Solar Impulse is on target to circle the world. Presumably Solar Impulse has the most current and efficient solar cells available, while those on the ISS range between 5 and 10 years old. How do the two different solar panel systems compare?
The efficiency of the panels on Solar Impulse is listed as 23%.
The panels on the ISS are much older than 5 and 10 years. The first array (Z-) was added in 2000, which implies a manufacture date of at least 1-2 years earlier. The remaining three sets were added in 2006, 2007, and 2009.
The ISS Panels get about 14% efficiency, which was pretty good when they were manufactured.
A good chart listing solar cell efficiency's as available for home installation, is available here. A screenshot of the table is below.
Thus Solar Impulse seems like it has much better arrays. Of course they are not space rated, which is a very different design (exposure to atomic oxygen, weight, etc).
The Russian Mir space station had an array on Kvant-1 with 12% efficiency but dropped to 5% at the end of life.