Photovoltaic (PV) Panel Waste Volumes

Photovoltaic (PV) Panel Waste Volumes Article Series: 8

Abstract

PV panels, as noted in previous sections, create unique waste management challenges along with projections of increasing waste flows. Outside the EU, end-of-life treatment requirements for PV panels worldwide are determined by waste regulations applied generally to any waste rather than those allocated specifically to PV. Waste regulations are based on the classification of waste. This classification is shaped according to waste composition, particularly in relation to any components considered hazardous.

Introduction

a-Si Panels a-Si PV panels have lost significant market share in recent years and do not contain substantial quantities of valuable or hazardous materials. Therefore, they will likely not require special waste recovery in the future. In multi-junction cell design, two or more cells are arranged in a stack. In any case, the upper cell or cells must be transparent in a certain spectrum to enable the lower cells to be active. By adapting the spectrum sensitivity of separately stacked cells, a broader range of sunlight can be absorbed and overall efficiency maximized. Such cell types are used in a-Si, c-Si and concentrator cells. Today, the low cost of c-Si enables cost-effective mass production of high-efficiency multi-junction cells. This can be combined with, for example, III-V alloys, chalcogenides and perovskites, which are expected to perform extremely well even in non-concentrating tracking applications.

Thin-Film Panels

Thin-film panel technology is more complex than silicon-based PV panels. For c-Si panels, glass content is likely to increase by 2030. In contrast, for thin-film panels, it is likely to decrease through the use of thinner and more stable glass materials. This will also encourage higher rates of compound semiconductors and other metals.

CIGS Panels

CIGS panels today consist of 89% glass and are estimated to decrease from 1% to 88% by 2030. Showing 1% increase by 2030, 7% aluminum and constant 4% polymer content. Other metals will experience a slight reduction of 0.02%, while semiconductors will see an increase of 0.2%. Among other metals are 10% copper, 28% indium, 10% gallium and 52% selenium. CIGS panel efficiency is currently at 15% and long-term targets are 20% and above. By 2030, the glass ratio as total panel mass in CdTe panels is expected to decrease from 97% to 96%. However, polymer masses are expected to increase by 1% from 3% to 4% compared to today. Compared with CIGS panels, material use for semiconductors as a proportion of panel use will decrease by nearly half from 0.13% to 0.07%. However, the share of other metals (such as nickel, zinc and tin) will rise from 0.26% to 0.41%. The main reason for this increase in other metals is a further reduction in CdTe layer thickness (this reduces the semiconductor content of the base semiconductor). However, efficiency improvements in recent years were also related to "band gap" rating effects that can be achieved through doping of other components into the semiconductor layer. The addition of other components to the mixture is reflected in the increase in other metals. Another reason for the increase in the proportion of other metals is the addition of a layer between the back contact metals and the semiconductor package. This reduces copper diffusion into the semiconductor and thus reduces long-term degradation and leads to thickening of the back plate metal stack. The PV industry targets efficiency above 25% for CdTe panel research cells and above 20% for commercial panels within the next three years. This is significantly higher than 15.4% achieved in 2015. New technologies are also expected to reduce the performance degradation rate to 0.5% per year.

Waste Classification

PV panel waste classification follows the basic principles of conventional waste classification. This method also considers material composition by mass or volume and the properties of the components and materials used (such as solubility, flammability, toxicity). It accounts for potential mobilization pathways of components and materials for different reuse, recovery, recycling and disposal scenarios (for example, the general purpose of these classification principles is to identify risks to the environment and human health that may arise during the end-of-life management of a product. The objective is to identify disposal and remedial application pathways to minimize these threats. The risk of leakage of materials from end-of-life products or components into the environment is highly important, and evaluation of this threat helps define necessary protective measures. However, this is only a potential risk. Other examples evaluated through waste characterization include flammability and human exposure hazards through skin contact or inhalation. The risks evaluated may vary depending on the country and decision-making principles. Depending on national and international regulations such as the Basel Convention on the Control of Transboundary Movements of Hazardous Wastes and Their Disposal (UN, 2016), wastes can be divided into various categories such as inert waste, non-hazardous waste and hazardous waste. To some extent, waste origin is also considered by defining sub-categories such as industrial waste and domestic waste, and product-specific categories such as e-waste, construction waste and mixed solid waste. Different classified waste categories then determine permitted and prohibited shipment, processing, recycling and disposal pathways. In 2015, two-thirds of PV panels installed globally were c-Si panels. Typically, more than 90% of their mass consists of glass, polymers and aluminum, which can be classified as non-hazardous waste. However, smaller components of c-Si panels may present recycling challenges due to containing elements such as silicon, silver and trace amounts of tin and lead (together constituting approximately 4% of the mass). Thin-film panels (9% of global annual production) consist of more than 98% glass, polymers and aluminum (non-hazardous waste) and also modest quantities of copper and zinc (together approximately 2% of the mass), which are potentially environmentally harmful waste. They also contain semiconductors or hazardous substances such as indium, gallium, selenium, cadmium telluride and lead. Hazardous substances require special processing and may fall into a specific waste classification depending on jurisdiction.

Basic Criteria for PV Panel Waste Classification: Leaching Tests

Table 1 summarizes typical waste characterization leaching test methods in the USA, Germany and Japan. The overview provides one of the most important characterization metrics currently used in PV waste classification worldwide. The basic criterion for determining waste classification is the concentration of specific substances in a liquid exposed to fragments of broken PV panels at a specific rate over a specific period. This leachate typically dissolves some materials present in the solid sample and can therefore be analyzed for mass concentration of certain hazardous substances. Different jurisdictions, such as Germany, the USA or Japan, provide different threshold values for permitted leachate concentrations for a waste material to be characterized as non-hazardous waste. For example, the leachate concentration threshold for lead that permits a panel to be classified as hazardous is 5 milligrams per liter (mg/l) in the USA and 0.3 mg/l in Japan. The hazardous threshold for cadmium is 1 mg/l in the USA, 0.3 mg/l in Japan and 0.1 mg/l in Germany. These are compared with leaching test results in the literature and publicly available for c-Si and CdTe PV panels. For cadmium, values range between non-detect 0.22 mg/l and for lead non-detect 11 mg/l. Therefore, in different assessment areas, CdTe and c-Si panels can be considered non-hazardous or hazardous waste according to these test results.

Regulatory Classification of PV Panel Waste

From a regulatory perspective, PV panel waste largely falls under general waste classification. An exception exists in the EU, where PV panels are defined as e-waste in the WEEE Directive. The term 'electrical and electronic equipment' or EEE is defined as equipment designed to be used at a voltage rating not exceeding 1,000 V for alternating current and 1,500 V for direct current, or equipment whose proper operation depends on electric currents or electromagnetic fields, or equipment for generating such currents, or equipment for transmitting such currents, or equipment for measuring such currents. Therefore, waste management and classification for PV panels in the EU is regulated by the WEEE Directive in addition to other relevant waste legislation (e.g. Waste Framework Directive 2008/98/EC). This comprehensive legal framework also ensures that potential environmental and human health risks associated with waste management and treatment are adequately addressed. By establishing a Waste List (European Commission, 2000), the EU has created a reference terminology providing common terminology across the EU to increase the efficiency of waste management activities. The classification of hazardous and non-hazardous wastes provides a basis for common waste characteristics coding as well as decisions related to waste transport, installation permits and waste recyclability, and for waste statistics. Some codes from the EU's waste list applicable to:

PV panels are given in Table 2:

Dr. Cemil Koyunoğlu Yalova University Faculty of Engineering Department of Energy Systems Engineering