The Guggenheim Solar ETF (NYSEArca: TAN) and the Market Vectors Solar Energy ETF (NYSEArca: KWT) are up an average of 13.9% year-to-date and, over the past month, investors’ bullishness toward solar stocks has been accelerating.

Over that period, TAN and KWT are an average of almost 13%. TAN entered Thursday’s session as the fourth-best non-leveraged ETF this year. Superlatives to be sure, but while fundamentals for the solar industry are solid, solar ETFs are facing some technical challenges.

“Thus far, 2015 is shaping up nicely for solar names (+15%) but the charts are saying the party could be short lived. Since peaking in March of 2014, prices have developed a subsequent pattern of lower highs. Recent momentum has driven TAN back above its 50 and 200-day moving averages but prices are about to bump heads with a major trend-line ($40). To add salt to the wound, on a relative strength basis versus the S&P 500, TAN is also hitting a major resistance line,” notes Tom Psarofagis of Agd Capital Management.

Again, fundamentals are robust. The U.S. solar industry, though, is in the midst of a growth spurt with 174,000 employed in the industry, up 22% in a year, and accounted for one in every 78 new jobs over 2014, reports Jane Wells for CNBC.

More homes and commercial properties are adding solar electricity as a 30% federal tax credit continues to make solar more affordable. The Solar Foundation also believes that “states like Indiana, Virginia and Tennessee will install more solar capacity this year than in all previous years combined.” [Market Growth not Reflected in Solar ETFs]

There are global tailwinds, too. Last month, India’s Prime Minister Narendra Modi reiterated plans for the country to install as much 100 gigawatts of photovoltaic capacity by 2022 while President Obama stated that the U.S. will “stand ready to speed this advancement with additional financing,” Bloomberg reports.

In comparison, China is currently undergoing a photovoltaic expansion that targets 100 gigawatt capacity by 2020 and currently has 33.4 gigawatts installed. [A Boost for Solar ETFs]