Forever is an awfully long time, but individual investors know the importance of maintaining a long-term mindset. While the stock market transitions through periods of expansion and contraction, investors capable of removing emotions from the decisions governing their portfolio have consistently enjoyed increases in wealth.

Of course, it's important to buy and hold great businesses with solid long-term growth opportunities. That's why I think clean-energy Swiss army knife SolarEdge Technologies (NASDAQ:SEDG) and engineered paper leader WestRock (NYSE:WRK) are worth a closer look.

A worker installing a rooftop solar module.

Image source: Getty Images.

Capitalizing on multiple renewable energy trends

Not that long ago, Wall Street pondered what would happen to SolarEdge Technologies as an increasing number of competitors started to take aim at its core market of power inverters for solar modules. As it turns out, competition has heated up, but the global market has so far expanded fast enough to comfortably accommodate multiple major players. That's allowed the business to maintain its sizable market share and gross margin over 30%. 

In fact, SolarEdge Technologies reported year-over-year revenue growth of over 29% in Q1 2019 at a gross margin of 31.7%. While the latter has indeed been pressured by competition, the business continues to generate healthy operating cash flow, which stood at $56.5 million during the most recent quarter.

Financial strength has prodded SolarEdge Technologies to diversify into an impressive number of clean-energy solutions beyond its legacy power optimizer products. In the past 18 months, the business has acquired its way into electric vehicle powertrain, electric vehicle charging, lithium-ion battery cell assembly, and energy storage markets. That's led to a surge in R&D expenses recently, but management thinks the eventual payoff will be well worth it.

Despite consistently delivering solid growth and laying out an ambitious long-term strategy, the stock trades at an attractive valuation. The company is valued at a market cap of $2.7 billion, which puts shares at just 15 times future earnings and a PEG ratio of 0.8. It seems Wall Street is taking a wait-and-see approach to the diverse list of growth initiatives now under way, but investors willing to be more patient and trust a management team that's delivered to date could pick up shares on the cheap. 

A line of individuals passing cardboard boxes from one end to the other.

Image source: Getty Images.

This income stock's valuation makes no sense

Multiple trade wars and fears of slowing global economic growth have led Wall Street to sour on the pulp and paper industry, but the long-term trends of a growing global middle class, surging e-commerce sales, and increasing demand for sustainable packaging suggest that now's a great time to grow a position in the industry.

WestRock is one of the leading producers of corrugated packaging materials, which is a technical term for cardboard. It might be a little boring, but the popularity and convenience of online shopping has led to record demand and prices for cardboard in recent years. That's allowed the business to splurge on trajectory-altering acquisitions and make sizable capital investments to modernize its manufacturing fleet. Those efforts continue to deliver handsome windfalls.

The paper leader expects full-year fiscal 2019 adjusted segment EBITDA to climb to $3.35 billion, up from $2.89 billion in fiscal 2018 and $2.29 billion the year before that. WestRock has also embarked on an ambitious strategy to strengthen its business-to-business relationships. The results so far: 143 customers purchase at least $1 million in products. Those customers represent $6 billion in annual sales, compared with just $4.7 billion from the same group two and a half years ago.

Wall Street has rewarded all of that progress by sending the stock tumbling 40% in the past year. That means WestRock trades at a market cap of just $9.4 billion, which represents just 80% of book value. It also means shares trade at 9 times future earnings and a PEG ratio of 0.85 and sport an annual dividend yield of 5.6%. Investors with a long-term mindset might find this to be one of the best bargains on the entire stock market right now.