No EV currently in production offers V2G (Vehicle to Grid) as yet.
The onboard AC EVSE charger is not bi-directional and can only sink power from your house AC supply and cannot source it back again. Therefore to achieve this you will need access to the HVDC link and will need a suitable inverter to create a 50Hz sine wave from the vehicles (variable voltage depending on State of Charge (SoC) battery). The problem with this is that all EV’s disconnect their HV battery when turned off (for safety) and if you short cut the system at take out power when the car is “turned off” then that power will not be counted by the Battery Management System and hence it will report an incorrect SoC, leading to all sorts of knightmare-ish problems!
Far better, as suggested, to buy a secondhand battery pack, unless you have a really massive solar array then actually you don’t need that much capacity, and use an off-the-shelf solar inverter to generate the AC output. The biggest issue is how to integrate that AC feed into your current grid fed AC feed. Current rules require standalone inverters etc to turn off on a loss of grid voltage in order to protect line workers etc from back feeding making parts of the system un-expectidly live. One option would be to install a second AC ring main in your house, for certain high consumption items (like washing machines etc) or to run say the lighting off the system (low load but long hours). That inverter could also be programmed to try to minimise incoming current from the grid supply (ie measure current at your incomer, and increase it’s output to try to get that incoming current to zero)