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Tidal energy is not renewable

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Re: Tidal energy is not renewable

#211

Post by ChuckMcM »

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…

Extrapolation is always a bad thing :-). That said, this guy has some interesting thoughts. Of course he misses out that if you pump the tides you can speed up the rotation of the earth and thus "renew" the lag (think moving your legs while swinging).

Similarly solar isn't renewable because at some point the Sun is going to run out of hydrogen, and if you made a dyson sphere to capture all of the Sun's energy you would wipe out life on earth.

Re: Tidal energy is not renewable

#212

Post by alwayslikethis »

kps wrote: post #197
FriedPickles wrote: post #23

Hmm so if we pump water to amplify the tides we can speed up the Earth's spin and get rid of the leap second.

We should draw tidal power until there are exactly 360 days in a year, to make the arithmetic nice, and incidentally give us 24 minutes extra sleep.

The other way of doing this is just pushing the earth a bit off its orbit. Better to do it in the other direction though to stop global warming. Let's make it 400 days instead.

Re: Tidal energy is not renewable

#213

Post by pcthrowaway »

dredmorbius wrote: post #153
uoaei wrote: post #3

Then technically neither is wind, since it slows down surface air currents and widens the effective boundary layer of the atmosphere. Technically-technically, no forms of energy "generation" (technically just conversion) are 100% efficient so something is always lost to heat. I guess the important question is, what is the net effect in changing that kind of energy into purely thermal energy?

No, wind is ultimately fed by solar energy and is driven by differential heating of Earth's atmosphere and surface. That is, there's a constant incoming energy flux. That's not to say that there isn't some maximum amount of available wind energy, or some maximum amount of energy that can be extracted from wind without causing other effects (even excepting, say, bird strikes and the like). But wind isn't "used up", th…

But capturing wind surely creates a local warming effect? I believe I read that somewhere. Enough wind energy could accelerate global warming.

Re: Tidal energy is not renewable

#214

Post by kbenson »

dredmorbius wrote: post #166
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 lesson that constant percentage (that is, exponential) growth cannot continue endlessly is the fundamental message behind the concept of Limits to Growth. That is, there exist intractable limits to growth , and that no matter how convenient it may be to pretend otherwise, humans ignore this fact at their extreme peril. Long-term ongoing economic growth, expressed as a constant percentage, is baked in to most curr…

> Long-term ongoing economic growth, expressed as a constant percentage, is baked in to most current orthodox economics and economic policy.

Whether it is or isn't, the optimal strategy for a nation is likely exponential growth until it can't, and then switch as quickly as can be done with the least problems.

Since nations are competing, and we're talking about exponentials here, the cost for cutting off exponential economic growth too soon is likely to become irrelevant to the future, which every nation is going to strive to avoid.

Re: Tidal energy is not renewable

#215

Post by strken »

Nition wrote: post #78
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…

Humanity needing that amount of energy seems obviously absurd, but then I suppose a CPU with 100 billion transistors seemed clearly impossible in 1960. Maybe a few hundred years from now, Internet archaeologists will find your comment as one of the first harbingers of the coming World Energy Crisis, much as we see the 1912 Rodney & Otamatea Times "Coal Consumption Affecting Climate" snippet today.[0] Then they'll fin…

I don't think it's impossible for energy consumption to scale to those levels, but presumably it can only happen in conjunction with massive changes (maybe orbital manufacturing? maybe we run server farms on Mars and do our futuristic energy-intensive computing there?) that invalidate the entire frame of the argument.

Maybe in 1950 people would have argued that soldering all those vacuum tubes would be too difficult, and they'd have been correct, but transistors and CAD changed the entire reference frame.

Re: Tidal energy is not renewable

#216

Post by Vecr »

caesil wrote: post #6
hirundo wrote: post #2

> ... if we were to extract the rotational energy just to supply 1% of the world's energy consumption, the rotation of the Earth would lock to the Moon in about 1000 years ... and most life on Earth could be wiped out. Important safety tip.

There's an award-winning sci-fi book with a tidally locked planet as its premise: https://www.goodreads.com/en/book/show/37534907

The City in the Middle of the Night by Charlie Jane Anders if the link does not work for you either.

Re: Tidal energy is not renewable

#217

Post by kbenson »

XorNot wrote: post #190
dredmorbius wrote: post #185

Earlier quoted context omitted.

The problem with this, or any other hypothetical "decoupled growth" argument is that, well, it's purely hypothetical. There's no evidence whatsoever that economic growth can be decoupled from resource, and most especially energy, usage. There are instances of increased efficiencies , which thanks to the Jevons Paradox increase overall resource utilisation (economically, efficiency is equivalent to a reduced price, an…

Conversely the people who argue against growth never have any answers they want to elaborate on. They have "well we can't have endless growth" and that's where the conversation stops. They never want to examine the consequences of that thought (no growth means we're into a zero-sum game) or whether they think we're even plausibly close to the limit (instead they want to have a proxy argument about environmental damag…

The optimal strategy now for unlimited growth and some future limit on growth bei g hit when there are competitors are likely the same. Take advantage of it as much as possibly for as long as possibly.

Given two countries where one lints it's economic growth and the other doesn't, if they're given another few hundred years before a limit is hit, which one is in a better place to respond when that limit is hit? Does the country that minutes itself even still exist as it did, or was it taken over by a stronger one (whether economically, militarily or culturally)?

Re: Tidal energy is not renewable

#218

Post by pyaamb »

dredmorbius wrote: post #152
btilly wrote: post #71

Earlier quoted context omitted.

A lot. Look up Hadley cells. https://groups.seas.harvard.edu/climate/eli/research/equable... Warm air rises near the tropics, rotating with the Earth. It then goes towards the temperate zone, still rotating with the Earth to form the jet stream. It then falls, creating the trade winds as it slows down. It then is sucked back towards the tropics, creating a reverse trade wind because it is only going as fast as the te…

Hadley cells determine wind patterns but not the energy content of the wind, to any appreciable degree, which comes from solar flux. Wind energy is solar energy once removed. Wave energy is solar energy twice removed (solar -> wind -> waves).

if we harvest wind do we still deplete waves?

Re: Tidal energy is not renewable

#219

Post by dredmorbius »

pcthrowaway wrote: post #213
dredmorbius wrote: post #153

Earlier quoted context omitted.

No, wind is ultimately fed by solar energy and is driven by differential heating of Earth's atmosphere and surface. That is, there's a constant incoming energy flux. That's not to say that there isn't some maximum amount of available wind energy, or some maximum amount of energy that can be extracted from wind without causing other effects (even excepting, say, bird strikes and the like). But wind isn't "used up", th…

But capturing wind surely creates a local warming effect? I believe I read that somewhere. Enough wind energy could accelerate global warming.

That energy is already present in the environment, as kinetic energy of wind, which will ultimately be reduced to entropic heat. A wind turbine doesn't affect that fact, though it may change the location at which the kinetic -> thermal energy transformation occurs.

The more likely impact would be of wind turbines removing sufficient energy from wind that thermal transport of the atmosphere itself is disrupted, though this would occur only within an immediate locale and at lower altitudes. Even very high turbines are only about 260 m (850 ft) tall.

The mechanism here would be a reduction in the distribution of solar heating within the immediate vicinity, similar to urban heat island effects.

And searching as I write this for "wind turbine heat island" I find precisely that mechanism described in this paper:

Wind plants can also impact local atmospheric conditions through their wakes, characterized by reduced wind speed and increased turbulence. We explore the extent to which the wind plants near an atmospheric measurement site in the central United States have affected their long-term measurements. Both direct observations and mesoscale numerical weather prediction simulations demonstrate how the wind plants induce a wind deficit aloft, especially in stable conditions, and a wind speed acceleration near the surface, which extend ~30 km downwind of the wind plant. Turbulence kinetic energy is significantly enhanced within the wind plant wake in stable conditions, with near-surface observations seeing an increase of more than 30% a few kilometers downwind of the plants.

"Wind plants can impact long-term local atmospheric conditions", Nicola Bodini, Julie K. Lundquist & Patrick Moriarty, Scientific Reports volume 11, Article number: 22939 (2021)

https://www.nature.com/articles/s41598-021-02089-2>

But that's not from energy transferred from the wind via the turbine, but of disruption of existing wind flows.

Re: Tidal energy is not renewable

#220

Post by dredmorbius »

pyaamb wrote: post #218
dredmorbius wrote: post #152

Earlier quoted context omitted.

Hadley cells determine wind patterns but not the energy content of the wind, to any appreciable degree, which comes from solar flux. Wind energy is solar energy once removed. Wave energy is solar energy twice removed (solar -> wind -> waves).

if we harvest wind do we still deplete waves?

In theory, yes.

In practice, wave action is caused by fetches across hundreds or thousands of kilometres of sea surface, and even offshore wind farms tend to be located within a few km of shorelines.

As with other impacts described, the potential interactions with bird life (strikes, kills, behavioural disruption), and of the artificial-reef effects of offshore turbine foundations and anchorages (probably largely positive) would all but certainly dominate these by many orders of magnitude.

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