[dogtimeimmortal]

Thanks for this! Something has always bugged me when I hear about big plans for tidal energy.

TLDR, the 1000 year estimate is is derived from the geometric series proof(i needed a refresher). Wolfram explains it pretty well: https://mathworld.wolfram.com/GeometricSeries.html

...then i needed a refresher on exponents and logarithms: https://wou.edu/mathcenter/files/2015/09/Exponents-and-Logar...

It's good to do the math and think about the big picture sometimes. ;)

p.s. i tend to feel somewhat skeptical about a lot of renewable projects i read about in the news. And even if the math all works out and it really IS The Best Solution i cant help feeling we are ignoring the elephant in the room(population growth). Maybe human beings should start preparing themselves to live with less(and be happy with that).

[ComputerGuru]

Population growth is effectively over.

[Cthulhu_]

Even if that were true (and it won't be for another 5-6 decades using current predictions at least), energy consumption is anything but. And if there is a risk of electricity usage plateauing, they'll just find something new like training AI models or spinning GPU's to churn out digital money (where said churning is entirely artificial).

[dogtimeimmortal]

Little addition, couldn't resist sry:

After reading a bit of the comments thread above, i couldn't resist adding a bit more.

> The single most important assumption in this paper is that energy consumption will increase by 2% per year.

Quick reality check: 1.02^1000years = 398,264,652x increase! This could potentially be an unrealistic projection. Let's consider what we know from the article(and google).

Here's a few numbers pulled from the article for reference: ~1.73 x 10^20 J tidal energy lost per year naturally 5.67x10^20 J was the total global energy consumption in 2013(10^18 is 1%)

So 398,264,652 x 5.67x10^18 J = 2.258 x 10^27 J! That does seem like a lot. In comparison total sunlight absorbed on earth's surface each year is roughly 3.85 x 10^24 J.[1]

> It might also be that tidal energy extracted by humans, comes out of some fixed 'budget'

So lets compare that to what is already being consumed and think about what amount of energy generated might be realistic. Top google result tells me global energy consumption is about 5.80 x 10^20 J2 these days.[2]

I guess the next question is what would be a realistic upper limit for the amount of energy we could harvest globally from the tides? Referencing the Stanford article again, we have an estimated annual energy loss of 1.73 x 10^20 J total from natural friction of the tides globally. Is it realistic to think we can harvest an equivalent amount of energy for the grid? I wonder what sort of impact a turbine project that size would have on the earth? Is it even possible? For sake of being rational, let's say we think a network of turbines 1% of that size(10^18J) is potentially possible. How many turbines might you need to make for something that size?

So lets take the kite-turbines from the article at the top. Each one of the produces 1.2MW. Does that mean it produces 3.78×10^13 J annually? Or is it closer to half that(1.89×10^13J)? In a 10^13 J ballpark we would need to produce about 10^17 to approach our max limit 10^20 J harvested. Correspondingly a project 1% the size still needs 10^15(a quadrillion) of these turbines globally. That seems like a lot and it just sort of seems in my mind(maybe i'm wrong) that there would be some sort of environmental impact. Also, now that you have shrunk your project the total energy produced is now a fraction of 1% of the current total global annual energy consumption, and grows more insignificant every year consumption rises.

Not sure I agree that population growth is over, but isn't it true that energy consumption per capita is also increasing? Either way I think we still have the realistic expectation of continued 2% growth in global energy consumption for the next few decades at least, doubling every 35 years. Unless we can find ways to harvest larger quantities of tidal energy without breaking the ocean it just doesn't seem like a silver bullet to me as far as climate goes. Assuming we could harvest 25% the quantity of what occurs naturally, that only gives us 0.4325x10^20J annually, which is only 7% current global consumption - in 35 years that number will only equal 3.5% of the total consumption. I guess it's a question of how much you want to screw up the environment in order to save it.

TLDR, saving the planet with tidal energy seems kind of misrepresented imho. Build wooden megaliths instead. ;)

[1] https://www.ucdavis.edu/climate/definitions/how-is-solar-pow...

[2] https://www.theworldcounts.com/challenges/climate-change/ene...