When a manufacturer states their solar panel's power ratings, one must bear in mind that this is only a nominal reading. Unless power tolerance data is shown in the specifications, there is likely to be quite a range of possible power outputs.
Several of the solar panels we offer are made with genuine SunPower® cells which are only sold by SunPower®, directly to known manufacturers, who have passed their scrupulous inspection. And like many manufacturers, there are different grades of SunPower® cells - the higher the grade, the higher the price to the manufacturer, however the better the output. Solara and Solbian use only the geniune, high grade cells themselves on their SunPower® solar panels.
When looking at solar panels, ask to see the specification for the panels themselves. For example, Solara's Ultra glass panels show a power tolerance of -0%/+4.99%, so they are guaranteed never to be less than the nominal rating.