When a grid tied inverter is sourcing electricity into the grid from an on site power source, such as a photovoltaic panel, what is the loss in efficiency for a standard household if they are sinking an equivalent resistive load as the PV panel is sourcing. More specifically, if a house is sinking 1KVA of resistive rated incandescent lighting, and the PV panels are at the same time sourcing 1KVA actual energy into the system, what is the loss of efficiency because the lights are experiencing higher voltage than the grid line voltage, and how do you calculate the loss, does it depend on the parameters of the transformer (pole pig) feeding the house, and are there any universal generalities?