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.

Hong Kong-listed GCL-Poly and First Solar are the only top-10 TAN holdings that have not delivered triple-digit returns this year. TAN was up almost 141% at the start of Monday, or more than double First Solar. The smaller KWT has offered nearly double the returns of Arizona-based First Solar.

TAN has seen 2013 inflows of $171.5 million, a decent though not jaw-dropping number.  Yes, that is half the ETF’s assets under management, but it also says investors prefer solar stocks to ETFs. To this point in the year, preferring First Solar to TAN or KWT has been a losing bet.

TAN vs. First Solar Year-to-Date