Quote:
Originally Posted by sjastro
I doubt that very much given that his calculation for the energy to lift 28 Gl of water is based on the formula for gravitational potential energy
PE= mgh.
I'm pretty sure he had the same idea in mind with rain drops otherwise changing the subject from rest mass energy to gravitational potential energy midstream in a thread seems quite unusual to me.
But then again what do I know....
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Eratosthenes' first post was simply a claim about the amount of energy in a single raindrop, with no other context:
...and yet a single rain drop at rest can potentially unleash about 9,000,000,000,000 Joules in energy
I took it as self-evident that this referred to the potential fusion energy, as this is a totally unfeasible amount of kinetic or gravitational potential energy for a single raindrop. (But my later "back-of-the-envelope" calculation suggests a more credible figure is actually about 9 GJ not 9 TJ.)
I then made the comment that the useful stored energy of 18 TJ in the Wivenhoe Pumped Storage Hydro Scheme is "about the same" as Eratosthenes' figure for a single raindrop - and yes, the stored energy of Wivenhoe pumped storage is simply the gravitational potential energy of 28 GL of water sitting 100 metres higher than the main dam reservoir.
However, it seems that it would actually take the fusion of the hydrogen in about 1,000 raindrops to liberate the same amount of energy - so it's actually a one-shot espresso cupful (50 mL), rather than a single raindrop ....
Even with these "back-of-the-envelope" figures, it's pretty obvious why nuclear fusion of hydrogen is such an attractive source of energy for the future.