Published on June 18th, 2012 | by Guest Contributor0
Building Integrated Photovoltaics
A promising way of approaching renewable energy is with Building Integrated Photovoltaic (BIPV) construction that, in 2011, received a big move forward as Sunlogics PLC, which is a US solar panel manufacturer, purchased Phoenix Solar Holdings Corp and their operating subsidiaries. One of those subsidiaries was EPV Solar Germany GmbH, which has facilities to manufacture amorphous thin-film PV panels in both Germany and the USA.
Previously, Sunlogics had developed a successful partnership with GM to provide a service to any dealerships that sold the Chevy Volt by retrofitting the solar-powered charging canopies. These sun canopies used a proprietary amorphous thin-film form of technology that had been developed by a business called EVP Solar.
Analysts are of the opinion that distributed photovoltaic systems are going to achieve great commercial success before systems that are large and centralized. A distributed system, which is often referred to as a micro-generator or a micro-inverter, is situated at the point where it is used. In Spain, UK, Germany, and Italy, they have proven popular already, as there have been good financial incentives from Feed-in Tariffs for distributed photovoltaic systems.
Due to reduction of associated building costs, BIPV construction systems appear even more financially appealing. BIPV panels are included as part of the construction materials — so, for instance, a normal home may have a number of PV panels put on the roof but a BIPV property would actually construct the roof using PV panels. This would reduce the cost of roofing materials, but value would be added to it as a PV micro-generator.
However, certain materials are unsuitable for BIPV applications such as thick crystal solar panelling, as they are made up of poly-crystalline or multiple crystalline silicon wafers that are put in an array and then wired together.
However, in contrast, amorphous thin-layer solar panels, like the ones owned by Sunlogics, are both flexible and rugged, being formed by the deposit of a very thin film of a non-crystalline silicon onto either glass covering plates or metal substrates. The majority of the films are deposited with either a sputtering or thermal technique.
Silicon, with the substrate, is added to a vacuum chamber during the process of thermal vacuum deposition and is then resistively heated. During the vaporizing of the silicon, a thin film is created by the condensing of the gaseous silicon on the substrate that then cools. The vacuum increases the silicon’s vapor pressure and removes molecules of atmospheric gas, as it may have collided with the silicon that has been vaporized and could then stop it from getting to the substrate. Film created using this technique can actually be only 10 nanometers in thickness. A type of vacuum deposition known as molecular beam epitaxy is capable of producing layers that are a mere single atom in depth.
Rather than use resistive heat to boil silicon away, the process of sputtering results in argon plasma being shot at the silicon. When the argon plasma hits its target, the silicon atoms are hit free and get stuck to the substrate surface where a thin film of atoms is built up. The sputtering process is done under vacuum to remove any impurities that could affect the deposition. Sputtering is the chosen way of doing this, as elevated temperatures are not needed.
Normal crystalline solar panels are twice as efficient as amorphous thin-film PV solar panels, which is a big problem since PV panels are relatively inefficient already. Normally, a crystalline silicon PV solar panel will provide between 10 and 12 watts for each square foot of surface panel that is in full sunlight, but amorphous thin-film solar panels only produce between four and five watts for each square foot of surface panel that is in full sunlight.
Although not as efficient, thin-film PV panels are not as expensive to make as thick crystal solar panels. The nanometer films can be put onto cheap substrates and only use small amounts of photovoltaic materials. Also, they do much better at converting low levels of light into electricity, as they perform well with overcast skies, which standard solar panels do not.
The panels can easily be used as part of the structure as described earlier and, since the thin film cells are almost not visible when in the glass panes of windows, they can be introduced into daylighting designs to enhance certain functions. There are also a number of technologies that utilize the emissions from artificial light.
Sunlogics is of the opinion that, production costs being low, the technology having a wider range of more productive light conversion, and the potential for greater use in the construction process will result in amorphous thin-film technology being the future way forward for renewable energy.
Image: BIPV via 3S Photovoltaics