Computation of irradiance in a solar still by using a refined algorithm

A refined solar algorithm from the ESP-r system has been used to calculate the distribution of solar irradiation inside a basin-type solar still. In the approach, surface finish, view factors and multiple reflections are taken into consideration in the computation of the solar radiation that reaches the surface of the saline water in the distillation system. The algorithm was applied to a solar still tested at the University of Strathclyde in Glasgow (55 520 N, 4 150 W). Under the prevailing meteorological conditions, it was found that previous models overestimated the computed solar load on the saline water surface. The present modelling approach is demonstrated to exhibit a higher degree of accuracy than previous methods for irradiance distribution prediction, yielding new insights into approaches to solar still performance improvement. The modelling outcomes are presented and discussed

The Solar Photospheric Nitrogen Abundance: Determination with 3D and 1D Model Atmospheres

We present a new determination of the solar nitrogen abundance making use of 3D hydrodynamical modelling of the solar photosphere, which is more physically motivated than traditional static 1D models. We selected suitable atomic spectral lines, relying on equivalent width measurements already existing in the literature. For atmospheric modelling we used the co 5 bold 3D radiation hydrodynamics code. We investigated the influence of both deviations from local thermodynamic equilibrium (non-LTE effects) and photospheric inhomogeneities (granulation effects) on the resulting abundance. We also compared several atlases of solar flux and centre-disc intensity presently available. As a result of our analysis, the photospheric solar nitrogen abundance is A(N) = 7.86 +/- 0.12.Comment: 6 pages, 4 figure

Radiation modeling

Modelling of atmospheric effects in solar and terrestrial radiation regimes is discussed. Radiative effects of surfaces and the problem of data validation are also considered

Double skin façade: Modelling technique and influence of venetian blinds on the airflow and heat transfer

The demand to reduce building cooling load and annual energy consumption can be optimised with the use of Double Skin Facade (DSF). Computational Fluid Dynamics (CFD) methods are frequently used for the analysis of heat transfer through DSF. However, considerable uncertainty exists regarding few key parameters, such as modelling strategies and the solar heat transmitted to the indoor space as a function of the blind tilt angles and positioning within the façade channel. In this paper we have investigated four modelling strategies and the influence of blind tilt angle and their proximity to the façade walls. The DSF system used in this investigation is equipped with venetian blinds and facades that absorb and reflect the incident solar radiation and transfer the direct solar heat gain into the building. A finite volume dis- cretization method with the SIMPLE solution algorithm of the velocity-pressure coupling involving the low-turbulence keε model is used. A ray-traced solar model is coupled with long wave radiation model to solve the complete solar and radiation fields along with convection and conduction fields. On the modelling strategies, three dimensional domains were cast over three computational zones; external zone with solar radiation entering the outer skin of glass; buoyancy-driven air cavity zone with convection and transmitted solar radiation; and an internal zone. Also investigated is the thermal behaviour of the DSF due to the blind tilt angles (30o , 45o , 60o , and 75o ) and its position from the facade walls (104 mm, 195 mm, 287 mm and 379 mm). Validations of the results are based on experimental data from the literature and the predicted trends compared very well with the experimental measurements. The heat gain due to direct solar radiation and convection through the facades to the internal space are presented. Comparative analysis of the four modelling strategies shows little variation of the results. The implication is a reduction in complexity and cost of modelling, since the additional effort requires in the CFD modelling is not justified by a significant improvement of the results. The variations of the blinds tilt angles as well as its proximity to façade walls significantly influences the convective flow within the façade cavity and the heat gains to the indoor spac

Model for computation of solar fraction in a single-slope solar still

A new model that calculates the distribution of solar radiation inside a single-slope solar still has been proposed. In this model, the solar fraction on a vertical surface is divided into beam and diffuse parts and the optical view factors of surfaces inside the still are taken into account. To validate the model, outdoor tests of a conventional solar still were conducted under different weather conditions at the University of Strathclyde. The proposed model is compared with the previous one. It is found that the beam solar fraction is affected by both the geometry of the solar still and position of the sun in the sky. In contrast, the diffuse solar fraction is only dependent on the geometry of the solar distiller. The present model exhibited a lower root mean square error than that of the previous model. It appears that splitting the solar fraction into beam and diffuse parts improves the accuracy of modelling the performance of a single-slope solar still

Modelling, iterative procedure and simulation results for a monocrystalline solar cell

This paper focuses on the modelling and simulation for a photovoltaic system formed by monocrystalline solar modules. The objective is to find the parameters of the nonlinear I-V equation by adjusting the curve at three points: open circuit, maximum power, and short circuit. This paper brings a novel iterative procedure to find the value of diode ideality factor, series and equivalent shunt resistances. Simulation studies are carried out in order to uncover temperature dependence, solar radiation change, and output power variation. Finally, conclusions are duly drawn

2D radiative modelling of He I spectral lines formed in solar prominences

We present preliminary results of 2D radiative modelling of He I lines in solar prominences, using a new numerical code developed by us (Leger, Chevallier and Paletou 2007). It treats self-consistently the radiation transfer and the non-LTE statistical equilibrium of H and, in a second stage, the one of He using a detailed atomic model. Preliminary comparisons with new visible plus near-infrared observations made at high spectral resolution with THeMIS are very satisfactory.Comment: 4 pages, 2 figures (to appear in the Procs. of Solar Polarization Workshop #5, eds. Berdyugina, Nagendra and Ramelli), revised +2 citations, better figure

Quiet-Sun hydrogen Lyman-alpha line profile derived from SOHO/SUMER solar-disk observations

The solar radiation in the Lyman-alpha spectral line of hydrogen plays a significant role in the illumination of chromospheric and coronal structures, such as prominences, spicules, chromospheric fibrils, cores of coronal mass ejections, and solar wind. Moreover, it is important for the investigation of the heliosphere, Earth's ionosphere, and the atmospheres of planets, moons, and comets. We derive a reference quiet-Sun Lyman-alpha spectral profile that is representative of the Lyman-alpha radiation from the solar disk during a minimum of solar activity. This profile can serve as an incident radiation boundary condition for the radiative transfer modelling of chromospheric and coronal structures. Because the solar radiation in the Lyman lines is not constant over time but varies significantly with the solar cycle, we provide a method for the adaptation of the incident radiation Lyman line profiles (Lyman-alpha and higher lines) to a specific date. Moreover, we analyse how the change in the incident radiation influences the synthetic spectra produced by the radiative transfer modelling. To take into account the Lyman-alpha variation with the solar cycle, we used the LISIRD composite Lyman-alpha$ index. To estimate the influence of the change in the incident radiation in the Lyman lines on the results of radiative transfer models, we used a 2D prominence fine structure model. The analysis of the influence of the change in the incident radiation shows that the synthetic spectra are strongly affected by the modification of the incident radiation boundary condition. The hydrogen H alpha line can also be considerably affected, despite the fact that the H alpha radiation from the solar disk does not vary with the solar cycle.Comment: 17 pages, 7 figures, 2 appendices (A, B), to be published in Astronomy and Astrophysic

An alternative model to estimate solar radiation

Solar radiation is extremely useful in modelling many agricultural applications, but is hardly used due to the difficulty in obtaining data, and the time consuming process in estimating it by the angstrom (1924) formula which uses world geographical relationships. To estimate solar radiation at the Coconut Research institute, Lunuwila (7o 20'N;71o 53'E;30.5m) an alternative model was developed from measured sunshine hours data only. The model had good fit (R2=0.90,P0.001) and was found to have agreement with the estimates obtained from the Angstrom model. The alternative model is more flexible and useful in estimating crop evapotranspiration, and for crop-weather modelling. The mean daily solar radiation at Lunuwila was estimated to be 18.3 MJ m-2d-1 and the total annual solar radiation receipts is 6680 MJ m-2 (66.8 TJ ha-1). The monthly solar radiation was highest in March (21.7MJ m-2 d-1) and the estimated 75 per cent probability value was 22.5 June had the lowest (16.1 MJ m-2 d-1) value and the estimated 75 per cent probability value was 17.8