# Power: hydroelectric vs. standard

Maybe that thread title isn’t the most descriptive ever. What I’m wondering, in these days of energy crises, is how hydroelectric power compares to your more standard oil-based power. Another way to put this would be: how many barrels of water does it take to equal the energy output of one barrel of oil?

Well, I’m not sure about the barrel/barrel comparison, but 1 barrel of oil will produce more electricity than a barrel of water. However, both have virtually the same efficiency rating, of ~30%. (30% of the chem energy of the oil/coal goes to electricity, while 30% of the mechanical energy of the moving water goes to electricity). At least, this is what I understand so far. If you ask this again in 5 months, I’ll be able to give you a MUCH more detailed answer. I just started an EE class on Power Systems.

Jman

Despite the fact they have the same efficiencies, don’t forget the fact that Hydro is free.

Before you jump the gun, I mean free as far as fuel. Of course we need to spend money to build the thing. Geesh.

A barrel of water doesn’t have energy (per se). Hydro electric energy comes from the pressure differences on both sides of the dam. The pressure is directly proportional to the difference in the surface levels on both sides of the dam. If you could construct a dam 2400 miles high with the surface level behind the dam to match, then the energy output of one barrel of water flowing through the turbines would be equivalent to one barrel of oil. Even a dam as high as Hoover Dam (700 feet) takes about 20 thousand barrels of water flowing through it to equal one barrel of oil,

Efficiency and all other factors aside, if you’re in a desert or some other area where you have no significant water sources, hydroelectric power isn’t worth a shit (I couldn’t bring myself to say damn). That’s a pretty major drawback.

patiently waiting for Anthracite to check in on this one

First, let me re-state something that has been said before:

OK. Got that out of the way.

bizerta has it right. You cannot do any direct comparison, because the water itself contains no energy. It is the change in potential energy, which is related to the height of the dam, that gives the water the “energy” as you percieve it. Thus, the short answer is that the water has somewhere between no energy at all and nearly as much as the oil - provided you have a dam that goes into outer space (I did not do the calcs myself, so I hope bizerta is correct…)

Also - hydroelectric power is not “free” per se. It is certainly cheap, but there are significant operations and maintenance costs associated with the dam operations. Also, the dam cannot be operated at all time of the year, due to both water reserve and environmental concerns (I just spoke to the Glen Canyon dam operators about this a few weeks ago, in Page, AZ)

I guess the real question you are asking is how cheap is hydroelectric power overll compared to other sources of power. Well, the short answer is that it is the cheapest source of power, provided that it is available and you can use it.

[nitpick] Umm a dam that goes into outer space? Erm, wouldn’t that water be defying gravity? [/nitpick]

Love ya Anth.

While there is no monetary cost for the water, there is ecological costs associated with hydroelectric power. Since hydro can be brought online nearly instantly for the morning and evening peak power demands, the water levels downstream of the dams fluctuate a great deal.

In the Grand Canyon, for instance, the water levels rising and falling has removed most of the sand from the little beaches. I believe they have made arrangments to reduce the fluctuations and preserve the ecosystems.

This isn’t to say that there isn’t a place for hydro, but it does have a different set of costs.

Hey thanks!

But there’s still plenty of gravity at 2400 miles to keep the water down. What would happen, I fear, is the water would boil off into space due to the very low pressure. But we are talking silliness here anyhow.