Citi analyst Praful Mehta upgraded NRG Energy to Buy from Neutral and raised his price target for the shares to $38 from $33. The analyst downgraded the shares to Neutral on July 30. In a research note partially titled "We Were Wrong. Story Stronger," Mehta says the strength of NRG's model was shown in last week's Q2 report. The analyst boosted his 2019 EBITDA estimate by $300M and 2020 estimate by $150M. He views his sum-of-the-parts valuation of $38 per share as conservative since it includes no value for buybacks or return on excess cash. NRG's "strong execution and ERCOT tightness" drives the upgrade back to Buy, Mehta tells investors in a research note.