Two massive gravity batteries are nearing completion

a reply to: Arbitrageur

"Compressed air energy storage pre-dates electric power, but the efficiencies I've seen are in the 40-60% range which is not that great compared to a gravity battery using water which is probably 70-80% efficient and I've seen lots of efficiency claims well over 80% though I'm not sure if they are accurate."

The efficiencies could perhaps be increased if a coastal based water reservoir was used in conjunction with tidal power. Allowing the moon to do most of the heavy lifting.

a reply to: Dalamax

I think electrochemical batteries will dominate all energy storage. The inefficiency, capital costs and maintenance of anything that moves physically, storing energy with gravity or pressure, is too high. Any of those could have been deployed decades ago---no new technology really needed---but haven't been.

Battery storage plants are pretty small for the power and energy, and can be easily sited at the distribution areas where they are the most valuable.

Soon enough there will be battery chemistry streams distinct from the demand of batteries for vehicles, as the chemistries specialize into stationary vs mobile storage. Stationary (like what we're talking about here) needs cheap, reliable and repeatable (low degradation with time and use); mobile needs high energy density by mass and volume (lithium ion currently). Sodium ion and Sodium-Sulfur look promising to me.

Batteries are difficult but there is now a major worldwide R&D effort across a variety of battery types. The capital investment in the factories will make battery storage the primary one quantitatively. It's like wondering why CMOS electronics and chips dominate everything---they're much better and cheaper for 99% of use cases than other chip chemistries.

CATL with their new sodium ion battery might be the new General Electric or Intel of the 21st century.

A large structure like this could be supplemented with wind turbines. Some of them could even be fully mechanically linked to the cranes so the wind lifts the weights without electricity.

originally posted by: glend
a reply to: Arbitrageur

"Compressed air energy storage pre-dates electric power, but the efficiencies I've seen are in the 40-60% range which is not that great compared to a gravity battery using water which is probably 70-80% efficient and I've seen lots of efficiency claims well over 80% though I'm not sure if they are accurate."

The efficiencies could perhaps be increased if a coastal based water reservoir was used in conjunction with tidal power. Allowing the moon to do most of the heavy lifting.

There are separate projects for pumped storage hydroelectricity, and for tidal power generation

If I understand your post, are you suggesting some combination or merging of the two technologies somehow? While not completely unfeasible, I can see numerous complications.

One is the timing cycles of the two technologies.

Tidal power obviously is timed based on the tides, and so power is extracted according to the schedule of the tides.

Pumped storage hydroelectricity timing is typically based on the 24 hour clock that most people sleep at night, and less high power demand occurs at night, like air conditioning. So water is typically pumped to a higher elevation at night when there's excess generating capacity due to low demand, and then during the day when there is higher demand and everyone wants to run their air conditioner at the same time, the water flows downhill generating electricity to meet the peak demand.

While there will be times the two schedules may be somewhat in sync, the schedules will not stay in sync, because tides cycles move around on the 24 hour clock the pumped hydroelectric storage typically uses. See this tide chart for example:



See how the times of the tides change every day? But the times of the pumped hydroelectric storage cycles are fairly consistent within a given season.

So I'm not sure how you're going to work out the discrepancy in those schedules. I didn't crunch any numbers but if I did I'd expect to find something like this:
roughly a quarter of the time the times may line up to where the tide cycles add to hydroelectric pumping cycles.
roughly a quarter of the time, the tide cycles will be opposite to what is needed for hydroelectric pumping
The remaining half of the time is somewhere in-between where it may not be much of a help or a hindrance.

So if this guess is anywhere near correct, there would be 25 % of the time that there would be a benefit, the other 75% might have to just turn off the tidal part since it might not help. That guess may be wrong and if someone has crunched good numbers showing otherwise I'd like to see them. But that's not a great start.

The other issue is look at those tide numbers, which are typically 2 feet or less. That's not nothing, but it's a relatively small fraction of the heights used in the pumped hydroelectric storage projects I've seen. For example, the Bath County Pumped Storage Station has 1260 feet difference in the height of the reservoirs, so what's 1 or 2 feet of tides compared to that? So is all the extra complication in design, maintenance, site location, schedule problems, and so on worth the extra typically less than 2 feet in say this location? (Though places with higher tides might be better prospects).

If you're interested in tidal power, you might be interested in looking at the European Marine Energy Centre which claims to "provides developers with the opportunity to test full-scale grid-connected prototype devices in unrivalled wave and tidal conditions." The tidal currents in the area are relatively strong without even building any reservoirs, so it's a good place to test tidal power generation which is being done there. But still there may be half the time (or whatever) the tides are not productive due to almost no tidal flow at or very near high tide or low tide, so "To balance the fluctuating tidal power and supply the 670 kW hydrogen electrolyser, a 1.8 MWh Vanadium redox battery was installed in 2022." That's a big battery!

Big battery to store tidal energy

a reply to: Arbitrageur

Thank you Arbitrageur for your very detailed reply. In Australia the tidal range varies on coastlines to maximum of 11 metres. With perhaps 20-30% of australia coastline experiences such large tides. The largest variance in the world is Canada's Fundy Bay that experiences 16 metres. An example of such tides is drone video of what is called Horizontal Falls in Western Australia...



The tide variances is said to be caused by the "shape and depth of ocean basins, bays, and estuaries, which can have a funnelling effect". It might be possible to replicate nature to enhance the variance but its perhaps more economically viable to use nature and transport the electricity longer distances.

Tidal power obviously is timed based on the tides, and so power is extracted according to the schedule of the tides.

Yes with the simplest implementation flowing water from tides can directly power turbines (A). But tides are also capable of filling reservoirs thus storing energy (B). Which can be released when power is required during low tides. Offering two six hour windows a day. There are no reasons why both techniques couldn't be used. (A) to power the gravity battery that pumps water in a much higher reservoir that can be used during high tides. Whilst (B) releases power from the lower reservoir during low tides.

I do not know if tidal forces have enough energy to meet worlds energy demands. But it wouldn't surprise me one bit if they did.

Thanks for the links.

a reply to: glend

originally posted by: glend
I do not know if tidal forces have enough energy to meet worlds energy demands. But it wouldn't surprise me one bit if they did.

If they did, extracting that energy could destroy the earth that much more quickly. But most people don't seem to realize tidal energy extraction can destroy the earth.

According to this paper, meeting just 1% of the global energy demands with tidal power could stop the rotation of the earth in as little as 1000 years. Hopefully it's self evident how that results in the destruction of the earth. On the way to the moon, the Apollo astronauts performed what they called a "Barbeque roll" so the spacecraft was constantly spinning to keep the temperature in balance, so one side wouldn't get too hot and the other side too cold. The moon is already tidally locked with the Earth, and eventually an earth with slow enough rotation would get tidally locked with the sun so the same side always faces the sun.

Destroying the Earth by Using Tidal Energy

Sciences and technologies have been advanced to a level that they can be used to destroy the Earth, if in a wrong hand. However, you might be surprised to hear that the Earth may also be destroyed by using tidal energy, even with a positive intention!? Consuming tidal energy is actually taking, therefore reducing, the rotational energy of the Earth, which decelerates the rotation speed. Based on current pace of world energy consumption, if we were taking the rotational energy just to supplement 1% of world energy requirements, the rotation of the Earth could be literally stopped in about ​1000 years​. ​As a consequence, one side of the Earth would expose to the Sun for much longer time than it is today. The temperature would be extremely high on this side, and extremely low on the opposite side. The environment would be intolerable and life would be wiped out from the Earth.

I didn't check his 1000 or 1031 year math, and he admits it's a rough estimate based on predicted energy consumption, but the principle is sound that extracting the tidal energy will slow the earth's rotation. Tidal energy is mostly in the experimental stage today but if it ever goes past that, it could be a cause of great concern not for you and me, but for our descendants in the future. This is almost a real life version of the script of how the technological geniuses on the planet Krypton didn't realize the consequences of their technology on the planet until it was too late, and by that time the destruction of their planet was inevitable.

I don't think life would be wiped out on Earth completely as the author claims, but I don't see how it could support even 1 billion people much less 7-10 billion, if the Earth gets tidally locked to the sun. The twilight zone between the eternal day and eternal night may be somewhat habitable, but it would be hard to farm there with sunlight at such a low angle, and I expect the winds would be violent there:

What would happen if the Earth became tidally locked to the Sun?

If the Earth somehow became tidally locked – in which one hemisphere of the Earth is perpetually facing the Sun while the other remains shrouded in darkness – it would be bad news for life. There would be no seasons, and temperatures on the Sun-facing side would get hot enough to boil water.

Meanwhile, the dark side would become frigid, with the only source of heat being the ocean circulation and winds from the sunny side. The huge difference in temperatures between the two hemispheres would likely create extremely violent winds and copious thunderstorms.

Such a hugely unstable climate would probably mean that all but the most resilient life forms would have to cling to survival along the strip of land between the day and night hemispheres.

That little strip of land is not very big, or since the Earth's surface is 70% water, what if the twilight strip occurs mostly over the ocean? In that case, there might be little or no habitable land on a tidally locked earth.

So I ask you, it it better to campaign for tidal energy, or against tidal energy? I suppose some might say they don't care what happens 1000 years from now, they want their energy now, but I can't agree with that. I think we are stewards of the planet and should make an effort to pass the planet to future generations in habitable form, and not to destroy it.

a reply to: Arbitrageur

I looked through the paper, and it seems mostly correct---except for one assumption. And it's a whopper. There's an assumption that the Earth's energy consumption increases by 2% every year.

This means in the last year of the doom scenario of 1031 years, the energy consumption of humans on earth is 735,829,316 times the energy consumption around now. And that tidal energy is extracting 1% of that.

So firstly, no, energy consumption by humans will not increase by 2% for 1000+ years without stop. And there isn't any way to extract 1% of 7e8* today's energy consumption from tides. Tides will be the same as they are approximately, but something like that would mean rigging up the entire ocean. There probably isn't that much energy available to extract from tides in the first place.

a reply to: mbkennel
Right, as I said "he admits it's a rough estimate based on predicted energy consumption" and you're saying you disagree with his prediction by a lot and I suspect you're right. I've seen estimates Earth's population might top out around 10 billion, but it's hard to even be sure of that prediction and who knows what will happen after 2100? If population eventually stops increasing, then it would be reasonable to presume that per capita energy demand may eventually flatten and thus increases in global energy consumption would also flatten.

The world population is projected to reach 10.4 billion people sometime in the 2080s and remain there until 2100, according to the United Nations Population Division. But Gerland stressed the further that demographers look into the future, the more speculative and uncertain their predictions become.

If population predictions are highly speculative after say 2100, then energy usage predictions would necessarily also be speculative. I'll bet very few people or maybe nobody 20 years ago predicted the vast amounts of energy we would be using to mine cryptocurrency now, and that's only 20 years. It's really hard to predict what will happen in 1000 years.

But I don't know if you or I can make an accurate prediction of what energy consumption will be 1000 or 10000 years from now, so we should not only be very skeptical of the prediction in that paper, but perhaps any other prediction as well.

The rate of Earth's rotation is already slowing even without extracting any tidal energy, and that's due to tidal interaction with the moon: the earth loses energy which it gives to the moon. So maybe a more practical way to look at it would be, to ask the question:

"How many megawatts on average do we need to extract from tidal energy on a global scale, to double the rate at which Earth's rotation is slowing down?" and see if we can live with the consequences of that. Or maybe we establish some kind of global limit on how much tidal energy can be extracted?

Humans do have a tendency to overdo things that seem to be freely available, like overfishing the oceans for example. How much tidal energy can actually be extracted? Maybe you're right, maybe it's not much, but glend seems to have a different opinion, and I'm not even sure how to crunch the numbers so I can't say who is right.

a reply to: Arbitrageur

I now champion the case against tidal energy! But when I look up the effects of solar panels on climate there are also suggestions that in vast enough numbers, they too will be detrimental to our environment here. It seems that there is no easy answer to shifting the world away from fossil fuels. We might have to follow India's lead with thorium powered nuclear plants in which waste remains radioactive for only 500 years.

Thank you for explaining.