What is the level of danger you think this poses ? - that will depend what else is on that RCD, and perhaps on the power level and installation method of the PV inverter.

Are other things wrong?  - Are the  isolators and so forth suitable, is the overload protection appropriate etc.

Are there also batteries as part of the installation ?

Mike

What is the level of danger you think this poses ? - that will depend what else is on that RCD, and perhaps on the power level and installation method of the PV inverter.

Are other things wrong?  - Are the  isolators and so forth suitable, is the overload protection appropriate etc.

Are there also batteries as part of the installation ?

Mike

Are you thinking along the lines of DC currents present and masking fault currents, preventing the RCD from operating?  

If the inverter is capable of DC feedback