When considering PV technological advances, people usually focus on PV conversion efficiency. Conversion efficiency provides a measure of how effectively a PV technology converts sunlight to electricity. The amount of electric energy produced by a PV installation over its useful life is almost directly proportional to its conversion efficiency that will result in the amount of savings or revenue from the PV installation.
While conversion efficiency is an important factor to consider when comparing PV technologies, it is only one factor. A PV technology with a phenomenal conversion efficiency that cannot be economically manufactured, involves the use of toxic elements, is difficult to install or has a short life, would only be a laboratory curiosity and have no practical value. When considering the future of PV in the building industry as well as competing technologies, all of the factors that impact the PV system’s lifecycle costs and benefits need to be considered.
Crystalline silicon PV is the most common technology used in building applications today. Crystalline silicon PV cells are usually panelized and these panels are usually either roof-mounted or located on the surrounding building grounds.
Crystalline silicon PV panels have a typical conversion efficiency of between 10 and 13 percent. Today, traditional crystalline silicon PV is being challenged by thin-film amorphous silicon PV cells that currently have a lower conversion efficiency between 5 and 8 percent but have other more desirable characteristics. However, research and development (R&D) promises to continue to increase thin-film PV conversion efficiency in the future.
Even without increased conversion efficiency, thin-film PV has advantages that make it preferable to traditional crystalline silicon PV panels in many building applications. Thin-film PV conversion efficiency is better than crystalline silicon PV in low or diffused light making it more efficient on cloudy days.
Thin-film PV is less expensive to manufacture and can withstand hot climates. Thin-film PV can be manufactured using a roll-to-roll process similar to that used to print newspapers, which has the potential to significantly decrease PV unit costs and increase output.
Building-integrated PV (BIPV) is the future of PV in the building industry and thin-film PV lends itself to BIPV much more readily than crystalline silicon PV, which is usually installed as a separate building system. Thin-film PV can be integrated directly into exterior building materials such as roofing, glass and curtain wall materials.
As a result, installation costs associated with BIPV are significantly decreased because PV becomes part of traditional building materials and no separate structural support or bracing is required. BIPV also increases the amount of a building’s surface area available to generate electricity. This is because the entire exterior skin of the building can incorporate PV rather than just the roof, which is typical for traditional crystalline silicon PV panels. Integrating PV into the building’s vision glass and skylights also extracts energy from the incoming sunlight and results in a lower building air conditioning load.
Integrating PV into exterior building materials may be just the start. Organic and dye-sensitized PV materials are currently under development. These use carbon and other compounds instead of silicon for converting sunlight into electricity and can also be manufactured using a roll-to-roll process using plastic as a substrate.
Organic and dye-sensitized PV could be economically integrated into wall coverings and ceiling materials, allowing them to harvest energy from incoming sunlight as well as light from artificial light sources, further improving building energy efficiency.
Their projected shorter life than silicon-based PV would not be a problem with interior applications because the cost to produce and install organic and dye-sensitized PV would be significantly less than silicon-based PV. Plus, building interior finishes are changed often over the life of the building. In the future, nanotechnology may make it possible to integrate PV into paint. EC
GLAVINICH is an associate professor in the Department of Civil, Environmental and Architectural Engineering at The University of Kansas and is a frequent instructor for NECA’s Management Education Institute. He can be reached at 785.864.3435 or firstname.lastname@example.org.