Andy,
Both really, there is an extreme shortage of over 35,000 wind farms on LU, production clearly can't keep up.
Additionally, most Wind Farm Corporations barely make money, because they have high material costs, but their profit margin percentage is small. That means that although they are theoretically profitable, that profit is wiped out by the market quality downgrade when selling to the global market.
Players won't make enough Wind Farms to supply the market when the corporations hardly make money.
Personally, I'd recommend raising the base output of Wind Farm Corporations, (without raising input requirements) to help solve both problems.