Let me know where I can mine a kilo of sunlight, and when you've got a container I can put it in.

Opining that energy density isn't a useful metric is silly to the point of disingenuousness.

But the metric says nothing about availability. I'm just taking the metric at face value, and showing that it is absurd.

Your answer is absurd. You could also have given the energy density of a black hole and your answer would still not make any sense.

You have demonstrated the point.

Let me know when you can mine a kilo of enriched uranium

I'll bite: the energy density of sunlight on average is something like 1.4 kW/m^2

If you put down a square meter of solar panel, weigh it and run it for an hour to get an equivalent wh/kg and compare to almost any other energy source (except maybe wind?) you will find it to be complete garbage.

The only thing solar has going for it is it's free, basically no waste products and you can find it literally anywhere on the surface of the earth.

That's areal power density.

The energy density of sunlight itself is energy available per kg of mass-energy. That mass-energy can be totally converted to usable energy, unlike nuclear reactions or chemical fuels.

Of course, what this shows is that energy density, as was being used, is a silly metric. By that I mean that it's useful for d--- measuring contests, but not for making any actual decision about what technology to choose.

> basically no waste products

Only true if we can 100% recycle all materials that go into harvesting solar energy, which is not true today (and not a priority, either).

It seems you've written c² in units of Wh/kg? But the fact that per arbitrary mass, you can theoretically get more energetic reactions than by fission or even fusion doesn't mean comparing the productivity of fission to oil is silly. The issue is realistic ways of efficiently liberating and harnessing energy from matter.

One better than fusion not impossible option is carefully feeding small black holes and extracting their huge output of energy. The feedstock for the black hole might even be lifted from the sun. In the meantime, fission is a productive and practical option to add to the energy mix that will more than serve until we've worked out fusion.

One place I think I agree with you is that phrasing it as energy density, rather than focusing on efficiency of a given unit of mass or fuel at yielding energy can be a bit obscuring. That is, it's better to focus on sustainability of fuel source. Energy density (J/m^3 and J/kg, specific energy) are units more appropriate for talking about energy storage and bombs.

> Energy density of sunlight: 25,000,000,000,000 wh/kg.

You can get a scoop of sunlight from where, exactly?

You have failed to understand the point I was making. See upthread.

You're comparing the wrong things. Those weights are of energy stored, but with light it is in motion. Maybe if you manage to get some light stuck in a crystal we can have a meaningful comparison.