Interesting that people comment about getting more output than their panel ratings.
All solar panels have the capability to produce more than their rated output. This is not some some magic which belongs to particular brands of panel.
It is almost entirely the result of the energy delivered by the sun on the panel and the alignment angle of the panel to the sun. (There are also second order losses due to wiring, power conversion and temperature)
Panels are rated by all manufacturers according to standard test conditions with a reference insolation power of 1000W/sqm. After production, the panels are subjected to exactly this level of insolation (artificially and accurately produced), directly on the face of the panel and the output power is measured. The panels are then sorted into groups depending upon how much power they produce. This is why the manufacturers have a range of different panel power ratings, say 390W, 395W, 400W and 405W, on their top of the range products. There is no difference in the production process, but there is a natural tolerance spread. This way of grouping panels tends to be more common with newer panels at the highest end of performance. Its a competitive thing because they want to quote the highest performance/efficiency number to beat the competition, so will advertise heavily, for example, the 405W performance. It may be that only 1% of the produced panels reach this level, and so they are also very expensive. As technology moves on, the manufacturers keep producing these panels, but after a while they are not at the bleeding edge of performance, and end up being rated with only one power, which is generally the minimum achieved in production. They will also move to sample testing only, which keeps the price competitive.
In the real world, the insolation level is not always 1000W/sqm and of course our panels are not perfectly aligned to the solar axis. Sometimes the insolation from the sun is much more than 1000W/sqm and if our panels happen to be well aligned at that time then they will of course produce more than their rated power. Unfortunately, most of the time they produce less !
The highest levels of efficiency at the moment for commercially available panels is around 22-23%. That means that a top performing panel of area 1sqm when subjected to a perfectly aligned reference insolation power of 1000W/sqm, will produce 220-230W. Beware of panels advertising more than 230W/sqm performance, they don't exist yet.
If you stick to a reputable manufacturer, you should receive an accurately calibrated product which produces less than rated output most of the time, but sometimes if you are in the right place and you align your panel properly, you might get 10, 20, 30% more than rated output.
I really need to get back to my boat!
SV Stella A54-154