David Metacarpa

Life cycle assessment of photovoltaic manufacturing consortium (PVMC) copper indium gallium (di)selenide (CIGS) modules

PurposeThin film copper indium gallium (di)selenide (CIGS) photovoltaic (PV) modules show promise for significant growth. The Photovoltaics Manufacturing Consortium (PVMC) is leading research and development of CIGS in New York State. This study presents the results of a life cycle assessment (LCA) study of CIGS technology, currently being advanced by PVMC, and compares the environmental performance of several emerging alternative materials and processes. The results provide manufacturers with an understanding of how to produce CIGS sustainably.MethodsThe cradle-to-gate LCA study followed the International Standards Organization (ISO) 14040 series. In addition to analyzing CIGS cells, the study evaluated zinc oxysulfide (Zn(O,S)) as an alternative for cadmium sulfide (CdS) for the junction partner, and an integrated cell interconnect (ICI) system as an alternative for the screen printing and stringer. Life cycle inventory data for the CIGS cell and alternatives were obtained from PVMC for the product manufacturing stage. Global Solar Energy, Inc. (GSE), a PVMC member and CIGS manufacturer, provided data for the ICI alternative. This data was supplemented by secondary data, from thinkstep, and modeled in GaBi6. The end-of-life stage was not modeled due to limited inventory data.Results and discussionThe results identified the following key drivers of environmental and toxicity impacts from the manufacture of CIGS photovoltaic cells: (i) silver used in the stringer and screen printing processes, (ii) metals comprising the CIGS layer, (iii) surface washing of the stainless steel substrate, and (iv) copper in the cable for the balance of system. In addition, the study found that the zinc oxysulfide alternative had lower overall impacts compared to cadmium sulfide. Substitution of the ICI system also reduced impacts of the CIGS system, by decreasing the silver needed. Finally, comparison of the overall life cycle impact results to similar systems in literature, which focused primarily on greenhouse gas emissions, found that the CIGS system fell in the lower end of the range of estimated global warming impacts.ConclusionsPVMC’s CIGS module impacts are likely lower than those made by other manufacturers due to their use of a stainless steel versus glass substrate and reliance on a relatively clean energy mix in New York State. To further reduce impacts, PVMC may wish to substitute the ICI component for the stringer and screen printing processes, recycle additional waste materials, substitute recycled metals for virgin materials, and substitute the cadmium sulfide with the zinc oxysulfide alternative.

Novel application of Yttria Stabilized Zirconia as a substrate for thin film CIGS solar cells

Yttria Stabilized Zirconia [YSZ] has a number of qualities that make it attractive as a substrate for fabrication of thin film copper indium gallium diselenide [CIGS] solar cells: these include flexibility, a smooth surface, lack of impurities such as iron and the ability to scale to a roll-to-roll format. As an insulator, YSZ is compatible with monolithic processing and its high temperature capabilities enable high efficiency deposition temperature. Small area [0.41 cm2] CIGS solar cells were fabricated on a YSZ substrate yielding a 17.3% efficient device.

Effects of light-soaking and temperature on different PV technologies

A set of photovoltaic panels including CIGS, CdTe and c-Si were subjected to different light soaking conditions of varying irradiance, module temperature, light soaking under load and under open circuit. It was observed that for every technology, light soaking under load results in improved performance. This improvement is of the same order for CIGS and c-Si panels, and higher for CdTe. A calculation of the temperature coefficients based on each experiment allows the conclusion that the variations in performance with load are not due to thermal effects. Temperature coefficients are in general agreement with published values. Protocols developed for PV modules performance test should include a provision to always carry out measurements under load.

Cost and market analysis of integrative lightweight PV systems for low-slope commercial rooftops

A lightweight PV (LPV) system that weighs less than 2.5 pounds per square foot (psf), designed for the membrane-based commercial rooftop market, effectively reduces installed system costs by 10% when compared to traditional racked and ballasted systems. By focusing on key cost reduction areas, LPV minimizes hardware, labor, and permitting costs. The system utilizes next-generation rigid CIGS modules to maximize electrical performance and minimize roof load. Simulation studies indicate that the use of CIGS modules will provide 10% more energy at the inverters as compared to equivalent c-Si modules. The U.S. Photovoltaic Manufacturing Consortium (PVMC) is conducting a time-and-motion study to accurately evaluate installation labor and identify additional cost reduction opportunities.

Selenium flux effects on Cu(In, Ga)Se 2 growth rate, and control by in-line X-ray fluorescence

In-line X-ray fluorescence (XRF) is demonstrated for Cu(In, Ga)Se2 (CIGS) co-evaporation source control. XRF is found to accurately measure film composition for direct metals source control, as well as an indirect monitor for selenium rate using the nature of the self-limiting diselenide. It was found that below an optimum Se flux value, the film growth rate is limited by the Se atom availability, while a higher Se overpressure reduces the growth rate by gas phase scattering. This correlation allows the growth rate to act as a monitor and possible control mechanism for production scale CIGS thermal evaporation. It is also possible to use the thickness measured by XRF as a feedback control for the Se overpressure.

Demonstration of PV modules with lightweight mounting systems on commercial rooftops

Lightweight mounting systems reduce hardware and labor costs associated with a typical rooftop PV installation. PVMC fabricated innovative lightweight mounts for PV modules that eliminated traditional racking and ballasting materials. Seven (7) prototype systems (each system <; 3 kW) using rigid and flexible PV modules from multiple manufacturers were deployed on TPO (Thermoplastic Polyolefin), EPDM (Ethylene Propylene Diene Monomer), and standing seam metal roofs. A Prototype Demonstration Facility (PDF) consisting of a mock roof at ground level was built to deploy these PV systems and allow easy installation and maintenance access. The prototype PV systems are under electrical monitoring to determine the effects of the mounting mechanism on the performance of PV modules.

Reduced Balance of System Costs using Lightweight photovoltaics integrated with roofing material membranes

A cost analysis was completed using PVMCs Balance of System Cost Analysis Tool (BOS-CAT) for Lightweight PV (LPV) applications to evaluate mounting installation methods and associated BOS costs of flat membrane commercials roofs. The use of a sacrificial membrane allows for increased speed of module installs by adapting tools and know-how from the roofing industry. Using the BOS-CAT, two integrated modules types were designed (690W and 1.5kW) using commercially available LPV modules. A series of integrated modules were fabricated and installed on PVMCs Prototype Demonstration Facility (PDF) roofing. Installations verified that the approach resulted in greater than a 40% reduction in hardware labor costs.

CIGS PV reliability - Current practices, challenges and approaches

The long term sustainable output power production from any photovoltaic array (PV) array depends on the climate (temperature and humidity) in which PV modules are deployed. The degradation of CIGS PV modules outdoors is complicated by various packaging methods (flexible or rigid), interconnect options (cell to cell interconnects or monolithic integration), the different manufacturing methods used to fabricate films in the CIGS stack and the corresponding material and interfacial properties of the semiconductor layers. There is a need to address the challenges in designing indoor accelerated tests with appropriate stress conditions to replicate the observed failure mode and in identifying the failure mechanisms responsible for the failure. This review paper gives an outline of the current practices, challenges and approaches in identifying the stress factors and degradation mechanisms responsible for the device failure by designing appropriate combinatorial stress tests and test structures for indoor accelerated stress tests and relating the results to outdoor module reliability.

Identification of changes in power through DC granular monitoring

In a competitive PV market, where different technologies are closing the gap in efficiencies at the module level, there is a need to reduce the cost of the overall PV system and its operation. This could be achieved either by reducing the cost of the installed PV system or reducing the long-term maintenance and operational cost of the array by cost effectively optimizing the performance of the PV system, thereby increasing the revenue from a PV array. To reduce the operational cost and maintenance, certain factors like soiling, module replacement and visual inspection needs to be carried out. For a large array of thousands of modules, maintaining a system at a regular basis is complicated. This could be achieved by investing upfront in a detailed monitoring of the system at a granular level. The level of granularity needs further attention which could offset the cost of operation and maintenance from a long term perspective. Understanding the module performance at an array, string, and module level has different resolutions on the information that can be obtained and individual module reliability is easier to be determined as the granularity becomes finer. The advantages and disadvantages of granular monitoring are discussed in this paper for four ~25kW photovoltaic arrays of three different technologies (c-Si, CIGS, and CdTe) deployed by the US Photovoltaic Manufacturing Consortium (PVMC).

Cost analysis and criteria for achieving the SunShot target of

In order to meet the SunShot Initiative cost targets of