Actually, the majority of the weight would be in steel rope. For one type [0], the safe limit is a tensile load of about 134-150 MN/m^2 (= MPa) [1]. At a densi

Actually, the majority of the weight would be in steel rope. For one type [0], the safe limit is a tensile load of about 134-150 MN/m^2 (= MPa) [1]. At a density of 8 g/cm^3, the limiting length of a uniform cable is ~1.7 - 1.9 kilometers. If you have a stationary, suspended cable of this length, its own weight puts it at its maximum load; it can't lift anything else. Steel rope on McMaster is around $10,000/ton [of rope]. So, these assumptions are a dead end. You can't solve this by using shorter cables, because that decreases your energy capacity at the same rate. If you use cables of 1/10th the length (~100 m), you get only 1/10th the potential energy storage per ton. The cable thickness per lifted ton is constant. [0] http://www.engineeringtoolbox.com/wire-rope-strength-d_1518.html http://www.engineeringtoolbox.com/wire-rope-strength-d_1518.... [1] The breaking limit of rope is far higher (~700 MPa), and the breaking limit of a single wire strand -- the tensile strength -- is higher still (1,770 MPa according to [2]) For the cross section area, I'm assuming a circular rope (not accurate). [2] http://www.gabaswire.com/en/overview/grades-of-wire-rope.html http://www.gabaswire.com/en/overview/grades-of-wire-rope.htm...