Question: What is the beginning date of this inaugural season of a new FIA Champoinship for electrically powered cars, in which the Buenos Aires ePrix was first raced?

Context paragraphs:
2015 Buenos Aires ePrix: The 2015 Buenos Aires ePrix, formally the 2015 FIA Formula E Buenos Aires ePrix was a Formula E motor race held on 10 January 2015 at the Puerto Madero Street Circuit in Puerto Madero, Buenos Aires, Argentina.  It was the first edition of the Buenos Aires ePrix and the fourth championship race of the single-seater, electrically powered racing car series' inaugural season.  The race was won by António Félix da Costa.

2015 Miami ePrix: The 2015 Miami ePrix, formally the 2015 FIA Formula E Miami ePrix, was a Formula E motor race held on March 14, 2015 at the Biscayne Bay Street Circuit, Miami, United States.  It was the fifth championship race of the single-seater, electrically powered racing car series' inaugural season.  The race was won by Nicolas Prost.  Miami was subsequently dropped from the Formula E schedule for the 2015–16 season.

2017 Buenos Aires ePrix: The 2017 Buenos Aires ePrix (formally the 2017 FIA Formula E Buenos Aires ePrix) was a Formula E motor race held on 18 February 2017 at the Puerto Madero Street Circuit in Puerto Madero, Buenos Aires, Argentina in front of a crowd of 21,000 people.  It was the third round of the 2016–17 Formula E season and the third running of the event.  The 37-lap race was won by e.Dams-Renault driver Sébastien Buemi after starting from third position.  Jean-Éric Vergne finished second for the Techeetah team and Audi Sport ABT driver Lucas di Grassi came in third.

2014–15 Formula E season: The 2014–15 FIA Formula E season was the inaugural season of a new FIA championship for electrically powered cars.  It began on 13 September 2014 at Beijing in China and finished on 28 June 2015 in London after eleven races.  Nelson Piquet Jr. came first in the overall standings, and so became the first ever Formula E champion.

Buenos Aires ePrix: The Buenos Aires ePrix is an annual race of the single-seater, electrically powered Formula E championship, held in Buenos Aires, Argentina.  It was first raced in the 2014–15 season.

2014 Punta del Este ePrix: The 2014 Punta del Este ePrix, formally the 2014 FIA Formula E Julius Baer Punta del Este ePrix is a Formula E motor race held on 13 December 2014 at the Punta del Este Street Circuit in Punta del Este, Uruguay.  It was the first Punta del Este ePrix and the third championship race of the single-seater, electrically powered racing car series' inaugural season, the first in America.

2014 Beijing ePrix: The 2014 Beijing ePrix, formally the 2014 FIA Formula E Evergrande Spring Beijing ePrix, was a Formula E motor race that was held on 13 September 2014 at the Beijing Olympic Green Circuit in Beijing, China.  It was the first Championship race of the single-seater, electrically powered racing car series' inaugural season.  The race was won by Lucas di Grassi for the Audi Sport ABT team, ahead of Franck Montagny and Sam Bird.

Berlin ePrix: The Berlin ePrix is an annual race of the single-seater, electrically powered Formula E championship, held in Berlin, Germany.  It was first raced in the 2014–15 season.

2015 Beijing ePrix: The 2015 Beijing ePrix, formally the 2015 FIA Formula E SWUSP Beijing ePrix, was a Formula E motor race that was held on 24 October 2015 at the Beijing Olympic Green Circuit in Beijing, China.  It was the second edition of the Beijing ePrix and the first race of the second season of the electrically powered racing car series.  The race was dominated by Sébastien Buemi, who won starting from pole position.  Since he also recorded the fastest lap, he became the first driver to score the maximum of 30 points from a single ePrix

2016 Buenos Aires ePrix: The 2016 Buenos Aires ePrix was a Formula E motor race held on 6 February 2016 at the Puerto Madero Street Circuit in Puerto Madero, Buenos Aires, Argentina.  It was the fourth championship race of the 2015–16 Formula E season, the single-seater, electrically powered racing car series' second season.  It was also the second Buenos Aires ePrix and the 15th Formula E race overall.  Sam Bird won the race for his first win of the season.

Supporting paragraphs: Buenos Aires ePrix 2014–15 Formula E season
Answer: 13 September 2014