It makes perfect sense to look at energy + container subsystems.

It doesn't make sense to look at that in a vacuum. Energy transport over wire via electricity is much "denser" than transport via liquid or gas.

"It depends" is the correct answer, but the equation is shifting quickly towards solar + electricity.

	▲	jacquesm 2 hours ago \| parent [-]
		You're the one looking at it in a vacuum. Engineering is all about looking at it in context and the main context where density of energy is important is in vehicles of all shapes and sizes. That's where the rubber quite literally meets the road. You can then theorize about what the 'weight' of the electrical energy is but it is pointless: the weight of container dwarfs the weight of the energy carriers (effectively the electrons) themselves. In the case of fossil fuels the ratio is more balanced, the container will weigh a couple of kilos and the fuel will way a bit more (say 10:1 or 20:1). So to compare the one with the other we weigh the batteries and ignore the electrons and we then compare that with the fuel because that is the dominant factor. Solar + electricity are not directly suitable for powering electric vehicles, that's where the batteries come in. Comparing apples (transport of electricity via wires) with oranges (transport of energy via liquid or gas) misses the elephant in the room: you are not going to be able to use those electrons without a suitable temporary storage medium unless you plan on carrying a very long and impractical extension cord behind your now very light EV.

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tavavex an hour ago | parent | prev [-]

Why? In the context of the electrical grid, has the amount of storage you can have in the backburner ever been a choke point? If anything, fossil fuel power plants have the very same batteries to buffer some energy. But for the vast majority of power consumers that can just exist on the grid, power storage is nearly irrelevant because it can go directly from producer to consumer. Even in places where storage is relevant (anything that can't be tethered to the grid, like vehicles) the equation is different because the infrastructure you need to convert fuel to power (engines vs electric motors) don't weigh the same. Yes, even with that, pure electricity still falls behind somewhat, but it's getting better. And I was mainly talking about the power grid anyway, with how universal and important it is. Fossil fuel straight up loses in that sector, like what I said before, so replacing it is an easy choice... and yet we don't do that.

	▲	jacquesm an hour ago \| parent [-]
		The only context in which comparing power densities makes any sense is the vehicular one.