Single adjective meaning "does not use much energy"

Is there a single adjective that means "does not use much energy" / "not using much energy"?

I do not mean "efficient".

Efficient means something that does not waste much energy - something efficient could use a lot of energy for a specific purpose, yet not waste much energy on actions that do not achieve that purpose/not waste energy as heat or sound or whatever.

However, something *word I seek* may or may not be efficient, i.e may waste very little, or very much energy, in trying to perform a task, but does not/will not use or consume much energy in trying to perform the task - whether some of this energy is wasted or not.

Solution 1:

I suggest "economical".

"Economical" does not just mean sparing, or careful in the use of one's money. It can also apply to resources such as energy use. Use of energy can be "economical" by increased efficiency, or a higher power/input ratio. It can also just mean sparing in terms of energy use.

Solution 2:

low-power or maybe low-powered

From a physics standpoint Power = Work / Time. A low-power device does not take in much (electrical) energy. (In the end, all that energy comes out one way or the other. Often much of it as heat.)

Solution 3:

Energy-saving is the adjective that is generally used and that may fit your description: ​

• relating to products, systems, etc. that use as little electricity, gas, etc. as possible:
  • an energy-saving appliance/light/product energy-saving technology/material an energy-saving initiative/measure/step

Cambridge Dictionary