[liquidise]

tldr: If global energy usage grows at 2% every year, and we generate 1% of the total demand annually with tidal energy, the Earth's rotation will cease in ~1000 years.

While i won't dispute that tidal energy is not truly sustainable, at least not in the way solar appears to be, i think we can agree that in the short team (a few centuries) cargo ships saving fuel would be a net positive with no measurable impact on the rotation of the planet.

Edit: after some more napkin math, i have a hard time taking this paper seriously at all. It appears to suggest that the available tidal energy would remain constant throughout this process? Also, 1.02^1000 equates to a roughly 400 million factor increase in the current energy demands of the planet. That's not something i'd expect such an advanced civilization to be trying to generate out of some waves.

[HPsquared]

I think the general lesson is that 2% annual growth - of anything - is not sustainable for long.

[cryptonector]

Or even 1%. Neither is shrinking continuously.

None of this is to say that we're at a maximum.

[kurthr]

The rule of 72 is useful. It would give roughly doubling every 35 years for a 1000years means 28 doublings or a bit over 256million x increase in power usage. Only off by ~50%.

I'm guessing that would put the population over a quadrillion, as well, with efficiency increases.

[HPsquared]

Can also think in terms of half-life.

For example at an inflation rate of 2%, that rule of thumb means the value of money has a half-life of 72 years.

[mjan22640]

A day needs more than 24h anyway.