Spaced-apart cable modules in wellbore energy storage and retrieval

1. A system for storing and retrieving energy comprising:

a cable;

a weight connected to the cable;

a plurality of cable modules attached at spaced-apart locations to the cable above the weight, each cable module being configured to prevent the cable above and below the cable module from coming in contact with a neighboring stationary wall; and

a hoist configured to controllably raise and lower the weight by sequentially grabbing each neighboring cable module.

2. The system of claim 1 wherein the weight is in excess of one ton.

3. The system of claim 1 wherein the hoist includes at least one hook configured to sequentially grab each neighboring cable module when controllably raising and lowering the weight.

4. The system of claim 3 wherein the hoist includes multiple hooks, each configured to sequentially grab each neighboring cable module when controllably raising and lowering the weight.

5. The system of claim 4 wherein the hoist is configured such that at least two of the multiple hooks grab two neighboring cable modules at the same time when controllably raising and lowering the weight.

6. The system of claim 1 wherein each cable module has at least one wheel configured to reduce friction between the cable module and the neighboring stationary wall as the cable module moves with respect to the neighboring stationary wall.

7. The system of claim 6 wherein each cable module has multiple wheels configured to reduce friction between the cable module and the neighboring stationary wall as the cable module moves with respect to the neighboring stationary wall, at least one of the wheels having a rotational axis that is angularly displaced from the rotational axis of another of the wheels.

8. The system of claim 6 wherein each cable module has multiple wheels configured to reduce friction between the cable module and the neighboring stationary wall as the cable module moves with respect to the neighboring stationary wall, at least one of the wheels having a rotational axis that is longitudinally offset from the rotational axis of another of the wheels with respect to the longitudinal axis of the cable.

9. The system of claim 1 further comprising:

a motor connected to the hoist and configured to cause the hoist to pull on the cable causing the weight to rise, thereby converting energy that drives the motor to potential energy;

a generator configured to capture energy generated when the weight is lowered, thereby converting at least some of the potential energy to kinetic energy; and

a controller configured to deliver energy to be stored to the motor during one time period, thereby storing the energy in the weight, and to allow the weight to be lowered while driving the generator during another time period, thereby retrieving at least part of the stored energy.

10. The system of claim 9 further comprising a brake configured to controllably prevent the weight from being raised or lowered.

11. The system of claim 9 wherein the motor and the generator are in different housings.

12. The system of claim 11 wherein the motor and the generator share a common shaft.

13. The system of claim 11 wherein the motor and the generator do not share a common shaft.

14. The system of claim 9 wherein the motor and the generator are in the same housing and share a common shaft.

15. The system of claim 9 further comprising a transmission positioned between the cable and the motor and/or the generator to modify the torque that the motor applies to the cable and/or the cable applies to the generator.

16. The system of claim 15 wherein the amount of torque modification provided by the transmission is controllable.

17. The system of claim 9 further comprising a wellbore in which the weight is positioned.

18. The system of claim 17 in which the length of the weight is approximately half the depth of the wellbore.

19. The system of claim 9 further comprising further comprising a brake configured to controllably prevent the weight from being raised or lowered.

20. The system of claim 19 wherein the controller is configured to:

actuate the break when energy is not being transferred to or from the weight; and

deactivate the break when energy is being transferred to or from the weight.