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Comment by wcoenen | Hacker News Reader

The same could be said about wind power.

Ultimately, wind and ocean currents are driven by the 170,000 terawatts of solar irradiance continuously hitting the earth[1]. Human civilization uses about 17 terawatt[2], so we still have a ways to go before we get in the same ballpark.

(On the other hand, give it a few centuries of exponential growth and let's see where we end up.)

[1] https://news.mit.edu/2011/energy-scale-part3-1026 https://www.theworldcounts.com/stories/current_world_energy_...

[2] https://www.theworldcounts.com/stories/current_world_energy_...

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And with this one, currents - mainly ebb and flow - are caused by the gravity of the moon pulling on the oceans.

But yeah, it will have an effect; the other question to ask is, how significant is this effect, and how does it compare to other forms of power production, e.g. fossil fuels?

The global warming caused by fossil fuels has a bigger effect on the oceans; with decreasing salinity due to the melting of ice caps / glaciers, the gulf stream is slowing down and will eventually stop, causing distribution of heat across the planet to stop, causing the northern seas to cool down and the southern ones to heat up.

Tidal flows are a pretty massive energy reservoir - basically you’ve got all the potential and kinetic energy of the moon’s orbit to draw from. That’s (according to my crude Wolfram Alpha based research) about 3e28J of kinetic energy plus 7e28J of potential energy, for a total of 10^29 Joules. Technically a non renewable resource, but you would be hard pressed to make a dent in that energy budget with any kind of human scale extraction project.

I think it’s the rotational inertia of the earth, not the kinetic energy of the moon. Since the earth is spinning faster than the moon orbits, the tides actually are pulled ahead of the bulge the moon creates, transferring energy from the earth to the moon.

Eventually the earth will be tidally locked to the moon (just like the moon is to the earth), and the moon will be in a higher orbit.

I guess the turbines will speed this up? As they’ll keep the bulge farther ahead of the moon.

EDIT: Wikipedia link https://en.m.wikipedia.org/wiki/Tidal_acceleration

That's true - for some reason I was thinking of tides as following the moon's orbit, when of course they're caused by the earth spinning underneath the moon (tides occcur daily, not monthly. Always check your working against reality, kids).

Weirdly, the resulting pool of energy is pretty much the same size - wikipedia quotes the rotational kinetic energy of the Earth as being 2.138E29J.

So we're still talking about an insane amount of energy.

If you use 17.7TW as the total power consumption of all of humanity, if we were to somehow derive ALL of our energy needs from tidal generation, it would take 358 million years to deplete the rotational energy of the earth.

Would the turbines make the rotation decay faster, or would they just put some of the energy of rotation decay that happens anyways on a slightly different path towards heat?

Technically a non renewable resource...

How's that? Can we consume it? What would be the reaction? Moon altering its orbit?

Yes this technically degrades the moons orbit. Do it long enough and hard enough and the moon will hit the earth. Shouldn't be of any concern though, because the kinetic energy the moons movement is carrying is insanely high.

This doesn't degrade the moon's orbit lol. The energy is there regardless of whether we are using it or not, it will go somewhere, this is just making "useful" work out of it (if anything humans do to the environment, other than going extinct, is really value added for the environment)

Huh. Would Ice 9 also make the moon crash?

I think this is targeting ocean currents, which are solar-powered convection between the tropics and the poles, rather than tidal currents.

Currents, on the large scale, are not caused by tides. Surface currents (down to 300m or so) are driven by prevailing winds, and deep currents driven by differences in temperature and salinity (which affect water density), both also affected by Coriolis effect.

That 170,000 terawatts hitting earth is dwarfed by the 400 trillion terawatts output by the sun, so we can always build some fraction of a Dyson sphere if we start to run short with the 170,000

The sooner we stop using these feeble fossil fuels the better

Fantasy solutions don't work for real problems. We have the capability to make real problems via terraforming.

A Dyson sphere is just as much fantasy as physics, true of most of today's technology just 50 years ago.

Solar and wind are needed today, but Starship could bring launch costs down enough that some highly optimized space solar panels with microwave power beaming could be viable within a decade.

I believe the solar panel part, but not on the microwave power beaming; has that been proven to work already? How efficient is it? What is the effect on anything flying through or being near where said microwaves are received?

Solar panels in space is the believable part; rays of concentrated energy being sent back to earth is what I'm skeptical about. Besides, solar panels have a limited lifetime; I don't believe space solar panels are a cost effective solution to solving the energy crisis.

This idea keeps being brought up and people keep reminding everyone that for all intents and purposes this is the closest to a cartoon supervillain death ray that we can create.

I think the important point is that we’re reasonably certain we can create it.

Yes but could we please not? Orbital death rays for power generation seem like a bad idea when we have options like rooftop solar and wind turbines.

Right, but what do we do when we’ve covered every surface of the earth with solar panels and wind turbines?

We’ll need to move into space sooner or later if we want to continue exponential growth.

We'll just have to clear some area, I suggest the quickest way would be with the giant orbital heat beam! :D

(100% agree that getting into space is important, and that if we want to continue exponential growth we'll need more than one planet. In fact, we'll need more than all the planets and we fairly rapidly (in cosmic terms) hit the point where the available volume of our light cone isn't enough. Maybe indefinite exponential growth isn't something we should feel entitled to...)

We're nowhere close to that. Covering all land in solar would be ~100x our current energy needs, and then we still have ocean (most of the surface) available.

Besides, anyone who's played simcity knows the damage that can be done by a wayward microwave power beam.

Why would we build a solar panel that has a microwave emitter instead of just building a mirror?

Is our atmosphere more or less transparent to some parts of the frequency spectrum than others? Is the diffusion different?

> Is our atmosphere more or less transparent to some parts of the frequency spectrum than others?

Yes. The frequencies that are not blocked are called "atmospheric windows". And there is indeed such a window for microwaves. These windows also exist for visible light and a range of IR, but those depend more on weather conditions.

https://glossary.ametsoc.org/wiki/Atmospheric_window

This is the point. High energy needs to be transferred in a narrow beam, and be minimally impacted by all layers of our atmosphere

How would capturing the beamed energy on earth be any easier than capturing sunlight directly?

Maybe illuminate existing solar arrays during nighttime? Any other energy receiver would be so far behind PV on the price / manufacturing learning curve

Main benefit is avoiding transmission losses through our atmosphere. Capturing the signal is easy (we have satellite communication already)

>> Maybe illuminate existing solar arrays during nighttime?

I never thought about this. Is there some orbit where this becomes feasible?

A sun synchronous orbit above the terminator would do it.

Receiving energy that was not supposed for earth will increase planet heat output (because electricity in the end will heat things). Who knows how that would affect the planet.

The only way to preserve the Earth is smart planning, reducing energy usage and moving industry to the space. IMO Earth should be sanctuary for people to enjoy their origins and for some rich people inevitably. Most people should move to other planets or space objects where pollution does not matter.

Terraforming is a fantasy that won't work for real problems

>We have the capability to make real problems via terraforming. [emphasis mine]

Yes, they slightly misread, but it's a fair retort. Terraforming is pretty fantasy, but it happens.

We’re carbon (de-)terraforming the earth everyday on a global scale, haven’t you heard? It’s very real

This with assumption that there is linear relation without butterfly effects, even if there are negative effects, most likely they are negligible when compared to green house effect on the planet, my false intuition tells me that power generation from wind and ocean currents would contribute to planet cooling, no idea if electricity converted to work will radiate heat faster into space then air and oceans passively.

Just to point out, we would be harvesting a lot more than we use because of inefficiencies in capturing, storage, and transmission strategies. Also note that the amount we use is lower than it would otherwise be if we had access to more energy, industry is energy-constrained.

In the case of something like PV, would that matter too much? The inefficiency doesn't mean the rest is lost, just that it stays in the local environment rather than get transmitted away somewhere else on a wire.

Pretty much. As an examples, in deserts, there can be a modest increase in local IR radiation because of the change in albedo from PV panels compared to sand, but the overall decrease in IR from avoiding the CO2/etc emissions of fossil fuel generation is much, much larger than the local increase.

10% reducation in currents and wind surely would have massive impacts on the planet?

Well 1) living has a massive impact on the planet because everything we do leaves a mark and everything we eat redirects energy into our bodies so that ship has sailed and 2) a 10% reduction in currents and wind specifically would have massive impacts on the planet’s currents and wind if we built enough power plants that used those sources of energy specifically to power the entirety of human civilization. We have other options, and the way we source power (as a planet, never mind individual jurisdictions) is basically an “all of the above” energy strategy in practice. However we can source energy, we do it.

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