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.
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.
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).