Earnings season is quickly coming to a close and as it does investors want to look back and see who performed well, and who didn't, from the growing universe of renewable energy stocks.

Three Fool.com renewable energy contributors were impressed with this quarter at Bloom Energy (BE 0.82%)Enphase Energy (ENPH -2.17%), and TPI Composites (TPIC -9.20%), who came out as winners long-term. Here’s a look at why we liked what they reported.

Renewable energy farm

Image source: Getty Images

Stay the course

Travis Hoium (Bloom Energy): If you followed Bloom Energy's stock following earnings it may not seem like the company crushed investor expectations. That's because it didn't beat analyst estimates, but that's not the goal if you're a long-term investor. What I look for is whether or not a company is growing, improving operations, and expanding its addressable market. On those metrics, Bloom Energy crushed my expectations in the second quarter of 2021

Revenue was up 21.6% to $228.5 million on the back of a 41.5% increase in acceptances, or fuel cells accepted by the end customer. This implies that prices are going down per watt sold, but higher volume is overcoming price reductions. That's actually a good trend in renewable energy, especially if gross margin trends higher at the same time. 

Despite lower average sales prices, gross margin improved from 14% a year ago to 16.3%, or 18% on an adjusted basis. And that includes a low-margin order that management considers an "outlier." For the full year, management expects adjusted gross margin to be around 25%. 

On the market expansion front, today Bloom Energy is primarily a U.S. commercial and industrial energy backup company, using fossil fuels as a fuel source. But over the next five years it expects to grow internationally, into hydrogen with electrolysis and clean hydrogen projects, into biogas, and even into the marine market. Altogether, management thinks these markets will have a more than $2 trillion addressable market.

The market seems to fall in and out of love with Bloom Energy, but long-term this is a company that continues to perform well and is moving toward breakeven very quickly. With a market potential that's measured in trillions, this is still a stock I am bullish on today given earnings trends we're seeing right now. 

Overall positive trends continue

Howard Smith (Enphase Energy): Solar system technology company Enphase Energy just announced its second-quarter earnings, and for the fourth quarterly reporting period in a row, the company beat average analyst estimates for earnings per share by more than 25%. There's a good explanation for that, too. 

As the company continues to grow its business with increasing sales, it also has been growing its gross margin. That helps more profit fall to the bottom line. The trend of increasing revenue and gross margin has been fairly steady over the last three years. Note that the outlier data point from the third quarter of 2020 occurred because of a one-time tariff refund. 

ENPH Revenue (TTM) Chart

ENPH Revenue (TTM) data by YCharts

The company's sales should continue to grow as solar power generating capacity continues to increase. Enphase has also expanded its business beyond just solar panel microinverters -- the system components that convert DC power at the solar panel into the AC used in the home.

Enphase has expanded into power storage solutions as well. And by adding technology that delivers more convenience to customers, it is seeing accelerating demand. The company said the storage option also offers homeowners "the ability to conserve their energy consumption by shedding non-essential loads during an outage and thereby extending the backup duration." In late June, the company launched its Encharge storage system in Germany, the product's first expansion into a market outside of the U.S.

In its second-quarter report, Enphase offered guidance for the third quarter that implies revenue growth will continue at a rate of 93% over last year's pandemic-impacted third quarter. But it also would be a 9% bump sequentially over second-quarter 2021 revenue at the midpoint of the outlook. 

Enphase shares are highly valued, with a forward price-to-earnings ratio of 84, based on data by YCharts. But if the company continues to crush estimates, it won't take that long to grow into its valuation. 

Ripping off the proverbial bandage

Daniel Foelber (TPI Composites): Independent wind blade manufacturer TPI Composites didn't necessarily crush earnings, per se. But it succeeded in providing investors with some better insight as to when it will return to growth. This positive news may be why shares are up 8% over the last week. 

For context, TPI pre-announced some of its second-quarter figures in late July a couple of weeks before earnings. The numbers weren't good, calling for little to no top-line growth in 2021 compared to 2020. That news, combined with broader weakness in the wind energy industry, sent the stock down 53% from its high over a five-month stretch.

Although TPI's Q2 results and full-year forecast were little changed from the July update, management did indicate during its earnings call that regulatory uncertainty and material costs were the main cause of its poor guidance, not the underlying business. Rather, the extension of the federal renewable electricity production tax credit paired with an anticipated renewable spending package by the Biden administration reduces the pressure for companies to launch utility-scale projects. The extension is great for operators or investors in these projects, and it supports suppliers like TPI in the long term. But in the short term, it negatively impacts TPI because its customers aren't in a rush to buy more blades than they've already contracted.

However, TPI is confident in its long-term future. The company has spent the last few years expanding its production capacity across the U.S., China, Turkey, and Mexico in anticipation of heightened global renewable energy investment. The timing didn't work out in TPI's favor, as its investments have yet to pay off. The issue is that increased capacity costs money, which raised spending and resulted in back-to-back years of annual losses (and likely another annual loss this year) and higher debt on the balance sheet. As a growth stock, TPI Composites has definitely hit a snag. The good news is that management ripped off the proverbial bandage by telling investors early that it's going to be a poor year. The discount in the share price -- paired with potential upside for those that are patient -- could make TPI stock worth buying now. 

Playing the long game

Each of these companies is playing the long game in renewable energy and their futures look promising. These may not be stocks that make big headlines, but they're disrupting every part of the renewable energy industry. And with earnings trending in the right direction they may have room to move higher.