Hm, looking further, this NY times article says the Talatan Solar Park is 162 square miles, which would be 263km². But as you say, I also don’t know how they’re measuring it, so it’s difficult to nail down a solid number to use.

at 263km² it would take 22 years, and at 100km it would take 60 years to build enough panels. That’s a pretty huge gulf between them, so it’d be nice if we had more concrete stats to work from. If we assume that global solar manufacturing will increase in the future (during the build out), and account for global production and not just China, I still think we could fit it somewhere around 30 to 35 years.

Plus your math assumes we stop using solar panels worldwide and 100% production goes to our new little Apollo Program for the however many years.

The article mentions that there would be significant environmental drawbacks if every square inch of that 320,000km was turned into solar farm, it just uses it as an example of how much more efficient the biofuel land would be with panels in any percentage. It seems to make sense to convert it wherever possible, at least as a more effective use of the land, production and emissions-wise.

My calculations presumably still mostly work (I think) assuming all solar panels manufactured globally are eventually installed somewhere, not necessarily only on biofuel land. It seems fairly inevitable due to the economics of solar and wind that virtually everything produced will be installed somewhere (though some countries will be slower to adopt than others depending on how much the fossil fuel industry has control over local politicians), and thus if things continue as they are, we could almost certainly be totally off fossil fuels within our lifetimes.