If a solar panel is rated for 300W how much power will it produce?
First of all, no it will not produce 300W all of the time. This rating is known as STC (Standard Test Condition) and it is calculated within a laboratory setting under ideal conditions, which realistically are not always possible with dust, shade, clouds and other factors that will affect your solar panel. A more realistic rating is the PTC (PVUSA Test Condition).
For example, the PTC rating for the Peimar 300W Model SG300M is 269.7 watts. Peimar produces high-quality, high efficiency (18.33% module efficiency for the SG300M) solar panels.
Solar Cell Temperature
2.2 mph (1 m/s)
Aside from the lower PTC rating, solar panels generate power at different rates throughout the day. Thus, the way the panels are installed is crucial to how much energy they will output. Note that solar panels usually stay facing in one direction, and thus there’s a specific window of time when the sun hits them to produce energy. For example, your 300W solar module might be producing 100W in the early morning, and then go up to 269.7W for a couple hours around noon. If there’s shading, this causes even greater losses, so make sure your panels are installed correctly; see our Obstruction Shading Calculator.
Your PV panels will also generate different amounts of energy throughout the year, for example, you can generally expect more power produced in Summer versus Winter. Where you are located geographically also affects how much much energy is available to be harvested by your 300 watt solar modules.
The solar panel’s peak comes when the weather conditions are ideal and the sun is pointed straight at the panel surface. To calculate how much your system using 300 watt solar modules will produce throughout the year, there’s an easy calculator you can use (and we made a quick video on how to utilize it).