I disagree with the comment that manufacturers lie panel ratings are set in a standardized process but the performance you see on any given day and over the course of the year will depend on a number of other.
Why do solar panels have a peak power.
Photovoltaic solar panel power production works most efficiently in cold temperatures see reference 5 final paragraph cold sunny environments provide optimal operating conditions for solar panels.
60 cell solar panels and 72 cell solar panels.
60 cell solar panels are typically 5 4 feet tall by about 3 25 feet wide and have a power output in standard test conditions of between 270 watts to 300 watts depending on the exact efficiency of the cells in them.
The rated power of solar panels is determined under carefully controlled laboratory conditions that simulate optimal operation.
The panel will generate 300 w if as craig lawrence said it is kept at 25 deg c and receives 1000 w m2.
For example if two solar panels both have 15 percent efficiency ratings but one has a power output rating of 250 watts and the other is rated at 300 watts it means that the 300 watt panel is about 20 percent physically larger than the 250 watt panel.
Since the panel heats up as the sunlight hits it s surface 85.
The average efficiency of solar panels falls between the 17 to 19 percent efficiency range.
That may or may not be a problem.
But solar panels have become much more efficient and less expensive.
The usable ac power from that panel will almost always be less than 300 watts.
This is the average peak solar radiation received on the surface of earth on a summer day with clear skies.
The highest efficiency solar panels on the market today can reach almost 23 percent efficiency.
How the rated power is determined.
Factors that affect solar panel efficiency.
The solar panel is subject to 1000 watts of radiation per square meter.
Most pv solar panels are labelled with their peak power output this is the maximum power measured in watts which that panel can generate in full sunlight.
So solar power is now often the same price or cheaper than most other types of electricity and production has soared so much.