Why is Hydro electric power's EROI number so high?

[Mangosteen]

http://img.photobucket.com/albums/v61/GarySiegel/th_578px-EROI_-Ratio_of_Energy_Returned_on_Energy_Invested-_USAsvg.png

[Terr]

@Mangosteen

http://img.photobucket.com/albums/v61/GarySiegel/th_578px-EROI_-Ratio_of_Energy_Returned_on_Energy_Invested-_USAsvg.png

Tiny, tiny pic.

[Fubaya]

@Terr

Tiny, tiny pic.

Here, I fixed it.

[Duckster]

@Fubaya

Here, I fixed it.

Too blurry.

How about just linking to the source?

[Snarky_Kong]

Energy return on investment

[Duckster]

A cited article from oildrum.com

In summary dams can have very high EROI and have the potential to produce a moderate amount of additional, high quality electricity in the developing world, but are often associated with extremely high environmental and social costs. Many authors see run of river hydropower as the future because it does away with massive relocation projects, minimizes the effects on fish and wildlife and does not release any GHG emissions (because there is generally no reservoir) while retaining the benefits of a clean renewable cheap source of energy. On the other hand the relatively low power density available in run of the river projects relative to the high heads made possible with a dam limits the potential of this approach.

[Terr]

Ok - I saw the graph - why are you surprised that the ratio is very high for hydro? Yes, building a dam is very energy-intensive, but afterwards what you have is basically free energy for decades.

[iamthewalrus_3]

Because the sun does all the work.

[leahcim]

@Terr

Ok - I saw the graph - why are you surprised that the ratio is very high for hydro? Yes, building a dam is very energy-intensive, but afterwards what you have is basically free energy for decades.

And the dam is actually a very small part of the total mechanism. The bulk of the “energy collection” apparatus is the watershed that drains into the river you’re damming up. Essentially you have a gigantic machine that collects gravitational potential energy from rainwater, but you only have to build and maintain a tiny part of it.