Sustainable Energy – Class Notes

Week 5

Betz’s Law of turbine efficiency

The first time I heard it, I thought we were saying “Bete’s Law” as in French for “Fool’s Law”. But it turns out it is quite clever – basically, once a body of water moves from side A to side B, it is now in the way when you want to move the next body of water. Like somebody who walks through a doorway and then just stops dead the minute they get inside.

It doesn’t have to be water – could be air, some other gas/liquid mixture, gravel – pick your fancy. Same principle.

Gordon Dam, Tasmania

Monica gave an excellent presentation on hydropower later, which put the turbine back in context for us. The thought of flooding miles of natural preserves in Patagonia is chilling – especially given so many less permanent options and the increasing efficiency of electronics and other energy users.

I first heard about the destruction dams cause through Douglas Adams and Mark Carwardine’s “Last Chance to See”, which is a touching but hilarious account of their attempt to document species on the verge of extinction. Adams gives a talk on it here and talks at length about the freshwater dolphins of the Yangtzee River, now long since victims of the Three Gorges Dam. Monica’s presentation reminded me that this will just keep playing out anywhere people consider themselves owners of land but not caretakers.


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