I was trying to estimate the mining footprints of solar and nuclear, and came up with some
very tentative rough estimates that ore input for solar energy might have an energy density (per
unit mass) ~ 5 to 80 times
coal, while nuclear (convential US fuel cycle) may be ~ 20 times
coal — on the solar side, this doesn't include some balance of system components, and on the nuclear side, it only includes the U, but on the solar side, the actual energy density could get much higher with recycling of the same material into multiple successive generations of solar energy devices, and on the nuclear side, breeder reactors.