I have my quite positive experience with solar too. But "90% population" claim is unrealistic.
For starters, solar needs batteries to be truly effective. Batteries need rare-earth metals which is a narrow bottleneck. It's fine to buy 4 batteris for yourself but procuring a million will raise prices and probably break backs of many projects. A trillion, and you probably igniting wars for resources.
Also we can't multiply a homesteader's optimum a million times and expect it to be close to what a million people industrial city really needs.
At a large enough scale everything gets different.
Yet the US government just asked for $200 billion to materialize out of thin air to support a needless conflict. Even if it cost a trillion dollars, that is decades of long term energy independence.
Battery chemistries for grid storage are moving toward commodity elements and rapidly reducing reliance on rare earths. Sodium and Iron/Air batteries can take over fairly easily.
For starters, solar needs batteries to be truly effective. Batteries need rare-earth metals which is a narrow bottleneck. It's fine to buy 4 batteris for yourself but procuring a million will raise prices and probably break backs of many projects. A trillion, and you probably igniting wars for resources.
Also we can't multiply a homesteader's optimum a million times and expect it to be close to what a million people industrial city really needs.
At a large enough scale everything gets different.