I have an inverter and a battery 20 Amperes.Daily sun shine approx. 7 Hours.Do I need to buy anything or should I connect the solar panel to the Battery direct?
No, don't connect the panel directly to the battery. You need to isolate the solar panel charging output from the AC-powered charger. A couple of high-current diodes arranged with their anodes connected to the charging sources in the positive supply line will allow either the charger or the solar panel to lift the voltage high enough to charge the battery, albeit with about 0.6 volts dropped across the diode. Both cathode ends would be connected to the battery. This arrangement allows a positive current to flow from either or both charging sources at the same time, although in practice, one will generally be higher than the other. Also, if the AC charger's voltage is significantly higher than the solar panel, the charger may always charge the battery. You would need to regulate its output to be slightly lower than the solar panel when it's near it's minimum useful operating voltage. (note that the 0.6 forward bias voltage on the diode might prevent the solar panel from completely charging the battery if it has any voltage regulation on its output)
connect the solar panel to the Battery direct during the day time that's how it works in ALL situations !
