Gravity Energy Storage

tahanson43206 · 2019-11-24 17:26:01

For SpaceNut ...

Your new post seems (to me at least) to deserve its own topic.

I'm pretty sure that somewhere in the NewMars archive there is a report about using railroad cars loaded with gravel to store energy on the side of a mountain.

In any case, the energy storage method is eminently applicable to Mars, which (if I recall correctly) has the Solar System's tallest mountain.

SearchTerm:GravityEnergyStorage

Table of Contents:

Post for concrete counterweight: http://newmars.com/forums/viewtopic.php … 44#p187344

Post for iron counterweight: http://newmars.com/forums/viewtopic.php … 45#p187345

Post for lead counterweight: http://newmars.com/forums/viewtopic.php … 46#p187346

Post for lead counterweight encased in iron: http://newmars.com/forums/viewtopic.php … 47#p187347

(th)

SpaceNut wrote:

Using mountains for long-term energy storage
Mountain Gravity Energy Storage, constitutes of building cranes on the edge of a steep mountain with enough reach to transport sand (or gravel) from a storage site located at the bottom to a storage site at the top.
A motor/generator moves storage vessels filled with sand from the bottom to the top, similar to a ski lift. During this process, potential energy is stored. Electricity is generated by lowering sand from the upper storage site back to the bottom.
If there are river streams on the mountain, the MGES system can be combined with hydropower, where the water would be used to fill the storage vessels in periods of high availability instead of the sand or gravel, thus generating energy. MGES systems have the benefit that the water could be added at any height of the system, thereby increasing the possibility of catching water from different heights in the mountain, which is not possible in conventional hydropower.
"One of the benefits of this system is that sand is cheap and, unlike water, it does not evaporate - so you never lose potential energy and it can be reused innumerable times. This makes it particularly interesting for dry regions," notes Hunt. "Additionally, PHS plants are limited to a height difference of 1,200 meters, due to very high hydraulic pressures.
Research Report: "Mountain Gravity Energy Storage: A new solution for closing the gap between existing short- and long-term storage technologies"

Added 2021/11/13 ... data extrapolated from work by Calliban: Shows concrete counterweight height vs distance to drop to deliver 2 Kw for 24 hours

Compute points for Gravity Drop Tower: height vs distance

height distance product
2546 3 7638
2446 3.12264922322159 7638
246 31.0487804878049 7638
146 52.3150684931507 7638
46 166.04347826087 7638

Update 2021/11/17 ... The sweet spot for concrete is Height of near 84 and drop of 91~

The solution is available from the equation: X * Y = Constant (ie, 7638)
The shaft depth is equal to twice the square root of the constant.

Total shaft depth for a 1 meter diameter concrete counterweight is 175 meters

Height Drop Product Total Shaft Depth
84 90.928 7638 174.928571428571

(th)

Last edited by tahanson43206 (2019-11-24 17:26:57)

louis · 2019-11-24 17:57:11

Yes, I've referenced rail systems for gravity energy storage before now.

It's certainly a possibility but in terms of Mars, it will require a lot of labour input to create the infrastructure.

SpaceNut · 2019-11-24 18:15:29

To save the excess energy you expend energy to place what ever you desire as the working material whether its liquid, gas or solid as in the sand its that expendature that moves it to the storage that is not the only waste.

Once you need that stored energy you must expend again energy to get it back at another resonable lose of what we called excess.

Sure the storage can also lose energy while in the halted state waiting for use depending on what is used.

It does not matter what we store or how its going to have a total lose to trying to save the energy for later its just how much can we afford to live with that is the question.

tahanson43206 · 2019-11-24 19:05:14

For SpaceNut re #3

As you will have noted in the article, the argument presented for use of sand as the storage medium is precisely the LACK of loss of energy content.

Unless the gravitational field of the body against which the mass was lifted into place changes, the potential energy of the raised mass will remain constant.

For Louis re #2 ... thanks for the input. It will be possible to reduce the search results by looking for Louis and train. A search for gravity yields too many results.

***
However, this is for Calliban ... There is a possibility of increasing the efficiency of energy recovery, by equipping the load cars with permanent magnets.

If the loaded cars are released to move down an incline at a regulated pace, and if there are coils under the cars to accept sweeping by the magnets, it should be possible to convey the energy recovered from the moving cars to a distribution grid.

In that case, there would be no moving parts except for the wheels rolling on steel rails.

The article cited in the first post of this sequence offers cable suspension as the means of moving mass. Cables would presumable cost less, or perhaps much less than a rail system.

(th)

SpaceNut · 2019-11-24 19:49:44

The energy is not so much in the stationary storage location is in the reloading of the tram in order to get motion that is the energy loss.

The steel cables will only need to lift the mass hung on it as the weight of the cable is support at equal distances along the path to the top same as a gondola ride or a ski lift.
The image indicates the top the mass is dumped into a holding tank or pit but to get the energy out the mass needs to be reloaded into the down path of the cable.

The rail car was to do with AG traveling along at speed to give the appearence of gravity I think first proposed for the moon surface.
The magnets along the steel rail would need to not be able to touch the coils as it travels at a fixed distance from each surface as the car moves But having the added mass means more energy must be used to get it to move as the coils will be adding in more mass.

tahanson43206 · 2019-11-24 20:44:45

For SpaceNut re #5

The cable system would have distinct advantages and disadvantages. Hopefully other forum contributors will be inspired to develop both sides of the issue.

The idea that there would be artificial gravity in this situation is interesting. On Earth, gravity is "natural", and on Mars or the Moon gravity is "natural".

Energy would be stored by lifting a mass in a natural gravity field. Energy would be captured as the stored mass is allowed to descend in a natural gravity field.

In my concept, the cars would be equipped with permanent magnets to generate current by sweeping across coils which would be embedded in the track.

The mass of the magnets would contribute to the stored energy of a car lifted in a "natural" gravity field.

There should be no energy required to cause a car at the top of the incline to start to move, because the "natural" gravity will be constantly tugging at the car, so that when the car is released to begin its descent, "natural" gravity will accelerate the car along the incline.

On Mars, and possibly on Earth as well, it might be advisable to enclose the incline in a weather shield, but that would be a refinement that might well prove unnecessary, or not worth the expense.

(th)

SpaceNut · 2019-11-24 21:06:39

The function of a moving coil over a fixed magnet strength only changes the cycle and amplitude as each pole change to create AC in the coils output which for the downward glide would create energy for the short trip. The initial push to get the mass riding down the track or cable is not all that much as thats how a roller coaster works.

The slope of the ramp and mass means you need a breaking system at the end before its derailed or crashes at the end of its journey. The energy created needs to go somewhere for storage.

Since the car is a fixed size it might make more sense to change where the parts are located as the car mass plus magnets with the coils being along the tracks allow for the same coils to be used to push the train back up to the top on the same tracks.

tahanson43206 · 2019-11-24 21:45:07

For SpaceNut re #7 and topic in general ...

The application proposed in this topic would be an example of a linear motor.

I asked Mr. Google to find examples of linear motors used for energy recovery, and found this example:
https://pdfs.semanticscholar.org/7e05/e … c0627d.pdf

The invention described is intended to provide electrical power through conversion of mechanical action, such as pushing a button. The intended application is a security system which requires electricity to unlock a facility, but batteries are unsuitable because periods between activities would exceed battery life.

Linear motors are used for a variety of transportation applications, such as Maglev trains and certain amusement rides.

The suggestion of employing linear motors to lift a mass up an incline makes plenty of sense.

The use of linear motors to RECOVER stored energy is likely to be less well documented.

That is essentially what is proposed in this topic.

There should be no need for a braking system at the end of the incline, since the energy stored in the mass should be drained off as the car descends.

There should be no need to store the energy coming from the car, since the purpose of the exercise is to deliver power to the grid for consumption.

To recap, following the example of the cable car sand storage system, the proposed inclined railway would store energy by lifting mass up an incline, and then recover that energy by draining it to an electrical distribution system using a form of linear motor to generate electrical current.

(th)

Calliban · 2019-11-25 06:23:48

Gravity storage is already used extensively in the form of pumped storage. This involves pumping water from a low reservoir to a high reservoir and then releasing it back to the low reservoir through a turbine. Practical efficiency is about 75% in large scale facilities. Not bad. Relatively low energy density. A cubic metre of water raised through a head of 1km, will store about 10MJ. The energy stored is proportional to height and volume.

The advantage of using a liquid is that it can be pumped through pipes, which is logistically much easier than having to lift blocks by crane and then recover energy using some sort cable winch. That involves a lot of moving parts and is labour intensive.

louis · 2019-11-25 07:21:25

I think we could use it on Mars. We would need a floating aerogel layer over the water and reflectors as well to direct solar radiation on to the water reservoir. Of course Mars has loads of craters which should be pretty perfect for water storage once lined with clay. You just need to find a couple of craters in close proximity on different levels, to give you the drop.

The real issue is whether you can keep the water above freezing. You will probably need a lot of reflectors to achieve that. But it could be worth it as reflectors can be cheaply deployed on Mars.

Calliban wrote:

Gravity storage is already used extensively in the form of pumped storage. This involves pumping water from a low reservoir to a high reservoir and then releasing it back to the low reservoir through a turbine. Practical efficiency is about 75% in large scale facilities. Not bad. Relatively low energy density. A cubic metre of water raised through a head of 1km, will store about 10MJ. The energy stored is proportional to height and volume.
The advantage of using a liquid is that it can be pumped through pipes, which is logistically much easier than having to lift blocks by crane and then recover energy using some sort cable winch. That involves a lot of moving parts and is labour intensive.

tahanson43206 · 2019-11-25 07:33:03

For Calliban re #9

Thank you for your contribution to this topic.

I'm hoping to find time to research the history of gravity energy storage by human beings. My guess is the first examples would go back thousands of years, and it seems likely that water storage would be the most probable technology to be developed.

Water storage of energy would seem (to me at least) to work best where water is abundant and can reasonably be allocated to such a purpose.

The cable system that SpaceNut found in his Internet searches is interesting (again, to me at least) because it has distinct advantages over competing methodologies. In thinking about the cable system overnight, it came to me that the idea of storing sand in bunkers at the top and bottom of the incline does seem available for improvement. The gondolas need not be emptied. They can be disconnected from the cable at the ends, and rolled on rails to a storage location.

This system could be used in many locations on Earth where water is scarce, and it could be used all over Mars where slopes are available for the purpose.

The point about "labor intensive" certainly would be true if we were back a hundred years, but in the year 2019, there seems little point in allocating precious human time or energy to an active roll in the process. Certainly human supervision would be needed, and occasional maintenance of mechanical points of wear, such as the roller bearings which will be carrying the load, or the clamps on the gondolas which will be at risk of failure over time.

I am hoping that someone in the forum with the appropriate knowledge and skills, and above all, the interest, can compute the likely efficiency of a well designed automated gravity energy storage system using the model SpaceNut found, with enhancements.

It should be possible to implement such a system on a small scale, at a cost affordable to an average home owner who can afford one of Elon's power walls, for example.

Returning to history for a moment ... Gravity energy storage has been in use for hundreds of years (if not thousands) for operation of escapement systems for driving pendulum movement for measurement of time.

Thanks again for your support of this topic. I hope it has the capability of yielding a set of knowledge that could be put into use by a reader of this forum in the not too distant future.

Edit: Why disconnect the gondolas? The cable could be extended along the plateau at the top of the incline, and the gondolas could be rolled away from the edge to the extent of the storage run. It this adaptation of the basic idea were put into use, then the same storage concept would be needed at the bottom of the incline. In that case, the hassle of disconnecting and reconnecting the gondolas could be eliminated, and the system could be more easily automated.

(th)

Last edited by tahanson43206 (2019-11-25 07:36:24)

SpaceNut · 2019-11-25 10:07:41

The reservior tank on the hill is also used to pressurize the water delivery system during the day to keep home sink tap pressure steady as man uses the water at your home as well.

tahanson43206 the edit in post #11 removes the load and unloading of the mltiple payload cars from the cable and does save that energy loss. The the permanent magnet motor, generator would be rotary in nature due to the cables motion.

The train car concept using permanent magnet linear designs still needs work but its 1 set of tracks and with the addaptation of the car staying loaded along the top of the ridge of the montian does save the energy of loss of moving the materials again.

Louis post #10 with Calliban quoted post works out quite well once we have the levels of water to fill the system for continual use. The efficiency will only drop if water quantity or it getting frozen for the amount of energy out of the systems design.

tahanson43206 post #8 linear motor design does not work out well as the car is on a track or rail with the car having the field coupler plate and interupting skeem of open areas as the method to allow the magnets field to bridge to the steel magnetic material running down the center. The laminated steel plates which make contact to the magnets allow for the flux loop to be created through the coil as the coupling passes by the lamination pairs for positive and then as it moves forward to the negative field direction through the coil. Then the next position is a space that is open to any field or coils gives the break between cycles of the created ac voltage and currents. The laminations are chosen over a ferrite core as the motion is low frequecy.

The drawing in the pdf shoes 4 magnets sets (north south pairs) with for coils to make 2 phase in parrellel power creation.

Most things on earth use 3 phase for power so a change in layout would gain in power from this concept.

The field coupler plate can bind from dirt and dust intrusion is the only thing I see for mars that is a problem.

more design pages
http://www.pmgenerators.com/linear-perm … erators-i/
systemdesign.illinois.edu/publications/Niu13a.pdf
www.iosrjournals.org/iosr-jeee/Papers/Vol10-issue6/Version-2/K010628690.pdf
www.asee.org/public/conferences/1/papers/1731/download

I have post rotary in several other topics of mars cart, light rovers, the bike topics as a hybrid for pedal power...

Calliban · 2019-11-25 11:01:09

A historical example of gravity storage is the raised weight hydraulic accumulator (see below).

https://en.wikipedia.org/wiki/Hydraulic_accumulator

Useful in situations where relatively small amounts of energy need to be delivered at high power - e.g. raising a crane boom with load or raising a bridge.

Let's say I have a small power source delivering a few kW and I want to use it to power a device that consumes hundreds of kW of mechanical power for just a few seconds, every few minutes. A raised weight hydraulic accumulator is useful in these applications.

A cheaper way of doing the same thing would be a polyethylene bladder located at the bottom of a deep pit. Above the bladder would be a deep layer of Martian fine dust, which would put downward pressure on the bladder, essentially exerting hydrostatic pressure in the same way as water - but somewhat denser. We would inflate the bladder with fluid, either CO2 or water. The dust would be pushed up the shaft and would fall back down the shaft as pressurised water or CO2 was extracted.

Regarding the use of train cars to extract gravity energy - this idea was used from the 18th century onwards and could still be relevant today. Say you have a mine located within a hill. You want to remove mine tailings and transport them to a railway or canal boat several hundred feet below. The weight of the full trucks will carry them down the hill and will also pull empty trucks back up the hill in a loop. In principle, one could extract additional energy from the falling material and use it to power the mining operation. One could couple a generator to a cable that is fixed beneath the cars and pulls over a pulley system. The energy extracted could be electrical or even pneumatic - powering air tools for the mining process.

Last edited by Calliban (2019-11-25 11:23:04)

tahanson43206 · 2019-11-25 12:08:22

For Calliban re #13

Thank you for that very interesting (to me for sure) historical example from the days of mining with rail cars.

Someone in the work crew had a good idea, and management was willing to invest the resources to make it happen.

Then competitors would have copied it << grin >>

For SpaceNut re topic in general ...

Is it feasible for a small consortium in your state to try to implement either of the stored mass concepts we've been discussing here?

The state where I live is flat as a pancake for the most part, although some modest hills are part of the landscape further South.

(th)

SpaceNut · 2019-11-25 19:10:14

Part of the issue for linear power is that the time spent in any 1 section is limited to the length of the car and for how many there are in the train of them.
Lets look at each of the media types and methods to generate the power.as there are drawbacks to each.
Links with water movement:
How pushing water uphill can solve our renewable energy issues

When there is excess electricity, water is pumped through a pipe or tunnel, to the upper reservoir. The energy is later recovered by letting the water flow back down again, through a turbine that converts it back into electricity. Efficiencies of 90% in each direction are possible.

So if we started with 100w we will only have 80w to do work with after efficiency losses using turbines and pipes, and a reserviour to hold the water at the top. Which is the limiting factor for capacity stored....

For earth the Potential energy of a gallon of water at 200 feet = mass of gallon of water * acceleration due to gravity * height
calculations in units of the metric system, so its [8.34lbs*(1kg/2.2lbs)] *[9.8 m/s^2]* [200ft*(0.3048 meters/foot)] = energy required = 2264 Joules.

Lets say you use 10 gallons of water a day. That's [2264 Joules * 10] =22,640 Joules in a day due to lifting the water, or [22,630 Joules/day * (1 day/86400 seconds)] = 0.262 Watts (this is somewhat of a false statistic, because this assumes you're slowly lifting small amounts of water at a constant rate, adding up to 10 gallons at the end of the day). Watts are the number of Joules per second.

https://www.tractorsupply.com/tsc/cms/l … ter-uphill
http://adviceandbeans.com/2011/07/how-t … out-power/
https://www.engineeringtoolbox.com/pump … d_753.html
https://www.homesteadingtoday.com/threa … ll.497739/
https://www.shopyourway.com/questions/1004694

I think that my property has at least a 50 ft rise from a source of water in a small stream for part of the year, so how to generate free electricity to prove out a design followed with quantatative measurements for mass moved to energy returned.

For mars the gravity factor is 3.711 m/s^2

I was wondering if we could use solar heated helium to make the source of power to use to move the mass during the day up the hill versus making use of other power sources.

tahanson43206 · 2019-11-26 05:53:20

For SpaceNut re #15 ...

I liked the TractorSupply.com story about the water ram ... It's nice to see 1700's technology working so well today.

The article was free of numbers, but I'm assuming the amount of water lifted is a fraction of the amount coming from the spring, and the article describes losses along the way to the garden and other destinations, but if the supply from the spring is abundant, then the supply delivered to the needy plants is sufficient.

Thanks for the calculations of a water storage system.

(th)

SpaceNut · 2019-11-26 18:40:06

The term storage implies that we are creating a backup to the primary power system and that if the supply system can not throttle back its energy creation that we have a means to store it for later use. Its the storage for later use that can take many forms for mars. Mars does not have a global grid to moderate the energy use versus creation and will not have one for quite some time. Its also something that need not be delivered from earth and or only the critical parts to which it might be built with.

Another form of storage can be the using of the energy used to do work ahead of schedule for future use and for expansion of the settlement that will happen.

Anyway back to storage as its not just volume and mass as its how much will be the flow rate of either to create the energy from the mars gravity and with the table of values that one can create for the different media we use for the mass.

tahanson43206 · 2019-11-26 19:34:00

Recently a forum contributor described a perfectly reasonable pattern for consumption of solar power collected on Mars (or probably anywhere).

The idea was to "make hay while the sun shines". I'm pretty sure that quote was from Louis, but someone else led the discussion.

Solar power would be consumed while current supply is strong, and then as current supply falls as the planet rotates away from the Sun, consumption would drop to match the available supply.

Today, I got to see a creative thinker in the midst of a perplexing (and very complex) situation. A group was attempting to work out an optimum layout of a physical area, given fixed components of various sizes, and a need to maximize accessibility to all the components. An option was to break apart the components, which were shipped bolted together. I confess that like everyone else, the idea of breaking apart the factory shipped components was simply not available to me at the time. This particular individual earns a living chasing hackers, so it is perfectly in character for this person to mentally shift away from the default. The resolution of the problem was to break apart one of the double units, and stack the parts on top of double units that were already in place. Magically, the needed space for access appeared, and the client group was all smiles.

I say this because I am about to offer what I hope is a way of turning the solar energy usage model on its head. If we combine the gravity cable system that SpaceNut found with Louis' favorite energy source, a field of solar panels, we can slowly lift a set of gondolas up Mount Olympus through the sunny part of the day, running the lifting motors at a slow pace optimized for the available current.

At night, the stored energy can be released in prodigious quantities for industrial purposes, using heavy duty generators turned by the same cable as it is released to flow the gondolas out onto the valley floor.

The power delivered would be of short duration as compared to the painful slow accumulation of energy during the sunny hours, but it would be sufficient (for example) to heat a melt of iron ore (or similar intense application).

Is anyone willing to make a spreadsheet able to show the range of possibilities?

Variables would be:

1) Mass of gondolas
2) Length of cable
3) Desired massive energy flow (ie, current)
4) Duration of desired massive energy flow (ie, work to be done)
5) Solar cell field needed to lift the gondolas to meet objectives 3 and 4

No doubt there are other variables I've overlooked.

(th)

Last edited by tahanson43206 (2019-11-26 19:37:54)

SpaceNut · 2019-11-26 20:27:45

Other items on the design would be the space between gondolas since we would want more than a single trip up or down to prolong how long the energy will be created.
The area at the top and bottom of the mountain must be able to hold these in a waiting state.
The HP of the motor to move the gondola from bottom to top and idle level movement of that gondola to the next location as the next one goes up the hill. Repeating until all are up the hill and on the level area still attached to the cable.
The solar array size must have also batteries to allow for the surge power that will be needed for the HP of the motor to move the gondola one at a time up the hill.
A useable information point would be the ski gondola for part of what is being designed for information of the bottom to top transition.

The track concept if its like train cars would still need a level area at the top to park on and at the bottom there is got to be a slow down up lift to artifically break the cars to a stop.

Something else for the mind to think of is the slope of the rise and its length as well as the hieght of the mountian to calculate the potential energy.

I remembered seeing a conveyor belt lofting the crushed rock to a hieght abouve a waiting truck as the means to fill it and wonder if the idea would apply to getting the mass up the mountain while using the cars to only fore fill the creation of power when released.
Now the amount of energy required to raise an empty car versus a full one must be calculated to see if the conveyor is a better method of mass movement or not.

tahanson43206 · 2019-11-27 05:33:35

For SpaceNut re #19

Thank you for your thoughtful development of the basic idea. The study of existing ski cable transport systems is a helpful suggestion, as is the interesting idea of using a conveyor belt to move mass up the mountain side as a potentially more efficient system.

Overnight I came up with a couple of additional thoughts to add to the mix. The cable idea seems most efficient to me, as a way of transferring energy back and forth between the lift motors and the output generators. However, a monorail system would help to avoid excessive strain on the cable. As originally envisioned in the example that you found, the cable would have to support the gondolas against gravity as well as the strain of lifting them or letting them down gently for power removal.

Today I'd like to add a monorail to the system, to achieve a hybrid effect. The monorail would provide two important functions:

First, it would ease the strain on the cable, by offloading the gravity vector to a rail that would be firmly mounted on the side of the mountain.

Second, it would provide a braking backup system, because otherwise the cable would bear ALL the responsibility for regulating the movement of the gondolas, and that is taking risk a bit too far.

In a monorail system, as in a railroad train in common use today, if the pressure in a safety system releases, brakes would be applied automatically on all gondolas simultaneously.

The engineering team who design the system for Mount Olympus (or any other similar terrain) will secure the measurements of the slope in order to feed them into the calculations for specification of system components.

A possible refinement is to eliminate the landing area at the top, but to extend the roll-out area at the bottom.

What I'm thinking of here is making the storage component the slope itself. The upslope segment of the track would be long enough to accommodate the energy storage needs of the facility at the bottom of the slope, where available power would be drawn off for industrial applications such as melting ore.

The roll-out segment would be the same length, plus a bit more to insure all cars come to a stop.

Regarding any energy left over after the trip down the slope: There should NOT be any energy left, if the generator has done its job of draining that kinetic energy and shoving electrons down the wire to the waiting load.

Edit: It should be possible to build a working model of this system on a property with a 50 foot drop from top to bottom.

The system could be constructed using automobile motors and alternators to lift the gondolas and to draw off stored power.

Local utility power could be used to lift the mass upslope, as a reasonable substitute for solar panels, which can be assumed to work as intended.

The purpose of the exercise would be to take careful measurements of the efficiency of the system, and particularly the practicality of drawing off the stored energy more rapidly than the storing phase. That energy could be dumped into a heating apparatus designed to heat water (for example). The heat delivery could be accurately measured, given knowledge of the volume of water and the temperature change.

The energy input to the system can be measured by any of a number of available digital current/voltage/power measuring devices on the market today.

Losses would be expected in the motors which lift the mass against gravity, the generator/alternator that pulls the energy out of the system, and in various other subsystems such as cables to deliver power between components.

It seems to me (as a wild guess) that 50% efficiency should be achievable, but the ** real ** question is whether the needed heat at the output is delivered.

(th)

Last edited by tahanson43206 (2019-11-27 05:44:44)

Calliban · 2019-11-27 06:12:31

tahanson43206 wrote:

Recently a forum contributor described a perfectly reasonable pattern for consumption of solar power collected on Mars (or probably anywhere).
The idea was to "make hay while the sun shines". I'm pretty sure that quote was from Louis, but someone else led the discussion.
Solar power would be consumed while current supply is strong, and then as current supply falls as the planet rotates away from the Sun, consumption would drop to match the available supply.
(th)

I do think this is the only practical way of using renewable energy. Storing energy is always quite expensive per unit of energy, both financially and in terms of embodied energy. And then there are losses. The embodied energy of renewable energy systems is already quite high, because of their inherently low power density. Adding storage makes the situation worse, as you are effectively building a whole extra power station to supply power when the sun or wind isn't there. Energy losses in storage then direct reduce the output of the system. The combination of these effects absolutely tanks the effective EROI of the system, which is usually weak to begin with.

Traditionally, wind powered ships would sail more slowly when the wind was low and wind millers would grind corn, varying the rate of input, according to the wind speed. In becalmed conditions, they took time off or maintained their equipment. Any realistic transition to renewable energy would need to work the same way. Back-up is ultimately expensive, because in addition to fuel costs, you must pay for capital, maintenance and labour costs for a power plant that is only operating part time. Up to now, renewable energy additions to power grids have been backed up by fossil fuel power plants, that are often old and long ago paid off their capital costs. Renewable energy under those conditions offsets the cost of fuel and total system costs are tolerable. But those conditions won't last forever and they impose a very definite ceiling on how much renewable capacity can be deployed. At present, there is no practical capacity for demand management within national economies.

There are definite problems to implementing this approach. It would mean running factories, retail, domestic loads and transport according to the weather, which is inherently unpredictable, especially on Earth. On Mars, the amount of sunshine is at least relatively more predictable, such that human activities can be planned around the day-night and seasonal cycles. Either way, it is the only workable solution, because it is the only solution that allows reasonable whole-system EROI. It will mean that people are required to work when energy is available, even if it requires 20 hour shifts. Time off will be taken during lull periods, which may begin and end at unpredictable times. Trains will run more slowly when energy production is low and journeys will be variable.

I still think it is a tall order relying on solar power on Mars. Future Martians will need far more electric power per capita than Earth citizens have up to now. They may be able to tolerate the intermittency, but low EROI, expensive power really won't cut the mustard. And the sunlight intensity on Mars is half what it is on Earth. I have looked into solar thermal power on other threads recently. Although it has only half the realistic efficiency of PV, the embodied energy of the systems is potentially lower and they are simple, which should at least equalise EROI. Most critically of all, the hot and cold from the panels can be stored, allowing smooth baseload power production over diurnal cycles. I think this could be very valuable, given the required embodied energy and losses associated with storage of PV power.

Ultimately though, I don't think people will be prepared to tolerate the difficulty of these systems for very long before they opt to build nuclear reactors. We are basically asking people to tolerate being poorer, because we don't like the idea of splitting atoms. How long will any population anywhere willingly tolerate those sorts of conditions?

Last edited by Calliban (2019-11-27 06:28:44)

Calliban · 2019-11-27 06:41:40

tahanson43206 wrote:

For SpaceNut re #19
Thank you for your thoughtful development of the basic idea. The study of existing ski cable transport systems is a helpful suggestion, as is the interesting idea of using a conveyor belt to move mass up the mountain side as a potentially more efficient system.
Overnight I came up with a couple of additional thoughts to add to the mix. The cable idea seems most efficient to me, as a way of transferring energy back and forth between the lift motors and the output generators. However, a monorail system would help to avoid excessive strain on the cable. As originally envisioned in the example that you found, the cable would have to support the gondolas against gravity as well as the strain of lifting them or letting them down gently for power removal.
(th)

I cannot see there being much application for gravity storage using a complex system of carts, wheels, towers and cables. There is just too much complexity, too many stressed moving parts and too much embodied energy in the whole system, to make this useful as anything other than a niche application. Ultimately, this system would have to compete with a pumped storage system, where the only moving parts are the pump and turbine and the fluid drains itself from the storage lake, without any manipulation, through a feeder pipe leading to the turbine. Why attempt to build complex systems handling solids, when such a simple system is available?

That being said, there are niche applications where (solid) gravity storage has and could be useful in the future. (1) We have mentioned the weighted hydraulic accumulators. Useful for supplying modest amounts of energy at high power. (2) If we are mining materials and have numerous deposits at different elevations, it would be beneficial to site the mine in a hill, where we can take advantage of gravitational potential energy. (3) Grandfather clocks are powered by falling weights and this arrangement is still occasionally used for portable devices, where the short lifetime and high cost of batteries demands a more sustainable solution: search for 'gravity powered lights'.

Overall, weighted hydraulic accumulators would be a useful addition to small scale solar power systems, in which power output is limited. Say I wanted to run a load consuming 10kW for a few minutes every hour, but my panels are only capable of supplying power at a rate of 1kW. Gravity storage would be useful for balancing power requirements in a situation like that. A similar situation would be using compressed air tools that have very high power requirements but modest total energy use over a period of an hour, say. We would use a solar powered compressor to fill a weighted air accumulator, and allow time between usage for the accumulator to refill. Such technologies could be very valuable on Earth and Mars.

Last edited by Calliban (2019-11-27 06:52:35)

SpaceNut · 2019-11-27 10:28:14

Calliban wrote:

I cannot see there being much application for gravity storage using a complex system of carts, wheels, towers and cables. There is just too much complexity, too many stressed moving parts and too much embodied energy in the whole system, to make this useful as anything other than a niche application.

The issue for mars is the source of water which is locked up as moisture in the soils at very low amounts and being found to being solid ice in other locations. That leaves basically sand to be used as the working storage with minimal energy input to make it useable as a storage item that can be had. Its the added issues of packaging it for storage that is the issue for movement.

tahanson43206 wrote:

Edit: It should be possible to build a working model of this system on a property with a 50 foot drop from top to bottom. The system could be constructed using automobile motors and alternators to lift the gondolas and to draw off stored power.

The water is plausible for what I have available but design is still less so...
What is missing so far for the water pipeline is the water head pressure and lifting to fill the storage tank size. The inlet to the storage is at the top of the tank while the outlet for the power creation is at the bottom.

As for mars its use of over production of energy above the baseline usage that we can not store from at this point is a single source solar energy production array versus nuclear. A few types of backups that could be done with the excess but most of those mean sending materials, equipment to mars to make them possible.

tahanson43206 wrote:

Today I'd like to add a monorail to the system, to achieve a hybrid effect. The monorail would provide two important functions:

Monorails are unstable for load shifting due to settling or other vibration caused change movement of mass in the container which is true for sand or water suspended on a cable as its going to want to change to stay plumb to gravity so a hinge at the connection point is required for a cable system.

Calliban · 2019-11-27 16:59:13

Interesting gravity storage idea from Heindl energy.

https://heindl-energy.com
https://www.slideshare.net/mobile/Eduar … -2012-rome

On Mars, liquid CO2 could replace water, as the pressure beneath the rock-piston could be up to tens of atmospheres.

SpaceNut · 2019-11-27 19:43:05

Adding a ramp mass in the tank to pressurize the water or as you made note of liquid co2...This is a simular concept to the well tanks that use an inner tube to pressurize the water for you home.

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