Based on the price my father recently paid to put some solar panels on his roof, that 3 million could have been spent putting solar panels on the roofs of ~100 houses, each with enough panels to have them be a net source of power.

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Very, VERY simple argument here:

No, it doesn't, not significantly. The cost there is largely energy input. 20 trillion is a very approximate number, so if you want to knock a couple of trillion off, go right ahead. Does it change the picture at all?