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2. USEnergy Information Administration, Natural Gas Prices, 2019, https://www.eia.gov/dnav/ng/ng_pri_sum_dcu_nus_m.htm.
3. Renewables 2018 Global Status Report;Zervos,2018
4. Record Drop in U. S. Coal-Fired Capacity Likely in 2018;Feaster,2018
5. North American Electric Reliability Coorporation, Reliability Guideline. Gas and Electrical Operational Coordination Considerations, Technical Report September, 2018.