SunPower has set yet another solar panel performance record with an NREL-verified 22.8 percent module efficiency.

While Swanson's law concerns itself with solar panel cost reduction as a function of growth in manufacturing volume, there's not really a rule of thumb describing the rate of PV efficiency improvement. In any case, NREL's champion efficiency chart continues to trend up and to the right. And some years later, commercially available solar panels start to approach those once world-record performance levels.

A table from April of last year, compiled by M.A. Green, shows SunPower at 22.4 percent +/- 0.6 (PDF).

Late last year, SolarCity made the claim that solar panels coming off of its 100-megawatt Silevo pilot production line were setting world records for solar module efficiency as "the world’s most efficient rooftop solar panel, with a module efficiency exceeding 22 percent." A week later, Panasonic claimed the crown at 22.5 percent module efficiency.

There's a bit of confusion and specsmanship in the way that modules are measured in terms of aperture versus full module area. The chart below might help clear things up.

Admittedly, these small advances fall within the margin of error and highlight the lack of clarity of some of these measurement systems.

SolarCity’s panel was measured with 22.04 percent module-level efficiency by the Renewable Energy Test Center (curiously, not by one of five designated test centers, and also curiously, measured out to the hundredths place). The silicon-based bifacial PV cell combines n-type substrates, copper electrodes, thin-film passivation layers, and a tunneling oxide layer that yields high conversion efficiencies.

SolarCity claims that its module will be "the highest-volume solar panel manufactured in the Western hemisphere." Most of the new solar panels will be produced at SolarCity’s 1-gigawatt factory in upstate New York. Full production will be between 9,000 and 10,000 solar panels per day when the Buffalo facility hits full capacity.

SunPower claims its X22-Series panels offer efficiencies of more than 22 percent. Average cell efficiency across all SunPower lines was close to 23 percent during Q3 of 2015, according to the company.

Panasonic: As covered in PV Magazine, the Panasonic panel’s 22.5 percent conversion efficiency was verified by Japan’s National Institute of Advanced Industrial Science and Technology "and builds upon the 25.6 percent efficiency record the company set in 2014 at the cell level."

SunPower is the record-holder for now.