Temperature is the physical quantity that defines the grade of a heat source, or an application of thermal energy. That includes sources of electromagnetic radiation, such as the sun (6000K), lightbulbs (3000K) and lasers (the laser itself may be cool, but its radiation is very high grade because a focussed beam can really cook things.)

With chemical reactions you are looking at measures based on Gibbs free energy (at constant pressure) or Helmholtz free energy (at constant volume).

Mechanical and electrical energy are generally considered to be very high-grade. However, only a few mechanical and electrical devices can actually operate without any degradation of energy. Superconductors are the obvious example.

So much for the physics. In the real world, you have to decide how much physical perfection your budget will stretch to - as SteamyTea implies.

I was hoping you would remind us, ST