The Indo-US solar war at WTO has many layers of complications. Here is an article discussing the nitty-gritty of the WTO rules, and whether subsidies can be provided or not (as per the rules, which everyone breaks as per their requirement!). Follow the link to read the whole article, a short summary of the findings is as follows.
A policy relating to Domestic Content Requirement or local content requirement under JNNSM Policy, Phase II, Batch I will almost certainly infringe the national treatment obligation under the WTO rules. If challenged, a country enforcing such requirement (in this case India) is unlikely to be able to defend the challenge unless there is an element of government procurement involved. In the context of the Indian solar energy sector a domestic content requirement will be successful if it is backed by incentives strong enough to encourage even global manufacturers to set up manufacturing capacity in India.