Technical evaluation of two 6-kW mono-Si photovoltaic systems at the National Renewable Energy Laboratory

This paper presents an analysis of performance data on the two 6-kW{sub ac} grid-connected photovoltaic systems at the National Renewable Energy Laboratory (NREL). The performance parameters analyzed include dc and ac power, aperture efficiency, energy, capacity factor and performance index which are compared to plane-of-array irradiance, ambient temperature, and back-of-module temperature as a function of time, either daily or monthly. Power ratings of the systems were also obtained for data corresponding to different test conditions. This study has shown, in addition to expected seasonal trends, that system monitoring is a valuable tool in assessing performance and detecting faulty equipment. In addition, methods applied for this study may be used to evaluate and compare systems employing different cell technologies

Energy yield modelling of PV systems operating in Namibian conditions

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.The greatest part of Namibia (except the coastal region) receives a large amount of solar radiation throughout the year, yet very few photovoltaic (PV) systems have been installed. The installation of PV systems is associated with high initial capital cost and, typically, an investor would seek a maximum return on investment at minimum risk. To increase the confidence level in the performance of PV systems it becomes imperative that an accurate prediction of the energy yield of systems, operating in the specific Namibian conditions, be achieved. One of the most reliable criterion for the assessment of the performance of a PV system is its annual energy production. The accurate estimation of the energy yield requires the use of a PV simulation software. A number of modelling software packages are currently available that provide a greater or lesser success in accurately predicting the energy yield of PV systems. The success in modelling the yield accurately depends on the skills, knowledge and understanding of the modeller as well as on the uncertainties of the modelling technique. In this work, PVsyst 6 package has been used for modelling an already operational roof-top grid connected PV system. The uncertainties in the modelled and measured data have been assessed and comparison of modelled and measured energy yield has been performed.cf201

Evaluating the relationship between electroluminescence (EL) imaging and the power output of photovoltaic modules

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.Electroluminescence (EL) is a useful solar cell and photovoltaic module characterisation technique as it is fast, non-destructive and sensitive to the effects of shunt and series resistance and recombination processes. EL is emitted by a solar cell under forward bias, as injected carriers recombine radiatively and can be detected by a cooled silicon CCD camera in dark conditions or with appropriate optical filters. There is a relationship between the localised intensity of the emitted EL and the corresponding photo-response of the cell at a point [1-3]. Thus EL imaging allows cracks, breaks and defects to be identified. These defects can have a significant effect of the performance and longevity of the module. Cracks result in inactive areas which limit the current generated by the cell. Cells are connected in series in a module so the power output of the entire module is affected. This study investigates the relationship between the EL image of observed features and the power output of the module. It is shown that the extent to which the power and current of a module are affected by cell fractures depends on the area and position of the fracture. Other features such broken contact fingers and small micro-cracks are observed to have a minimal effect on the power output.dc201

Optical design of low concentrator photovoltaic modules

This paper addresses the necessary procedures that need to be considered when designing an optical sub-system of low concentrator photovoltaic (LCPV) module. CPV systems make use of optical elements and solar tracking to concentrate solar flux onto a photovoltaic (PV) receiver. The performance of a concentrator module is highly dependent on the configuration and alignment of the optical elements in the system. In this study, various design considerations were taken into account to construct a LCPV module that was characterised with respect to optical design and electrical performanc

Effects of current mismatch due to uneven soiling on the performance of multi-crystalline silicon module strings

Photovoltaic (PV) module operation is critical in PV systems for optimum generation of electrical power. Modules installed in the field suffer uneven soiling caused by bird droppings and dust build-up on their front surface. This study investigated the impact of partial shading caused by non-uniform soiling on the electrical characteristics of multi-crystalline silicon (mc-Si) modules and strings, and compared this with simulated I-V parameters. Light and heavy uneven soiling on mc-Si solar cells resulted in current mismatch which can be simulated. The effects of partial soiling on the I-V characteristics of mc-Si module strings were experimentally measured and agreed with the simulated results

Thermal modelling of low concentrator photovoltaic systems

Efficient thermal management of low concentrator photovoltaic (LCPV) systems will allow maximizing of the power output and may also substantially prolong operating lifetime. For this reason, it is necessary to develop a thorough understanding of the thermal transfer and dissipation mechanisms associated with an LCPV system. The LCPV system under consideration uses a 7-facet reflector optical design, providing a geometric concentration ratio of approximately 4.85. The LCPV system succeeded in increasing the short circuit current from 1A to 5.6A, demonstrating an effective concentration ratio of approximately 4.75. LCPV system temperatures in excess of 80°C were recorded without a thermal management system. A basic thermal model was developed and assessed under various environmental conditions. The effectiveness of a heat-sink, which reduced the temperature difference between the LCPV receiver temperature and the ambient temperature by 37.5%, was also evaluated. The results discussed in this paper will assist the future development of techniques aimed at reducing the high temperatures associated with LCPV systems

Dust in Supernovae and Supernova Remnants I : Formation Scenarios

Supernovae are considered as prime sources of dust in space. Observations of local supernovae over the past couple of decades have detected the presence of dust in supernova ejecta. The reddening of the high redshift quasars also indicate the presence of large masses of dust in early galaxies. Considering the top heavy IMF in the early galaxies, supernovae are assumed to be the major contributor to these large amounts of dust. However, the composition and morphology of dust grains formed in a supernova ejecta is yet to be understood with clarity. Moreover, the dust masses inferred from observations in mid-infrared and submillimeter wavelength regimes differ by two orders of magnitude or more. Therefore, the mechanism responsible for the synthesis of molecules and dust in such environments plays a crucial role in studying the evolution of cosmic dust in galaxies. This review summarises our current knowledge of dust formation in supernova ejecta and tries to quantify the role of supernovae as dust producers in a galaxy.Peer reviewe

SERF photovoltaic systems. Technical report on system performance for the period, August 1, 1994--July 31, 1995

This report presents an analysis of performance data on the two identical, 6 kW{sub ac}, grid-connected photovoltaic systems located on the roof of the Solar Energy Research Facility building at the National Renewable Energy Laboratory in Golden, Colorado. The data cover the monitoring period August 1, 1994, to July 31, 1995, and the performance parameters analyzed include direct current and alternating current power, aperture-area efficiency, energy, capacity factor, and performance index. These parameters are compared to plane-of-array irradiance, ambient temperature, and back-of-module temperature as a function of time, either daily or monthly. We also obtained power ratings of the systems for data corresponding to different test conditions. This study has shown, in addition to expected seasonal trends, that system monitoring is a valuable tool in assessing performance and detecting faulty equipment. Furthermore, methods applied for this analysis may be used to evaluate and compare systems using cells of different technologies. The systems were both found to be operating at approximately 7% below their estimated rating, which was based on Photovoltaics for Utility-Scale Applications test conditions. This may be attributed to the design inverter efficiency being estimated at 95% compared to measured values of approximately 88%, as well as the fact that aperture-area efficiency that was overestimated at 12.8% compared to a measured value of 11.0%. The continuous monitoring also revealed faulty peak-power point tracking equipment

Monitoring the natural recovery of potential induced degradation in poly-crystalline photovoltaic modules

Potential induced degradation (PID) is a defect that has a severe effect on the performance of photovoltaic (PV) modules in field conditions. It is caused by leakage currents and the accumulation of sodium ions (Na+) between the anti-reflective coating and the encapsulation. In the experiment reported on here, PID was artificially induced through a PID stress test, where the surface of a poly-crystalline p‑type module was covered with an aluminium sheet connected to the positive terminal of a high voltage power supply (1000 V), while the short-circuited module terminals was biased to the negative terminal. This stress test was applied to two similar poly-crystalline p‑type modules, A and B, for 48 hours and 20 hours respectively. The duration of the stress test determines the degree of PID severity induced. The length of the test resulted in Module A’s power decreasing by 88% and Module B’s by 40%. Electroluminescence and current-voltage measurements were taken at regular intervals over a period of more than a year to monitor the natural recovery of the modules. These measurements show that the natural recovery of severe PID modules is possible, but slow. After the test period, the maximum power of Module A and Module B had recovered to 63% and 96% of the original level. PID experienced in the field is generally less severe than for the modules in this study, so PID recovery could be achieved by adopting a process of setting affected strings at open-circuit in turns

Infrared thermography study of the temperature effect on the performance of photovoltaic cells and panels

International audienceSilicon solar cells are widely used in the Photovoltaic (PV) industry. The silicon PV electrical performance is described by its current–voltage (I–V) characteristic, which is a function of the device used and material properties. The PV cell efficiency is strongly temperature dependent. This work studies the electric performance of a polycrystalline Si solar panel under different atmospheric conditions by using thermographic images. The PV performance study is carried out as function of the junction temperature and solar insolation. An infrared analysis as close to the junction temperature has allowed measurements of the cells surface temperature in order to increase the measurement accuracy and to make a reliable assessment of the PV module performance