In the “it’s just another day at the office” category, the Guggenheim Solar ETF (NYSEArca: TAN) is up 3.5% on volume that was more than twice the daily average less than two hours into Monday’s session.

Just as Elon Musk’s SolarCity (NasdaqGM: SCTY) has recently served as a catalyst for boosting TAN and the rival Market Vectors Solar ETF (NYSEArca: KWT), FirstSolar (NasdaqGM: FSLR) is doing the same Monday. Shares of First Solar, the largest U.S. solar firm, are up 12% on more double the average daily turnover. [SolarCity a Big Deal for Solar ETFs]

To be fair, First Solar has played a leading role in lifting TAN and KWT throughout this year’s solar sector renaissance. The stock is 5.84% of TAN’s weight and nearly 8% of KWT. [First Solar Lifts Solar ETFs to new Highs]

In a testament to the strength of solar stocks this year, there this tidbit: Prior to Monday, First Solar was the worst-performing stock among TAN’s top-10 holdings. That is correct. A 56% year-to-date gain heading into Monday made First Solar the “laggard” of TAN’s top-10 lineup, a group that equals 51.6% of the ETF’s weight.