When one decides to use gravity to store energy the subject of efficiency dominates the design of any method used. The material used for energy storage is important. A rigid object placed in the Carriage of a Lifter gives one several advantages. It can be designed to support itself and depending on the type of material, it may have a high density and occupy less space. Despite these obvious advantages, using a solid mass in the Lifter requires the lowering of the mass in a controlled manner to retrieve its stored energy. This means the Carriage must be supported as it is lowered and the energy extracted by some combination of pulleys, wheels, gears, chains, etc. It doesn't take many mechanical stages for a real efficiency loss to add up. Most lifting machines use the same mechanical method to lift an object as they use to lower it. This doubles the efficiency loss of the method and if the method is used to store energy it is quickly seen to be ineffective for that purpose. Hydro storage is a storage method that can and does use the same turbines to pump water up to a storage area and to flow water back through its turbines to extract the stored energy. This method claims to be 80% or greater. It would be advantageous for a Lifter to use some of this technology. A Lifter, configured to use water or some other material, with a fluidic nature, can realize some of the efficiency benefits seen in hydro storage.
The drawing to the right shows a Lifter design using water as the material in its Carriage. Since water weighs about 63 lbs/cu-ft and concrete weighs 150 lbs/cu-ft, the actual size of the Carriage will be larger. There are several advantages to using water. One advantage would be the lack of a need to have a strong physical method to lower the Carriage, since the Carriage is not lowered to extract the energy stored. This means that it is possible to discard low efficiency mechanical stages to extract the stored energy in the Lifter. The water in the Carriage is simply allowed to flow out of the Carriage down to a paddle wheel, turbine, or some similar device. Using this method to extract stored energy makes it easy to apply a variable force to the extracting device. One merely increases or reduces the flow of water and the output power will change.
Looking at the drawings it will be seen that, despite the obvious advantages realized by using water, there are some disadvantages. Figure 1 shows a side view and Figure 2 shows a front view of a Lifter using water in its Carriage. The Carriage, before being tilted up, occupies a carriage refill position at the base of the Lifter. This position is low enough to allow it to be filled from a refill tank. The distance from the refill position to the top of the refill tank represents an efficiency loss due to the fact that the Carriage will have to be tilted past the refill tanks before the height of the raised water can contribute to storing any energy. This distance is also an efficiency loss when extracting energy from the system due to the fact that the energy recovery area must be high enough to allow the recovered water to drain back into the refill tanks. The second drawing shows how efficiency is impacted by a Lifter of this design. As the height of the Lifter increases, so does its overall efficiency. This is counter-intuitive, as most lifting machines do not increase in efficiency simply by increasing the distance they lift. The table shows that as the height of the Lifter increases the combined height of the refill area, the reservoir and the energy recovery area, becomes less of a factor. Keeping this in mind, a tall Lifter has a greater efficiency.
A Lifter of this design would provide an output efficiency comparable to one using gears, pulleys, etc. when the Lifters usable height is low compared to the operating space of the refill area, reservoir and the energy recovery area. By increasing the overall height of the Lifter and keeping the reservoir height as low as possible, the effective efficiency will be increased.
Here you may see a small model, designed for teaching and demonstrating water power, the PowerWheel and another with some additional useful information, the Water PowerWheel. They use a Pelton water wheel, which is considered to be very efficient. Also, I didn't know that water power was widely used in some cities in recent times to power household items. Water Motors