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Photovoltaics in the Realm of Energy
December 31, 1969 |Estimated reading time: 6 minutes
By Jennie S. Hwang, Ph.D.
As highlighted in my January column "The Electronics Industry Going Forward," "Innovations in…optoelectronics, photovoltaics and other energy-related electronics…" are the main thrusts…" In this upcoming series of ten parts cascading from the big picture to specific topics, I will dedicate this column to photovoltaics, particularly the areas that are closely connected with the electronics industry and SMT manufacturing.
Old and NewExploration and use of solar energy has risen and sunk with oil prices and electricity bills; it is both an old and a new thing. This makes one wonder whether it would be ever real. The old is that the solar cell was developed in 1954 with an energy efficiency of 4.5% and was fervently explored in the late 1970s during the oil shock. I recall that, while I was on campus at the last stage of completing my Ph.D. dissertation, I was recruited by a major energy conglomerate to join their photovoltaic team. That was three decades ago!
The new is that global momentum finally has pushed aside the years of political, economical, technological, and social barricades and is moving forward in implementing solar energy. Although solar energy has been used in spotty niche applications within or outside the photovoltaic field since the 1970s, it has not been a mainstream business, nor in the broad-based deployment. But it is real this time!
Energy SectorThe U.S., with only about 5% of the world population, consumes roughly one-fifth of the world's total energy. Electricity and transportation industries consume the majority of energy. At present, the U.S. total energy sources rely on approximately 40% oil, 23% coal, 22% natural gas, 8% nuclear, and 7% renewable that are largely from hydropower and biomass.1
Within electricity, 85% of the global electrical energy usage of 13 teraW is generated by burning fossil fuels. Energy sources used in generating electricity in the U.S. in 2006 comprised 49% coal, 21% natural gas and other gases, 19% nuclear, less than 2% petroleum, 7% hydroelectric, and less than 3% other renewable.
On the impact of energy usage on the environment and climate, carbon dioxide concentration in the atmosphere has risen about 40% since the beginning of the industrial revolution from 270 parts per million (ppm) to 380 ppm is believed to have contributed to global warming and ensuing climate change. The U.S. in 2006 emitted a total of 712 million metric tons of carbon, 412 million metric tons of which came from road petroleum use.2 The country emits more energy-related carbon dioxide per capita than any other industrial nation. At present, the U.S. emits approximately one-fourth of the world's greenhouse gases, and its CO2 emissions are projected to continue to rise, as are worldwide emissions.
Photovoltaics' Role in Energy SectorSunlight is the most abundant energy source on earth and solar energy is one of the viable renewable energy paths. However, solar energy is less than 0.1% of the world electricity supply. It is miniscule indeed. As energy needs are mushrooming throughout the world, particularly in developing countries, every bit of energy supplement counts. By integrating with other renewable, alternative, and conventional energy sources, the uncertainties surrounding energy supplies from politically volatile regions can be eschewed. As a clean energy, solar further circumscribes the concerning carbon footprint.
In recent years, government incentives bestowed to solar energy were largely outside the U.S. and the U.S. Congress has failed to include solar energy in its most recent energy bill (2008). Countries like Germany, Japan, Spain, and Australia are the vanguard in implementing solar cell energy.
With a small economic scale to start, solar energy including but not limited to photovoltaics provides ample growth opportunity in business and in technology. The consensus on anticipated growth rate falls around 2550%, varying with geographic locations and other factors. Technological advancement to increase solar panel energy conversion efficiency and to decrease usage costs will continue to be a main factor for future solar energy deployment.
Scientific Principle of PhotovoltaicsWhen sunlight shines on the semiconductor solar panel, the light can be reflected, pass through, or be absorbed. The sunlight absorbed by the solar panel (photons) is then converted to electrons in the atom structure of the semiconductor of the solar cell material, resulting in electrical current in an electrical circuit.
It is a photon-electron conversion. But the conversion efficiency lacks. Overall, it is the story of the power play of the atom, relentless energy of the photon and the free path of the electron.
Categorically, we can view photovoltaic technology in three generations: thick film/bulk polycrystalline silicon, thin film/amorphous silicon or other substrates, and nano-based organic cells. Currently, the first generation occupies the majority of commercial application space.
Electronics and SMT's Role in PhotovoltaicsIn application, solar panels consist of several major components and steps: making solar cells, assembling modules, connecting arrays, and installing systems. There are many similarities and transferable processes between SMT manufacturing and solar cell manufacturing.
In materials, two critical materials for solar cells are conductors and silicon wafers. Today, the most-used substrate material is polysilicon with a purity level of 99.9999999, as opposed to the purity of 99.999999999 for semiconductor chips. Thick-film paste is the most widely used conductor. The thick film paste comprising conductive metal particles, organic vehicle system, and inorganic binder system is equivalent to the hybrid circuit thick-film paste. It also is analogous to solder paste in multiple aspects: rheology, chemical and physical properties, printing, formulation, etc. Printing is the primary paste deposition technique. In equipment, the printer is a part of production line with an oven (albeit with different process parameters) that fires the conductor thick-film paste to make permanent conductor traces. Then the indispensable process of soldering is a technique used to assemble the modules and panels.
Solar heating and cooling and other automotive electronics (outside photovoltaics) like sensors, computers, and electric motors also contribute to future fuel-efficient hybrid vehicles.
Global CompetitivenessIt generally is viewed that the lower the ratio of a country's energy consumption to gross domestic product (GDP), the lower the cost of the tradeoff between inflation and GDP loss. Oil imports account for two-thirds of U.S. oil consumption. Higher U.S. oil imports not only enhance OPEC's monopoly power, they also have a deleterious long-term impact on the U.S. economy.
Future energy portfolio will be concocted by availability, supply stability, price stability, affordability, sustainability and security. With or without the energy-independent and carbon-free ideals, the strategy and action to meet future energy demand can only be accomplished by combining strategies of energy conservation, energy diversification (fossil fuel, alternative energy, and renewable energy), and technological advancement. As to photovoltaics, no country can capture another country's photons.
REFERENCES:1. Statistics supplied by The National Academies.2. James A. Baker, Energy Forum.
APPEARANCESDr. Hwang will speak on Environment-friendly Lead-free Manufacturing in Shanghai, China on November 20, 2008, and on Lead-free Reliability for Harsh Environment Electronics and Manufacturing Defects/Issues and Remedies at JEDEC/IPC International Conference on December 8, 2008, in Austin, Texas.
Jennie S. Hwang, Ph.D., an SMT Advisory Board member, is elected to the National Academy of Engineering, inducted to the WIT International Hall of Fame, and named an R&D-Stars-to-Watch. During the 28-year SMT manufacturing establishment, she has helped improve SMT production yield and solved challenging reliability issues. She is a member of the U.S. Commerce Department's Export Council, and serves on the board of Fortune 500 NYSE companies and civic and university boards. In addition to technical publications, she is an international speaker and author on trade, business, education, and social issues. Contact her at (216) 839-1000; jenniehwang@aol.com.