If you are finding your solar panels have a low Peak Output, much lower than the nominal kWp output that they are rated at then the most likely cause is temperature. PV Solar panels are less efficient the hotter they get and their rated output is measured at 25C. It is very noticeable that on a cloudy day the output can peak at very high levels, close to the maximum rating of the panels.
For some mixed sunny/cloudy days in April we got 3kW peak output from our 3kWp solar panels when the sun came out from behind a cloud. For consistently sunny days during May the daily peak has been far lower at around 2.3kW.
|Solar panel low peak output on hot days|