Solar Technology

Recently, the solar power debate has been heating up. Spurred in part by China’s burgeoning interest in solar as a long-term energy solution—the Chinese government announced last year that it intends to spend $454 billion over the next decade on alternative energy and to quintuple its solar production by 2020—governments, researchers, and pundits in the United States and other countries are forging the next steps in harnessing the sun. While many debates have focused on the costs – which are still high but dropping steadily – of rolling out the technology on nationwide scales, or on improving the efficiency of existing solar technologies, a more fundamental debate may shape the future of the industry. This is the question of whether traditional or thin-film solar panels provide the best way forward.

 

The debate is not a simple one, and here we have room to highlight just a few major points. By “traditional,” we refer to solar photovoltaic (PV) cells composed of polysilicon; this is, by far, the most prevalent bulk material for solar cells. “Thin-film” refers to a variant class requiring less material and composed of cadmium telluride (CdTe) or other compounds, of which CdTe is the most cost-competitive.

First, we discuss the traditional option. Without delving too far into the technical details, it can be stated that the traditional PV cell generally possesses a higher energy conversion efficiency than its thin-film counterpart, and hence a smaller area consumption per watt production. Additionally, the natural resources from which these cells are manufactured are plentiful. Key to their manufacture is a compound known as “trichlorosilane.” More commonly known as TCS, it is a colorless liquid containing silicon, hydrogen and chlorine. It is also a chief ingredient in the production of extremely pure polysilicon, a substance used in the manufacture of traditional PV solar panels.

One company with a deep appreciation of the value of TCS is U.S.-based SunSi Energies, which is involved in acquiring, developing and operating a range of TCS production facilities in China. A key economic reality lies behind SunSi’s strategy: Companies involved in the manufacture of TCS achieve the highest profit margin on the “solar value chain.”

The existing barriers to enter the solar energy industry vary depending where along the solar value chain a company wishes to become involved. Becoming a TCS or polysilicon producer – at the front end of the chain – is difficult, because it requires special permitting and large capital investment, in addition to several years of planning and construction. This accounts for the higher profits to be made by companies such as SunSi that have managed to set up their business around these early links in the chain. One of the most significant barriers to entry is the expertise needed to run a TCS plant (SunSi’s engineers have more than 30 years of experience). Even with unlimited funding, the engineering expertise in building the plant and the process itself is not a trivial matter.

“SunSi has embarked on a campaign to acquire a range of China-based TCS production and distribution facilities, with a goal of controlling 140,000 metric tons of TCS annually by the end of calendar 2012,” SunSi CEO David Natan says. “We estimate that this will equate to a 20 to 25 percent market share in China. In light of the anticipated future growth of the solar energy industry within China and worldwide, combined with the fact that TCS is used in approximately 75 percent of solar cell production globally, we expect to occupy an extremely advantageous position within the solar PV value chain.”

In sharp contrast to SunSi’s strategy is that of companies such as Arizona-based First Solar, which is currently the largest manufacturer of thin-film solar panels in terms of yearly power produced. There are several advantages touted for this second type of solar cell, which was included in Time magazine’s list of best inventions of 2008. Unlike traditional panels, flexible thin-film panels can be applied to a wide variety of surfaces, including cars, windows, and even backpacks and clothing. Thin-film panels are said to lose less voltage than traditional panels when they heat up, and they do not require the glass and aluminum casings of traditional cells because the materials within them are flexible.

Of course, there are disadvantages to thin-film solar cells as well. Perhaps chief among them is a limited global supply of their chief ingredient, cadmium telluride, which also happens to be a toxic compound. The efficiency of thin-film cells has lagged anywhere from 50 to 70 percent behind that of traditional PV cells. However, with the current efficiencies available, one would require approximately 50 percent more room with thin-film solar to produce the same electricity as a traditional solar setup. Also, because thin-film solar is usually applied directly to a surface, they can retain more heat. Traditional panels generally are installed with a standoff, meaning there is space between the panel and the supporting surface, allowing for air to cool the panels. Thin-film solar may retain more heat, creating a balance between this and its benefit of better performance at higher temperatures.

Despite these facts, many large companies are throwing their research muscle behind thin-film solar, including Shell, Honda and Nanosolar.

As this brief overview has attempted to show, the future course of the solar power industry hinges to a significant extent on which basic form of solar cell – traditional or thin-film – is used. Developments within both branches of the industry today, coupled with choices by science policy decision makers in the United States, China and other nations, will shape the solar world of tomorrow.

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