Just guessing here - I'd say betwen 100-200 Watts. I think thats about 72 kilowatt hours per month.

The answer is not simple. Firstly, "cell tower" does not equal "cell site". There may be several carriers' sites operating from the same tower, each with its own powerful radio and signal amplification equipment. Secondly, the electricity load varies throughout the day, depending on the call volume and data rates handled by each site. Downtown sites see their highest usage during office hours, and especially at lunchtime; freeway "corridor" sites peak during rush hour. Rural sites covering large areas may handle relatively few calls for much of the time. The "resting" load of a site (when there are no calls in progress) can be as low as 20 W. Finally, the number of radios and amplifiers in a site determines its range (its "coverage") and the maximum volume of calls it can handle (its "capacity"). Some sites, especially in busy urban areas, are enormous, housing as many as 12-24 radios per sector for GSM and 1-3 per sector for W-CDMA, for a total of 39-81 radios, plus associated amplifiers and HVAC units for cooling. These sites may need a 400 A AC feed (or more) and draw a whopping 30-75 kW at peak use. More typically, a cell site runs at an average of about 0.5-3.5 kW, so total electricity usage in a month would be between 350 kWh and 2500 kWh, or from about half-a-house to three-times-a-house.