In the LCOE equation, the nominator includes C_ann,tot, which reduces by any revenue due to grid sells. And in the denominator, E_served is taken into account. In this way, the COE are double effected by any grid sells. Is this really what is meant so show? Isn't that a double bonus for energy sold? We think the COE are displayed too low.

Yes, you are correct in saying the "grid sales" are already accounted for in the numerator. However, that is the revenue from grid sales. Because that revenue stream has been included in the total cost (numerator), we also need to include the amount of energy from that revenue stream in the total energy (denominator).  
 
The grid sales are not being double counted, because the value in the numerator is a cost rate ($/yr) while the value added to the denominator is an energy rate (kWh/yr).