Not sure, i could try to figure it out by my bill. I do know that it dont really matter because mexico is on a rated scale where the more you use, the more you pay per kw. If you really use the ac and get your meter up there, the rate per km goes up!
From what I remember, there is a three tier scale for residential use with a higher cost per kwh for each tier. If your consumption is low, you stay in the first tier. Each tier has a maximum kwh limit, spilling over into the next tier with increasing consumption. I believe there is a discount during the summer months.