concentrator profile and geometry is also carried out to improve the overall performance; this parametric study includes the concentrator height, solar incidence angle and aspect ratio of the ellipse. The overall performance of the concentrator was assessed based on the acceptance angle, effective concentration ratio and optical efficiency. Finally, the flux distribution on the receiver area for different concentrator heights is also presented. [Copyright &y& Elsevier]

The dynamic velocity range of particle image velocimetry (PIV) is determined by the maximum and minimum resolvable particle displacement. Various techniques have extended the dynamic range, however flows with a wide velocity range (e.g., impinging jets) still challenge PIV algorithms. A new technique is presented to increase the dynamic velocity range by over an order of magnitude. The multiple pulse separation (MPS) technique (i) records series of double-frame exposures with different pulse separations, (ii) processes the fields using conventional multi-grid algorithms, and (iii) yields a composite velocity field with a locally optimized pulse separation. A robust criterion determines the local optimum pulse separation, accounting for correlation strength and measurement uncertainty. Validation experiments are performed in an impinging jet flow, using laser-Doppler velocimetry as reference measurement. The precision of mean flow and turbulence quantities is significantly improved compared to conventional PIV, due to the increase in dynamic range. In a wide range of applications, MPS PIV is a robust approach to increase the dynamic velocity range without restricting the vector evaluation methods. [ABSTRACT FROM AUTHOR]

Abstract: Heat transfer to an obliquely impinging air jet is investigated experimentally. Distributions of the mean and the fluctuating component of the surface heat transfer are reported for a jet Reynolds number of 10,000, nozzle to impingement surface distance, H/D, from 2 to 8 and angle of impingement, α, from 30° to 90° (normal impingement). Flow velocity measurements along the impingement surface are related to heat transfer distributions. At specific locations the surface heat transfer and the local fluid velocity are measured simultaneously and coherence and phase difference information between the signals are reported. The vortical characteristic of the flow is shown to vary considerably with the angle of impingement; depending on the distance between the near nozzle edge and the impingement surface, vortices at different stages of development impact with the target surface. The influence of naturally occurring vortices in an impinging jet flow on the magnitude of heat transfer in the near wall jet is reported. [Copyright &y& Elsevier]

Synthetic jets are used for active flow control and enhanced heat transfer, and are typically generated by an orifice connected to a cavity with movable diaphragm actuator. Low-power operation is achieved by matching actuator and Helmholtz resonance frequencies. This brief communication presents an analytical model derived from simplified gas dynamics, for estimating the synthetic jet velocity and actuator deflection, based on a cavity pressure measurement. Model closure is provided by a damping force in the orifice, which agrees with established pressure loss correlations for steady flow through short ducts. The model is validated against experimental data obtained for an axisymmetric synthetic jet. The valid frequency range extends from zero, over the Helmholtz resonance frequency, up to a geometry-dependent limit frequency. This model presents a reference against which synthetic jet velocity can be calibrated. [ABSTRACT FROM AUTHOR]

Abstract: Impinging jets are a means of achieving high heat transfer coefficients both locally and on an area averaged basis. The temporal nature of both the fluid flow and heat transfer has been investigated for Reynolds numbers from 10,000 to 30,000 and non-dimensional surface to jet exit distance, H/D, from 0.5 to 8. At the impingement surface simultaneous acquisition of both local heat flux and local velocity signal has facilitated a comprehensive analysis of the effect that fluid flow has on the heat transfer. Results are presented in the form of surface heat transfer and fluid velocity signal spectra, and coherence and phase difference between the corresponding velocity and heat flux signals. It has been shown that the evolution of vortices with distance from the jet exit has an influence on the magnitude of the heat transfer coefficient in the wall jet. [Copyright &y& Elsevier]

Abstract: Impinging jets provide a means of achieving high heat transfer coefficients both locally and on an area averaged basis. The current work forms the first stage of a two part investigation of heat transfer distributions from a heated flat surface subject to an impinging air jet for Reynolds numbers from 10,000 to 30,000 and non-dimensional surface to jet exit spacing, H/D, from 0.5 to 8. In the present paper, the relative magnitudes of the local heat transfer coefficients are compared to the fluctuating components and to the mean and root-mean-square local velocity components. It has been shown that at low nozzle to surface spacings (<2 diameters) secondary peaks in the radial heat transfer distributions are due to an abrupt increase in turbulence in the wall jet. In particular the velocity fluctuations normal to the impingement surface have a controlling influence on the enhancement in the wall jet. [Copyright &y& Elsevier]

• Improved methods for embodied energy could reduce life cycle energy in retrofits. • Fabric first retrofit design is not well supported by typical life cycle energy approaches. • A prescriptive life cycle approach could improve design decisions for materials and systems. • A framework providing focused life cycle impacts for fabric first retrofit measures is proposed. Reduction of energy for space heating through retrofit interventions is imperative to meet carbon reduction targets in many temperate climates. A Life Cycle approach to retrofit design has the potential to reveal the balance between projected operational energy savings, and embodied energy invested in an intervention, and therefore optimise the extent of retrofit. However, life cycle energy analysis (LCEA) suffers from inconsistent methodologies across studies, and is rarely used for retrofit projects. A preliminary meta-analysis was conducted, drawing on LCEA data from domestic new builds and retrofits from the last twenty years. Whilst recent literature conversations indicate that embodied energy increases with decreasing operating energy, the meta-analysis is inconsistent with this. This review critiques the limitations and sources of variation in LCEA, focuses on how these compromise its value as part of the building design process and when comparing between projects, and recommends approaches which add value for building designers. This review has identified a need for research to elucidate a transferrable approach for determining the lowest life cycle energy for any retrofit, and also a need for a more robust data set of domestic retrofit LCEA. [ABSTRACT FROM AUTHOR]

• A novel concept of freeze-tolerant flat plate solar collector is conceived. • Design concept enables to reduce installed costs of relevant solar thermal systems. • Predictions show the serpentine type compares favorably with the header riser type. • Modified Chinese micro heat pipe flat plate collector performs better than the reference panel. A novel design concept of Flat Plate Solar Collectors (FPSCs) is conceived and developed by integrating with a freeze-tolerant (so-called 'ice immune') solution using flexible silicone tubing. It is intended to directly run water in the solar thermal systems with the FPSCs instead of using expensive anti-freeze fluids, and to remove secondary heat transfer facilities (e.g. an extra tank with a buried heat exchanger). Successful development of such kind of solar thermal collectors will enable a reduction of installed cost of conventional solar thermal systems without needing secondary heat transfer facilities. In the prophase design, thermal performances of FPSCs with two configurations, i.e. the serpentine tube type and the header riser type, were predicted based on the collector lumped thermal capacitance model alongside CFD (Computational Fluid Dynamics) calculations. Then two prototypes of FPSCs with the ice-immune silicone tubing (one AES serpentine tube type, one modified Chinese micro-heat-pipe-array panel) were made to determine the collector performance and compared to an original AES solar keymark reference panel via experimental tests. The results show that the Chinese micro-heat-pipe-array panel performs better than the AES header riser solar keymark panel in terms of flow rate per m2 collector aperture area, while the AES serpentine tube panel with silicone tubing performs somewhat lower than the solar keymark with T m ∗ ≤ 0.035 and better than the solar keymark when T m ∗ > 0.035. The serpentine tube panel and the Chinese micro-heat-pipe-array panel both integrated with silicone tubing for freeze tolerance are proven to be effective as the modification doesn't compromise the collector thermal performance markedly. [ABSTRACT FROM AUTHOR]

Highlights: [•] The experimental analysis of a static 3-D EHC prototype has been presented. [•] The performance of EHC studied for different experimental conditions. [•] The experimental study has also been carried out to estimate outlet temperature. [•] The flux distribution on the receiver for the EHC configuration has been presented. [Copyright &y& Elsevier]

Abstract: In this paper, a novel multi-stage evacuated solar desalination system is developed by utilizing latent heat recovery. A transient model is proposed for the solar desalination system. The effect of various design and operating parameters on the system performance is studied to optimize the configuration. The distillate yield increases initially due to enhanced evaporation caused by the presence of a thin layer of water in the stages. The distillate yield decreases with increase in salinity of water due to an increase in ion activity and the reduction of thermodynamically spontaneous change from liquid to vapor. The optimum number of stages, gap between the stages and the supplied mass flow rate for the system were found to be 4, 100mm and 55kg/m2/day respectively throughout the year. The overall thermal efficiency of the system is found to be 53.9% and 29.6% for the months March and December respectively in India. The maximum yield of 53.2kg/m2/day is found in March at an operating pressure of 0.03bar. The multi-stage evacuated solar desalination system is a viable option to meet the needs of rural and urban communities. [Copyright &y& Elsevier]

Abstract: Natural convection heat transfer from a single horizontal cylinder and a pair of vertically aligned horizontal cylinders is investigated. Surface heat transfer distributions around the circumference of the cylinders are presented for Rayleigh numbers of 2×106, 4×106 and 6×106 and a range of cylinder spacings of 1.5, 2 and 3 diameters. With a cylinder pairing the lower cylinder is unaffected by the presence of the second cylinder; the same is true of the upper cylinder if the lower one is not heated. However, when both cylinders are heated it has been found that a plume rising from the heated lower cylinder interacts with the upper cylinder and significantly affects the surface heat transfer distribution. Spectral analysis of surface heat transfer signals has established the influence of the plume oscillations on the heat transfer. Thus, when the plume from the lower cylinder oscillates out of phase with the flow around the upper cylinder it increases the mixing and results in enhanced heat transfer. [Copyright &y& Elsevier]

Monitoring the performance of concentrating photovoltaic technologies under actual operating conditions is crucial for the prediction of energy yield. This requires an in-depth understanding of the behaviour of such systems through extensive outdoor characterisation and modelling. Detailed information on the outdoor performance of concentrating photovoltaic technology, taking into account the parameters that influence it, is therefore necessary for the evolution of the technology. In this work, a concentrating photovoltaic monomodule was characterised in a high desert climate (in Albuquerque, New Mexico). Due to the complexity of the outdoor performance evaluation of this technology, three relatively clear-sky days that exhibited different atmospheric conditions were selected in order to reduce the noise on the measured parameters and therefore provide a better understanding of its behaviour. One-minute resolution data were accumulated in order to assess the behaviour of the monomodule under real operating conditions. Initially, the monomodule is electrically characterised based on spectral changes. Different spectral indices are evaluated to enable a direct comparison amongst them. The diurnal electrical characteristics and temperature of the monomodule as a function of spectral, irradiance and ambient conditions is then analysed. The results of the three selected days show a maximum operating efficiency of 23.2% while maximum temperatures of 70.3 °C and 67.6 °C are observed on the diode and heat sink respectively. The importance of considering the influence of the atmospheric parameters on the performance of concentrating photovoltaics is also highlighted. In particular, spectral gains of up to 5% are exhibited due to lower aerosol content and higher precipitable water combined. [ABSTRACT FROM AUTHOR]

High concentration photovoltaics, equipped with high efficiency multijunction solar cells, have great potential in achieving cost-effective and clean electricity generation at utility scale. Such systems are more complex compared to conventional photovoltaics because of the multiphysics effect that is present. Modelling the power output of such systems is therefore crucial for their further market penetration. Following this line, a multiphysics modelling procedure for high concentration photovoltaics is presented in this work. It combines an open source spectral model, a single diode electrical model and a three-dimensional finite element thermal model. In order to validate the models and the multiphysics modelling procedure against actual data, an outdoor experimental campaign was conducted in Albuquerque, New Mexico using a high concentration photovoltaic monomodule that is thoroughly described in terms of its geometry and materials. The experimental results were in good agreement (within 2.7%) with the predicted maximum power point. This multiphysics approach is relatively more complex when compared to empirical models, but besides the overall performance prediction it can also provide better understanding of the physics involved in the conversion of solar irradiance into electricity. It can therefore be used for the design and optimisation of high concentration photovoltaic modules. [ABSTRACT FROM AUTHOR]

The spectral sensitivity of a concentrating triple-junction (3J) solar cell has been investigated. The atmospheric parameters such as the air mass (AM), aerosol optical depth (AOD) and precipitable water (PW) change the distribution of the solar spectrum in a way that the spectral, electrical and thermal performance of a 3J solar cell is affected. In this paper, the influence of the spectral changes on the performance of each subcell and whole cell has been analysed. It has been shown that increasing the AM and AOD have a negative impact on the spectral and electrical performance of 3J solar cells while increasing the PW has a positive effect, although, to a lesser degree. A three-dimensional finite element analysis model is used to quantify the effect of each atmospheric parameter on the thermal performance for a range of heat transfer coefficients from the back-plate to the ambient air and also ambient temperature. It is shown that a heat transfer coefficient greater than 1300 W/(m 2 K) is required to keep the solar cell under 100 °C at all times. In order to get a more realistic assessment and also to investigate the effect of heat transfer coefficient on the annual energy yield, the methodology is applied for four US locations using data from a typical meteorological year (TMY3). [ABSTRACT FROM AUTHOR]

The spectral sensitivity of a concentrating triple-junction (3J) solar cell has been investigated. The atmospheric parameters such as the air mass (AM), aerosol optical depth (AOD) and precipitable water (PW) change the distribution of the solar spectrum in a way that the spectral, electrical and thermal performance of a 3J solar cell is affected. In this paper, the influence of the spectral changes on the performance of each subcell and whole cell has been analysed. It has been shown that increasing the AM and AOD have a negative impact on the spectral and electrical performance of 3J solar cells while increasing the PW has a positive effect, although, to a lesser degree. A three-dimensional finite element analysis model is used to quantify the effect of each atmospheric parameter on the thermal performance for a range of heat transfer coefficients from the back-plate to the ambient air and also ambient temperature. It is shown that a heat transfer coefficient greater than 1300 W/(m 2 K) is required to keep the solar cell under 100 °C at all times. In order to get a more realistic assessment and also to investigate the effect of heat transfer coefficient on the annual energy yield, the methodology is applied for four US locations using data from a typical meteorological year (TMY3). [ABSTRACT FROM AUTHOR]