13b parameters works out to about 9GB. You need a bit more than that since it needs more than just the model in memory, but at 24GB I'd expect at least half of it to go unused. And memory doesn't use much power at all by the way. LPDDR4 uses something like 0.3 watts while actively reading/writing to it.

The actual computations use more, obviously, but GFX cards are not designed for this task and while they're fast most of them are also horribly inefficient.

I run 13b parameter models on my ultra portable laptop (which has a small battery, no active cooling (fanless) and no discrete GPU). It has 16GB of RAM not GPU memory - RAM, and I'm running a full operating system, web browsers, etc a the same time. Models like llama2, stable diffusion, etc get perfectly usable performance without using much battery at all (at a guess, single digit watts while performing the calculations).

There is efficient hardware now and there will be even more efficient hardware in the future. My laptop definitely isn't designed to run these models and on top of that the models aren't designed to run on a laptop either. There's plenty more optimisation work to be done in the years to come.