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How did photovoltaics transform from being an Downloaded from http://asmedigitalcollection.asme.org/memagazineselect/article-pdf/142/10/38/6574719/me-2020-oct3.pdf by guest on 25 September 2021 expensive, niche electricity source to the least costly power on the grid?

hen photovoltaic (PV) cells first burst into the facturing at scale played a part, but so did German industrial public consciousness in the 1960s and 1970s, policy and a focus on improving the complete power system, they were useful for producing electricity only not just the PV cells. in applications where no alternative could be In short, the revolution in photovoltaics is a triumph of found. Satellites in geosynchronous orbit, for engineering. instance, were too far away from Earth to refuel, and it was inconvenient to keep replacing batteries on low-power, pocket-size Solar power has had a futuristic sensibility for 70 years, electronic calculators. For other applications, but rudimentary photovoltaic technology dates back nearly however, the cost of electricity from PV cells two centuries. Edmond Becquerel first observed the phe- was too exorbitant to be acceptable. nomenon of conversion of sunlight into electricity In the second decade of the 21st century, (photovoltaic effect) back in 1839 while experi- the situation has been inverted. During the menting with two silver-coated platinum last five decades, the cost of PV modules electrodes by placing them in an acidic dropped from $100 per peak watt (Wp) solution and exposing one of the elec- down to as low as $2/Wp in 2019 “IN SHORT, THE trodes to sunlight. Other scientists, (for utility-level PV systems). In one working in the 1870s, were able to real-world example of this trend REVOLUTION IN turn light into electricity using the from the past year, the Kaneland metal selenium. School District of Maple Park, Ill., PHOTOVOLTAICS The became a center signed a power purchase agreement of research in the mid-20th cen- to have 1,051 kW solar PV installed IS A TRIUMPH OF tury. , Calvin Fuller, at three schools; the district will have ENGINEERING.” and Daryl Chapin, while working to no upfront costs and will buy elec- develop transistors at tricity produced by the panels at $0.048 in 1954, found that silicon solar cells were per kWh as compared to the market rate of much more efficient than the selenium cells, $0.0693 per kWh. producing electricity with an efficiency of 6 per- Not only is PV power becoming cheap, but it is also cent. The first commercial application of PV cells was now widely available. On a global basis, very few industries powering of a radio for a satellite named Vanguard that was have expanded as quickly as PV. According to the Interna- launched in 1958 by the U.S. Naval Research Laboratory. The tional Energy Agency, 165 GW of PV systems came online in PV-powered communication satellite, the Bell Labs-built 2016, about two-thirds of the world’s net power generating Telstar, was launched in 1962. sources. Research spurred by the oil embargoes of the 1970s was What breakthroughs led to this veritable revolution in often funded by independent oil-producing companies photovoltaics? The commonly told story is that China started such as Exxon, Shell, and British Petroleum. Exxon funded manufacturing lower-quality panels and dumped them on research by Elliot Berman of Solar Power Corp. that led to the world market at prices near (or even below) the cost of the discovery that multiple silicon crystal in place of single production. The truth is more complicated. Chinese manu- crystal could lower the cost of PV cells significantly.

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In the early 1980s, the Federal Republic of Germany engaged in a proactive policy, including solar power price support, which catapulted PV technology development and manufacturing, albeit at a comparatively higher

cost per watt produced than would Downloaded from http://asmedigitalcollection.asme.org/memagazineselect/article-pdf/142/10/38/6574719/me-2020-oct3.pdf by guest on 25 September 2021 normally be economic. A series of renewable energy laws—beginning with the Electricity Feed Act (Stromeinspeisungsgesetz) in 1991— required utilities to facilitate power purchase agreements (PPA) for PV systems so that the excess energy produced would be purchased. The PPA, in the form of feed-in tariffs, made it possible for the PV systems to compete with the conventional sources. Such developments started to improve the economics of photovoltaics. According to some estimates, the increase in cell efficiency alone helped to reduce the inflation-adjusted costs by 24 percent during the period from 1980 to 2001 and 12 percent from 2001 to 2012. Other factors, such as research (around 60 percent) and mass manufacturing (around 20 percent), played critical roles in bringing In the 1950s, Bell Labs researchers Gerald Pearson, Daryl Chapin, down the costs. and Calvin Fuller (left to right) discovered that silicon photovoltaic The biggest effect of these cost reductions has been in cells could efficiently convert light to electricity. Photo: Courtesy of AT&T Archives and History Center removing the barriers to utility-scale deployment of solar power. While the output of small-scale systems has roughly which was interested in developing low-cost sourcing of the tripled in recent years, data from the U.S. Energy Infor- PV modules to support its aggressive solar power plans and mation Administration shows that electricity production provided both technical help and financial assistance. In from large grid-connected PV power plants increased from order to establish its presence and gain a major PV module 76 million kWh in 2008 to a staggering 63 billion kWh in market share, the Chinese government proactively engaged 2018—nearly a factor of 1,000. in providing direct subsidy in a variety of ways to its manu- facturing units. In addition to the direct subsidies, supports were extended to provide research grants, access to low- The commercial-scale manufacturing of PV modules interest loans, inexpensive land, and tax benefits. started in the United States. So why didn’t the U.S., where At the early stages, China imported most of the silicon, the solar PV technology was invented and put to practical and the equipment to manufacture PV module from other use, continue to become the market leader? Many accounts countries. The lack of knowledge in producing high-purity of the breakthrough of solar power to the utility market polycrystalline silicon was an impediment that China had to begin—and end—with Chinese government support of overcome in mass producing multi crystalline PV module of manufacturers to mass produce photovoltaic modules. And high quality and durability. Specifically, China was plagued it’s important to understand that part of the story. with energy intensive manufacturing, scalability issues, and Chinese companies started manufacturing PV equipment poorly trained workers lacking required skills. in the late 1990s and began to expand rapidly in the early In time, however, China was able to manufacture finished 2000s. This was partly enabled by the German government, modules relatively cheaply using inexpensive labor and effi-

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Bell Labs engineers mounted the Telstar to a rocket in preparation for its 1962 launch. The satellite was powered by photovoltaic cells. Photo: Courtesy of AT&T Archives and History Center Downloaded from http://asmedigitalcollection.asme.org/memagazineselect/article-pdf/142/10/38/6574719/me-2020-oct3.pdf by guest on 25 September 2021

cient module encapsulation. Chinese manufacturers began Today, PV module production is dominated by Chinese ramping up manufacturing capacity to meet a rapacious manufacturers. The International Energy Agency reported demand for PV among China’s domestic customers, but it that Chinese PV companies in 2017 produced about 60 was so great—more than the existing worldwide demand— percent of world’s PV modules while consuming around 50 that it flooded the market to the extent that PV module percent of the global demand. prices fell by 75 percent. By some analysis, this dramatic cost reduction was due not just to inexpensive labor, but also ease of capital The burgeoning dominance of Chinese photovoltaic including free loans, infrastructure, and availability of land. module manufacturers is certainly a major part of solar’s According to a George Washington University report, fol- breakthrough into the utility-scale market. But it isn’t the lowing the German model, China started offering heavily only factor. While Chinese factories were able to mass pro- subsidized tariffs for rooftop solar systems that invigorated duce PV modules resulting in a substantial drop in prices, its domestic solar market. Germany concentrated on developing reliable power elec- Undoubtedly, China’s state-controlled economy and tronics—namely the inverters for residential, commercial, targeted subsidies have been major factors in overcoming and large-scale PV applications. the barriers, and relatively quickly China caught up with its Germany is known for its long and cloudy winter days. inadequacy in both the technical knowledge of PV manu- Southern Germany, the region with the most sun with about facturing and the precision machinery manufacturing of PV 1,700 solar-hours per year, has a lower photovoltaic power cells and modules. R&D laboratories were built to advance potential than even the cloudiest parts of the continental PV research in increased efficiency of cell development United States. (The sunniest parts of the U.S., such as Yuma, and module manufacturing techniques. A similar situation Ariz., have a solar power potential that’s more than double.) existed for robust silicon ingot-slicing processes and manu- With so much annual gloom, solar would seem to be an facturing of ultra-thin wafers. unlikely source of energy to power its homes, office build-

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ings, and factories. And the cost of solar was exorbitant. companies became the market leader in the area of solar Against all these odds, the German policy makers and the PV power electronics, especially the inverters. The impor- people chose solar photovoltaic. tance of this critical component for a PV system, vis-à-vis its During the 1980s, the reduction of costs in preunified stable and reliable controllability feature, is key and cannot Germany began to accelerate as the commercial-scale PV be overemphasized. systems became widely used in offices and various compa- Solar energy is an intermittent source, and stable and rable properties. In 1992, after unification, the German PV reliable output from a PV system—either to a dedicated load

manufactures could offer modules at $7 per Wp; by 2008, or to a grid—is critical from the utility’s availability and reli- Downloaded from http://asmedigitalcollection.asme.org/memagazineselect/article-pdf/142/10/38/6574719/me-2020-oct3.pdf by guest on 25 September 2021 the price was half that, thanks mostly to planned initiatives ability points of view. Inverters allow electricity produced such as the 1,000 Solar Roofs Program of the early 1990s and by the PV modules to be fed into the load and excess power the 100,000 Solar Roofs Program of the early 2000s. to the grid or to the storage system. In spite of this support, the 2008 global economic crisis This key component converts direct current, such as the had a detrimental effect on the German PV module manu- electricity produced by photovoltaic systems, to alternating facturing industry. Some plants were shuttered and others current. In photovoltaic system applications, these devices had to cut back production severely. On top of that, around will either feed that ac onto the electric grid or store excess 2012, Chinese modules became cost-competitive, further electricity in batteries. Inverters also feature integrated diminishing the business viability of the German PV module communication for individual module optimization, so that manufacturers. Nevertheless, the German PV market began if a fault is detected by the inverter’s processor, a message to expand and the PV energy production increased from 0.2 will be sent to the system operator so action can be taken to TWh in 2002 to 28 TWh in 2012. rectify the problem. Germany’s deliberate move to solar provided opportuni- German inverter manufactures introduced silicon ties to become a significant player in the field of photovol- carbide-based components in place of silicon, eliminating taic power technologies and manufacturing beyond the the need to derate power below an outdoor temperature of simple production of PV cells. Thanks to robust research 50 °C, achieving enhanced power conversion efficiency and and development efforts and a trained workforce, German minimizing losses. And the inverters provide energy man-

Technicians from Yingli Solar check a solar panel in the final stage of production. Chinese manufacturers dominate the PV industry. Photo: Getty Images

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This view shows the interior of a 100-kW central power inverter for use in solar power applications. Power electronics developed in Germany have helped support the explosive growth in installed solar power capacity. Photo: KACO

agement solutions offering marketing

of power both actively and reactively, Downloaded from http://asmedigitalcollection.asme.org/memagazineselect/article-pdf/142/10/38/6574719/me-2020-oct3.pdf by guest on 25 September 2021 as well as “shade management” func- tionality, thereby ensuring maximum yield in case of excessive shading. To connect high-voltage storage systems to the inverter, Germany has developed high switching fre- quency, three-phase nongalvanically isolated dc-to-dc converter utilizing metal-oxide- field- effect transistors made of silicon carbide. In addition to offering dc surge protection and upgradable ac protection, these inverters are also capable of providing communica- tion interface protection. Monitoring portals have also been included, so an operator can observe the perfor- mance of a PV system or each of the modules without interruption, thereby offering maximum system availability facilitating ease of system planning and dispatching options. In 2014, approximately 1.5 million PV systems were installed throughout Germany ranging from small rooftop systems to large-scale PV power plants, including a 100-MW central PV power plant. By 2016, the total installed capa- city was 41.3 GW, second only to China. Other countries—South Korea in particular—are entering the PV inverter field. In a January 2019 article, PV Magazine reported that the leading German inverter is the watchword. Germany’s contribution allowed solar manufacture KACO sold its central inverter manufacturing PV to take a first step toward being a mainstream source of technology to its Korean subsidiary while concentrating on electricity. string (PV modules wired in series) inverters and its energy Clearly, the PV industry has great growth potential. If storage business. the last five decades of increased PV cell efficiency trajec- The power electronics developed and manufactured tory, reduced manufacturing costs, and advances in power primarily in Germany has been an unsung factor the emer- conversion and inverter technology development is any gence of solar power. To be sure, the low-cost PV modules guide, the growth should continue provided challenges such produced with significant government support by Chinese as regulatory policies to reflect changing market conditions, manufacturers have brought down the cost by dizzying training of skilled professionals, and reliable grid intercon- amounts. But without the smart power electronics, utilizing nections are mitigated. ME advanced materials, a skilled workforce, and engineering prowess, it would be all but impossible for solar power to AMIYO K. BASU is an engineering consultant based in Austin, Texas. He became an integrate itself into the electric power grid, where reliability ASME Fellow in 2002.

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