If you take a look at the comment that I was replying to, you will have your answer for the first question

I didn't include coal plants because we weren't talking about coal plants.

So I should just ignore the first paragraph of your comment, where you introduce your own context for the rest of the comment and mention replacing coal, oil, and nuclear plants?

Let's play around with the thought of powering all of America with renewables. America’s coal, gas, petroleum and nuclear plants generate a combined baseload power of 405 GWavg, or “gigawatts average.” (Remember, a gigawatt is a thousand megawatts.) Let’s replace all of them with a 50 / 50 mix of onshore wind and CSP (solar)

The person you replied to suggested a solar panel array. You stated you wanted to "play around with the thought of powering all of America with renewables" but then excluded all forms of renewables from your analysis except for two very specific options.

Solar is not one of the "most expensive" forms of renewable.

Who said it was? I said you chose the most expensive way of implementing it with concentrated solar power, a giant array of mirrors that focus light into a central tower. What about regular solar panel installations that don't require a gigantic central facility hundreds of miles from population centers?

Your analysis reads like pure misinformation intent on leading people to believe our only two choices are to stick with coal, oil, and nuclear or pay multiples of our nation's GDP and use several years worth of resources like steel in order to go the "renewable" route.

It'd be like me "playing around with the thought of powering all of America with renewables" and suggesting our only course of action with renewables is putting a giant dome over Hawaii to harness geothermal power from the active volcanoes and then running multiple 10ft thick cables 2,500 miles across the Pacific in order to feed the mainland at a cost of 200 trillion dollars and a 100 year supply of copper. It's an absurd and misleading proposal.

This right here, we could more easily transition to nuclear from coal/oil while building up the infrastructure and scale needed for renewables. In time we can phase out nuclear but at least we could have a stop gap fix in the meantime.

It should be nuclear AND renewables.

It really shouldn't be. Nuclear plants don't emit co2, that's right and that's nice. However, they have so many disadvantages that I can't wrap my head around how they could be considered a viable alternative to renewables.

• They are not economical. Full stop. Building and running them is expensive as fuck, like an order of magnitude over renewables.
• They're risky. People usually argue that this point would be fearmongering, but there's a simple solution for that: get insurance. That's impossible though, no company wants to offer an insurance for nuke plants. Gee, I wonder why? This point adds to the economical issues - if the risk was properly calculated and the according price added to every watt, they would be even more expensive. The only solution here is to socialise the losses and risks - if one of them should ever blow up, society just has to eat it. There's no other way to ruin these things.
• They need to be cooled. With the climate crisis just getting started, this is hard to calculate, but it's already showing. France, with their 80-something percentage of nuclear power, has constant issues to power the country in summer when the rivers get too warm to efficiently cool the reactors. And god forbid one of those larger rivers ever running dry.
• The fuel is hard to get. Most countries need to import the fuel from countries you don't want to depend on, like Russia. It's also limited.
• It's a very centralised solution. That means you'll probably have to rely on corporate solutions, with community-run or private projects being essentially ruled out. That means, power will remain in corporate, for-profit hands. This is also the reason why I think a lot of astroturfing is taking place. Of all the carbon-neutral methods to generate electricity, this is the only one that is almost guaranteed to remain in the hands of the largest corporations. I also predict that any reactor that is at least said to be runnable by smaller communities won't deliver on that promise for whatever reasons, probably safety and security.
• It's not available. A new plant takes decades to build. Any of the new designs that are at least said to offer a solution to one or two of all those issues are not yet tested and will take even longer to be built in larger quantities. We need, however, to ramp up carbon neutral energy production now, not in ten years.

There's my unpopular opinion.