The effect of intermittent solar radiation on the performance of PV systems

The effect of the intermittency of solar radiation on the performance of photovoltaic (PV) systems with battery storage is investigated. A model is developed that enables system energy flows to be simulated with one-minute and hourly solar radiation values. It is found that the variations in solar radiation that occur during partly cloudy conditions can cause significant fluctuations in system currents, particularly battery currents. These fluctuations are readily apparent from simulations using one-minute solar radiation data, but not in simulations carried out with hourly data. The implications of these fluctuations for the lifetime of batteries used in solar PV systems is discussed. Differences in the battery state of charge between minute and hourly simulations can arise during periods of intermittent solar radiation

Constitutive model for large strain deformation of semicrystalline polymers

A constitutive model for large strain deformation of semicrystalline polymers has been formulated to predict the complex elasto-viscoelastic-viscoplastic material response. The general form of this model can be represented by three parallel rheological components corresponding to each of the modes of deformation. It will be shown that such a configuration is well suited to the mechanical nature of polymers as observed in recent studies. The constitutive stress-strain-time relationships are drawn from continuum mechanics which are more suitable than simple linear expressions from rheology. The result is a large strain, fully three-dimensional constitutive model, derived from a thermodynamic basis. The proposed model can be fit to macroscopic experimental data and is highly suited to numerical analysis. The paper reviews the literature relevant to constitutive representation of semicrystalline polymers, provides conclusion and validation of the most suitable form of constitutive model and presents the relevant constitutive mathematics

Evaporation from an open cylinder

The rate of evaporation from the wetted floor of a tube open at the top to a relatively dry environment is investigated analytically, numerically and experimentally for the case of a light vapour. Though buoyancy forces ensure that the heavier external gas is always in motion, it is found that inside the tube both stagnation (diffusion-dominated evaporation) and convection are possible. In contrast to previous studies, axisymmetry of the postcritical flow is not assumed, leading to a reduction in the predicted critical Rayleigh number by a factor of 5 and much better agreement with experiment

Relationship between sunshine duration and solar radiation

This paper examines the relationship between sunshine duration and solar radiation received on the earth's surface. Sixty-nine thousand pairs of sunshine-radiation readings from 670 sites were analyzed. A generalization of the Ångström-Prescott equation of the form K=Kclear[β+(1-β)Sγ] was found to most efficiently fit the data and suggests the relationship between the average daily atmospheric transmittance K and the sunshine fraction S is non-linear. The suggested reason for this non-linearity is that a reduced sunshine fraction not only decreases the clear sky radiation duration, but also the radiation transmitted through clouds, i.e. clouds get optically thicker with decreasing S. This finding is supported on theoretical grounds and by analyzing instantaneous solar radiation measurements from Australia and Germany.Representing the sunshine fraction in terms of the proportion of beam radiation reaching the earth's surface S=Hb/Hb,clear leads to a fundamental connection between the monthly average diffuse fraction and the sunshine-radiation relationship. Moreover, it confirms the non-linearity of the latter relationship, which was previously questioned because of limited data and/or poor quality sunshine measurements

Heat transfer across corrugated sheets and honeycomb transparent insulation

This paper describes the design of a simple guarded hot-plate apparatus for the measurement of heat transfer across transparent insulation. The apparatus is used to measure the heat transfer coefficient across a transparent corrugated (zigzag) sheet and honeycomb transparent insulation. The sheet and honeycomb are made from cellulose acetate film, which has high absorptance for long-wave thermal radiation and high transmittance for short-wave solar radiation. The corrugated sheet performs well, however, honeycomb transparent insulation of the same height and material appears to be superior due to greater thermal radiation blockage and better solar transmission characteristics. A numerical model for a honeycomb is developed which shows good agreement with the experimentally measured results