Irradiance

In the present work we investigated the contribution of N availability to the changes in some antioxidant systems and in fatty acid composition of chloroplast membranes, in order to evaluate their role in the high light acclimation in coffee plants. Young coffee (Coffea arabica L. cv. Catuaı́) plants, grown under low irradiance (up to 150 μmol m−2 s−1) with high (2N), medium (1N) and low (0N) N availability, were exposed to high irradiance (up to 1500 μmol m−2 s−1) for a maximal period of 15 days. Changes in several parameters were monitored during that period in the two top pairs of mature leaves. The formation rate of superoxide (O2⋅−) estimated by ESR (Kf) did not differ among N-treatments before the onset of high light, but increased 70 and 30% in 0N and 1N plants, respectively, and decreased 33% in 2N plants by the end of the stress. By this time, the chloroplastic activities of Cu,Zn-superoxide dismutase (Cu,Zn-SOD), ascorbate peroxidase (APer) and glutathione reductase (GRed) increased, respectively, 18, 225 and 138% in 2N plants. The 0N plants presented a 120% increase in Cu,Zn-SOD activity (which agrees with the higher Kf of O2⋅−) and a 68% decrease in APer activity, suggesting an increase in H2O2 levels, while GRed activity decreased 20%. The total carotenoid content was higher in 2N plants and increased (about 20%) only in these plants by the end of stress. After 12 days of high irradiance, the total fatty acid (TFA) content increased about 30% in 2N and 1N plants, but did not significantly change in 0N plants. In 2N and 1N plants a preferential synthesis of palmitic acid (16:0) and a decrease in the linolenic acid (18:3) percentage caused a decrease in the unsaturation level, which may have made the chloroplast membranes less susceptible to peroxidation. The N dependent changes observed in 2N (and to a lesser extent in 1N) plants could represent adaptive features under the new high irradiance conditions, which increased the protection of the chloroplast structures against photooxidative stress.

Extensive works exist in literature about modeling solar power generation by photovoltaic cell. However, some fundamental aspects of the design making it flexible and exploitable for other research works remain difficult and unclear under Matlab Simulink. This work proposes an understandable model of PV cell, suitable for upgradability and further use for other designs. After dealing with a sound analytical model on the PV cell, the paper presents a clear modeling under Simulink. The model is designed to take excitation from three inputs including temperature, irradiance and voltage. Simulations were run and results in terms of peak power and current were analyzed. In total the similarities were quite satisfactory as compared to previous works. However, some little differences in the responses of the model to various inputs were observed. These results, further confirm the novelty of the proposed model.

The Photovoltaic standalone system is gaining its high importance mostly for rural application like pv water pumping, solar lighting, battery charging etc.Considering environmental effects and scarcity of fossil fuel the trend has developed towards the use of more and more renewable energy.In this paper a basic circuit of boost converter is designed in MATLAB/Simulink with constant dc source voltage. However a comparative study has also been done for the converter connected with pv system directly with the converter connected with mppt tracking technique. Perturb and Observance (P&O) algorithm is implemented for providing the necessary duty pulse and makes the system operate at maximum power point.The boost converter connected with PV system without mppt operates at any other point other then the maximum power point and hence the output voltage decreases.But with mppt the proposed system performs better.

Solar cells are highly sensitive to temperature, which affects its operating parameters. The study has its aim in accessing the impact of temperature (in excess above the maximum operating cell temperature) and irradiance source on the efficiency of polycrystalline photovoltaic (PV) solar panels in an environment where the temperature and irradiance level can be fully controlled. For the study to achieve its aim, a solar box and tungsten light bulbs were used to create an environment where the irradiance level and the temperature can be controlled. The solar panel was placed inside the solar box facing the light source while the irradiance level and temperature were measured and held constant. Results show a steady decrease in voltage with increasing temperature while the performance ratio and efficiency of the photovoltaic module followed a similar trend as that of voltage once the temperature exceeds the maximum operating cell temperature. Results also show the output voltage of t...

For testing the integration of the remote sensing related technologies into the water quality monitoring programs of Lake Garda (the largest Italian lake), the spatial and spectral resolutions of Hyperion and the capability of physics-based approaches were considered highly suitable. Hyperion data were acquired on 22nd July 2003 and water quality was assessed (i) defining a bio-optical model, (ii) converting

ABSTRACT In this paper, the accuracy of soft computing technique in solar radiation prediction based on series of measured meteorological data (monthly mean sunshine duration, monthly mean maximum and minimum temperature) taking from Iseyin meteorological station in Nigeria was examined. The process, which simulates the solar radiation with support vector regression (SVR), was constructed. The inputs were monthly mean maximum temperature (T max), monthly mean minimum temperature (T min) and monthly mean sunshine duration ( \( \bar{n} \) ). Polynomial and radial basis functions (RBF) are applied as the SVR kernel function to estimate solar radiation. According to the results, a greater improvement in estimation accuracy can be achieved through the SVR with polynomial basis function compared to RBF. The SVR coefficient of determination R 2 with the polynomial function was 0.7395 and with the radial basis function, the R 2 was 0.5877.

The paper presents a method for calculation of Inverter power clipping loss due to PV array oversizing or high DC to AC ratio. For calculation, a PV plant installed in southern region of India having DC to AC ratio 1.4 was selected. Since a PV plant runs at full load in peak hours only (i.e. 11 am to 2 pm) when the irradiance level is ≥ 1000 W/m2 , which results in inverter power clipping (InPC) whereas at lower irradiance the produced PV power is also low which will not lead inverter power clipping. The high DC to AC ratio, increases the generation at lower irradiation but when the irradiance is high i.e. ≥ 1000 W/m2 , the inverter limits the input DC power and hence the inverter power also limited as per rated capacity of inverter. Hence the power generated by oversized PV array is lost at high irradiance and termed as Inverter power clipping loss. The significance of calculation of clipping loss is to optimize the inverter DC to AC ratio & also to estimate the guaranteed PV plant PR (performance ratio) as due to clipping loss the PV plant PR drops & it leads misinterpretation to observer as low performance of PV plant. If clipping loss is added to the observed PR, then the actual PR will rise to meet the expected PR. Hence the paper presents the method to calculate the simulated power as per expected PV plant PR & irradiance to provide the inverter power clipping loss

Our objective was to evaluate the physiological response of Fischerella ambigua FS18 to the combined influence of pH (5, 7 and 9) and light intensity (3 and 300 μmol photon m−2 s−1). Growth rates were similar at pH 9 and pH 7. There was no growth at pH 5. Increasing light intensity did not have any considerable influence on growth rates. Chlorophyll concentration was higher at pH 7 at all light intensities. Chlorophyll concentration decreased with increasing light intensity from 3 to 300 μmol photon m−2 s−1. Synthesis of the phycobiliproteins (PBP), phycocyanin (PC) and allophycocyanin (APC) had the highest rate in pH 7. Increasing irradiance decreased the concentrations of all PBPs. The light-saturated photosynthetic rate was clearly higher at high light intensity. With respect to nitrogenase activity, the highest rate was at pH 9 and 300 μmol photon m−2 s−1. Irradiance did not affect significantly this activity at pH 7. This cyanobacterium seems to be alkalophilic with maximum nitrogenase activity and photosynthesis at pH 9. It can also adapt its photosynthetic apparatus to the variable factors that are found in rice fields.

Solar cells are highly sensitive to temperature, which affects its operating parameters. The study has its aim in accessing the impact of temperature  (in excess above the maximum operating cell temperature) and irradiance source on the efficiency of polycrystalline photovoltaic (PV) solar panels in an environment where the temperature and irradiance level can be fully controlled. For the study to achieve its aim, a solar box and tungsten light bulbs were used to create an environment where the irradiance level and the temperature can be controlled. The solar panel was placed inside  the solar box facing the light source while the irradiance level and temperature were measured and held constant. Results show a steady decrease in voltage with increasing temperature while the performance ratio and efficiency of the photovoltaic module followed a similar trend as  that of voltage once the temperature exceeds the maximum operating cell temperature. Results also show the output voltage of the photovoltaic  to be higher under the tungsten light than the sun, but the efficiency  achieved by the photovoltaic under the sun far exceeds that obtained under  the tungsten light.

Many emerging light-emitting diode (LED) applications require short-distance illumination. For that, we derive an exact formula of the illumination profile produced by Lambertian LEDs, in which all parameters are fundamental constants. Moreover, we propose a general, simple, but accurate mathematical model of the irradiance pattern, valid for Lambertian and non-Lambertian LEDs at short distances. This model provides the irradiance profile as a function of both the LED-target distance and the coordinates of every point on the irradiated surface. The model is formulated in terms of simple sigmoid functions, in which LED size and light flux are fundamental parameters. The accuracy of the irradiance pattern model is tested both with theory and with experimental measurements.

Background: In Indonesia, the burden of severe hyperbilirubinemia is higher compared to other countries. Whether this is related to ineffective phototherapy (PT) is unknown. The aim of this study is to investigate the performance of phototherapy devices in hospitals on Java, Indonesia. Methods: In 17 hospitals we measured 77 combinations of 20 different phototherapy devices, with and without curtains drawn around the incubator/crib. With a model to mimic the silhouette of an infant, we measured the irradiance levels with an Ohmeda BiliBlanket Meter II, recorded the distance between device and model, and compared these to manufacturers' specifications. Results: In nine hospitals the irradiance levels were less than required for standard PT: < 10 μW/cm 2 /nm and in eight hospitals irradiance failed to reach the levels for intensive phototherapy: 30 μW/cm 2 /nm. Three hospitals provided very high irradiance levels: > 50 μW/cm 2 /nm. Half of the distances between device and model were greater than recommended. Distance was inversely correlated with irradiance levels (R 2 = 0.1838; P < 0.05). The effect of curtains on irradiance levels was highly variable, ranging from − 6.15 to + 15.4 μW/cm2/nm, with a mean difference (SD) of 1.82 (3.81) μW/cm2/nm (P = 0.486). Conclusions: In half of the hospitals that we studied on Java the levels of irradiance are too low and, in some cases, too high. Given the risks of insufficient phototherapy or adverse effects, we recommend that manufacturers provide radiometers so hospitals can optimize the performance of their phototherapy devices.