Nicoleta Sorloaica-Hickman

Efficiency determination of an electrostatic lunar dust collector by discrete element method

Lunar grains become charged by the sun’s radiation in the tenuous atmosphere of the moon. This leads to lunar dust levitation and particle deposition which often create serious problems in the costly system deployed in lunar exploration. In this study, an electrostatic lunar dust collector (ELDC) is proposed to address the issue and the discrete element method (DEM) is used to investigate the effects of electrical particle-particle interactions, non-uniformity of the electrostatic field, and characteristics of the ELDC. The simulations on 20-μm-sized lunar particles reveal the electrical particle-particle interactions of the dust particles within the ELDC plates require 29% higher electrostatic field strength than that without the interactions for 100% collection efficiency. For the given ELDC geometry, consideration of non-uniformity of the electrostatic field along with electrical interactions between particles on the same ELDC geometry leads to a higher requirement of ∼3.5 kV/m to ensure 100% particle ...

Effect of UV-Ozone Exposure on PCBM

The effect of ultraviolet (UV)-light ozone exposure on phenyl-C61-butyric acid methyl ester (PC61BM) is studied using solid-state modification of the material. In this study, solution processed PCBM films that have been deposited and dried over glass were exposed to UV ozone at ambient temperature and pressure from 0 to 120 min. Core-level and valence-band photoelectron spectroscopy studies indicate that the UV-ozone-induced oxidation results in C-O-C bonds in PCBM and a change in the highest occupied molecular orbital level, respectively. The modification of PCBM with C-O-C binding was observed from 5 to 60 min, but further exposure, typically beyond 120 min, was found to degrade the material. A solubility study also showed an exposure time-dependant solubility change of the material, in solvents like toluene and acetone, where it indicates the change in the chemistry of the material that can be related to the C-O-C binding of the material by the exposure. The method is an easily implementable approach for flexibility on choice of solvents for PCBM, and it has implications on the processing and stability of the material.

Efficiency Evaluation of an Electrostatic Lunar Dust Collector

The accumulation of solar-based charges on lunar grains leads to levitation of the like charged particles. The lunar dust deposit on sensitive and costly surfaces of investigative equipment is a serious concern for lunar missions. Benefitting from the inherent trait of lunar particles which are naturally charged, an electrostatic lunar dust collector (ELDC) is hypothesized by this study as a highly efficient way for particle collection and equipment protection in the vacuum. The idea is a grid layer of charged conducting plates in front of the surface to be protected to provide the electrostatic field. Discrete Element Method (DEM) was applied to investigate the effect of electrical particle interactions on collection efficiency. Validation of this Lagrangian-based model was done by comparing to the analytical collection efficiency equation (Eulerian-based model) in the absence of electrical particle interactions. Then, electrostatic screening feature was turned on to address the difference in collection efficiency. The obtained results from Lagrangian-based method were close to the Eulerian-based solutions and indicated a small reduction in collection efficiency compared to the predicted analytical results. At the worst case scenario, all the 100-μm-sized particles would be collected by providing approximate electric field 6.4 kV/m. Both the Eulerian-based and Lagrangian-based methods confirm the adequacy of the proposed system for prospective applications.

Comparative study of the performance of field-aged photovoltaic modules located in a hot and humid environment

Long-term monitoring of systems installed in the field is the ultimate standard for evaluating photovoltaic components and systems. This study, which involves the long-term outdoor exposure in a hot and humid climate, intends to address the performance degradation and failure mechanisms which are difficult or impossible to simulate in the lab during time constrained accelerated tests. Experimental data including irradiance, temperature, DC/AC current and voltage has been collected on diverse generations of photovoltaic modules installed throughout the state of Florida. Long term module reliability and lifetime are evaluated using a two pronged approach. 1) Modules have been deployed outdoors for long time periods with systematic - 15 minutes interval- climatic and performance measurements 2) Real-time climatic and performance measurements of modules following long-term outdoor exposed. Visual, IR and electrical insulation inspections were performed are also presented in this paper. Multiple analytical methods are used to quantify energy production and power degradation over time, including Performance Ratio analysis, and PVUSA regression analysis. Real-time field measurements were reviewed for both overall return rates and compare them with the nameplate performance values and to identify the failure mechanism that caused the return.

Optimization of the photovoltaic powered systems with dust mitigation technology for future lunar and martian missions

The dust mitigation technologies are critical for deployment of photovoltaic (PV) arrays in remote, dusty atmospheres such as the surface of the Moon, Mars and even Earth. As dust collects on the photovoltaic modules, the amount of light hitting the surface is decreased, thus decreasing the overall power output. In general, it is not practicable to use moving parts in high-dust areas due to the damaging effects dust has on joints and electronics. We developed a hybrid experimental system that incorporates a transparent Electrodynamic Screen (EDS) with a PV array allowing us to study the total efficiency of different technologies (GaAs, Mono Si and Multi Si). In order to give a qualitative and quantitative analysis of performance measures of solar cells with the integrated EDS technologies, prototypes were developed and tested in the indoor and outdoor conditions. The effect of the UV aging on the EDS coatings were performed in a Q-Sun Xenon Test Chamber Model Xe-3-H. The Jasco V-670 Spectrophotometer was used to measure the UV/Vis transmission in the wavelength range from 190 nm to 750 nm before and after each UV aging increment of 99 hours.

Transparent conductive film fabrication by carbon nanotube ink spray coating and ink-jet printing

The present work reports on the development of a class of thin-film transparent electrodes for the PV devices based on spray coating of carboxyl functional multi-walled carbon nanotubes (MWCNT-COOH) aqueous dispersion and thin-film transparent transistors based on ink-jet printing MWCNT-COOH inks with proper fluidic characteristics. The MWCNT-COOH inks were formulated by addition of PEDOT-PSS to MWCNT-COOH aqueous dispersion. SEM shows the spray coating MWCNT-COOH films and the ink-jet printing MWCNT-COOH films are uniform. UV-vis transmission spectra indicate high transparency. Four probe measurements show excellent sheet resistance. The present work demonstrates that spray coating MWCNT-COOH films are promising for transparent electrodes in flexible and large area PV electronics and that ink-jet printed MWCNT-COOH films in patterns are promising for transparent transistors.

Graphene transparent and conductive electrode for light harvesting solar cells

Transparent and conductive coatings were achieved on glass by dissolving graphene oxide into dionized water followed by spray-coating on preheated substrate, chemical and thermal reduction. SEM shows the spray-coating graphene oxide coatings and the reduced graphene oxide coatings are uniform. No obvious aggregation was observed. UV-vis transmission spectra shows 65% transmittance at 550 nm of the graphene coatings with 15 kΩ/□.