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Tidal energy is not renewable

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Re: Tidal energy is not renewable

#121

Post by littlestymaar »

gnfargbl wrote: post #93
wcoenen wrote: post #27

I'm not sure the author realized this, but they're actually making a statement about how crazy exponential growth is. Not about the sustainability of tidal power. This becomes obvious once you look closer at what that 2% growth rate (as assumed in the post) implies. Our global energy consumption in 2008 was estimated to be 474 exajoules. The total energy received by the earth from the sun during a year is about 5 mil…

Human energy use isn't going to continue to grow exponentially for the next 500 years. The world population is predicted to peak about 30% above where it is now and then fall back -- maybe to 7 billion people sustained. We seem to need about 200 GJ per person to be really happy [1], so let's assume 300 GJ per person. We should be able to get by, happily, on 2000 EJ per year sustained. By your figures, that's less tha…

> We should be able to get by, happily, on 2000 EJ per year sustained. By your figures, that's less than 1% of what the sun provides.

Then at that rate we'd have 100,000 years of Tidal energy available even if we used it for the totality of our energy needs (and 10,000,000 years if we use it for 1% of our needs as taken in the paper). And that was basically the point of the person you're responding to: it's not so much that tidal energy is non-renewable, the problem is that the paper assume exponential consumption growth, and exponential growth is unsustainable no matter what.

Re: Tidal energy is not renewable

#122

Post by pdonis »

qayxc wrote: post #77
pdonis wrote: post #15

Earlier quoted context omitted.

To the Moon's orbital angular momentum. As the Earth's spin slows, the Moon moves further away and its orbital angular momentum increases.

Incidentally, this also causes the tidal effects to weaken to a point where calculations show that tidal locking will actually never happen.

What calculations are you referring to?

Re: Tidal energy is not renewable

#123

Post by [deleted] »

giantg2 wrote: post #119
wcoenen wrote: post #27

I'm not sure the author realized this, but they're actually making a statement about how crazy exponential growth is. Not about the sustainability of tidal power. This becomes obvious once you look closer at what that 2% growth rate (as assumed in the post) implies. Our global energy consumption in 2008 was estimated to be 474 exajoules. The total energy received by the earth from the sun during a year is about 5 mil…

"Think about that: if energy consumption growth continues at the current pace, then in 500 years we'll either be using ALL solar energy received by the earth (leaving none for the biosphere), or we'll have figured out some magic technology to produce 5 million exajoules of energy per year." So nuclear?

[deleted]

Re: Tidal energy is not renewable

#124

Post by empath75 »

wcoenen wrote: post #27

I'm not sure the author realized this, but they're actually making a statement about how crazy exponential growth is. Not about the sustainability of tidal power. This becomes obvious once you look closer at what that 2% growth rate (as assumed in the post) implies. Our global energy consumption in 2008 was estimated to be 474 exajoules. The total energy received by the earth from the sun during a year is about 5 mil…

While this is true, a lot of economists build their models assuming unlimited exponential growth. It does seem that we're going to hit a brick wall in growth in a few hundred years if that doesn't stop. There seems to be some idea that we can continue exponential growth if we can just figure out renewable energy and we can't. There is _no such thing_ as renewable energy in a regime with unlimited exponential economic growth.

Re: Tidal energy is not renewable

#125

Post by pmontra »

RetroTechie wrote: post #104
blake1 wrote: post #32

The single most important assumption in this paper is that energy consumption will increase by 2% per year. This kind of exponential growth leads to outlandish estimates for the amount of tidal energy that society will demand. Energy consumption has decoupled from population growth rates and economic growth. How much energy will we consume in 1,000 years? Most projections of the population have it stabilizing at arou…

> The single most important assumption in this paper is that energy consumption will increase by 2% per year. There's a 2nd big assumption: That tidal energy extracted is additional Earth's rotational energy loss above what Earth does by itself. According to the paper, tidal energy is dissipated through friction between ocean water & the seafloor. This dissipated energy subtracts from Earth's rotational energy. And s…

Your observation seems to make sense.

Intuitively, if we extract energy from the tides, tides will be less tall and the speed of water will be smaller. Ocean currents will slow down too.

What I don't know is, less friction on the seafloor means that we would actually make Earth slow down less faster than it would do if left alone?

Re: Tidal energy is not renewable

#126

Post by DFHippie »

exitheone wrote: post #37
idlewords wrote: post #4

Every energy source becomes renewable on the right time scale.

That's not actually true. The conditions for the formation of coal and oil may likely never happen again because the bacteria to break decompose trees did not exist then but exist now, making oil formation impossible because trees decompose now. Unless they all die out, we won't get any new oil ever.

I'm curious about this. We certainly won't get any more coal, but a whole lot of carbon gets subducted into the mantle regularly. Some gets turned into diamonds. Some gets blown out of volcanoes. Is the oil we pump out of the ground produced directly in the continental crust or is it generated from some of this carbon subducted with oceanic crust that has been transformed by some process and then made its way back into continental crust?

I'm lazy, so I'm hoping some geologist will stop by and educate me.

Re: Tidal energy is not renewable

#127

Post by JamisonM »

littlestymaar wrote: post #101
WillPostForFood wrote: post #63

Earlier quoted context omitted.

Any sort of straight line extrapolation is useless. Look at the US energy consumed per capita, flat or declining for the last 50 years. Other parts of the world will follow as they develop. Likely the same for population growth. http://insideenergy.org/wp-content/uploads//2017/01/historic... from: https://insideenergy.org/2017/01/12/energy-explained/

> Look at the US energy consumed per capita, flat or declining for the last 50 years. This doesn't account for all the “imported energy” that comes when you outsource your industrial production abroad. Granted even then the energy consumption doesn't increase exponentially anymore, but it's not flat either.

Do you have some data to back up this assertion? For me what I see in the numbers is that Chinese domestic quality of living improvements correlate better with increases in energy consumption than does US imports (or Chinese exports).

What is also interesting is that China's "energy intensity" - energy used per unit of GDP is pretty flat, if wealthier nations were exporting energy demand via imports I would expect that number to be climbing. I am at a bit of a loss as to how to determine exactly what is going on TBH.

Re: Tidal energy is not renewable

#128

Post by [deleted] »

giantrobot wrote: post #90
eldaisfish wrote: post #79

Earlier quoted context omitted.

the rest of the world still has to catch up to these levels. Granted, they won't get to the absurd wastage levels of north america but they will continue to consume more energy. Just looking at the energy levels in one country doesn't tell you much.

Developing countries will increase their energy usage but have the benefit of buying things from developed countries. As we've seen developing countries today have been able to jump right to modern technology for infrastructure. They didn't need to build massive lines of analog telecommunications, they just jumped right to cellular and satellite technology. They can jump right to solar and other renewables as they el…

[deleted]

Re: Tidal energy is not renewable

#129

Post by crazygringo »

MichaelDickens wrote: post #86
crazygringo wrote: post #58

Tons of comments here highlighting that 2% annual growth rate in energy consumption is ludicrous. But so what if we made a more reasonable assumption that annual energy usage will stabilize at, say, 5X of what it is currently, and the (unreasonable) assumption that we get 100% of that energy from tides. Then how much of a rotational slowdown do we get after 1000 years?

According to the paper, tidal energy has a total capacity of 10^29 Joules, and current global energy consumption is 10^21 Joules per year, so if we converted 100% of current energy consumption to tidal energy and didn't increase it at all, it would last 10^8 = 100 million years (rounded to the nearest power of 10). Equivalently, after 1000 years, we'd see a rotational slowdown of around 0.001%.

Thanks so much. That feels much more in line with intuition.

So maybe not technically renewable, but many orders of magnitude more renewable than e.g. fossil fuels...

Re: Tidal energy is not renewable

#130

Post by [deleted] »

wcoenen wrote: post #27

I'm not sure the author realized this, but they're actually making a statement about how crazy exponential growth is. Not about the sustainability of tidal power. This becomes obvious once you look closer at what that 2% growth rate (as assumed in the post) implies. Our global energy consumption in 2008 was estimated to be 474 exajoules. The total energy received by the earth from the sun during a year is about 5 mil…

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