For each individual solar panel brand/manufacturer, there will be specific characteristics that will affect the whole solar photovoltaic system performance. To be more specific, we mean by the word "performance"; the output electrical power we can get from the solar system "the harvest".
Based on real testing procedures made be the solar specialists/experts, there will be approx. 10% difference in solar panel output power based on its own properties, which are represented by 3 major factors/specifications as following:
With the increase of solar panel power inverter temperature for each 1 C degree over the 25C, the max output power will be decrease by a certain ratio. And to recognize how the temperature factor affects the solar panel performance, suppose we have 2 solar panels with 2 different temperature coefficients, one of them is -0.3% / C and the other is -0.4% / C. So, at hot summer day with solar panel temperature reaches about 75 C degree, there will be output power loss for the first solar panel by (75-25) * - 0.3 = - 15% & for the second solar panel by (75-25) * - 0.4 = 20%.
You see, how temperature coefficient increase will reduce the performance of the solar panel and the whole solar system accordingly! That is why it’s very important to choose the best solar panel brand/manufacturer which can perform effectively in high temperature conditions.
Light intensity factor:
For each solar panel brand/manufacturer, there will be rated power listed on solar panel inverter name plate like, 400W, 300W, 250W, etc. This power capacity refers to how much power "watt", we can get from this solar panel at 1000W/m2 solar irradiance, but in reality, this 1000W/m2 irradiance can exist only in clear summer day at noon, however over the remainder of the day time, this powerful light is not exist, so the output power of the 400W solar panel will not be actually 400W at 700Wm2 or 600W/m2 irradiance, it would be 300W or less. So, choosing the best solar panel brand/manufacturer which can perform effectively in low light intensity conditions will make significant difference in the whole photovoltaic solar system performance.
This factor refers to how the solar panel inverter output power changes with its age. Generally, after certain number of years, the solar panel output power will be reduced. Some solar panels brand loses approx. 10% of its power after 10 years and some others lose approx. 5% after 10 years age, etc. So, it differs, and not all solar panels brands are equal, that why we need to choose the best lowest degradation ratio solar panel brand.