索諾馬郡太陽

After the 2004 season, the MPSL disbanded but a new men's league, the National Premier Soccer League, replaced the previous league and expanded on the territory of the MPSL by adding a Midwestern Division. The Sol was one of the founding clubs of the NPSL, specifically in the Western Division. Like the NPSL and its member clubs, the Sol falls under the auspices of the United States Amateur Soccer Association (USASA) and the United States Soccer Federation (USSF).

In 2005, the Sol finished second in the Western Division in the regular season standings, 3 points behind the Sacramento Knights, attaining the number 2 seed in the NPSL West playoffs. In the Western Division playoffs, the Sol beat the number 3 seed Chico Rooks at home in the semi-finals and then traveled to Sacramento to face the Knights in the NPSL West Championship Game. The Sol triumphed over the Knights in a hard fought match at the soccer stadium at Sacramento State University, garnering the NPSL West Championship. The Sol then hosted Midwest Champion Detroit Arsenal for the inaugural NPSL National Championship game in Santa Rosa, California.

Also in 2005, the Sol qualified as one of three NPSL West representatives for the Region IV U.S. Open Cup (U.S. Open Cup Website qualifying tournament, where the Sol won its group and then went on to beat the Salinas Valley Samba for the tournament championship and a spot in the USASA National Open Cup. The Sol would later meet the Samba in Santa Rosa in the first round of the U.S. Open Cup itself. At the USASA National Open Cup in the August heat of Frisco, Texas, in the semi-finals the Sol faced the AAC Eagles of Chicago who prevailed 2–1. With this result, the Sol's 2005 campaign came to an end.

In 2006 however, the Sol bounced back and prevailed in the USASA Open Cup. It started with a road trip to Seattle for the Region VI championships. The Sol beat out the Chico Rooks (NPSL) in group play to advance to the finals, where they defeated the Suaharos (sp?) 2–1 in the finals. Beto Sanchez, the back up goalkeeper, was subbed on as a forward due to injuries in the 80th minute, and netted the game winner in the 85th minute on a diving header. The Sol then traveled to Frisco, TX for the national finals where they defeated the heavily favored (and overrated) home side Dallas Roma FC 3–2 in double over time. They then went on to defeat the Lightning (Chicago) 1–0 in the finals to claim the USASA National open cup championship.

In 2013, following a first-place finish in the Golden Gate Conference during the regular season, the Sol would advance through the playoffs to the NPSL Championship Final, visiting RVA Football Club, but losing 2–0.