The market has been hot for over a year now, and some stocks have doubled, tripled, or more in price over that time. And those increases can make it difficult to see value in the market, particularly in growth stocks

Three of our contributors took a look at some of the hottest stocks on the market and analyzed whether it's too late to buy them. Here's our analysis of SolarEdge Technologies (SEDG 4.15%), Enphase Energy (ENPH 2.69%), and TPI Composites (TPIC 1.17%)

Blocks stacked to make higher arrows.

Image source: Getty Images.

A growth story that's ending

Travis Hoium (SolarEdge Technologies): One of the hottest stocks in the solar industry over the past five years has been SolarEdge Technologies, a producer of solar panel optimizers and inverters. The stock is up 817% over the last five years and has more than doubled in the last year. But this may be a hot stock whose run has gone too far. 

The problem can be seen below. Revenue growth has stopped and is now negative, and net income is falling, yet the stock's price-to-sales ratio is still over eight. This chart doesn't even include Q1 2021 numbers, which would show that the decline in revenue and net income has gotten worse

SEDG Revenue (TTM) Chart

SEDG Revenue (TTM) data by YCharts

The problem is that SolarEdge is running into limits on the solar market size overall. The company grew over the last five years by taking market share, but now it's the market share leader and needs to grow by expanding its product line. That's a much harder push, and at the same time companies like Enphase are coming for the power optimizer and inverter business with their differentiated microinverters. SolarEdge is still a great company, but the stock is too hot and could have a long way to fall to be a value again. 

Strong business, high valuation

Howard Smith (Enphase Energy): If you only look at 2021 returns, it would be far-fetched to call Enphase Energy a red-hot stock. But shares are up 432% since the start of 2020. Investors have been attracted to the solar technology and energy storage provider not just because it is in a promising sector, but because its business has been thriving. 

Over the last three years, Enphase has almost tripled trailing-12-month (TTM) sales, and gross profit margin has jumped by 75%. 

ENPH Revenue (TTM) Chart

ENPH Revenue (TTM) data by YCharts

The company is benefiting from the rapid growth in residential and commercial solar panel adoption. In its recently reported first-quarter 2021 financial report, Enphase said it shipped almost 2.5 million microinverters -- the components that convert power at the solar panel to what is needed in the home or business. That compares to the 2 million it shipped in the prior-year period, where growth had plateaued before the pandemic impacted sales. 

With the growth story back on track, investors may wonder why Enphase shares are down about 20% year to date in 2021. One reason is that market sentiment turned from the high-growth renewable energy sector that saw sharp gains in 2020. Another is that the company said its 2021 growth outlook has been tempered by supply chain challenges from the global semiconductor shortage. But maybe the biggest reason is the stock seemed priced to perfection, as it exited 2020 with a price-to-earnings ratio of about 175. 

Even without production headwinds from supply chain issues, the company needs some time to grow into its lofty valuation. But solar generation capacity is one of the fastest-growing renewable sources, with an annual gain of 22% in 2019, prior to pandemic impacts, according to the International Energy Agency. With that growth likely to resume, Enphase is in position to continue to benefit over the long term. Investors with that long-term time horizon may want to take advantage of the recent dip in shares, realizing that the company still needs more time to grow into its current valuation.

A pure-play wind energy opportunity

Daniel Foelber (TPI Composites): Shares of TPI Composites rose nearly 200% in 2020. As one of the largest independent manufacturers of wind blades, TPI benefited from investor optimism toward renewable stocks, falling interest rates, further divestment away from fossil fuels toward renewables, and a comparably weaker oil and gas market. Now the narrative has flipped.

TPI's customers are leading original equipment manufacturers (OEMs) like General Electric, Vestas, and Siemens. If these companies perceive that wind projects could become less profitable due to rising interest rates and supply chain issues, there's a good chance they will demand fewer blades from TPI and other wind and solar components manufacturers. The effects are reflected in TPI's guidance, which calls for a mere 8% increase in annual revenue -- discouraging for a growth stock that failed to turn a profit over the last few years.

However, there's a lot to like about TPI over the long term. Its performance is partially insulated from short-term cycles due to long-term supply agreements. It has also expanded heavily into key markets like China and Turkey, and most recently India.

TPI's strategy is simple. It is following the breadcrumbs of its customers and building manufacturing and R&D facilities where there's an opportunity for growth. Digging into the numbers, it seems that TPI is on the tail end of a growth spurt. After years of expansion, it is already reducing its spending. Its guidance suggests it could turn a small profit in 2021. The timing works in TPI's favor because interest rates are rising at a time when it could begin paying down debt, which should keep its interest payments manageable.

Despite its reputation as a growth stock, TPI is currently trading at a mere 1.2 price-to-sales (P/S) ratio, cheaper than the slower-growing, diversified OEMs it does business with, not to mention a much lower P/S ratio than many other independent components manufacturers. For investors who believe in the company's ability to execute, the stock's 15% slide over the past month could present a buying opportunity.

Hot stocks aren't always a great buy

We've differed here on whether each of these stocks is a buy, but it's clear that they're hot for a reason. They have tailwinds behind them and great operations, but investors should be aware that hot stocks can reverse course quickly if the market turns against you.