Suellen C. Costa

Fundamental Studies of Adhesion of Dust to PV Module Surfaces: Chemical and Physical Relationships at the Microscale

Photovoltaic (PV) module soiling is a growing area of concern for performance and reliability. This paper provides evaluations of the fundamental interactions of dust/soiling particles with several PV module surfaces. The purpose is to investigate the basic mechanisms involving the chemistry, morphology, and resulting particle adhesion to the first photon-incident surface. The evaluation and mapping of the chemistry and composition of single dust particles collected from operating PV module surfaces are presented. The first correlated direct measurements of the adhesive force of individual grains from field-operating collectors on identical PV module glass are reported, including correlations with specific compositions. Special microscale atomic force microscopy techniques are adapted to determine the force between the particle and the module glass surface. Results are presented for samples under dry and moisture-exposed conditions, confirming the effects of cementation for surfaces having soluble mineral and/or organic concentrations. Additionally, the effects of hydrocarbon fuels on the enhanced bonding of soiling particles to surfaces are determined for samples from urban and highly trafficked regions. Comparisons between glass and dust-mitigating superhydrophobic and superhydrophilic coatings are presented. Potential limitations of this proximal probe technique are discussed in terms of results and initial proof-of-concept experiments.

Fundamental studies of the adhesion of dust to PV module chemical and physical relationships at the microscale

PV module soiling is a growing area of concern for performance and reliability. This paper provides evaluations of the fundamental interactions of dust/soiling particles with a several PV module surfaces. The purpose is to investigate the basic mechanisms involving the chemistry, morphology and resulting particle adhesion to that first photon-incident surface The first-time evaluation and mapping of the chemistry of single dust particles from operating PV module surfaces is presented. The first direct measurements of the adhesive force of individual grains are reported, including correlations to the specific surface chemistry. Special nanoscale techniques using atomic force microscopy (AFM) are adapted to determine the force between the particle and the surface. Results are presented for samples under dry and moisture-exposed conditions confirming the effects of cementation for surfaces having organic/soluble mineral concentrations. Additionally, the effects of hydrocarbon fuels on the enhanced bonding and adhesive force of soiling particles to surfaces are determined for samples from urban and highly-trafficked regions. Comparisons between glass and superhydrophobic and superhydrophilic coatings are presented, showing the effectiveness of the lower-surface energy conditions on the particle adhesion. The potential, limitations of this novel proximal probe technique are discussed in terms of the results and initial, proof-of-concept experiments.

Soiling particle interactions on PV modules: Surface and inter-particle adhesion and chemistry effects

The understanding of the fundamental physics and chemistry of dust and the interaction of these soiling fragments with the PV module surface and each other is potentially important to developing viable mitigation approaches. This paper builds on our previous reports and observations investigating individual soiling particle adhesion on PV module glass using microscale proximal probe techniques. Specifically, in this presentation we report on the refinement of those adhesive force measurements by gaining and including information on the contact area of those particles with the surface, the specific chemistry of interactive surfaces, and the quantification of the force values using materials standard. We also investigate the adhesive forces holding the soiling particles together and the effects of the critical parameters of surface compositional properties, moisture (humidity), and hydrocarbons. This allows for the comparisons of the inter-particle adhesion to the adhesive force holding the particle to the glass module surface. These evaluations are performed on soiling particles collected from operating modules in differing climate zones in Brazil and Middle-East Gulf regions.

Dust in the wind: Soiling of solar devices: Is there a Holy Grail solution?(Conference Presentation)

Soiling, the sedimentation of particulate matter (on the size scale of 1/10 the diameter of a human hair) on the exposed surfaces of solar collectors, is a growing area of concern for solar-system performance, reliability, maintenance, and cost. In the case of photovoltaics (PV), the condition of this first-surface of interaction of the incident photons is critical for ensuring that the maximum-possible light reaches the conversion devices. This paper begins with a more than seven-decade historical look at the research invested into this problem, highlighting the motivation and milestones; the researchers and the progress. The current growing terrestrial markets for solar have brought a new focus on soiling and dust issues. That is because many of these new markets in the solar-rich geographic regions of our world are ironically also in the most dust-rich and soiling-prone ones as well. This paper continues to provide an overview of the status of current research efforts toward understanding the basic soiling mechanisms, the relationships to the PV technology approaches, the geographical differences (highlighting Brasil, India, and the MENA region) in the severity of the problem, the dust physics and chemistry—all relating to the current and future mitigation approaches. Included are some fundamental microscale through nanoscale examinations at how individual dust particles adhere to module glass surfaces—as well as how the particles might stick to each other under certain environmental conditions. These observations are used to show how fundamental science may lead to the macroscale engineering solutions of these soiling problems. This presentation is designed to both overview the soiling area and highlight some of the current and future research directions, speculate on short-term approaches preventing solar showstoppers, and speculate on some “holy-grail” schemes that might lead to the final solutions.

Development and prototype validation of a novel Bidirectional Intelligent Conversion and Connection Unit (BICC) for grid-connected photovoltaic-storage systems

This paper presents studies and the implementation of a novel grid-connected PV system with storage. The goal of this project is to validate the operation and to determine the benefits and limitations of integrating storage with grid-connected PV systems. The objective is to evaluate the viability of using complementary electricity storage for meeting the local evening peak demands - “night-time peak shaving” in a typical load curve of CEMIGs feeder. A novel and versatile control unit-the Bidirectional Intelligent Conversion and Connection Unit (BICC)-has been developed to control the flow of energy from the electricity sources (i.e., PV generator, battery bank, and electric-power grid). In designing this electronic system, we adopted a topology in which the inverter and the maximum power tracking (MPPT) optimize the available power by incorporating two separate and independent converters. In the first phase of the project, a prototype of the system that includes PV with storage and the BICC unit has been installed at GREEN Solar-IPUC in PUC Minas and been under test to evaluate its performance. These trials have been used to optimize system parameters in order to improve the BICC and its interfacing parameters and ensure safe operation of PV-storage system with the grid. This paper reports on the design and advantages of the BICC, the procedures used in the parameter optimization of the prototype, the effectiveness of the BICC in improving the control and connection, conformity to standards, and the viability of scale up for the second phase testing connected to the electric grid (for the utility CEMIG) with storage at the football stadium, Arena do Jacare, located in Sete Lagoas, Minas Gerais.

Development of a grid-connected photovoltaic-storage

This paper presents the design and studies performed in the first-phase implementation of the R&D project D308, in partnership with Energetic Company of Minas Gerais (CEMIG-D). The objective of this project is to evaluate the benefits and limitations of using storage with a grid-connected PV system. Specifically to evaluate injecting the energy stored in batteries charge by the PV into the electric grid in order to flatten the peak of the load curve of a feeder system (with evening peak-electricity consumption experienced in this area). The PV/storage system is being installed in the football stadium Arena do Jacare, located in Sete Lagoas, Minas Gerais. Initial studies have been performed to define the characteristics of the PV array, including surveys of the region characteristics, and solar resource/ climate data. Additionally, the characteristics of the optimum PV generator configuration and module technology have been evaluated, taking into consideration the stadiums limited available area and defined orientation--and the major design criterion to eliminate any shadow projection on photovoltaic modules that could reduce its performance. With the initial design of the PV generator structure and geometry, the system was performance was simuulated under projected conditions. An innovative feature of this project is a bidirectional conversion and connection unit, which has the capacity to store the energy coming from the PV generator and/or the electrical network in a battery bank. The unit can deliver the energy to the grid (a feeder operated by CEMIG in our tests) at specific defined times-such as the peak time in this area between 18:30 and 20:30. At the conclusion of this protype project, a larger scale of the system (photovoltaic system connected to the network with storage) will be installed at GREEN-IPUC/PUCMinas, utilizing the lessons learned and experiences and the equipment developed at the Minas Gerais Arena do Jacare Stadium.