Here is an interesting video that actually comes off more as a commercial from SunPower, though it is backed up with third party data.
Here is a more direct link to the third-party support for SunPower’s claims:
We are currently undertaking a comprehensive data analysis from as many of our systems as possible from which we can get clean data. At this point with our 340 grid-tied pv systems installed, about 20 use SunPower modules, and they appear to be performing very well although our in-house data analysis is not complete. As we are not a lab, each system has different installation characteristics and is in a slightly different location; our local micro-climates can complicate data comparison. We are working to integrate our performance data onto maps, and compare all other pertinent attributes such as pitch, azimuth, and shading, before making comparisons between manufacturers.
The main reason we have relatively few SunPower installations although we have been installing them for four years now, is that they are more expensive in terms of dollars per watt (in addition to being more efficient in terms of watts per square foot.) As we have not yet been able to quantify this, it has been difficult to justify a higher price for the product without feeling like we can make a substantiated claim for additional energy produced per KW. One of our goals is to see if we can objectively demonstrate more kilowatt hours of energy produced per rated kilowatt of module capacity. If we can do that, then our performance estimates can reflect that data, and the returns will look more attractive for the SunPower modules thereby easily justifying the additional price when our customers are comparing options.
We hope to have our data analysis completed by the end of August this year and will publish results we feel are rock solid.