CircuiTree - August 2008 - (Page 32)

[ Happy Thoughts ] By Happy Holden Have You Considered the New Market of Photovoltaics? P reviously I talked about solidstate illumination. This installment is about another new PCB market, photovoltaics, also known as solar cells. It’s curious, but the photovoltaic cell is another solid-state P-N junction, just like the LED, only it operates in reverse. Instead of producing light by passing a current, the photovoltaic cell produces a current because of light striking the P-N junction. You’re probably tired of hearing about global warming and greenhouse gasses, but alternative forms of energy production, especially green-renewable ones, favor our industry. But solar-generated electricity is anything but small. The only factor is that we are late to the scene, as usual. is required. Low cost: Although not as low as current electricity, it is becoming less expensive to install and is the easiest to scale. Self installation makes it possible to save 25 percent of total costs. Low maintenance: Maintaining photovoltaic panels are simple and installations can last for decades. Independence: Suitable for home use, or for remote cabins and RVs, their impact now is being felt by building-integrated photovoltaics to replace conventional building materials as part of commercial construction of ofﬁces and skyscrapers. The power distribution infrastructure is not required. Perspective What Is a Photovoltaic Cell? Photovoltaic solar cells are thin silicon disks that convert sunlight into electricity. The sunlight, which is photons (another form of electromagnetic energy), hits the solar cell and is absorbed by the semiconducting materials, such as silicon or CdTe. Electrons (negatively charged) are knocked loose from their atoms, allowing them to ﬂow through the material to produce electricity. The complementary positive charges that are also created (like bubbles) are called holes and ﬂow in the direction opposite of the electrons in a silicon solar cell. An array of cells is wired into a panel (Figure 1) and converts solar energy into a usable amount of direct current (DC) electricity. The DC can be used or stored or converted by an inverter that will turn it into alternating current (AC) electricity that appliances can use or sold back to the public utility grid. In 2007, the U.S. produced 71.4 quadrillion BTUs of electricity, and less than 0.1 percent came from solar. The breakdown looks like this: Coal Natural Gas (Dry) Crude Oil Nuclear Power Biomass Natural Gas (Liq) Hydroelectric Geothermal Wind Solar/ Photovoltaics 32.8% 27.5% 15.1% 11.8% 4.9% 3.4% 3.5% 0.5% 0.4% 0.1% Figure 1 Photovoltaic Cell and Cells Arranged Into Photovoltaic Panels (Source Wikipedia) Photovoltaic Technology Silicon Types Single-Crystal and Multicrystalline Silicon (c-Si): Including nanocrystalline silicon, are sliced from single-crystal boules of grown silicon; these wafers/cells are now cut as thin as 200 µm. Single silicon wafers solar cells have higher energy conversion efﬁciency (~15 percent) but are the most expensive. It has a lower bandgap than amorphous silicon and thus absorbs from the visible and infrared portion of the light spectrum as well. Amorphous Silicon (α-Si): The noncrystalline allotropic form of silicon. It has a higher bandgap (1.7 eV) than crystalline silicon (c-Si=1.1 eV), which means it absorbs the visible and ultraviolet portion of the spectrum. It can be deposited as a thinﬁlm by chemical vapor deposition (typically plasma-enhanced [PE-CVD]) from silane gas and hydrogen gas. Photovoltaics made this way tend to have lower energy conversion efﬁciency of around 10 percent. Thin Film Types Copper Indium Gallium Selenide (CIGS) and Copper Indium Diselenide (CIS): These materials from the Periodic Table from I - III - VI elements are of interest because of their high optical absorption coefﬁcients and Considering construction costs and distribution, solar/photovoltaics and wind may make a sizeable impact on imported crude oil and gas for electricity. History The term “photo-voltaic” has been in use in English since 1849. The photovoltaic effect was ﬁrst recognized in 1839 by French physicist Alexandre-Edmond Becquerel. The ﬁrst solar cell was not built until 1883 by Charles Fritts, who coated the semiconductor selenium with an extremely thin layer of gold to form the junction. The device was only around 1 percent efﬁcient. Russell Ohl patented the modern solar cell in 1946. The modern age of solar cells arrived in 1954 when Bell Laboratories experimented with semiconductors of silicon and germanium. Benefits No emissions: Rather than burning fossil fuels, you use some of the average 100 to 200 W/m2 sunlight that’s striking the earth (89 pentaWatts total-solar irradiance). No noise: And no moving parts to disturb your surroundings. No depletion of resources: The sun is the only resource but weather can reduce the efﬁciency and no sun at night, so storage 32 August 2008 • circuitree.com http://circuitree.com

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CirciuTree - August 2008 Contents My Line Industry Review Tech Talk Flexible Thinking Creating Connections Between Electronics Design and Manufacturing Happy Thoughts View From the Middle Market Outlook Fein Lines IPCA Showcase Technical Product Spotlights Classified Ads Upcoming Events Ad Index Buyers Guide

CircuiTree - August 2008

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