# Superconducting magnetic energy storage, practical?

1. Jan 28, 2015

### zhanhai

Storing energy in a system means to raise the internal energy of it. A system could be in superconducting phase because the latter has correspondingly lower internal energy. How can energy be stored in a phase that has the lower energy? When energy is injected into the system, it would leave superconducting phase.

Is there a dam-like mechanism between superconducting state and normal state? If yes, what is it?

2. Jan 29, 2015

### Staff: Mentor

The cooper pairs have a slightly lower energy than individual electrons, but you don't want to break them up in superconducting energy storages so this number does not matter.
The magnetic field around the superconductor (from the current flow) can store energy.

3. Jan 30, 2015

### zhanhai

If an electron becomes a carrier, the corresponding increase of magnetic energy is associated with that electron's state so its total energy increases, and the electron possibly could release some of its energy to avoid that the energy of the electron system becomes too high. I just tried a model and it did include such a process.

BTW, many web pages of SMES have become dead links. Is there any evidenced SMES device?

4. Jan 30, 2015

### Staff: Mentor

This is not true, as you can see from superconducting energy storages. The energy is in the field.
Every MRI system works as one, although a recovery of the energy is not done. The LHC magnets store a huge amount of energy (~10 GJ). Wikipedia has some non-dead links. They exist as commercial products.

5. Jan 30, 2015

Staff Emeritus
The question was "practical". The LHC has a capital cost of something like $2000000 per kWh, give or take a factor of 2. That ignores operating costs. The equivalent cost for a lithium-ion battery is$20. So, no, it's not practical, and costs will need to fall by something like 100,000 or more before it becomes so.

6. Jan 30, 2015

### Staff: Mentor

The topic has "practical", but the questions inside were purely about the possibility and if devices exist: yes they do. The LHC is not designed to be a cheap energy storage, obviously, as it is a particle collider.

7. Jan 30, 2015