In October, seven solar companies filed a petition to the US challenging China’s solar companies’ subsidies, protesting anti-dumping duties on low-cost Chinese products. This, along with recently publicized pollution incidents, has put the spotlight on Chinese solar manufacturers, who produce more than half the world’s solar panels.
At first glance, solar panels appear to be the epitome of sustainability, generating energy directly from the sun without any waste products or greenhouse gases. What’s often overlooked, however, is the entire lifespan of the product – the solar panel. What is it made of? How was it made? What will happen to it when we throw it away in 20, 30 years? These questions must be considered at every node along the supply chain when evaluating sustainability in solar power production.
Challenges created from corrosive byproduct: STC
For solar panels, this starts with the raw material for the wafers that absorb sunlight and turn it into electricity – most commonly, polysilicon. China occupies 30% of the global polysilicon market, and every ton of polysilicon produced results in up to 15 – 20 tons of a highly toxic and corrosive byproduct, silicon tetrachloride (STC).
In countries with more advanced technologies (e.g. America, Japan, and Germany), STC is recycled to produce the raw material for polysilicon again, forming a closed-loop process (Figure 1). However, most Chinese polysilicon plants do not have STC recycling technologies in place yet. Many producers either sell the STC waste as raw material for other industries, or simply outsource the problem to third-party waste disposal companies. If the company is unqualified for treating STC, they may dispose of it illegally, contaminating the environment and affecting public health and livelihood. Local governments often turn a blind eye due to the industry’s contribution to local GDP growth and tax revenues.
Perhaps the most famous pollution case, covered by the Washington Post in 2008, involved months of illegal STC dumping onto nearby farmland by the polysilicon producer Luoyang Zhonggui, in Henan Province. “The land where you dump or bury it will be infertile. No grass or trees will grow in the place…It is like dynamite — it is poisonous, it is polluting. Human beings can never touch it,” commented a Hebei Industrial University professor on the incident.
Eliminating STC waste
Local government officials often protect polysilicon and solar companies because of their contribution to local GDP growth and tax revenues. The Chinese Central government is however, moving fast and pushing towards more stable and sustainable development of the industry. The Polysilicon Industry Access Standards, issued in January 2011, mandates polysilicon manufacturers recycle 98.5% of all STC produced.
The most desirable option though, is for producers to eliminate the STC waste stream completely by recycling STC. Companies such as GCL Solar, Daqo New Energy, and LDK Solar, have begun adopting foreign STC recycling technologies over the last couple of years. But these technologies are still few in number, and, being patented, generally very expensive for Chinese companies to obtain. Moreover, foreign companies are often reluctant to export technology to China. Since existing STC recycling processes are very heat and energy intensive, many companies are also concerned with the financial impact.
Reusing Silicon Kerf
Another significant waste stream that can be eliminated through recycling is known as ‘kerf’. To make the ultra-thin solar wafers, multi-wire saws cut polysilicon blocks into thousands of wafers using an abrasive slurry. During this slicing process, approximately 40 – 50% of high-purity silicon is lost as dust, or kerf, which gets mixed into the slurry waste. While it is common for plants to partially recycle the slurry waste and reuse the abrasives and the cutting fluid, the nano-scale silicon kerf particles cannot be separated easily and are wasted.
Recently developed technologies, however, are capable of extracting silicon kerf from the slurry waste so that it can be melted into polysilicon blocks and reused for wafer production. Adopting this kerf recycling technology will drastically reduce the use of raw polysilicon material and the amount of slurry waste generated. This translates to significant savings for wafer production, currently 65% the cost of a solar cell.
The future of sustainable power in China
Though 98% of Chinese solar panels are currently exported to Western countries, this trend is shifting as China’s own installed solar capacity is projected to increase from 1 GW to 10 GW by 2015 and to 50 GW by 2040. China needs to be prepared to handle increasing amounts of used/defective solar modules, and consequently, solar manufacturers should invest now in recycling infrastructure and processes, including silicon recycling and handling of hazardous chemicals. Product design should assume that producers, not consumers, will be responsible for their products at the end of their lifecycle. This Extended Producer Responsibility (EPR) approach is already being implemented in Germany through the voluntary take-back program, “PV cycle”.
China has begun taking steps to address its growing e-waste problem. In September, an e-waste recycling exhibition was held in Beijing to promote technology exchange between China and Taiwan. To deal with the impending wave of solar e-waste, international cooperation and exchange between solar manufacturers should begin now so as not to repeat the mistakes of the electronics industry, which according to a UN report in 2007 still exported 70% of the world’s refuse to China, taking advantage of lagging environmental regulations and practices, and creating e-waste villages such as Guiyu.
As solar power becomes ever more affordable, it is critical for producers to ensure that the social and environmental costs of solar panels are not merely being passed on to other nations or future generations. Existing production flows should be examined to identify opportunities for efficiency improvements and waste minimization using available technologies such as STC and kerf recycling. Producers should develop processes now to handle the growing solar e-waste that will be generated in the future.
These efforts, together with continued research and faster technology exchange, will speed up the process of harnessing solar power in a truly sustainable way with many beautiful sunrises ahead.
This article was contributed by e8, a technology exchange platform that connects green technology entrepreneurs with industry experts and students to bring solutions to global environmental challenges (www.e8r.asia).
This article originally appeared in CHaINA Magazine (January-February 2012 Issue). Please refer to www.chainamag.com to read the full article and others. Those based in China or Hong Kong can contact email@example.com to subscribe to the print edition.