Hi,
I am no expert in the detail of their business, but i can give you some info that I know.

1. carbon credit, as far as i know for the Q3 just came out they sold some emission allowance to 3rd parties, which meant that they were in surplus of CO2 emission (they didn't produce enough CO2 to fully utilize the credit given by government)

2. coal price/power price difference is called dark spread, since they have a large proportion plants that are coal-fired, the logic implies that the lower the coal price, the higher the profit margin they will have. according to Q3 cc, dark spread has widen for the period.

3. Natural gas price/power price difference is called spark spread. In majorities of the power market such as PJM, the marginal NG price usually set the wholesale power price, so basically higher NG price, higher overall power price, greater profit margin.

However those are just the basics, as for the company, they have their own hedging strategies. For example, if the NG price has been rising during the period, they would see a higher margin but a lower realized hedge, vice versa. The net effect is usually up for higher NG price.

I would suggest you read their 10K/10Q and CC transcript for more detail.

Correct me if I am wrong.