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Comment by jfoutz | Hacker News Reader

I have high hopes for ARES [1]. just a heavy train on a hill with a regenerative break. Add lots of tracks, multiple trains per track, solar above the rails. Avoids needing all the water for pumped hydro storage. none of toxic stuff to deal with when batteries have reached their end of life. Zero carbon emission (aside from whatever is required for manufacturing) is just hugely appealing.

If solar prices continue as they have for another 3-5 years, the question is going to be pretty clear, how do we store all of this insanely cheap power. I'm a little mystified we're not taxing carbon emissions and subsidizing storage. But hey, there are clearly powerful forces at play, that don't agree with me.

[1] http://www.aresnorthamerica.com/

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I'm extremely skeptical that ARES will ever be cost efficient. Potential energy is proportional to mass * g * d_height - any reasonable grid storage option will need to be moving truly enormous amounts of mass.

Back of the napkin here:

California consumes 9.54 * 10^17 Joules of electricity / year, or 1.09 * 10^14 Joules / hour.

Suppose we wish to hold in storage enough energy to supply to grid for twelve hours, since the sun does not shine at night. Assume we have a 100% efficient method of recovering potential energy stored on a train. Suppose we find a suitable mountain with a 1000 meter height differential. Then according to e = mgh, we would need to shift a load of 1.33*10^11 kilograms to supply twelve hours of electrical demand.

Let's assume we use the cheapest rock we can to fill this mass. I assume you can get wholesale pea gravel for $8 a metric ton.

Then the cost of gravel alone is $1.07 billion.

That doesn't sound so bad, but remember, this project will need ~1333500 100-metric-ton freight cars. Suppose they cost $120,000 / ea. Then suddenly, the cost of the train cars is 160 billion.

This is on the order of magnitude of the entire California yearly state budget. And also ignoring a bunch of other cost factors that will increase the total price by another 1-2 orders of magnitude.

Pumped storage hydroelectric is viable precisely because the reservoir holds your water for essentially free. Train cars are far, far more expensive.

True, but all your math assumes that energy is used equally all 24 hours of the day. A large chunk of energy is consumed during the day, when the sun is shinning. Much less is used at night when the trains need to supply energy.

If anything I think my estimate is too conservative. Electrical storage must be adequate to meet demand in the worst case. The minute somebody's grandmother freezes to death because of brownouts due to wintry, overcast skies in December, and there will be riots in the state legislature.

No, we are long over designing systems for the worst case. This is what got us where we are today. The smart grid is about keeping grandmother alive tonight while drying your clothes during the light cycle tomorrow.

And pray that worst case scenarios don't happen.

Most people work during the light cycle.

Would this smart grid require that people only ever wash clothes on days they don't work?

The desire to be able to do whatever you what, when you want, is part of how we got to this climate-changing situation in the first place.

Good luck winning elections with that.

You can wash clothes while you're not there. It's even possible to schedule the washing so that it's done near the end of the light cycle so they don't sit in the machine for long after they are clean.

One could argue that, if people freeze to death because of brownouts due to wintry overcast skies in December (weeks of freezing weather probably would be something different), there's something wrong with the way houses are built.

Getting rid of oil addiction doesn't solely mean replacing oil with wind and solar; it also means thinking rationally about why we need so much energy.

Even the most energy efficient home needs a heater in freezing conditions.

Passive solar homes with heat storage may not.

A modern passive house could keep you warm in the winter with a heat source as minor as a candle. It's actually amazing how poorly our homes are insulated.

Don't you need souther exposure too?

Once you're talking about tearing down all existing houses and rebuilding them based on new and alien philosophies, your plan is starting to become a bit impractical.

> Getting rid of oil addiction doesn't solely mean replacing oil with wind and solar; it also means thinking rationally about why we need so much energy.

The prominent people who say this sort of thing usually have enormous mansions with heated pools and fly private jets everywhere.

>> the reservoir holds your water for essentially free

Once you build a dam, that is.

I suspect the whole 'needs a hill' and amount if land taken becomes a problem as this cant be taken for granted as available. There are other solutions that seem effective and take so much space. Maybe something like this? http://www.gravitybattery.info/

I don't know anything about freight car pricing, but these cars should be 1-3 orders of magnitude cheaper than regular high speed for expensive cargo.

The ideal one is basically a rock with wheels.

The Flintstones model of energy storage.

There is a very good chance i've screwed up my math, but my silly back of the envelope calculation says,

9.54 * 10^17 Joules/ (3.6 *10^9 Joules/mwh) = 265000000 mwh. Levelized cost, [1] (operating + construction + financing) works out to around $72 per mwh, over 30 years. (going with the cheapest average option) So if we were to throw away everything today, and be required start fresh, I get about $570 billion.

That's clearly a stupid thing to do.

However, my big point is, if solar falls another order of magnitude (which is a pretty big if), we can afford to spend a lot on storage. I think solar is now competitive with coal, but it's not dispatchable.

I'd argue solar would probably need 4x the amount of production of a similar coal plant, it's only going to work really well part of the day, and there are losses in storage (ares claims 20% loss, which is comparable to batteries)

there's not much weight difference between gravel and packed dirt. I figured they'd just use whatever mass is handy when they're building the track.

I don't know if $120k is a fair price. the cars have to have regenerative breaks, which are likely expensive. Just building something strong enough to support 100 metric tons can't be cheap. I don't know if there are any special features of regular freight cars that can be abandoned to cut down costs. On the other hand, if you're building a million of them, the costs would likely come down a bit.

Perhaps solar has reached the end, and any improvements will be slow. I don't believe that, and i do believe some sort of efficient storage will be the big focus in energy going forward.

[1] https://en.wikipedia.org/wiki/Cost_of_electricity_by_source#...

IF solar falls another order of magnitude, it will be far cheaper (which only has the conversion efficiency problem) to go for power-to-gas technology that has the additional advantage of being able to use gas (not gasoline) powered cars with normal range.

IIRC one of the big ideas behind ARES is to make money by supplying peak power for consumption and possibly even by taking peak power production off the grid.

Basically a grid scale AC capacitor equivalent.

I only have education in electronics and no other experience with High Voltage or big grids so I might be very wrong.

If power-to-gas means methane, it's bullshit. You'd need a source of carbon dioxide, and despite all the hype, it's only a trace gas in the atmosphere. (Personally, I think power-to-gas is a propaganda piece invented to link renewables and natural gas in the minds of gullible people.)

How does that compare to other energy storage though?

Favorably. 84% is 16% loss. batteries are 20-30% loss. hydro can compete, but the southwest has lots of sun and hills. not so much with huge supplies of cheap or free water.

the southwest is nice, because 300+ days of sun. cloud cover may reduce efficiency, but might actually improve it. clouds reflect more light from the ground.

There are many options for storage. Trains are very very good. You need to beat 80% to beat a train. Some things can do that, but they're not cheap, like land in the SW.

The further you build your renewable energy grid over peak consumption, the less storage you need, because if, let's say, an input of 50% electricity of installed capacity is 100% of peak consumption, the days where you actually need to draw from the storage will be less and the days where you can fill the storage will be more, in simple terms. There are studies on this.

You would need a lot less rail cars than that. Rails cars move the weights between the low and the high point, but they are re-used multiple times in a cycle, going back and forth constantly.

It wouldn't be very efficient to have a mobile piece of tech sitting idle for 99% of the time.

The main constraint would be to make the maximum use of cheap technology that is standard today. 100t freight cars are pretty standard.

Edit: nevermind, I was wrong

That's not how the proposal works. Each car picks up a box of rocks on a hydraulic jack and hauls it up the hill and then sets it down again and gets another one. Maybe the railcar makes 10 or 100 trips during the day.

Yes, you're both right. My fault – I misunderstood the ARES concept.

All three of you are right: Ares advertises two different concepts, only the one they call "grid storage" uses more ballast than they can fit on their rolling stock.

The one they call "ancillary services", intended only for short term grid regulation/stabilisation", uses fixed ballast that is never removed from the trains during regular operation. This is what the first prototype will be.

Everybody wins!

But you still need many cars to a supply high volume of energy per unit of time. You could do the whole project with a single train, but then it would be very slow at storing and retrieving energy.

It's not a forest of Sisyphean gravel funiculars which your calculation presumes.

According to the brochure on the site the Ares system seems to be an automated freight yard on a slightly sloping ground. Only a fraction of the total mass is on wheels at a time. The scaling issues might be a bit different.

>It's not a forest of Sisyphean gravel funiculars

I strongly feel this expression belongs somewhere. I just have no clue where.

Song lyrics, or poetry.

I personally like the idea of turning really deep mines into literal potential energy wells. Use renewable energy to lift loads (water, gravel etc) and then power generators at night by dropping the load back down. Basically enormous cuckoo clocks.

While I like the idea for its steampunk appeal, looking at potential/kinetic energy delta, you have two ways really: build overcapacity for solar, immovable, uses rare earth minerals, but other than dust, maintenance free and then that capacity will sit idle at night or you build capacity like these lifts at that capacity is going to sit unusued during the day, but it does require a lot more maintenance due to moving parts and potentially more resource heavy to build, but no exotic materials. I think the best way forward is to, of course use the least amount of energy possible - insulate from both heat and cold, make efficient CPUs and run everything you can in software and anything physical make it run during the day on solar. Once environmental costs are accounted for, it makes no sense to run things like cars and shops and washing machines at night.

Paul Simon song.

That system needs to be called Sisyphos.

A more apt figure from Greek mythology than the god of war, though, might be Sisyphus, who was condemned by the gods to push a rock to the top of a mountain, only for it to roll back down again so that he had to repeat the punishment for eternity. ARES does indeed push rocks uphill, only to let them roll down again. - See more at: http://www.aresnorthamerica.com/article/9232-sisyphus%E2%80%...

> will need to be moving truly enormous amounts of mass.

Use the extra energy to increase the spin of the earth, then harvest the spin to pull off energy.

If that was easy and cheap to do, our problem wouldn't be climate change due to greenhouse gases - it would be climate change due to the earth rotating slower since we'd been using it as an energy source for 200 years!

You'd speed it back up in times of energy surplus. It's a giant flywheel.

Rotational energy is already harvested using tidal power and wind power.

There are band type "windmills" it's a taught band with magnets on each end when it flaps it moves the magnets to generate power.

This is what every flywheel already does (unless it is balanced by a second flywheel going the other way). Conservation of angular momentum: as a flywheel gains angular momentum, it must be compensated by the Earth gaining the same amount of angular momentum in the opposite direction.

Usually this isn't referred to as "spinning up the Earth" though :-)

Actually you made it sound pretty attractive. It's only $160 billion (plus a few for yearly maintenance why not) to get California entirely on renewable energy. That's amazing and gives me hope.

You still need to generate the energy in the first place.

And now you do the same with pumping water back and forth... I get it that trains are handy when you have plenty of space and lack water, but many, many places around the globe lack the space for the hughe amounts of train tracks running up a 1000 meter high hill.

In addition, take into account the enormous amount of moving parts. Maintenance everywhere! Compare the tracks with carts to a large pump/generator and pipelines with water I guess the latter is much simpler to maintain and better looking to the eye. While train tracks should be kept clear of people you could easily see people using the lakes up & down the mountain for recreation.

As others said, you can reuse cars (if a car does 100 1km journeys per charge interval the materials cost for cars and gravel become comparable) and a custom built car can be cheaper, too.

The volume may be another challenge though: 1.33*10^11 kg is roughly 0.1 km^3 of gravel/dirt. So we need to move a cube of dirt ~450m in size up and down 1km each day.

Not impossible, but presents bit challenges on its own imo.

I would think the idea has merit if rather than purpose-built rails, the existing rail infrastructure is retrofitted (and built out) to act as a storage mechanism with freight that already has to move anyway. If that's done though, a proof of concept would need to be built first. So I wish these guys all the best, despite the fact that the economics look kind of silly on the surface.

In this case you are talking about electrifying the entire US rail infrastructure. Definitely not cheap...

And then you compare these costs to atomic power and it becomes clear that it is the only real option.

Just a few minor nits, you are off by a bit in your calculation of the cost of the train cars. A 5800CF open-topped hopper car will hold a little more than 200 metric tons of gravel and will cost less than 50K for the car and the gravel to fill it. Now you need 600000 cars at a cost of 50K each so the cost has dropped to around 33 billion. If you were buying rail cars at this sort of quantity you can probably also get a much better deal :)

I also seriously doubt there are going to be cost factors that add one or two orders of magnitude to the price here, but it is possible. The rail itself is very cheap and land to site the project is similarly easy to find since the rail line does not actually need to go anywhere and you can run lines in parallel instead of needing a long distance.

Definitely not cheap, but pumped hydro storage is in no way "free" and there are really no places you can do pumped hydro in any large scale that are not already used for existing dams and rivers. The lack of significant environmental impact is also a win for something like ARES.

What's the maintenance cost of the lines and equipment vs the hydro ?

Probably much much cheaper for rail lines. Rail doesn't leak. The entire infra is open to direct maintenance, and you can easily take segments of the system out of production for repair without having any significant impact on the productivity of the whole. You can extend or lay parallel track while your main system is still operational without too much bother so expansion is also easier.

I wouldn't be so quick to dismiss the maintenance cost for a ARES-type rail system. For pumped hydro, your ongoing maintenance is largely going to be maintaining a pumping system (to send water up) and a generator system. Hopefully you build your reservoir properly so that it lasts for 30 years. For rail, you have to have to maintain a large number of moving parts. It won't be cheap to insure all the parts are greased and good to go. I think it's a lot easier to maintain a set of pumps and generators than it is to maintain what is essentially a rail fleet filled with gravel on a mountain.

So for pumped hydro you have a massive up front cost and potentially smaller maintenance. Maintaining a large number of moving parts for rail might seem daunting, but these rail cars are made to operate for very long periods of time in unpleasant conditions with minimal maintenance; topping up lubrication systems and visual inspection is basically covering monthly maintenance for the system. I am not sure what the ongoing maintenance cost for most hydro installations is (pipe inspections, anti-silting and other water maintenance, inspections of the system, etc.), but I had to guess I would say that it is probably quite similar to rail.

Standard rail cars are sturdier than they'd need to be for this application - if you were going to buy that many you could pull out a lot of the cost by making them fit for purpose.

Continuing the back of napkin calculations, to compare train cars with batteries:

Rail cars costing $10^5 can hold 100 metric tons or 10^5 kg each. Cost is $1/kg. This will be amortized over the system's useful life. 1000 meter height differential at 10 m/sec^2 stores 10^4 J/kg. System stores about 10^4 J/$.

Tesla's Powerwall stores 10 kWhr for $3500. That's about 10^4 J per $ (since an hour is 3600 seconds).

What surprises me is that these order-of-magnitude costs are about the same -- 10^4 Joules per dollar.

A 5800CF open-topped hopper can hold 200 metric tons of pea gravel (at least according to the people selling them) so you just doubled the J/$ of the Powerwall. This is also using new rail cars, if you buy used then the price for the same rail car drops down to the 20K range according to online rail car brokers. Now we are looking at 1/4 the price for a train car solution.

California state budget is $167B.

Unless the state budget pays for the entire energy industry, that seems like a curious comparison to make.

You started with the total energy (I presume electrical) usage of the state. About how much do Californians pay for all that electricity per year?

Friendly calculator if you want to play with the various assumptions:

https://instacalc.com/50110

For reference, 133,350,000 metric tons is 1.81x the mass capacity of the US strategic oil storage, another grand energy storage scheme.

http://www.wolframalpha.com/input/?i=(133,350,000+metric+ton...

As neat as this sounds, in a Rube Goldberg sort of way, batteries seem more reliable without the moving parts. The new Lithium Titanium batteries are amazing. 10k cycle before loss of ~20% capacity and fast charge/discharge cycle of 6 min. Since they last a long time, less e-waste. And lithium is supposed to be relatively recyclable when the time comes.

We used to think building heliostats made more sense, but it turns out cheaper cells won out to complexity. I suspect this will be repeated in the energy storage market.

https://www.google.com/search?client=safari&rls=en&q=LTO+cel...

I would tend to agree that solid state is better than moving parts for reliability, but we have been building trains for like 150 years and the parts here that move seem to be just really big weights. We also don't have batteries that can do city scale storage economically, but a series of trains seems intuitively do-able. This is just intuition so could be wrong, but trains seem so simple.

Trains are not reducing in price like lithium batteries are. Lithium battery prices are coming down yearly. If it continues at this rate, I think we'll have a story like this about energy storage in 5-10 years where the price makes renewable storage the goto choice for general energy needs. That would be awesome, planet earth could use some good news like that.

I would like to point out that moving parts are what keep our civilization running. Intricate moving parts.

To feed the intuition:There are machines that have run with minimal maintenance for hundred years, such as the original newcomen engines used to pump water away from mines.

Each time an assault rifle is fired lots of small parts work together in a delicately timed dance. Now, take an AK-47 - due to it's massive parts and loose fitting it can be filled with dirt and sand and happily continue operation.

And, it's quite hard for me to imagine the turbines in electric plants and all the "piping" around them are any less "rude goldbergish" than the Ares system would be.

Machines are quite durable if they are designed that way.

> Now, take an AK-47 - due to it's massive parts and loose fitting it can be filled with dirt and sand and happily continue operation.

Not quite. It is statistically more reliable in such conditions in a sense that it will have a higher mean rounds to failure number compared to most everything else. But MRTF won't be infinite. In fact, it'll still be low enough that you will definitely notice.

Then there's the reason why. Loose fitting and massive parts, yes - but that also requires overgassing to move those massive parts (and then it also moves them faster than they actually need to be moving to cycle). So you're basically sacrificing energy efficiency for the sake of some extra oomph to clear problem. On any cycle that doesn't actually have a problem to clear, the sacrificed energy is wasted.

Then there's the normal metal stress and fatigue when running something 24/7 non-stop. Here's what happens when you do it to an AK - the guy is running a full auto rental range in Vegas for tourists, and shared his experiences about how soon guns fail, their failure modes etc: http://www.ar15.com/forums/t_4_64/159106_AK_abuse__update_on...

Good points. I doubt any rifle can be fired continuously for hundred years :). A boring combustion engine would have been a better example of mechanical robustness all together.

It's fun to read about a guy who's clients pay for him to shoot an AK-47. Where I'm from a male goes to jail (or other service) if he refuses to train for it (well, a local copy https://en.m.wikipedia.org/wiki/Rk_62). Another man's hobby is another man's burden :)

Based on what the guy said, his clientele is mostly young men who play video games like Battlefield or Call of Duty, and want to see how the same guns there work in real life. So they literally come asking for "that gun that was in CoD", hence why he mainly stocks things that are trending in games and movies.

Apparently, it's also popular with foreign tourists; especially from Asian countries, with more extensive civilian gun control than in Europe, where many wouldn't even see a military (or military-looking) firearm outside of service. It got to the point where some ranges added signage in Chinese and hired Chinese-speaking instructors to cater to the new audience:

http://usa.chinadaily.com.cn/epaper/2015-04/17/content_20457...

It is a bummer though that, from what little I know, the process to manufacture batteries is not good for the environment. That said, probably the process to manufacture all the parts of ARES is not either. And, probably, both of those issues pale at the moment in comparison to the need to shift to renewable sources of electricity.

South America produces most of it recycling may be clean but production seems dirty.

https://www.theguardian.com/technology/2016/mar/23/battery-l...

I've just read through the article: what do you see as 'dirty' about the salars? The fact that workers wear masks?

Like any mining operation you have to move a lot of earth use a lot of energy and dig up large regions.

The processing of the slurry to get the lithium after it's mined. All that water needed in a very arid region.

It was in contrast to lithium being easily recyclable compared to the vast scale of mining it.

The problem: Gravitational potential energy isn't a very efficient storage format. 1kg elevated 1m is only around 10j. A 10,000kg mass elevated 1km would be 98Mj- only 27kWh. And only with perfect conversions, which you won't get.

Each Tesla powerwall holds 14kWh for around $8000 each, and that price may fall over the.

If it's cheap to store the energy, and you can store it at large scale, the conversion factor starts to look less important.

If anyone had looked at the amount of energy that goes into an ICE car versus what makes it to the rear wheels, would we have autos today?

Yeah, especially with the front drive ones!

Just to put this in perspective - a gallon of gasoline holds about 33 kWh (about 10 kWh of electricity after thermodynamic losses). So lifting 10 tons a km vertically only gives you about 1-3 gallon of gas, give or take (however motor efficiency could be 95% which helps).

There is merit to lifting large loads like this, but IMHO they should be concentrating on weight instead of distance. Which basically takes us back to pumped hydro because we just don't have anything on the order of a million tons or more that can be moved cheaply and easily. I could maybe see a large carpet rolling a layer of sand or stones up into a cinnamon roll so it's self supporting. Probably not the safest place to stand under though!

What about using old shipping containers just filled with rock and dirt found on site?

If someone started with a hill or mountain at an almost suitable grade, then what they dug out to grade the slope properly could be put in second hand shipping containers at the top of a hill. Bring the containers up or down one at a time to get the power in or out.

Maybe have some one site solar or wind generation to try to bring and extra container up every once in a while.

People generally don't want steep slopes for much anyway so even the property ought to be cheap, it could even be municipal property for maximum cheapness.

The hardest part of any of this is the all electric trains with efficient regenerative brakes.

Water is worth it in very specific locations, because we can build a dam and let the natural shape of the Earth do the heavy lifting.

But a dry system, relying on weights? There isn't a material that is dense enough to make it worthwhile. Even a boxcar full of granite would need to be orders of magnitude heavier than it is for gravity storage to be economically useful.

I wonder if something using hydrogen as the buffer would work - it has a density of 37 kWh/kg (or 2.4 kWh/litre).

Instead of fuel cells (which are still expensive and relatively low capacity), using excess electricity to electrolyse water.

The oxygen and hydrogen can be stored in tanks, and when you need the power it can be combusted, generate steam and drive turbines.

There isn't really any new technology here, so it should be relatively cheap and quick to setup too. What am I missing?

The volumetric energy density of hydrogen is very low, so either you need enormous tanks or very strong tanks plus extreme compression. One way of making enormous "tanks" that can tolerate fairly high pressures is by solution-mining caverns out of natural underground salt formations. But this is geographically limited to where such salt formations occur, like parts of Texas and Louisiana.

The other problem is that the round-trip energy efficiency isn't great. You might expect 75% efficiency for electricity-to-hydrogen from electrolysis and then 60% hydrogen-to-electricity if you burn it in an efficient combined cycle gas turbine for 45% efficiency overall. Oh, and you irreversibly lose energy as heat when you compress the hydrogen, for further losses. And it's pretty expensive to buy big industrial-scale electrolysis units but run them only during the few hours each day when there's excess renewable energy you want to store (though it becomes a more attractive idea as the penetration rate of renewables, and corresponding excess generation times, increase.)

The conversion factor is not that important because without storage the excess energy would be lost anyway if we assume electricity demand doesn't shift from night to day.

Remember, the entire mass of the Earth @ 5.972 × 10^24 kg (which is 1.317 × 10^25 lbs) i.e. 5 septillion kilos or 13 septillion pounds) which is under you is enough to push you down with something like 150 pounds of force. A magnet with 150 lbs of holding power is able to fight all of that and takes up this massive amount of room:

https://www.amazon.com/CMS-Magnetics-Holding-Neodymium-Count...

Yes - that's a penny for comparison.

Gravity is soooo weak.

Your "Earth vs. Magnet" fight is not fair. For that magnet to hold up something of 150 pounds, the magnet has to be quite close to the object.

The Earth in that fight, on the other hand, is doing it with its center of mass (which is the relevant distance) about 6.7 x 10^6 meters away.

Squeeze the Earth down to the size of the magnet so you can move it close to your object too, and it won't seem so weak. The magnet would still win, I believe, but not by nearly as much.

Ah, good point! I'm not sure that it would still win versus point-sized Earth - according to this [1], shrinking Earth to half its size would increase gravity 4x. And a point is obviously much smaller than half.

But still, to see how incredibly weak gravity is consider that you don't even have to consider the gravitational pull of the magnet. Even if you walk next to a mountain you don't have to think twice about falling toward it. Gravity is negligible at even monstrously huge scales! It's just not a very large force at all, compared with magnetism, electricity, or e.g. solar radiation. It's truly weak. I've never had to think about the gravitational pull of any object other than literally the Earth or maybe occasionally the moon (which has a mass of 7.35x10^22 kg, or 1.2 percent of Earth's mass -- i.e. the Earth and the 5 septillion kilos I quoted is only 81 times as large.) The everyday pull of objects (for example the pull by which the building next to you right now is attracting you) is so negligible. It's weak!

[1] https://www.quora.com/If-the-earth-shrinks-half-of-its-radiu...

Yeah, I expressed myself poorly when I said shrunken Earth at the same distance from the object as the magnet would lose.

What I wanted to convey was that if you could get the mass closer to the object, you wouldn't need anywhere near 5.972 × 10^24 kg anymore. For instance, if you had a sphere whose center of mass was 1 m from your test object, and wanted it to exert the same force that the Earth exerts 6.7 x 10^6 meters from the object, you would only need your sphere to have a mass of 1.33 x 10^11 kg.

If we were using a sphere small enough that we could get its center of mass 10 mm from our test object's center of mass, it would only a mass of 1.33 x 10^7 kg.

So, the magnet is still winning in the sense that it still takes a lot of mass to counter the magnet, but we're talking 10^7 kg, not 10^25 kg.

>but we're talking 10^7 kg, not 10^25 kg

which, let's not forget, is still 10,000,000 kg!

But it gets worse. The thing I quoted, which generates 150 lbs of magnetism -- only weighs 0.3 ounces!! (0.01875 lbs or 0.0085 kg).

were your figures for 150 lbs or for 0.018 lbs of gravitational force from a point source? :)

It can be efficient in $$ terms since ballast is cheap.

Ballast is > 100x cheaper than powerwalls by the kWh in your equation[1]. 10 tons of rock just 5 m^3, you can put hundreds or thousands of this size of rock in a train[2]. You load/unload ballast instead of having all of it statically bolted onto rails and cars, so you get by with 1/50..1/100 carrying capacity[3] per trip vs total ballast amount.

The amount of raw materials (lithium mining and refining etc) required by the powerwalls is probably much higher too - good lithium deposits have ~ 1/100 of lithium content and turning ore into batteries is a heavy process consuming a lot of water, electricity, fossil fuels (ore transport/mining) etc. Not to mention limited battery service life.

[1] 2x powerwalls = $16000, even building material grade gravel is < $300 per 10 tons (50x cheaper) but here you could use sand or something from the site.

[2] big ore transport trains carry 10000-40000 ton loads, so 1000-4000 of our 10t rocks per train. You would probably use a smaller train for energy storage purpouse since the distance is small and you can have quick load/unload turnarounds

[3] if aiming for 1-day charge capacity, you can fit 100 15-min round-trips in 24 hours, or 50 30-min round trips

But it costs far more than just the ballast. The rails, the car, the huge system for pulling and releasing the cars, the dozens of km of land needed to have a train car be elevated by any significant amount.

Lithium systems are going to wind up being cheaper overall because of all of those costs, plus operating costs.

We already know how to cheaply and efficiently build rail, rail cars, huge systems for pulling and releasing the cars (they are called engines and overhead electrification :) and in fact you can pick up a lot of the materials used for less than half the cost of new. Dozens of km of land are damn near free in places in the southwest US where you can also dump lots of solar panels. Lithium may eventually be cheaper, but not within the next decade it won't.

Put the powerwall on the train as well and use both :)

The lead-acid battery in my car holds 660Wh (12V, 55Ah) and costs less than $100. That puts lead acid at a quarter the price of the Tesla powerwall (admittedly without an inverter).

If you tried to use it like a PowerWall it would fail before it had reached 1/4 of the PowerWall's rated cycle life. Lead-acid is not a good chemistry for grid tied storage.

What about a global power grid? Whichever side is receiving sunlight would power the other side of the Earth. We've already got communication cables running worldwide, couldn't we add cables for transmitting power? Perhaps, electric cables will weigh orders of magnitude than optic fiber comm links, but would it be infeasible?

You can't transport power that far without massive transmission losses. Communications cables use repeaters and fiber optics, so they don't have nearly the same problem.

https://en.m.wikipedia.org/wiki/Electric_power_transmission#...

Why not use superconducting cables?

https://www.extremetech.com/extreme/182278-the-worlds-first-...

Because they're very expensive and require liquid nitrogen cooling? Which itself represents energy consumption, so instead of losing energy as resistive losses you're spending it on cooling.

What's more likely is some form of energy-to-liquid-fuels process that runs during times and places of excess energy. The fuel can then be stored, pumped, trucked etc to other locations. This already exists, it's just not price-competitive with fossil fuels.

Cooling benefits from insulation - the energy loss does not scale as an exponential factor, and levels off very dramatically (the deep sea is already very cold).

We're trying to avoid the deep sea getting hot, remember?

What about electrolysis of water into hydrogen and oxygen during the day?

There's also the political issues to consider. You'd have to really, really trust the other countries you're relying on for the supply of electricity not to do something to mess with your economy. I could imagine it working politically in an area like the EU[1] or between the US and Canada, but across Asia or the Middle East there's likely to be too little trust.

An example with pipelines, Russia turned off gas pipelines into Ukraine in 2009 in winter: https://en.wikipedia.org/wiki/2009_Russia%E2%80%93Ukraine_ga...

[1] http://europa.eu/rapid/press-release_MEMO-15-4486_en.htm

http://spectrum.ieee.org/energy/the-smarter-grid/lets-build-...

Wow, that was an amazing article. I learned a lot reading it. Thanks.

One way to deal with night time electricity demands is to increase the cost of it. This will push demand to the daytime.

There's no reason to have uniform power rates 24 hours when the cost of providing electricity will vary dramatically from day to night.

Is this a real issue? My understanding was that there is a significantly lower demand for electricity at night. This is reflected in my energy tariff at least (daytime ~3x cost per kWh over night time).

Electric rates are the same around here 24/7. If it's more expensive to provide baseline load at night, increase the night rates.

Elastic uses of power, like charging car batteries, running the dryer, heating the water heater, etc., can be shifted to when power is cheaper.

I.e. reducing demand for night power is a cheap and effective means of dealing with the sun not shining at night.

Traditionally, the oversupply due to keeping coal and nuclear running at their optimum is available at night, when the demand is lower.

Many locations, like yours, already account for this by charging lower prices at night to incentivize people to shift their load to these times e.g. putting the dishwasher on a timer so it runs overnight. Many pumped hydro stations store energy at this time too, often they were built specifically to pair with nuclear stations to better map a steady supply to a variable demand.

In areas that are ideal for solar, and roll out solar heavily, they may end up in the opposite situation, with the supply and demand mismatch reversed and so try to push usage to the middle of the day by dropping the prices then. Since most usage is during the day due to air-con load and the fact that people sleep at night, this may mean lower prices overall.

Once you add the internet into the equation, rather than the blunt instrument of a block of hours at a lower charge you can do things like have specific plugs for electric cars or an irrigation pump on a farm that can respond on a second by second basis to over or undersupply of electricity by using more or less in exchange for a cheaper rate. This is called "demand response" and while it happens already with big industrial users, it's getting cheaper and easier for it to be used by more and more users. One neat product that already exists is an internet connected car charger that checks the carbon content of the grid and charges your car overnight only when the wind energy is a big part of the mix.

In my country (Poland, so not much renewable energy unfortunately) night-time (and weekend) rates are significantly lower (in some cases over 50% lower). You may choose uniform rate but it's not worth it (just remember to do your washing at night).

I worked in a company that sold energy-trading systems for many countries in Europe, and it was similar there (usually individual customers may choose uniform average rate, or much better offpeak rate and slightly worse peak rate, while the big energy market participants trade with different peak and off-peak rates almost always).

Okay, so we ask people not to charge their EVs during the day and now we won't want them to charge them at night? I know EV penetration isn't high but many utilities have good rates at night!

The best way to fix demand is to get all usage to be as efficient as possible, not restrict its use

Potentially relevant, with much less moving parts: A bigger kind of "Hubspeicherkraftwerk" (not sure about the english name, wikipedia does not offer one ;)) - carve out a large cylindrical block of a mountain and pump water below.

http://www.spektrum.de/news/ein-granitblock-voller-energie/1...

(In German, though the pictures should be enough)

What a fun system. I've added it to my notebook with the German 'hydraulic rock' (http://heindl-energy.com/) system. The latter doesn't need a hill.

What I like about the train system is that it should be cost effective and can be built without water. Cost effective because steel and concrete seem to be the bulk of the cost. The lack of water makes it more useful in places like the desert where water tends to evaporate over time and is hard to come by. It would interesting to understand the maintenance burden relative to the renewable energy source it is paired with.

Another, less talked about, issue is replacing peaker plants. Here is an article from 2015 on why that is a good idea (http://www.aiche.org/chenected/2015/04/battery-storage-takes...) using batteries. Even a "small" ARES system it would seem could address some of this need. The challenge being its hard to build something like that in an urban area.

Wow, I thought I had seen it all when it comes to energy storage, but this really takes the cake though. That piston is enormous! It might be the largest moving machine ever constructed if it was built.

I agree with you on solar. From my perspective, any energy we don't capture and harvest from the Sun as it hits Earth is wasted. Now allow me to offer you a different view on my buddy; Carbon. Carbon itself is a commodity and should be handled as such. We need it to make graphene, synthetic diamonds and carbon nanotubes which will in turn become the new silicon for the next decade or so.

What if all those things can be as accessible as what is common today? We must harvest every last molecule of carbon for this end. That include the crap we have overloaded the atmosphere with. I've already come up with a system for this that needs some fleshing out. With it we can make better solar panels, water filters, textiles of immense tensile strength, relativistic electrical conductivity and insulation.

Carbon is the fourth most common element in the universe or at least from what we can see. We must keep it that way if we want complete proliferation of this next generation of desktop and mobile quantum computers in every part of human society. So we need to capture and reclaim it from every corner of the Earth because the end goal is totally worth it.

Why not fill the rail cars with batteries as the ballast?

We should tax carbon emissions but we shouldn't subsidize storage. Anyone who developrs efficient storage will be able to make money on the energy markets directly (buy low and sell high). Let solar+storage compete on a level playing field with zero-carbon sources that can offer baseline power without requiring storage (hydro, nuclear, geothermal...)

Many governments (state and local) are in a position where taxing carbon isn't a possibility but subsidizing low-carbon forms of generation is.

They should not be handicapped.

They shouldn't be subsidizing one form of low-carbon generation but not another. That will distort the market and lead to buying subsidized forms that are more expensive overall.

I agree in principle, but given the huge proportion of energy which comes from fossil fuels, a carbon tax would have to be huge (and hence unpopular) if it were to match the market competitiveness of subsidies.

That is, to subsidize solar 33% (our current subsidy in the US), you would have to make a carbon tax equivalent to 50% of the current price of fossil fuels, or about $1.50/gal. This is obviously politically untenable in the United States.

The happy medium is probably to do a bit of both, and work toward the middle. Smart, targeted subsidies for carbon-neutral sources, and small, gradually increasing carbon taxes.

You can get away with a higher carbon tax if you return the money to the population.

In fact, there's a fair amount of popular support for basic income. Meanwhile a leading idea for carbon pricing is a flat fee per ton with the money returned to the population, equal amount per capita, which essentially is a small basic income funded by the carbon tax.

British Columbia has a revenue-neutral carbon tax (in their case by reducing payroll taxes accordingly) and reportedly it's popular. The opposition party ran against it and lost.

Washington State rejected one, unfortunately, one significant downside of the state solution is that some demand can just easily shift to another location. I wonder if there's a scheme where on state will pass it but only have it come into affect if neighboring states do as well.

A few states' actions wouldn't help much anyway. The real benefit of state carbon pricing was that the fossil industry was starting to come around on a national carbon price, because they'd rather deal with that than a bunch of different state systems.

Between the WA defeat and Trump win, that's probably pushed back a few years.

What about Cryogenic storage? http://www.bbc.co.uk/news/science-environment-37902773

I haven't looked into it much, but from the little I've seen it looks promising.

Build a proper electricity grid and sell power from sunlit areas to dark areas. You need the grid anyway. At the same time insist that all new dwellings are built to passivhus standard. Also arrange for all plugged in electric vehicles to be able to supply power to reduce peak demand from the net.

All this is scaleable and mostly going to happen to some degree anyway and avoids the need for massive capital projects that are susceptible to corruption.

Sounds like a good idea, but i do worry about how much overcapacity in energy storage would be required to handle the worst case scenario (a significant, extended drop in wind and solar output).

You can use natural gas for backup on demand energy generation. It isn't all or nothing.

And who pays for the backup on demand energy generation when it isn't in use?

The same people who pay for it now, the consumers.

Electricity grids have massive 'problems' with balancing themselves as demand varies throughout the day. Currently there are e.g. open cycle gas turbines on standby - they are paid a retainer in return for always being available, plus are price per MWh when they are generating. For the UK you can see them http://www.gridwatch.templar.co.uk, also see https://en.wikipedia.org/wiki/National_Grid_Reserve_Service

That works fine for a daily cycle. The backup plants still get paid every day.

But will it work for a yearly cycle, where solar/wind output varies from year to year?

Can a backup plant survive a year or two when it isn't needed and therefore isn't paid?

The problem is high start up cost and high real estate cost. Batteries are small and you can purchase and deploy them in small quantities.

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