We have a 4.4kW rated PV array but it produced that peak power today, two days after the equinox. They were installed at the last equinox in September and produced about the same then.
How are panels rated with respect to the amount of sun we can expect to get in the UK? Looks like they will easily max out our 5kW inverter in the summer, probably even in April.
They're rated at "Standard Test Conditions" - a specific solar irradiance level, temperature, etc. Basically these are just lab figures to allow you to compare different panels, and actual output may exceed this if the panel is new and it's cold.
Your 5KW inverter can handle 7.5KW of incoming solar - it just can't output more than 5KW of A/C power. If you've got a battery it can be charging that at the same time as outputting 5KW of A/C.
Seems like the standard irradiance must be about the same as clear skies at the equinox then. Roll on summer!
Depends where in the world you are, but also the temperature at the time as well as a fair few other factors.