🚀 go-pugleaf

The low current density of the new materials (order of 1000 A/cm^2)
is already history. Samples of the new material that were created by
vacum deposition techniques showed current densities arround
10^5 A/cm^2 at 77K. This is similar/better than the values for conventional
superconductors. In addition, critical current densities of up to
5*10^6 A/cm^2 were reported for the new material when cooled to 4K.

A superconducting energy storage device is simply a coil with a
superconducting switch. The stored energy is 0.5*I^2*L, were L is the
inductivity of the coil. Using ferromagnetic materials for the coil
is useless because their permeability decreases to 1 at high magnetic
fields. The real problem is to prevent the coil from destintegration due
to the high mechanical forces on the current carrying wire.

The inductivity of a cylindrical air coil is roughly 
    L = N^2*r^2/(9r+10l) *10^-6 Henry    (l,r are in inches here)
You see that the stored energy for a fixed size coil does not depend on N
(the number of turns). Assuming a D-cell sized coil (50% conductor, rest
mechanical support and current switch): l=2", r=0.5", N=1 => L=10nH
This coil uses about 5cm^2 to carry the current => I=500KA
Total eneregy storage would be 1250 Ws. A normal NiCd rechargeable battery
of the same size has roughly 18000 Ws!

On a larger scale, things look better for SC energy storage but the large
magnetic stray field might be unacceptable.

  --  Andreas