In order to clear space on the 40-man, left-handed relievers Fernando Abad and Tyler Robertson were designated for assignment.
Midnight tonight is the deadline for teams to set their 40-man rosters ahead of the Rule 5 draft. With these moves, the Nationals now have a full 40-man roster.
Solis, 25, is 10-4 with a 3.20 ERA in 33 games (32 starts) over three professional seasons. The Nats' second-round pick in the 2012 First-Year Player Draft had Tommy John surgery in March 2012 and came back this season to post a 3.32 ERA in 57 2/3 innings at high Single-A Potomac.
Solis also recently led the Arizona Fall League in wins (five) and strikeouts (29) while posting a 2.17 ERA in seven starts, spanning 29 innings. The lefty was recently rated by Baseball America as the Nationals' No. 6 prospect.
The 22-year-old Taylor hit .263 with a career-high 57 extra-base hits (41 doubles, six triples, 10 home runs), 87 RBIs and 51 stolen bases in 133 games this season with Potomac. He's already considered an elite defender and was listed by Baseball America as the "top athlete" in the Nats' system. The publication also ranks Taylor as the Nats' No. 7 prospect.
Taylor, the Nats' sixth-round pick in the 2009 draft, is currently leading the Puerto Rican Winter League with a 1.042 OPS (.381/.441/.595).
Barrett, 25, had a tremendous season at Double-A Harrisburg this year, posting a 2.15 ERA and 26 saves in 51 appearances (50 1/3 innings). A ninth-round pick in the 2010 draft, Barrett struck out 69 compared to just 15 walks, and ranked second in the Eastern League in saves.
Abad posted a 3.35 ERA in 39 games for the Nats in 2013. He was signed as a minor league free agent back in January.
The left-hander started his stint with the Nats on a hot streak, but he tailed off as the season went on. Left-handed hitters batted .306/.338/.452 off him this season, and he had a 6.75 ERA in the season's final two months. He only made four appearances in September.
Robertson was claimed off waivers from the Twins in June. The 25-year-old went 4-2 with two saves and a 3.04 ERA in 47 games between Triple-A Syracuse and the Twins' Triple-A affiliate in Rochester this season.