That HVDC transmission is far from free. If you have enough money, you can certainly use renewables for all electric power generation. If you have enough money.

And, even with such a system, can it provide the grid reliability we have today? And, how much excess capacity is needed.

Note that solar and wind levelized cost of energy is grossly underestimated - or more accurately, isn't the way to measure the cost. It does not include the cost of transmission, nor the cost of backup generation capability and backup power costs.

And, the "nameplate capacity" of most wind is way higher than the amount of energy you can actually get. (i.e. the "capacity factor" is low).

But lets say we do all of this, and beggar the US consumer with the costs. The mainland Chinese will keep on bulding coal plants, because they don't give a damn. India can't afford to give a damn, they have too much energy poverty. And Africa?

Better to look to mass produced nuclear plants, as Bill Gates is also doing. Nuclear power need not be as expensive as it is in the US. France has the lowest carbon emissions for electricity production in Europe, because it is 70% nuclear.