I think we have discussed this before!

Hydro just doesn't have a high enough energy density. Hoover Dam, one of the largest in the world, only produces about 1500MW of power, and it can't do that all the time (because there isn't enough water). Hyrdo power is great for "peaking" generation -- generation when you need peak bursts of power like on really hot days. It isn't good at steady-state production. Hyrdo gets the energy from the altitude drop of water (density x height x gravity = potential energy). To get power from this drop, they store up huge amounts of water behind the dam and release the water in bursts when they need the power.

If you run a hydro plant all the time, you are limited by the river's mass flow rate times the altitude drop, which probably isn't going to be anywhere near the 1500MW. The reservoir is the battery that allows you to store up potential energy and dump it quickly (power is work per unit time).

Where I live there is one major metroplex (Minneapolis) of about 2.5 million people and a surrounding area (mostly rural and a couple small cities) of another million. These 3.3 million or so people are served by an electric company with quite a few power plants:

15 Coal Plants 8,119 Mw
17 Natural Gas Plants 4,535 Mw
2 Nuclear Plants 1,665 Mw
27 Hydro Plants 495 Mw
7 Oil Plants 167 Mw
3 Refuse-derived (RDF) Plants 67 MW

You can see how small a contribution the Hydro is, even though they have way more hydro plants than anything else. Look at those numbers, you just can't compete with the energy density in fossil fuels (except with nucelar).

I was with a friend of mine (a former Apollo engineer) and we were watching a train go by. It was a coal train and we both started counted the number of cars. We had both done this since we were kids. The train had 115 cars. We laughed about it and then my friend told me an interesting thing.

He asked me if I knew that trains in the US had to be 1 mile long or less to fit between switches. That means that a train full of coal won't have more than 117 cars, *each* of which generally carries 240,000 lbs. of coal. My friend let this staggering amount of coal sink in and asked me how long I thought the entire train load would "keep the lights on in Minneapolis?" Think about it for a second, he was talking about the 3.3 million people served by (at that time) Northern States Power.

We went and looked up the energy density of soft coal (all of the hard anthracite coal is gone) and figured it out.

2.1 hours.

Imagine that much coal coming out of a coal mine every 2 hours, then multiply that by all of the cities in the world. This number isn't even for a city like LA or Houston, NYC, Chicago, Las Vegas, etc. Just a medium sized midwestern city.

I agree. We need nuclear. As troublesome as fission is, we need it until we can get fusion working. Most people just don't seem to understand how urgent this issue is. If there are 300 million people in the US alone, that means we need 100 train loads of coal every two hours! About 1 entire train load of coal per minute, just for the US.

Jim