The answer is China (well, Asia, really).
Now that we've answered that, let's pose a new question:
Why is China capable of such investment but not the United States, even though the United States has more money?
https://news.mit.edu/2018/explaining-dropping-solar-cost-112...
> China’s fledgling solar-electric panel industry dropped world prices by 80 percent, a stunning achievement in a fiercely competitive high-tech market. China had leapfrogged from nursing a tiny, rural-oriented solar program in the 1990s to become the globe’s leader in what may soon be the world’s largest renewable energy source.
https://www.scientificamerican.com/article/why-china-is-domi...
China has the plurality of solar installations, produces the majority, have given historically the most aggressive tax credits for production and use, and is forecasted to have the most growth.
I just wanted to point out that nations around the world had decades long plans around developing solar because it always made sense, and everyone who looked into it knew this.
The question of why China benefitted so much is interesting, and I personally think it comes down to them not having much local fossil fuels, and therefore not having the people who control fossil fuels as a political drag factor in their politics.
2. China has a centralized and powerful government in the mainland managed by a single party, when the supreme leader says "I want something", deem it as done. It cannot be worse when going in the wrong directly but vice versa, nothing can beat it when in right direction. Renewable energy is one example. Other examples such as high speed rail systems and fiber network rollout were almost exactly the same story. China's first generation CHR was not that good at all but after decades of massive deployment, I really cannot see any high speed rails system better than China's. China's national fiber rollout started around 2009 which was after Australia's NBN plan, when most of China's telecom infrastructures were actually copper. Now China's fiber networks has covered around 95% of the population but much of the NBN is still on HFC or VDSL.
For reason #1, no country can compete in short term. For reason #2, hard to say good or bad now. I used to hold a negative view on that. But recent COVID responses around the world just showed me a different perspective.
When highway construction offers bonuses for fast construction, things go quickly. When governments have no idea what something should cost and offer cost plus contracts, the costs skyrockets and the gravy train rolls slowly. https://www.nytimes.com/2007/06/02/us/02ramp.html