Crystalline silicon wafers have many drawbacks. They’re expensive. They’re usually encased in glass, which makes them heavy and brittle. Their manufacture is dependent on fossil fuels and results in pollution and waste. In spite of this, they dominate the PV cell market. Because crystalline cells are connected in series, if one breaks, is shaded or isn’t connected properly, the array is dysfunctional. Although technically they are more efficient than other kinds of photovoltaic cells, they often don’t perform as well because of the high temperatures on rooftops which reduce their efficiency. Enter amorphous photovoltaic cells made by Energy Conversion Devices or ECD.

In the late 1990’s, a subsidiary of ECD — Uni-Solar — revealed a new class of PV cells. Triple Junction PV modules are named for the three layers of PV junctions that are stacked atop one another, with each layer attuned to a different wave length of light i.e blue, yellow/green and red. Compared to old-style glass type panels, Triple Junction PV modules are 30% more powerful and are much more effective in high temperature applications. Because they are coated with Dupont Tefzel glaze, they are able to withstand golf ball-sized hail and similar impacts. An installation funded by the Department of Energy in Hawaii in 1998 is still holding up and working well.

Perhaps the most surprising and promising facet of the Triple Junction line is that it can be used for roofing, just like normal shingles, and even looks like conventional shingles. Because, unlike glass encased PV panels, there is no need for an aluminum frame, it takes far less time to install Triple Junction PV modules. The flexible panels are laminated to metal roofing, on site, and in some instances are actually less expensive than composite shingles. According to Stan Ovshinsky, the inventor of amorphous PV cells and ECD’s founder and former CEO, “production costs are well below any other PV product. Our problem is keeping up with demand.” (http://www.renewable-energy-world.com) Because of these lower production costs, Triple Junction PV modules have the fastest energy payback — the time it takes to recover the costs of making them — of any PV cell.

When compared to fossil fuels or nuclear power, the ECD product is miles ahead in terms of efficiency and even cost, when factors like pollution, land area to return and transportation costs are taken into consideration. Coal for instance, involves mining land and the disposal of waste which covers vast areas in some places in the US and other countries. Nuclear power is dangerous, subject to terrorist threats and has an unsolved problem with waste disposal. Nuclear power also depends heavily on government subsidies, a hidden but real cost.

ECD is the biggest player in the amorphous film PV cell industry, as well as a key manufacturer of other renewable energy technology. The Ovshinskys, Stan and his late wife, Iris, his working partner for more than fifty years, concentrated their research in two areas: information and energy, which Stan called the “twin pillars of the global economy.” Their subsidiary, Ovonics Universal Memory, is involved in multi-level technology, phase-change research and innovative approaches to memory storage and artificial intelligence. In addition to amorphous PV cell modules and IT technology, ECD and its subsidiaries produce NiMH batteries, hydrogen-based vehicles, hydrogen storage systems and fuel cells.

The Ovshinskys have received many awards including the Popular Science Grand Award. They have been featured in two PBS documentaries and honored by the American Chemical Society for “significant and lasting contributions to global human welfare with their invention of environmentally sustainable energy generation and energy storage applications.” Their IT work funds their PV cell research, which gives them much more latitude in research than companies with a single-technology approach to PV cell manufacture. Add to that their many other lines of hydrogen-based technologies and it’s clear that amorphous PV cell research will be fully supported at ECD far into the future. In 2001, the Forum of Chalcogeniders established the Stanford Ovshinsky Award for Excellence in Non-Crystalline Chalcogenides to honor his pioneering work and recognize the contributions of scientists and technologists in this field. (http://www.ovonic.com)

Although a French physicist named Becquerel first reported the photovoltaic effect, the first solar cell was probably constructed by Charles Fritts in the early 1880’s. Fritts coated selenium with a very thin gold layer, but the efficiency of this first solar cell was abysmal. It wasn’t until 1941 when Russell Ohl patented the silicon solar cell that efficiency started to improve appreciably. Soon, other scientists had improved on Ohl’s silicon solar cell to achieve a 6 percent return on energy conversion in strong sunlight. Bell Laboratories produced the first crystalline silicon solar cell in 1954, but its efficiency was merely 4%.Because the first large-scale use for solar cells was space satellites, government funding began to power the research, which had a galvanizing effect on solar cell research. By the 1970’s, the USSR had created Gas heterostructure solar cells with a high efficiency, although production was very limited until equipment design caught up to design theory. By the 1980’s, the US had produced a cell with 20% efficiency for use in the space program. And by early in 2000, efficiency was up to 24%. As of 2007, solar cells with an efficiency of 28% are manufactured by the two companies that dominate world solar cell production, Spectrolab and Emcore Photovoltaics.

While silicon wafer-based first-generation solar cells make up almost 90% of the solar cell market for terrestrial applications, second generation or thin-film solar cells make up the same percentage of the space applications. While nowhere near as efficient as their first generation relatives, these thin-film cells are much lighter and more pliable, prime considerations for space flight. Other cells are being developed at the present time including some that are dye sensitized, and thus able to respond to all light frequencies, unlike the silicon-based cells. There are even cells that are capable of using infrared frequencies, which would allow them to operate at night to some extent. Solar cell technology now in the research stage includes nanocrystal solar cells, photo electrochemical cells and polymer solar cells. One emerging leader in the solar cell technology race is Nanosolar at http://www.nanosolar.com, a company that is partially owned by the founders of Google, Sergey Brin and Larry Page.

There is very little to wear out on photovoltaic cells. It’s reasonable to expect a well-designed and properly installed system to have a lifetime of three decades or more. The most common failure in a photovoltaic system are the other components that are needed to convert electrons to AC current. The inverter, the batteries, the wiring — all are subject to corrosion, wear and aging. Batteries will need to be replaced at proper intervals, for instance. The cells themselves, however, should need no maintenance over the course of their lifetime unless they’re exposed to unusually harsh weather conditions.

Something that needs to be taken into consideration is the amount of sunlight that falls on the solar cells. This can significantly affect the electrical output. Mechanical devices to assist the cells in “tracking” the sun are often built into solar modules and arrays. Before installing photovoltaic cells, contractors often research the sun’s irradiance at the latitude of the installation. Irradiance can be determined by consulting the Department of Energy’s charts or at Advanced Energy Group’s website at http://www.solar4power.com.

Modules are groups of solar cells connected in a series and attached to a panel. Modules are constructed to deliver a range of output. Depending on the application, output is measured in watts or kilowatts and is calculated using a formula that takes into consideration peak power usage and average power output of each cell. Arrays are groups of modules and several thousand may be used in an electrical generating plant designed to power hundreds or even thousands of houses. Solar power is extremely adaptable to a wide range of applications, which puts it at the forefront of renewable energy sources.