This first of a ten-part column on photovoltaics explores the big picture of this renewable energy source, and particularly how these energy areas are connected closely to the electronics industry and SMT manufacturing.
This first of a ten-part column on photovoltaics explores the big picture of this renewable energy source, and particularly how these energy areas are connected closely to the electronics industry and SMT manufacturing.
Exploration and use of solar energy has risen and sunk with oil prices and electricity bills; it is both an old and a new thing. The old is that the solar cell was developed in 1954 with an energy efficiency of 4.5% and was fervently explored in the 1970s oil shock. Three decades ago, while completing my Ph.D. dissertation, I was recruited by a major energy conglomerate to join their photovoltaic team.
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 niche applications since the 1970s, it has not been a mainstream business, nor in broad-based deployment.
The U.S., with only 5% of the world population, consumes roughly one-fifth of its total energy. U.S. total energy sources rely on ~40% oil, 23% coal, 22% natural gas, 8% nuclear, and 7% renewable (largely from hydropower and biomass). Carbon dioxide concentration in the atmosphere has risen about 40% to 380 ppm since the industrial revolution, contributing to global warming and ensuing climate change. The U.S. emits more energy-related carbon dioxide per capita than any other industrial nation. Its CO2 emissions are projected to continue to rise, as are worldwide emissions.
Sunlight 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. 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. Countries such as Germany, Japan, Spain, and Australia are the vanguard in implementing solar cell energy.
With a slow 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 at 25–50%, varying with geographic location and other factors. Technological advancement to increase solar panel energy conversion efficiency and decrease usage costs will continue to be a main factor for future solar energy deployment.
When sunlight shines on the semiconductor solar panel, the light absorbed (photons) is converted to electrons in the atom structure of the semiconductor of the solar cell material, resulting in electrical current in an electrical circuit. This is the story of the efficiency of photon-to-electron conversion and the power play of the atom. But the conversion efficiency lacks. Therefore, economics call for continuous technology development. We 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 applications.
SMT’s role in photovoltaics
In 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 and solar cell manufacturing.
Two critical materials are conductors and silicon wafers. Today, the most-used substrate material is polysilicon with a purity level of 99.9999999, as compared to semiconductor chips’ purity of 99.999999999. 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 deposition technique. The printer is a part of production line with an oven that fires the conductor paste to make permanent conductor traces. Then the indispensable process of soldering is used to assemble modules and panels.
The lower the ratio of a country’s energy consumption to 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 enhance OPEC’s power and have a deleterious long-term impact on the U.S. economy.
Future energy portfolio will be concocted by availability, stability, price stability, affordability, sustainability, and security. With or without energy independence and carbon freedom, meeting future energy demands can only be accomplished by combining strategies of energy conservation, energy diversification, and technological advancement. As to photovoltaics, no country can capture another country’s photons.
REFERENCES:
Contact the author for a full list of references.
An unabridged version of this article is available at smtonline.com.
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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. 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. Contact her at (216) 839-1000; [email protected].
