As best I can tell, when trying to compare the over all efficiency of crystalline silicone PV modules to that of flexible thin film PV modules, it can’t really be done fairly. There’s too many differences between the two technologies. It’s like comparing apples to oranges.
What really matters is that you spend x-amount of dollars to put a solar system on your roof and you want x-amount of dollars in return. Pretty simple stuff.
Solar power is gauged by what’s known as “rated power”. This is determined under Standard Test Conditions ( STC ). These test take place in a laboratory, not on a roof. During the test, the modules are kept at 77 °F. Average roof top temperature conditions are never this low during the peak harvesting time of summer. Secondly the simulated sunlight of 1000 watts per square meter is flashed onto the module at the greatest absorption angle, that being perpendicular. Again not a real life, roof top scenario.
There are “Solar Radiation Data Sets” available that indicate how much solar energy strikes a surface at a particular location on Earth during a particular time of year. This data tells you how far off from perpendicular your fixed array will be so that a de-rate factor can be applied. That’s why installers have to point your silicone array as close to due South as possible. With thin film it’s not as important to be facing due South.
In addition to the above, crystalline silicone modules produce maximum power within a limited area of the visible light spectrum. Thin film modules produce power along a greater range of that spectrum. That’s why thin film modules produce power in the early morning, the evening and even on rainy days. Crystalline silicone modules don’t. Again, apples & oranges.
I believe a more simple standard should be developed. When researching the feasibility of the Affordable Power Panel I came across only one article out of hundreds that came close to defining this concept. It’s a white paper by Eddie Wu and Iris Lau about an experiment they did in Hong Kong back in 2007. You can see it here: http://tiny.cc/1j414w .
They’ve proposed an Overall System Efficiency standard. OSE = Total Net AC Energy / Total In-plane Irradiation. I believe some kind of temperature constant should be considered. In other words ( sun energy In = electrical energy Out ) K.I.S.S., simple. After all, what’s important here is how much money your solar system saves / makes you, right.