Non-Contact Measurement of POA Irradiance and Cell Temperature for PV Systems

This paper presents a non-contact measurement of irradiance on plane of array (POA) and cell temperature for PV systems. The idea is motivated from the diode model of PV, where POA irradiance and cell temperature are proportional to the photocurrent and modified ideality factor, respectively. Based on the recent progress of diode model identification, the photocurrent and modified ideality factor can be linearly determined from I-V characteristics, which makes it feasible to develop a non-contact measurement approach for POA irradiance and cell temperature, i.e., both of them will be derived completely from the diode mode parameter identification without the need of any sensors. The calibration of the proportional factors is done from the indoor module flash test and then applied to outdoor module testbed to show the accuracy and effectiveness of the proposed method

PV panel modeling and identification

In this chapter, the modelling techniques of PV panels from I-V characteristics are discussed. At the beginning, a necessary review on the various methods are presented, where difficulties in mathematics, drawbacks in accuracy, and challenges in implementation are highlighted. Next, a novel approach based on linear system identification is demonstrated in detail. Other than the prevailing methods of using approximation (analytical methods), iterative searching (classical optimization), or soft computing (artificial intelligence), the proposed method regards the PV diode model as the equivalent output of a dynamic system, so the diode model parameters can be linked to the transfer function coefficients of the same dynamic system. In this way, the problem of solving PV model parameters is equivalently converted to system identification in control theory, which can be perfectly solved by a simple integral-based linear least square method. Graphical meanings of the proposed method are illustrated to help readers understand the underlying principles. As compared to other methods, the proposed one has the following benefits: 1) unique solution; 2) no iterative or global searching; 3) easy to implement (linear least square); 4) accuracy; 5) extendable to multi-diode models. The effectiveness of the proposed method has been verified by indoor and outdoor PV module testing results. In addition, possible applications of the proposed method are discussed like online PV monitoring and diagnostics, noncontact measurement of POA irradiance and cell temperature, fast model identification for satellite PV panels, and etc

PV Outdoor Tests

The main purpose of this chapter is to survey the structure, operation, and design of photovoltaic (PV) systems. PV systems consist of solar cells and electronic units which convert directly produced electricity from solar irradiation to electricity in the form of demand by load or feed the produced electricity directly into the grid. The heart of the system is the solar cell or PV array. From individual solar cell to PV power plant and solar electricity conversion will be discussed in this chapter. Indoor and outdoor measurement of PV modules and performance of PV systems will be summarized. The performance of the system which is mainly the energy output depends on the operating condition, the location of the system, and the configuration of the system. The system modeling and its behavior under varying weather conditions which strongly affect the electricity output of the system will be discussed in this chapter

The photovoltaic (PV) energy conversion chain: irradiation to grid impact

The research presented in this thesis aims to enhance understanding of the influence of the inherent variability of solar irradiance on nationwide photovoltaic (PV) system performance. The spatial and temporal consistency of the solar resource is investigated. The case study area is the UK and the body of work presents nine publications written over four years with this objective in mind.The key research theme is to produce national solar resource maps from ground-based measurements of solar radiation. Geographical Information System (GIS) techniques are utilised to build a UK map of irradiation from geographically sparse data, requiring development of new tools to both generate and verify the map data. With an augmented understanding of the solar resource, PV system dispersal is then investigated, allowing analysis and prediction of the impact on the electrical grid. The papers describe: (1) determination of the most appropriate algorithm for interpolating ground-based irradiation measurements in the UK to countrywide coverage; (2) selection of solar irradiance component separation and translation models to obtain plane-of-array irradiation from the weather station global horizontal records; (3) justification of weather stations data as a fundamental model input; (4) statistical analysis of LiDAR data and application of GIS models to LiDAR data to obtain PV system tilts and azimuths as model inputs for (2); (5) conversion of solar irradiation to electrical output; (6) shading effects; (7) study of geographic divergence of generation; (8) aggregate grid variability; and (9) future installation scenarios.There has been no previous study which commences with obtaining irradiation values for PV and proceeds through the entire modelling chain to assess cumulative impacts on grid transformers. This study may be adapted as a guide when undertaking equivalent research in other countries. Specifically, the work presented here is more extensively validated than that of previous authors. A nationwide analysis of spatial and temporal variation of PV output is delivered and current and future impacts on the National Grid are taken into consideration.</div

Performance Assessment of Mismatch Mitigation Methodologies Using Field Data in Solar Photovoltaic Systems

Partial shading and other non-ideal conditions cause electrical mismatches that reduce the output power generated by a photovoltaic (PV) system. It affects the overall performance and efficiency of PV systems. Therefore, a model is developed in MATLAB, which analyses the performance of the PV systems under real irradiance profiles and temperatures for various available mismatch mitigation methodologies, i.e., bypass diode, DC power optimizer, and differential power processing (DPP). More specifically, this study will help to understand the best mismatch reduction methodologies for a solar PV system under different scenarios. The results also are validated by comparing them with a similar PV system installed in SolarTechLAB, which also operates under the same irradiance and temperature conditions under which these models are tested. This study also presents novel results, covering discussions on the reverse voltage distribution under mismatch scenarios among bypass diode, DC power optimizer, and DPP techniques

Building Applied Photovoltaic Array: Thermal Modeling and Fan Cooling

abstract: Thermal modeling and investigation into heat extraction methods for building-applied photovoltaic (BAPV) systems have become important for the industry in order to predict energy production and lower the cost per kilowatt-hour (kWh) of generating electricity from these types of systems. High operating temperatures have a direct impact on the performance of BAPV systems and can reduce power output by as much as 10 to 20%. The traditional method of minimizing the operating temperature of BAPV modules has been to include a suitable air gap for ventilation between the rooftop and the modules. There has been research done at Arizona State University (ASU) which investigates the optimum air gap spacing on sufficiently spaced (2-6 inch vertical; 2-inch lateral) modules of four columns. However, the thermal modeling of a large continuous array (with multiple modules of the same type and size and at the same air gap) had yet to be done at ASU prior to this project. In addition to the air gap effect analysis, the industry is exploring different ways of extracting the heat from PV modules including hybrid photovoltaic-thermal systems (PV/T). The goal of this project was to develop a thermal model for a small residential BAPV array consisting of 12 identical polycrystalline silicon modules at an air gap of 2.5 inches from the rooftop. The thermal model coefficients are empirically derived from a simulated field test setup at ASU and are presented in this thesis. Additionally, this project investigates the effects of cooling the array with a 40-Watt exhaust fan. The fan had negligible effect on power output or efficiency for this 2.5-inch air gap array, but provided slightly lower temperatures and better temperature uniformity across the array.Dissertation/ThesisM.S. Technology 201

Investigation of Efficiency Loss of Distributed Solar Power Due to Soiling and Efficiency Recovery by Rainfall

As the concern with global warming increases causing the need for CO2 reduction, renewable energy is of great interest as it has lower carbon footprint when compared to conventional sources (natural gas, coal, oil and nuclear). Solar energy has been drawing worldwide attention since it can transform sunlight directly into electricity with the use of photovoltaic (PV) cells. However, this technology has some drawbacks that need to be addressed including dust deposition on solar panels, also known as soiling. Soiling can decrease PV panel’s efficiency thereby resulting in less energy production. The soiling rates are very site specific and depend on the geographic location of the panels and the climate in that area. The solar panels can be cleaned naturally (by rainfall, snow or wind) or mechanically washed. This thesis addresses the impact of solar panel soiling and washing on the energy production of solar PV plants located at the UNLV campus. The objectives of this project were (a) to evaluate whether rainfall alone, in the desert environment with low rainfall, is sufficient to clean up the solar panels, and, if possible, determine the minimum amount of rainfall necessary to clean up panels.; (b) to examine the efficiency loss caused by soiling using different methods of analyses and (c) to evaluate if panel washing is worthwhile given the cost and the efficiency gain that is obtained by washing. To calculate the efficiency of the panels, a model was developed to generate parameters that were not measured at the site. Panel efficiencies before and after rainfall events were compared to determine the minimum amount of rain necessary to clean the panels. It was found that at least 0.2 inches of rain was needed to partially restore clean-panel efficiency. In Las Vegas, the recurrence periods of different depths rainfall were calculated using data from the past 29 years. It was observed that the 50th percentile recurrence period of a rainfall event with depth of 0.2 inches or higher was approximately 52 days. Student Union: -0.0044%/day, CBC-C: -0.00099%/day, and Dayton Hall: -0.0034%/day The amount of efficiency lost during the dry intervals (periods between rainfall events) was analyzed in three different ways. The average efficiency loss per day during the dry periods varied from -0.000171 % to -0.00533 %, depending on the method used and the building where the panels were located. However, there were some limitations to the calculations. It was not possible to completely isolate the effects of only soiling on the efficiency of the panels. The rate of decline seemed to be also impacted by seasonal effects. To better evaluate the effect of washing, a professional company was hired to wash a set of solar panels located on UNLV’s Student Union building. The panels were washed with water with a low concentration of TDS. The power output and the efficiency of those panels were analyzed from before and after the washing. There was a very small efficiency and power increase due to the washing. Therefore, it was concluded that washing in this area is not worthwhile, and that rainfall events in excess of 0.2 inches can adequately restore the efficiency of the panels. If there is a change in cost of energy, washing, water or a great increase in the efficiency of the solar panels, it would be necessary to reevaluate the analysis