Opto-Electro-Thermal Approach to Modeling Photovoltaic Performance and Reliability from Cell to Module

Thanks to technology advancement in recent decades, the levelized cost of electricity (LCOE) of solar photovoltaics (PV) has finally been driven down close to that of traditional fossil fuels. Still, PV only provides approximately 0.5% of the total electricity consumption in the United States. To make PV more competitive with other energy resources, we must continuously reduce the LCOE of PV through improving their performance and reliability. As PV efficiencies approach the theoretical limit, however, further improvements are difficult. Meanwhile, solar modules in the field regularly fail prematurely before the manufacturers 25-year warranty. Therefore, future PV research needs innovative approaches and inventive solutions to continuously drive LCOE down. In this work, we present a novel approach to PV system design and analysis. The approach, comprised of three components: multiscale, multiphysics, and time, aims at systemically and collaboratively improving the performance and reliability of PV. First, we establish a simulation framework for translating the cell-level characteristics to the module level (multiscale). This framework has been demonstrated to reduce the cell-to-module efficiency gap. The framework also enables the investigation of module-level reliability. Physics-based compact models -the building blocks for this multiscale framework are, however, still missing or underdeveloped for promising materials such as perovskites and CIGS. Hence, we have developed compact models for these two technologies, which analytically describe salient features of their operation as a function of illumination and temperature. The models are also suitable for integration into a large-scale circuit network to simulate a solar module. In the second aspect of the approach, we study the fundamental physics underlying the notorious self-heating effects for PV and examine their detrimental influence on the electrical performance (multiphysics). After ascertaining the sources of self-heating, we propose novel optics-based self-cooling methodologies to reduce the operating temperature. The cooling technique developed in this work has been predicted to substantially enhance the efficiency and durability of commercial Si solar modules. In the third and last aspect of the approach, we have established a simulation framework that can forward predict the future energy yield for PV systems for financial scrutiny and inversely mine the historical field data to diagnose the pathology of degraded solar modules (time). The framework, which physically accounts for environmental factors (e.g., irradiance, temperature), can generate accurate projection and insightful analysis of the geographic-and technology-specific performance and reliability of solar modules. For the forward modeling, we simulate the optimization and predict the performance of bifacial solar modules to rigorously evaluate this emerging technology in a global context. For the inverse modeling, we apply this framework to physically mine the 20-year field data for a nearly worn-out silicon PV system and successfully pin down the primary degradation pathways, something that is beyond the capability of conventional methods. This framework can be applied to solar farms installed globally (an abundant yet unexploited testbed) to establish a rich database of these geographic-and technology-dependent degradation processes, a knowledge prerequisite for the next-generation reliability-aware design of PV systems. Finally, we note that the research paradigm for PV developed in this work can also be applied to other applications, e.g., battery and electronics, which share similar technical challenges for performance and reliability

Emission-Diffusion Theory of the MOSFET

An emission-diffusion theory that describes MOSFETS from the ballistic to diffusive limits is developed. The approach extends the Crowell-Sze treatment of metalsemiconductor junctions to MOSFETs and is equivalent to the scattering/transmission model of the MOSFET. The paper demonstrates that the results of the transmission model can be obtained from a traditional, drift-diffusion analysis when the boundary conditions are properly specified, which suggests that traditional drift-diffusion MOSFET models can also be extended to comprehend ballistic limits

Assessing the MVS Model for Nanotransistors

A simple semi-empirical compact MOSFET model has been developed, which is called MIT virtual source (MVS) model. Compare to other model used in industry, MVS model requires only a few parameters, most of which can be directly obtained from experiment, and produce accurate results. One aim of this paper is to test the applicability of the MVS model to transistor made from MoS2 rather than silicon. Another target is to determine the sustainability of the MVS model under different transistor tests. To achieve these goals, the MVS model will be used to fit the experimental data on MoS2 transistors . Also, various tests will be implemented on the MVS model to see whether it is able to pass the tests. After the above steps, the fitting result suggests that MoS2 device has some special characteristic which cannot be described using MVS model. And the MVS model passes the symmetry tests well but fails in some other tests. Thus, despite the simplicity and accuracy of the model, more research can be conducted on this model in order to improve its generality

Large Scale Monolithic Solar Panel Simulation - A Study on Partial Shading Degradation

Shadow-induced degradation is a major concern for both power output and long-term reliability in solar cells. Apart from the obvious fact that shading reduces the amount of solar irradiance available to solar panels, it may lead to formation of hot spots, where solar cells are forced to reverse breakdown with localized heating, and potentially, permanent damage. To get a better understanding of shadow-induced degradation, we develop an electro-thermal coupled simulator that can self-consistently solve the electrical and thermal distributions of solar panel under arbitrary shading conditions. The simulation framework consists of two part: a) compact models that can describe the cell-level IV characteristics; b) a circuit network of thousands of compact models connected in series and parallel to form a solar module. The framework is based on open-source software, namely, Verilog-A for industrial standard compact model development and a SPICE-based circuit simulator capable of parallel computation. It is found that power loss due to shadowing is dependent on both the percentage of area shaded and its orientation. The degradation is more prominent for cells that have lower reverse breakdown voltage. The ultimate outcome of the framework is to create the first open source, physics-based module simulation tool to accelerate the pace of PV research and development in academia and industry and to reduce the cost of development by revising qualification protocols (e.g. IEC612125) to better represent the actual operating condition