I've read the issue is not so much capacity but curtailment as many of these renewable power plants are further out west, meaning getting the electricity to the big energy hungry cities further east is the problem, hence why China has been building out ultra high voltage UHV transmission lines. I have also read that at least in the past (I may be out of date) was how the electricity was bought. Namely that each kind of production would be given certain quotas meaning non-renewable energy power plants like coal would also receive quotas, so excess renewable energy capacity above their quota would be curtailed and not used. Past attempts at switching to more market driven pricing or prioritizing renewables in some provinces had been tried but had collapsed due to resistance from entrenched interests like the fossil fuel energy producers and power plants. I don't know whether they have attempted again.