What happens to electricity generated in solar panel when no load is connected?
There is no &quot;electricity&quot; produced when the panel is disconnected from a load.  For it to be actual electricity there must be both voltage and current.  With the load disconnected you have voltage (i.e. potential) but no current. Since the charge carriers liberated by the incoming light energy have nowhere to go, an equilibrium is developed in the panel.
So where does the energy go?  It becomes heat energy in the panel which is ultimately radiated or conducted away.  If you were to take two identical panels, one connected to a load and the other one not and place them next to each other, the disconnected panel would be hotter than the connected one.  Likewise, if you checked the temperature of the loaded panel and then disconnected the load, you'd see its temperature rise until a thermal equilibrium is reached.
When loaded, some percentage of the light energy is converted into an electric field which then is able to flow through the load.  Since we have an ongoing conservation of energy here, there will be a corresponding reduction of heat energy for the amount of electrical energy produced by the panel.