akash research methods project.docx

November 24, 2018 General Studies

A quantitative report on Solar radiation Measurement for High use of solar energyABSTRACT:This work presents the measurement of direct normal irradiance by pyrheliometer. A concentrating lens is used to focus the sunlight onto a small copper receiver disk. Four different focal lengths were tested to determine the best setup for highest accuracy. After preliminary results regarding the best focal length were obtained. From the temperature difference between the receiver disk and the collimating tube surface, the incoming irradiance can be calculated. An Eppley Normal Incidence Pyrheliometer (NIP) was used to calibrate and compare the irradiance measurements obtained with the ESC-MG-2. The ESC-MG-2-F4 pyrheliometer was tested under similar conditions. The accuracy of the ESC-MG-2-F2 and ESC-MG-2-F4 irradiation values is within ± 2% and ± 1.5%, respectively. The standard deviation for the instantaneous irradiance measurement under steady state conditions is 2 W/m2 for both instruments.INTRODUCTION: Solar energy can be divided into primary and secondary solar resources. Solar radiation is considered to be a primary solar resource whereas wind, wave power, and biomass, which are created by the sun indirectly due to density gradients or photosynthesis, are secondary solar resources. The focus of this work lies in the primary solar resource of radiation.The most common instrument used for measuring solar radiation is the pyranometer, which measures global radiation. However, for concentrating solar applications, only the direct beam component of the radiation is necessary. Pyranometers can be modified in order to measure only the direct beam radiation but a simpler approach is to use a pyrheliometer. Unlike commercially available pyrheliometers optics, we replaced four different optics through which data is extracted. Thus, an accurate and optimal optics pyrheliometer is a necessity.The direct beam component is measured using an instrument called a pyrheliometer. This is essentially a small blackened disk located at the rear end of a tube that is sufficiently long to collimate only that light which originates from the vicinity of the sun. The temperature of the blackened disk, as it is warmed by the incoming radiation, is measured by a thermopile whose output in mV has been calibrated against some reference standard so as to be interpretable as a radiation flux in units W m-2.THE PROBLEM STATEMENT:The use of a concentrating lens guarantees accurate results, even with less than precise tracking systems since the incoming radiation is focussed onto a small area of the receiver disc. The concentrating lens is of aspheric shape and made of acrylic glass. The benefit of an aspheric shaped lens is its very small spot size compared to a regular planoconvex lens. Figure 4.6 shows the two molded acrylic aspheric lens used, which were purchased from Edmund Optics. The NT48-183/NT48-184 are lenses with the focal number F#2 and F#4, with a corresponding back focal length of 45.8 mm and 97.2 mm , respectively.Methodology:The radiation effect on solar energy efficiency was critical but the devices used to measure the solar radiation were not that accurate so we are ought to find the better equipment or advances to be made for the equipments to define the maximum efficiency use of solar radiation. Hence pyrheliometer (a device which measure solar irradiancy was use) as discucced pyrheliometer equipment key part was the lenses used in the equipment for constant emissions of solar radiation and to concentrate the effect measurement. The lenses used in pyrheliometer was >>>>> and we have observed the varaitaion of solar radiation measurement with respect to the temperature measured. Highly calibrated thermocouples are placed to measure the temperature. Hence, we can define which lenses are correct to measure the solar radiation so that no energy gets wasted up.Experimental set up:Measurements of instantaneous irradiance were done using the ESC-MG-2 pyrheliometer and Eppley NIP. Integrating the irradiance over the course of the test run yields the main interest of the measurements,the irradiation. The NIP was used as a reference instrument to calibrate the ESC-MG-2. It was also used to compare with the subsequent results that were obtained The experimental setup consists of three main components: the pyrheliometer itself, the tracking system and the data acquisition. The following sections explain the details of the main components. The use of a concentrating lens guarantees accurate results, even with less than precise tracking systems since the incoming radiation is focussed onto a small area of the receiver disc. The concentrating lens is of aspheric shape and made of acrylic glass. Due to this high reflectance of wavelength outside the visual spectrum, only part of the solar radiation actually transmits through the lens onto the receiver disk. For a higher optical efficiency, an uncoated lens or a coating specifically for the visible and near-infrared wavelength range should be chosen shows the wavelength depending transmittance of solar radiation through an uncoated acrylic lens. Integrating the spectral irradiance between 350 nm and 1130 nm at a transmittance of 90% results in an increased optical efficiency of about 72%.Results and discussions:A small alignment hole in the lens holder cover allows the sun rays to pass through and a center bore in the tube bottom attachment is used for alignment. If perfectly aligned, the sun rays shining through the alignment leave a sun spot that is lined up with the center of the center bore Preliminary results are presented for lenses with four different focal numbers, F#8, F#6, F#4 and F#2. From these results, it was observed that the most accurate setup configuration was with the focal number F#4 and F#2. Following the preliminary results, this chapter presents data which was obtained from extensive testing with the focal numbers F#4 and F#2.Table SEQ Table * ARABIC 1 Observed temperature differences between receiver and collimating tube of four different focal lengthsS/No Focal Length Back focal Length(BFL) Receiver Día Change in temp at 1000Wm21 8 1.99 cm 0.18cm 260C2 6 1.48cm 0.136 cm 410C3 4 0..972cm 0.094cm 630C4 8 0.458cm 0.054cm 670CTesting on four different focal lengths F#8, F#6, F#4 and F#2 was done to investigate the influence of the collimating tube length and the accuracy depending on the temperature difference between the receiver disk and the collimating tube.Conclusion:All of the tested pyrheliometers yielded results within ±5%. However, due to the higher temperature difference for the smaller focal number setup, it was decided to focus only on the focal number 4 and focal number 2 for further design improvements. The time response of the ESC-MG-2-F2 and ESC-MG-2-F4 is about 125 and 150 seconds, respectively. The accuracy for both of the tested instruments for the integrated irradiation is within ±2% compared with the Eppley NIP. The steady state instantaneous irradiance of the ESC-MG-2-F2 and ESC-MG-2-F4 agrees well with the Eppley NIP, but they are time delayed for transient measurements.Future Scope:The following future work suggestions are meant to increase the accuracy, simplify the system and increase the chances to introduce it to the market:Testing of an uncoated acrylic lens should increase the optical efficiency by about 20%, thus increasing the temperature of the receiver and therefore increasing the resolution.Implement mechanical limit for hour angle rotation axisFurther investigations are needed to for various different lenses at different surface contexture by replacing the materials used in the surface contacted are around the lenses.


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