First, the home page lists some energy storage ideas, such as hot water heaters that store thermal heat. Click the link at the bottom of the page to see them.
Lift-Based Electrical Storage with Water Head: (Posted 1/16/2025)
Think ski lifts. An ES system could comprise a detachable cable lift running up a mountain, the lifted masses are then routed to lateral detachable lifts top and bottom to store. Mountain tops can store an almost unlimited amount of mass, and store it indefinitely. Nothing else comes close in that regard. So, the question is cost and round-trip AC to AC return efficiency (AC-AC RTE). Considering that cable/rope transmission systems are in the 80% efficiency range, it looks possible for a cable lift energy storage system to be in the range to compete in efficiency.
For comparison, here is a list of common Energy storage systems: (From: https://www.pnnl.gov/sites/default/files/media/file/ESGC%20Cost%20Performance%20Report%202022%20PNNL-33283.pdf )
AC-AC RTE: Lithium Ion: 83%, Lead acid: 75% ish, RFB flow batteries: 65%, Zinc Air: 70% ish, HESS: 32%, Gravity: 80-90%, PSH: 80%, CAES: 70% ish.
So cable lift storage looks to be competitive. But more interesting is that it’s possible to take heavy buckets uphill, and then tap some water mid mountain to fill the buckets for the downhill. In this case, a lift-based energy storage is a part mechanical hydroelectric power plant, functioning similar to a penstock system. There is the potential to get more electrcity out than electricity put in with the addition of the water head. The amount of water need not be that great, as the water head is high. Getting water from a mid-mountain stream does not require anything but a small diversion dam. With this addition, it looks like this installation could surpass all the other types of ESS. It should also be noted that lifts can last a long time. There is not the cycle degradation of batteries.
Large Reservoirs, Lakes, Rivers, or Oceans as PV Generators and Storage Devices: (Posted 9/4/2021)
Covering water with solar PV panels does two basic things. First, it generates electrical energy. Second, in reduces evaporation loss. It has been suggested by others to cover California's water canals for just these purposes. Lake Mead, for example, loses about 6 feet per year in evaporation. Cover a significant amount of the lake with PV panels and it might be possible to reverse the decades long reduction in the lake's height. Besides having a mostly unobstructed view of the sky, a lake's water can also be used to cool and clean the panels. So a lake is great place to put PV panels. (Wind or wave power can also be sited there.)
But the sun doesn't always shine, so storage is needed. It turns out, a lake is also an excellent place to store energy. Energy can be stored underwater using an evacuated space, such as a sphere. "To store energy water is pumped out of the sphere using an electric pump and to generate power water flows through a turbine into the empty sphere and produces electrical energy via a generator." (See: "Energy storage system of tomorrow tested for the first time in Lake Constance")
This idea, which comes from two physics professors from Goethe University Frankfurt and Saarland University in Saarbrücken("US9797366")). This ideas does not have to be limited to spheres. The shape could be a tube, which could be placed down the center of the lake at the lowest depths. In this way, a lake or reservoir can not only produce hydro electric power, but it can also provide solar generated power plus storage. Further, if the tank is evacuated, the lake level rises. Higher water height makes for greater electric hydropower generation, as power is only based on water height. The only visible part of the storage device is a small electrical cable coming out of the lake. Of course, that could be buried.
Thus, present hydroelectric dams throughout the world can be turned into much larger electrical power generating resources. So can lakes, rivers, and the ocean.
Here are some more new ideas:
Large flywheels: (Posted 8/29/2020)
If one compares how much energy can be stored in a large flywheel, it is generally quite favorable to storing energy as potential energy at a height. For example, if a mass at a 100 meter height is compared to a 100 meter radius flywheel, the numbers work out thus:
mgh = 1/2 * Jm * w2, where J = 1/2mr2 for a disc, and w = 2πnm. (nm is rotations/s)
Thus, m * 9.8(m/s^2) * h = 1/2 * (1/2)mr2 * (2πnm)2
"m" cancels and this simplifies to:
9.8(m/s^2) * h = (1/4) * r2 * (4) * π2 *(nm)2
"4" * "1/4" cancels, π^2 = 9.87, and rearraigning we get:
nm2 = (9.8(m/s^2) * h) / (r2 * 9.87)
For a radius and height of 100 meters:
nm2 = (9.8(m/s^2) * 100(m)) / (100^2(m^2) * 9.87))
Thus, nm = sqrt((9.8 * 100) / (10,000 * 9.87)) = 0.0996 or approximately 0.1 rotations per second
For 100 meter height and 50 meter radius, n = 0.1993, or approximately 0.2 rotations per second. The velocity of the outside edge equals 62.8 meters/sec or 140 mph. So, the average velocity would probably be about 2/3 of that.
So, a 50-meter flywheel spinning at 1 revolution per second would equal the storage height of about 500 meters, which is about 1500 feet.
What this shows is that it is entirely reasonable to consider large flywheels for energy storage. Flywheels have several challenges. First is friction. State of the art flywheels have rotors of carbon fiber spinning on magnetic bearings. This gives excellent performance, but at a cost. By contrast, a really large flywheel could rotate much slower. Spinning friction rises linearly with rotational velocity, so a slowly rotating large flywheel would not necessarily need expensive magnetic bearings. One advance of recent decades have been ceramic bearings. They can be run without lubricants and can be very efficient. So it is worth a look as to how much friction would be in a large flywheel at very low rotational velocities.
My idea would be to have a minimum of three stationary wheels on the ground supporting the giant disc. Ceramic bearing as large as eight inches are made, which can make for wheels that support a lot of mass. In this design, the wheels are connected to, or comprise electric motor/generators.
Now flywheels have some problems. One problem is vibrations that can increase and lead to failure. For a really large flywheel at a relatively slow rotational speed, vibrations shouldn't correspond with any resonant frequency. The wheel attachments to the ground could damp out any vibrations. Highly precise materials should not be required to balance the flywheel and it should be able to be made of inexpensive materials. The cost and tech should all be in the low friction wheels.
Regarding aerodynamic drag, a large flywheel rotating slowly would not have so much. There is no induced drag, just friction drag. Wind would cancel out. But, it could, of course, be in a low pressure/vacuum environment. Just how much energy could be stored in a structure of similar size and shape to the Pantheon in Rome?
The devil is always in the details, and I haven't really studied this much. One of the issues is the load on bearing from the change in position of the Earth as it rotates. Flywheels don't want to be rotated. The solution there is to align them to spin with the axis parallel to the Earth's axis. Regarding the rundown problem of flywheels, it seems that turning it into a partial water wheel might solve that. It seems large flywheels deserve a look.
Regarding MGH Storage: (Posted 8/29/2020)
"MGH" means mass times gravity times height. It is a simple way of saying that mass can be taken up to a height, and energy generated when the mass is lowered back down. There are several new projects currently happening now. Gravity based storage can have excellent return percentages. Ares, a company is building a first site in Nevada is using rail road equipment to carry weights up a hill. Steel wheels on steel rails happen to be quite efficient. Likewise, electric motor/generators are very efficient. So the electricity returned is expected to be about 80%, which is quite good.
I think this has a lot of potential, particularly if they move away from railroad equipment. Right now, they bulldoze a grade. If they could move to building by inserting a post, and then placing a beam between the posts, they can build over land without much disturbance at all. They also would not be limited to a specific grade if they think more creatively about using a specifically designed rail. This would open up many more sites. Here is a link to their site:
https://www.aresnorthamerica.com/
Other MGH ideas are out there. Some based around assembling a tower with a crane and then disassembling it to generate power. Pumped Hydro storage is also a form of MGH storage.
Regarding Compressed Fluid Storage: (Posted 8/29/2020)
There are interesting forms of compressed air storage that store the heat of compression, and then use that heat to warm the expanding air during the power generation stage. This is called near-isothermal compressed air storage. It has the potential to be much more efficient, as compressed air storage is generally bad, due to all the lost heat of compression. What I haven't seen are any that place a phase change material right into the storage tank. I could imaging having an underground, or in lake tank that essentially is at a near constant temperature year round. Then one could choose a PCM that phase changes at that temperature. One thing to realize here is that the conduction improves between the PCM material and the compressed gas, as the gas has a higher density.
These designs can also ultilize waste heat to further heat the stored air upon exit from the storage tank. It is possible to get good return rates with near-isothermal designs.
Pumped Hydro-based Electrical Storage: (Posted 7/19/2020)
Pumped hydro storage is known. In this form of electrical grid storage, water is pumped up hill to a water reservoir. The when electricity generation is required, the water height is used to make electricity. This works. But the round trip efficiency is not particularly good. One wonders if it would be better to lower water in an electrified railway, as steel wheels and electric motors combine for higher efficiency than turbines, but that is another subject.
Dams generally comprise the potential for pumped hydro. But most people underestimate, or don't know about penstocks. Penstocks generally have a small dam (forebay) that collects water, but not seasonal storage. What is generally missed is that the power to produce electricity is not determined by how much water is behind the dam, it is determined by the height of water behind the dam. So a thousand foot drop penstock can make ten times the power of a dam with a 100 foot head height.
So, the idea here is to simply make a penstock that is designed only to be used during peak electrical demand. The penstock dam would only need to store water for half a day, for example, and then run twice as much water through it during the other half. This might seem to be of higher cost, as the equipment is only used for part of the day. Also, it would have higher capital costs. But designing a system to handle, say, twice the flow rate does not cost twice as much. For an example, cost, a pipe that carries twice the flow rate should only need 1.41, or the square root of two, more material due to the scaling of area versus circumference. One would expect that construction costs would be barely more. So considering that a penstock designed to produce power for only half the day would be generating electricity at higher rates, then the higher initial investment pays off.
The suggestion here is to simply build penstocks larger than the flow of water would normall support for part time use. A penstock of this design would then avoid the uphill pumping losses of pumped hydro, instead simply storing water at a height in the forebay. This would be significantly more efficient. It would not, though, use excess electrical energy. But that is better done with hot water heaters.