Investing in energy stocks can be very hit or miss. Many companies in the energy industry are highly sensitive to commodity prices and supply and demand, factors that can shift unexpectedly, affecting both profits and share prices in the short term in ways investors may not see coming.

However, energy remains one of the most important of humanity's basic needs. And with humanity growing -- the global middle class will expand by 2 billion new members in the two decades ahead -- the energy industry is set for big growth ahead, in both fossil fuels and renewables.

Here are three that look worth buying right now: North America's biggest supplier of natural gas and biomethane for transportation, Clean Energy Fuels Corp. (CLNE -0.34%); diversified oil and gas midstream giant MPLX LP (MPLX -0.20%); and solar technology leader SunPower Corporation (SPWR 0.63%).

Man in suit grabbing a declining line on chart and forcing it upward.

Image source: Getty Images.

Keep reading below to learn why these three very different business all meet the "buy now" standard, and which might belong in your portfolio.

The "ready now" alternative fuel provider

Jason Hall (Clean Energy Fuels): In recent years, electric- and hydrogen-powered vehicles have gotten the vast majority of the attention from the media, with companies like Tesla and others proving the viability of non-gasoline or diesel technologies in light-duty transportation. More recently, attention has shifted to medium- and heavy-duty applications, and rightly so, as battery technology and hydrogen fuel cell technologies continue to evolve.

But they're not exactly road-ready today for most applications, and it's likely to be years before they are. Further, once they do hit highways, they will be expensive and limited in capability. That's something many fleet operators are realizing, and it's leading many to give natural gas a second look.

Clean Energy Fuels' last two quarters show that this is happening. After reporting 14% fuel delivery growth to close 2018, it just reported 12% growth to start 2019, and management set the tone that continued growth is expected for the rest of the year and beyond.

Moreover, Clean Energy's future isn't just as a "bridge fuel" to EVs and hydrogen: Its fastest-growing business is biomethane, which makes up half of its fuel growth and is produced from human-driven waste. The end result is a fuel that works in any trucking or transit application right now, while having a lower total emissions profile than you'd get from an electric vehicle, which may not even be available for another four or five years.

Add in the recent sell-off -- shares are down 17% from the 2019 peak, though they're still up 66% this year -- and Clean Energy is a great investment in the growth of alternative fuels in commercial transportation.

High yield but low risk

Matt DiLallo (MPLX): After a challenging 2018, master limited partnerships (MLPs) have bounced back this year. The average one in the Alerian MLP ETF is up about 14%. One notable laggard, however, is MPLX, which has only rebounded around 5% this year. Because of that, it's one of the most attractive buys in the sector, especially when factoring in its roughly 8% yield.

The company backs that payout with top-tier financial metrics. MPLX not only generates predictable cash-flow-supported fee-based contracts, but it covered its high-yielding distribution by a comfortable 1.33 times last year. Meanwhile, the company has a top-notch balance sheet backed by a conservative 3.9 times leverage ratio, which is below the 4.0 times comfort level of most MLPs.

The company uses its financial strength to invest in high-return growth projects. Those expansions position MPLX to increase its cash flow by about 11% this year and another 13% in 2020. That should support roughly 6% annual growth in the company's distribution. Meanwhile, the company's strategy to grow its payout at a slower pace than cash flow should further improve its financial profile.

MPLX is one of the more compelling MLPs these days. It trades at a lower valuation compared with peers due to its recent underperformance. The company also offers one of the highest yields in the sector, which it backs with sound financial metrics. Add in its visible growth prospects and MPLX is one of the top buys in the energy sectors right now.

Leading energy's brightest segment

Travis Hoium (SunPower): There are very few solar companies today that are differentiated in any meaningful way. Most are making or installing commodity solar panels or using standard financing mechanisms to make it easy for customers to afford solar. One company that's differentiating itself with superior technology is SunPower, manufacturer of high-efficiency solar panels. 

SunPower's core product is a back-contact solar cell that generates more electricity per square inch than competing technologies. The company leverages this product to sell into residential and commercial markets where space is constrained. It often packages solar panels with racking, inverters, monitoring, and even energy storage. This complete package is how SunPower adds more value to the solar sales process and tries to lower costs.

The challenge for SunPower has been stagnating sales and continual net losses. There are short-term factors that impacted earnings over the last few years (factory writedowns, yieldco sale, project losses), but management has shed noncore businesses and invested in new manufacturing technology that should lower costs and improve margins.

SPWR Revenue (TTM) Chart

SPWR Revenue (TTM) data by YCharts.

I think the solar industry has an extremely bright future, and now that management has focused the business on technology, SunPower has a leading role to play. This stock isn't without risk, given what we've seen from solar stocks the last decade, but what energy stock is without risk today? At least with SunPower, investors are betting on a segment of the industry with a bright future.