China is definitely pumping money into its manufacturing capabilities, but I don’t think cornering the international market is why.
What appears to be happening is that local officials pushed an industrial development policy to make economic numbers go up. Some provinces got to the point of building factories and leasing them out to companies for that sweet economic growth.
The Chinese national government is trying to find a market for this since it can’t afford for all Chinese local investment to be bad. Developing countries don’t have the funds for the cheap solar output and the other industrialized nations are putting up trade barriers since they are running massive trade deficits with China already.