Building Integrated Photovoltaic construction, or BIPV, is an extremely promising approach to renewable energy. BIPV received a big push in 2011 when US solar manufacturer Sunlogics, PLC acquired Phoenix Solar Holdings Corp and its operating subsidiaries. EPV Solar Germany GmbH, with amorphous thin-film PV panel manufacturing facilities in the US and in Germany, was one of the subsidiaries acquired by Sunlogics in the transaction.
Sunlogics had previously forged a successful alliance with GM to retrofit solar-powered charging canopies into dealerships where the all-electric Volt vehicle was sold. The sun canopies made use of a proprietary amorphous thin-film technology developed by EVP Solar.
Analysts believe that distributed photovoltaic systems will reach commercial success before large, centralized systems. Distributed systems, which are sometimes called micro-inverters or micro-generators, are sited at the point of use. They are already very popular in Spain, Italy, Germany, and Great Britain, where attractive Feed in Tariffs provide strong financial incentives for distributed photovoltaic system investments by many European home owners.
BIPV construction techniques make these investments even more financially attractive by reducing associated construction costs. BIPV panels are incorporated into the building envelope in lieu of conventional construction materials. For example, a conventional home using a PV system might have an array of PV panels placed upon the roof. A BIPV home would use specially designed PV panels as the roof, thus eliminating corresponding roofing material costs to the builder while adding value as a PV micro-generator.
Not all materials are suitable for BIPV applications, however. Thick crystal solar panels are composed of multiple crystalline or poly-crystalline silicon wafers placed into an array and wired together. These panels are not flexible and must be handled carefully. They are inappropriate as construction materials.
By comparison, amorphous thin-layer solar panels, such as those now owned by Sunlogics, are rugged and flexible. They are formed by depositing extremely thin films of non-crystalline silicon onto metal substrates or glass covering plates. Most of these films are deposited using either thermal or sputtering techniques.
In the thermal vacuum deposition process, silicon is placed into a vacuum chamber with the substrate and is resistively heated. As the silicon vaporizes, gaseous silicon condenses onto the substrate and cools, creating a thin film. The vacuum serves to increase the Vapor pressure of the silicon and to remove molecules of atmospheric gas that might otherwise collide with the vaporized silicon and prevent it from reaching the substrate. The films created with this technique can be as thin as 10 nanometers. Molecular beam epitaxy, which is a particular kind of vacuum deposition, can produce layers that are the depth of only a single atom.
Instead of boiling away silicon with resistive heating, the sputtering process bombards the silicon with argon plasma. As the plasma strikes the target, silicon atoms are knocked free. They stick to the surface of the substrate and create a thin film atom by atom. Sputtering is conducted under vacuum to eliminate impurities that might interfere with the deposition. Sputtering is the preferred technique because elevated temperatures are not required.
Amorphous thin-film PV panels are only half as efficient as standard crystalline solar panels. This is a tremendous issue, because PV panels are already inefficient. While a typical crystalline silicon PV panel will produce 10 to 12 watts per square foot of panel surface under full sunlight, thin-film amorphous panels produce only four to five watts per square foot under full sunlight.
Thin-film PV panels, although less efficient, are far less expensive to produce than thick crystal solar panels. The nanometer films use only minute quantities of photovoltaic materials and can be deposited onto inexpensive substrates. They also do a much better job of converting low light levels to electricity than thick crystal cells. Amorphous thin-film panels function on overcast days when standard solar panels produce no electricity at all.
They can be used as a direct replacement for batten and seam metal roofing, for traditional 3-tab asphalt shingles, and for the conventional façade of a structure, essentially converting the entire building envelope into a giant, albeit inefficient, solar panel. Utilizing new hydrocarbon plastics, thin-film cells are nearly invisible inside glass window panes. They can be seamlessly integrated into daylighting designs to increase functionality, and some technologies even utilize emissions from artificial lighting.
Sunlogics believes that low production costs, wider useful light conversion range, and construction applicability make amorphous thin-film technology the smart bet for the future of renewable energy.
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