Vasilis Fthenakis

Photovoltaic manufacturing: Present status, future prospects, and research needs

In May 2010 the United States National Science Foundation sponsored a two-day workshop to review the state-of-the-art and research challenges in photovoltaic (PV) manufacturing. This article summarizes the major conclusions and outcomes from this workshop, which was focused on identifying the science that needs to be done to help accelerate PV manufacturing. A significant portion of the article focuses on assessing the current status of and future opportunities in the major PV manufacturing technologies. These are solar cells based on crystalline silicon (c-Si), thin films of cadmium telluride (CdTe), thin films of copper indium gallium diselenide, and thin films of hydrogenated amorphous and nanocrystalline silicon. Current trends indicate that the cost per watt of c-Si and CdTe solar cells are being reduced to levels beyond the constraints commonly associated with these technologies. With a focus on TW/yr production capacity, the issue of material availability is discussed along with the emerging technologies of dye-sensitized solar cells and organic photovoltaics that are potentially less constrained by elemental abundance. Lastly, recommendations are made for research investment, with an emphasis on those areas that are expected to have cross-cutting impact.

End-of-life management and recycling of PV modules

Abstract Photovoltaics (PV) technology is undergoing a transition to a new generation of efficient, low-cost products based on thin films of photoactive materials. PV technology has definite environmental advantages over competing electricity generation technologies, and the PV industry follows a pro-active life-cycle approach to prevent future environmental damage and to sustain these advantages. An issue with potential environmental implications is the decommissioning of solar cells at the end of their useful life; a viable answer is recycling them when they are no longer useful. This paper presents a feasibility study for recycling thin-film solar cells and manufacturing waste, based on the current collection/recycling infrastructure and on current and emerging recycling technologies. Technology already exists for recycling PV modules and costs associated with recycling are not excessive.

Hazard and operability (HAZOP) analysis. A literature review

Hazard and operability (HAZOP) methodology is a Process Hazard Analysis (PHA) technique used worldwide for studying not only the hazards of a system, but also its operability problems, by exploring the effects of any deviations from design conditions. Our paper is the first HAZOP review intended to gather HAZOP-related literature from books, guidelines, standards, major journals, and conference proceedings, with the purpose of classifying the research conducted over the years and define the HAZOP state-of-the-art.

Life Cycle Greenhouse Gas Emissions of Crystalline Silicon Photovoltaic Electricity Generation

Published scientific literature contains many studies estimating life cycle greenhouse gas (GHG) emissions of residential and utility‐scale solar photovoltaics (PVs). Despite the volume of published work, variability in results hinders generalized conclusions. Most variance between studies can be attributed to differences in methods and assumptions. To clarify the published results for use in decision making and other analyses, we conduct a meta‐analysis of existing studies, harmonizing key performance characteristics to produce more comparable and consistently derived results. Screening 397 life cycle assessments (LCAs) relevant to PVs yielded 13 studies on crystalline silicon (c‐Si) that met minimum standards of quality, transparency, and relevance. Prior to harmonization, the median of 42 estimates of life cycle GHG emissions from those 13 LCAs was 57 grams carbon dioxide equivalent per kilowatt‐hour (g CO‐eq/kWh), with an interquartile range (IQR) of 44 to 73. After harmonizing key performance characteristics (irradiation of 1,700 kilowatt‐hours per square meter per year (kWh/m2/yr); system lifetime of 30 years; module efficiency of 13.2% or 14.0%, depending on module type; and a performance ratio of 0.75 or 0.80, depending on installation, the median estimate decreased to 45 and the IQR tightened to 39 to 49. The median estimate and variability were reduced compared to published estimates mainly because of higher average assumptions for irradiation and system lifetime. For the sample of studies evaluated, harmonization effectively reduced variability, providing a clearer synopsis of the life cycle GHG emissions from c‐Si PVs. The literature used in this harmonization neither covers all possible c‐Si installations nor represents the distribution of deployed or manufactured c‐Si PVs.

Life Cycle Greenhouse Gas Emissions of Thin‐Film Photovoltaic Electricity Generation

We present the process and the results of harmonization of greenhouse gas (GHG) emissions during the life cycle of commercial thin‐film photovoltaics (PVs), that is, amorphous silicon (a‐Si), cadmium telluride (CdTe), and copper indium gallium diselenide (CIGS). We reviewed 109 studies and harmonized the estimates of GHG emissions by aligning the assumptions, parameters, and system boundaries. During the initial screening we eliminated abstracts, short conference papers, presentations without supporting documentation, and unrelated analyses; 91 studies passed this initial screening. In the primary screening we applied rigorous criteria for completeness of reporting, validity of analysis methods, and modern relevance of the PV system studied. Additionally, we examined whether the product is a commercial one, whether the production line still exists, and whether the studys core data are original or secondary. These screenings produced five studies as the best representations of the carbon footprint of modern thin‐film PV technologies. These were harmonized through alignment of efficiency, irradiation, performance ratio, balance of system, and lifetime. The resulting estimates for carbon footprints are 20, 14, and 26 grams carbon dioxide equivalent per kilowatt‐hour (g CO‐eq/kWh), respectively, for a‐Si, CdTe, and CIGS, for ground‐mount application under southwestern United States (US‐SW) irradiation of 2,400 kilowatt‐hours per square meter per year (kWh/m2/yr), a performance ratio of 0.8, and a lifetime of 30 years. Harmonization for the rooftop PV systems with a performance ratio of 0.75 and the same irradiation resulted in carbon footprint estimates of 21, 14, and 27 g CO‐eq/kWh, respectively, for the three technologies. This screening and harmonization rectifies previous incomplete or outdated assessments and clarifies variations in carbon footprints across studies and amongst thin‐film technologies.

Toxicity of Cadmium Telluride, Copper Indium Diselenide, and Copper Gallium Diselenide

This paper reviews recently derived toxicity data for Copper Indium Diselenide (CIS), Cadmium Gallium Diselenide (CGS) and Cadmium Telluride (CT), promising new materials on which a new generation of thin-film photovoltaic cells for generating electricity may be based. The new data deal with systemic and reproductive toxicity, acute pulmonary toxicity, and comparative pulmonary absorption, distribution and toxicity of these materials in laboratory rats. CT is shown to have higher lung toxicity than CIS, with the CGS toxicity being the lowest in the group. These data are extended to human exposure levels and exposure limits for CT are derived. The implications of these findings to the photovoltaic industry are also discussed. Published in 1999 by John Wiley & Sons, Ltd. This article is a U.S. Government Work and is in the public domain in the United States.

Photovoltaics: Environmental, Health and Safety Issues and Perspectives {

The photovoltaic (PV) industry must continue its pro-active approach to prevent accidents and environmental damage, and to sustain PV’s inherent environmental, health, and safety (EHS) advantages. This paper presents an overview of EHS issues related to current and emerging PV technologies and gives examples of this pro-active approach. We summarize the hazards related to potential accidental releases of toxic or flammable gases used in photovoltaic cell production, and strategies for reducing such risks (e.g., choosing material and process options which inherently have small risks, and preventing accident-initiating events). Other issues discussed herein include reducing the use of toxic or carcinogenic materials in powder form, managing liquid hazardous waste, and recycling solid waste and spent modules. As the PV industry approaches these issues and mitigation strategies in a vigilant, systematic way, the risk to the industry, the workers, and the public will become minimal. An example is also discussed of environmental benefits from a large scale PV implementation, that is the potential of PV in reducing CO 2 emissions. Published in 2000 by John Wiley & Sons, Ltd.

NEMS and MARKAL-MACRO Models for Energy-Environmental-Economic Analysis: A Comparison of the Electricity and Carbon Reduction Projections

The Annual Energy Outlook forecasts published by the United States Energy Information Administration (EIA) of the Department of Energy are based on results from the National Energy Modeling system (NEMS). This paper compares NEMS, which is used only in the U.S., with the U.S. version of MARKAL-MACRO (USMM) model, which is used in more than thirty-five countries. The two models predict similar results for the base 1999 US Annual Energy Outlook (AEO), but their results with carbon constraints are quite different. The differences of the models and those of their predictions are explained. USMM can be used to provide an alternative and complementary approach to projections of renewable technologies penetration and their potential in reducing carbon dioxide emissions in the USA.

Economic Feasibility of Recycling Photovoltaic Modules

The market for photovoltaic (PV) electricity generation has boomed over the last decade, and its expansion is expected to continue with the development of new technologies. Taking into consideration the usage of valuable resources and the generation of emissions in the life cycle of photovoltaic technologies dictates proactive planning for a sound PV recycling infrastructure to ensure its sustainability. PV is expected to be a green technology, and properly planning for recycling will offer the opportunity to make it a double-green technology - that is, enhancing life cycle environmental quality. In addition, economic feasibility and a sufficient level of value-added opportunity must be ensured, to stimulate a recycling industry. In this article, we survey mathematical models of the infrastructure of recycling processes of other products and identify the challenges for setting up an efficient one for PV. Then we present an operational model for an actual recycling process of a thin-film PV technology. We found that for the case examined with our model, some of the scenarios indicate profitable recycling, whereas in other scenarios it is unprofitable. Scenario SC4, which represents the most favorable scenario by considering the lower bounds of all costs and the upper bound of all revenues, produces a monthly profit of

Assessing the Economic Benefits of Compressed Air Energy Storage for Mitigating Wind Curtailment

107,000, whereas the least favorable scenario incurs a monthly loss of