A gravity turbine idea

Ok so breaking this idea down into parts:

1. Using the potential/gravitational energy released from a large quantity of mass being lowered down a height, be that water in a hydro power plant, or heavy mass lowered down a shaft, or a large mass moving up/down on rails is known physics and at various scales, proven. However to store energy in any significant quantity, generally requires a combination of very significant differences in height between start/end points and very large quantities of mass than can be transferred. Potential energy = mass x gravity x height

Hydro dams and pumped storage use natural or man-made bodies of water with huge capacities for storing water, i.e. mass, to provide that energy storage. Compare that to a mine shaft, where is that huge mass of water or other material going to be held - does it need a large reservoir at the top? Likewise at the bottom, can the mine accommodate those large quantities of water flow into the base or will it need mining further to expand the capacity? Which then raises questions about constructing a large underground reservoir at significant depth.

There are projects looking at using mine shafts but these tend to be based around the use of solid weights/masses being raised/lowered up and down the shaft on ropes. The challenge of these though would be the quantity of mass, and hence energy stored, is much, much lower due to the limited mass involved. Some designs propose arrangements of using multiple masses, large numbers of weights, but then there's a practical question of handling, connecting, lowering, disconnecting, moving around the weights/blocks. It's comparatively complex compared to using a liquid like water, which simply flows and can be pumped between upper and lower reservoirs.

2. Extracting the energy from the system - with conventional hydro generators, the turbine extracts the energy from the flow of water driving the generator, and they do this with high efficiency. In a system raising/lowering masses along a vertical shaft, so effectively a lift, this would be ropes/chains/pulleys and a gearbox connected to a motor-generator, again likely to be quite efficient. And in both cases, the major mechanical devices and generators are fixed in a stationary position (very useful for construction, operation and maintenance)

I am not sure what benefit is gained from having the generator directly connected to the mass, moving vertically up/down the mine-shaft with the load, I guess it is akin to the concepts of using heavily loaded trains for energy storage, only rather than using inclined rails, this would be a vertical lift shaft. You refer to a cylindrical stator, how long is this cylindrical stator, is it moving with the rotor and connected mass, or is it fixed extending for the whole of the mine shaft with the rotor and mass moving inside the stator?

Ok so breaking this idea down into parts:

1. Using the potential/gravitational energy released from a large quantity of mass being lowered down a height, be that water in a hydro power plant, or heavy mass lowered down a shaft, or a large mass moving up/down on rails is known physics and at various scales, proven. However to store energy in any significant quantity, generally requires a combination of very significant differences in height between start/end points and very large quantities of mass than can be transferred. Potential energy = mass x gravity x height

Hydro dams and pumped storage use natural or man-made bodies of water with huge capacities for storing water, i.e. mass, to provide that energy storage. Compare that to a mine shaft, where is that huge mass of water or other material going to be held - does it need a large reservoir at the top? Likewise at the bottom, can the mine accommodate those large quantities of water flow into the base or will it need mining further to expand the capacity? Which then raises questions about constructing a large underground reservoir at significant depth.

There are projects looking at using mine shafts but these tend to be based around the use of solid weights/masses being raised/lowered up and down the shaft on ropes. The challenge of these though would be the quantity of mass, and hence energy stored, is much, much lower due to the limited mass involved. Some designs propose arrangements of using multiple masses, large numbers of weights, but then there's a practical question of handling, connecting, lowering, disconnecting, moving around the weights/blocks. It's comparatively complex compared to using a liquid like water, which simply flows and can be pumped between upper and lower reservoirs.

2. Extracting the energy from the system - with conventional hydro generators, the turbine extracts the energy from the flow of water driving the generator, and they do this with high efficiency. In a system raising/lowering masses along a vertical shaft, so effectively a lift, this would be ropes/chains/pulleys and a gearbox connected to a motor-generator, again likely to be quite efficient. And in both cases, the major mechanical devices and generators are fixed in a stationary position (very useful for construction, operation and maintenance)

I am not sure what benefit is gained from having the generator directly connected to the mass, moving vertically up/down the mine-shaft with the load, I guess it is akin to the concepts of using heavily loaded trains for energy storage, only rather than using inclined rails, this would be a vertical lift shaft. You refer to a cylindrical stator, how long is this cylindrical stator, is it moving with the rotor and connected mass, or is it fixed extending for the whole of the mine shaft with the rotor and mass moving inside the stator?

Ok, I will try to reply as best I can.

The initial idea is to use mine shafts to house the turbine; some mine shafts are very long with significant galleries that may offer storage and/or drain aways, though geologists would be better placed to comment.

As suggested, if the water supply for the turbine comes from underground reservoirs, supplied by river storm surges, then this could supply the water not far from the surface, given that water can be transported utilising only small drops in levels. As a country, we have to look at ways in which we can mediate flooding given the likelihood that it will become more prevalent and more damaging as time goes on; building the underground reservoirs would thus be, potentially, doubly beneficial. I realise that the volume of water that could be stored and used, would need to be considered, but there may be the potential.

There is no suggestion that the water, as a mass, or as free flowing water, would be moved up and down the shaft. The idea is that the water is ejected when it reaches the bottom of the spindle, reducing the weight of the rotors that needed to be raised to the top of the spindle.

The idea is that the stator covers the run of the rotor, it's run being dictated by engineering limitations and mineshaft depth.

Forgive me if I have failed to address any of your points; I struggle to hold information in my head these days (significant executive function impairment), and trying to go between lists of technical points using very difficult; please do get back to me if I've neglected anything.

If the upper reservoir is a near-surface, but underground, mined reservoir then I think this would be very expensive to construct. It's very expensive to construct a reservoir that's above ground, being underground would add to that cost and complexity significantly. 

The bottom reservoir, at the end of the mineshaft, over time may accumulate water as water is ejected but not returned to the upper reservoir - depending on the natural level of the ground water, mines can naturally flood and can need pumping out so with regular in-flows it could fill up.

An economic factor which would make it very difficult, is how much water would be available to supply the upper reservoir. Typically hydro reservoirs are on the surface, they have large catchment areas and are fed by rivers and steams all year round, relying on significant in-flows. I'm not sure how an underground reservoir could secure sufficient annual water flow.

For the stator, electrical stators are constructed from reasonably expensive materials - magnetic steel laminations, insulated copper windings, frames to hold the assembly together, protective varnishes and coatings. They are engineered to be compact because being big makes them both expensive and incredibly heavy due to the magnetic steel cores, the largest stators you might find on a very large power station are under 8 metres in length, with relatively small bores. compared to a mine shaft.

Constructing a stator that extended over the length of the mine shaft reaching into the high tens or hundreds of metres would, in practice, appear to be impossible due to the size, cost and weight of such a stator. 

Unfortunately even very mature energy storage technologies like hydro, using well established proven technologies are incredibly challenging in terms of the economics to make the projects viable, which is why there have been so few built in recent years. Hydro project of any scale are in the realm of very large projects, they're of a size that even very large companies approach cautiously because of the costs involved.

I do not know the volume of water required to flood a river basin but many river basins flood a number of times over autumn, winter and spring, and, as rainfall tends towards heavier rainfall events, floodings may become numerous. Mitigation of flooding has to happen, at a certain cost; the idea is that some of this money could be funneled towards the building of these reservoirs.

Regarding the feasibility of building the stator; I know that CERN and the LHC use a similar structure, and they are a number of kilometres long, though I accept that the funding model of those projects is in an entirely different realm; I do not know the cost of such a structure as I have solely been concerning myself with the mechanical viability of the turbine.

There is much that remains unknown about the idea, and most of it I simply cannot know; I have tried to turn my thoughts to potential difficulties and to work through possibilities, but my knowledge is limited in every field. But what I do know, and this is certainly true of engineering (though there will be cost parameters at play that don't hinder other projects), is that you never know what can be achieved if the question isn't asked!