Thin Film Solar Technology - Building Integrated Photovoltaic

So-called thin-film photovoltaic devices are usually based on mixtures of elements other than silicon — most notably copper indium gallium selenide (CIGS) — applied in a thin layer to plastic, even organic, components. Using nanotechnology and advanced materials science, thin film is able to produce power with a fraction of the materials. Similar techniques are being tried using ultra thin layers of silicon on a glass substrate, reducing what is now a 250 - micrometer (um) - thick wafer to less than 20 um.

Thin film also has the potential to be mass-produced for a fraction of the cost of mono-or polycrystalline silicon, because the film can be applied to long rolls of substrate and manufactured in continuous processes, unlike the laborious process of making wafers. And because highly refined silicon is so expensive to make — about 45 percent of the cost of a solar cell — thin film also represents the greatest potential for cutting the cost of PV.

Such innovations have the potential to make solar so cheap and cost effective that it can be deployed anywhere, from the first world to the developing world. Already, Kenya buys more than 30,000 small panels each year for as little as $100 each.

While thin-film solar is considerably cheaper than traditional polysilicon solar, it has also suffered from low efficiency. Most of the thin-film products brought to market in the past 10 years had only 4 to 5 percent efficiency — less than half that of their traditional counterparts — so they took up twice as much space or more to achieve the same output. If you wanted to use thin-film solar, you needed the same amount of money but twice the surface area — not a recipe for huge success. However, intensive research over the past two years or so is changing all that. Exciting innovations in photovoltaic are cropping up everywhere. Researchers in the Materials Sciences Division of Lawrence Berkeley National Laboratory recently made an unexpected discovery that could enable solar cells to convert the full spectrum of sunlight — from the near infrared to the far ultraviolet — into electricity.

Some commercially available thin-film solar cells have achieved efficiency levels as high as 9 percent, putting them within competitive reach of traditional silicon modules, but at a lower cost. And in the lab, we’re seeing efficiencies as high as 19.5 percent. That particular efficiency was achieved by Ascent Solar (NASDAQ:ASTI) . Other solar cell manufacturers such as Arise Technologies (TSX:APV) and Sun Power (NASDAQ:SPWR) are taking a different approach, combining both traditional polysilicon and thin-film photovoltaic wafers in a hybrid cell with 18 percent efficiency — right at the top end for commercially available traditional solar cells. Another player in the thin-film space is Nanosolar, a privately held Silicon Valley company that is building its first manufacturing plant, which will churn out a kind of solar foil in long rolls using a modified printing press. If successful at commercial scale, the process could slash PV production cost to one-tenth of what it is today, on a rapid production line, and build fabrication plants for one-tenth the capital outlay.

The ultimate goal of this photovoltaic, however, is what is known as building integrated photovoltaic (BIPV), which incorporates photovoltaic directly into roofing and other materials, eliminating solar panels entirely. Building integrated photovoltaic modules not only produce power, but also function as a roofing membrane, just like composite asphalt shingles. Some models integrate very well aesthetically with composite shingles, making the solar portion hardly noticeable. Solar roofing tiles are already being installed on some new homes, and their popularity far exceeds their availability. Initiatives like California ’ s SB 1, part of Governor Schwarzenegger’s Million Solar Roof campaign, requires solar to be offered as an option for single-family home developments of more than 50 units as of 2011, and other incentives in the state are already leading developers to offer solar as a standard option.

With such mandates in place, building integrated photovoltaic has a guaranteed market. Thanks to the steady demand outlook, manufacturers now have the green light and the confidence to invest the hundreds of millions of dollars it will take to scale up the production of BIPV modules to commercial levels. Beyond standard building integrated photovoltaic, a new generation of solar called hybrid photovoltaic/thermal (PV/T or PVT) is also emerging, which uses a layer of PV material over a thermal collector to heat air or hot water. Not only does this capture more solar energy overall, but it actually increases the efficiency of the photovoltaic layer by keeping it cool. This is because photovoltaic lose efficiency, or derate, as they heat up. Research into PVT has been going on intensively for the last several years, and now a few manufacturers are starting to bring it to market, usually as BIPV equipment, where the house can be designed around it from the beginning.