A Primer on Photovoltaic Module Efficiency VS Output

There is much talk in the solar industry about the efficiency ratings of the various photovoltaic technologies, and it is well known that crystalline photovoltaic technology is the king of efficiency. With rated factory efficiencies of 19% or higher being claimed by some photovoltaic module manufacturers, there is no doubt that crystalline photovoltaic modules have a higher factory rated efficiency than thin film modules. This is well documented and confirmed.

Many companies choose to offer crystalline photovoltaic technology only. Regardless of the roof type, size, orientation, etc., they only offer crystalline photovoltaic systems as the solution. While this is their choice, it certainly does not reflect the majority of the solar electric industry. Since this is the sole technology that these companies offer, their sales literature and efforts extol the superior efficiency of crystalline photovoltaic modules, as compared to lower efficiency thin film photovoltaic modules. There is much information provided to the customer about how thin film modules are less efficient, and according to these companies, less productive.

Beachside Solar Technologies installs both technologies, as every project is different and therefore application specific. We provide our customer with the best available information to make an informed decision about the photovoltaic system that will occupy space on his roof or acreage for the next twenty-five years. While crystalline technology is the unabashed king of rated factory efficiency, there are certain characteristics of amorphous thin film photovoltaic modules that in most installations make them the ideal photovoltaic module for projects in Hawaii. In the following paragraphs are three characteristics that are documented by scientists and photovoltaic experts worldwide, indicating that thin film technology is an excellent choice for most photovoltaic projects in a climatologically diverse area such as Hawaii. It should also be noted that the only thing that efficiency affects is the amount of square footage required to install comparable system sizes. Unfortunately, many customers confuse efficiency with output. This is due to the incomplete information provided to customers by companies that choose to install only one type of photovoltaic technology. It is well documented that crystalline photovoltaic modules can have highly rated factory efficiencies but experience low kWh output, due to the climatology and temperature of the area where the modules are installed.

Most customers tell us that they want their photovoltaic system to produce as many kWh's as possible. Therefore, every photovoltaic system that Beachside Solar Technologies designs is done so based on the best technology for the application that will provide the customer the maximum kWh output for the amount of money spent.

In many cases amorphous thin film photovoltaic technology is the logical choice for a system design. The three contributing factors for higher output performance of thin film photovoltaic technology over crystalline photovoltaic technology in Hawaii's varied climatology are:

When combined, these three factors make thin film photovoltaic systems the superior producer of power in Hawaii's varied climatology. Substantiating results were obtained during a case study in a side-by-side test of thin film modules and crystalline modules in Florida. On a hot summer day, the thin film modules produced over 30% more energy per rated watt than the crystalline modules, particularly during the hottest part of the day.

• Lower Temperature Coefficient: Thin film technology has a performance advantage over crystalline technology as a result of fundamental differences inherent in the amorphous thin film semiconductor. Most importantly, thin film dominates in warm, sunny conditions due to its lower power-loss temperature coefficient. In addition to the more favorable temperature coefficient, numerous studies have shown that high module operating temperatures actually improve the performance of thin film photovoltaic modules.
• Obscure & Low Light Conditions: It is proven that thin film technology has a wider spectral response to blue light than crystalline technology. Blue light is what is most abundant when the sun is at its zenith and brightest. Thin film not only responds better to blue light when the sun is bright, but also responds much better to red and green light, which is abundant in cloudy, obscured and low light conditions. This makes thin film a better kwh producer when the sun is brightest, as well as the better kwh producer in low and obscured light conditions.
• Thermal Annealing: Both crystalline and thin film photovoltaic technologies drop off in efficiency at higher temperatures. However, crystalline photovoltaic technology loses efficiency at a much greater rate than thin film. This means that thin film photovoltaic modules actually perform better than crystalline at higher temperatures, such as what we see daily on rooftops in Hawaii.

When combined, these three factors make thin film photovoltaic systems the superior producer of power in Hawaii's varied climatology. Substantiating results were obtained during a case study in a side-by-side test of thin film modules and crystalline modules in Florida. On a hot summer day, the thin film modules produced over 30% more energy per rated watt than the crystalline modules, particularly during the hottest part of the day.

Reference: The Advantages of Amorphous Silicon
Photovoltaic Modules In Grid-tied Systems
Kai W. Jansen1, Suparna B. Kadam2, and James F. Groelinger 1
1Energy Photovoltaics, Inc., Princeton, NJ 2kadam Consulting, E. Brunswick, NJ