In order to produce one megawatt hour of power approximately one million gallons of water have to flow through a turbine if the water has approximately three hundred feet of water above it. The Hoover Dam is 726 feet tall so for this dam to produce 2080 megawatts approximately 860 million gallons of water have to flow each hour if the dam is full. As the dam is not full due to the drought, the turbines are not capable of producing their full nameplate capacity of electric power.
The Hoover Dam is a awesome structure but it really only provides a minute fraction of the power consumed in the USA. Also if we were all to buy Tesla Electric Motor Cars we could not charge too many of these cars simultaneously. The Tesla Roadster has a battery storage capacity of 54 kilowatt hours and charges in 3 hours. This means the Tesla draws 18 kilowatts of power. With a capacity of 2080 megawatts or 2,080,000 kilowatts the Hoover Dam could simultaneously charge 115,555 Tesla Roadsters. The charging is accomplished in 3 hours and the Tesla is good to go for 4 days if you drive 50 miles a day. Performing the requisite math in the 4 days you could charge 32 times 115,555 vehicles or 3.698 million cars provided it takes no time to hook-up the next series of vehicles to their chargers. Unfortunately, this is fewer vehicles than we have in the Bay Area, therefore the entire output of the Hoover Dam would not be sufficient to power all the vehicles on the road in the Bay Area even if they were Tesla Roadsters with state of the art batteries and power control systems. http://www.teslamotors.com/
One cannot fault gravity for the limit of how many vehicles the Hoover Dam can power. Rather we should fault ourselves for driving vehicles that weigh 15 times what we weigh and that we drive all over the place to work, shop, or enjoy some entertainment. Even if we moved to Jupiter, a planet that experiences 2.54 times the gravity on earth, we would still not be able to propel many more vehicles from the power generated by a Lake Mead on the surface of Jupiter. Yes we would generate 5,283 MW from the same lake on Jupiter but alas our cars and our bodies would also be 2,54 times as heavy. The power required to propel a car does have some relationship to the mass but is mostly related to the energy required to overcome air (atmospheric) resistance. No one has been able to measure the atmospheric pressure of Jupiter so I cannot tell you the range a Tesla Roadster would have on that planet. I can tell you it would be better to go to Mars with our Tesla Roadster and our Lake Mead. The atmospheric pressure on Mars is only 1% that of earth so atmospheric resistance will be negligible. Gravity on Mars is 38% that of gravity on earth. Our Lake Mead would only generate 790 megawatts but we would all weigh 62% less on Mars. Hummers would be fuel efficient on Mars due to the low gravity and very low atmospheric resistance. I will call the CEO of GM tomorrow and advise him where he can sell all of his spare Hummers. As for his spare Saturns I have no idea what he can do with those. http://coolcosmos.ipac.caltech.edu/cosmic_kids/AskKids/mars_gravity.shtml