Considered by posterity as the quintessential "oil baron," John D. Rockefeller had amassed a fortune when he died in 1937 that in today's dollars would be worth roughly $340 billion. That's equal to 1.5% of the total economic output of the U.S. He holds the record as the richest American ever and certainly one of recorded history's richest persons this side of Croesus.

For generations, the Rockefeller surname has been synonymous with vast wealth. How did he reach the pinnacle of capitalist success? By accumulating undervalued energy investments that exponentially appreciated in price as they went on to dominate their markets. Investors now face a similar once-in-a-lifetime opportunity with renewable energy.

Indeed, renewable energy just racked up another blockbuster year. According to a recently released report by the nonprofit research group REN21, "An estimated 147 gigawatts (GW) of renewable power capacity was added in 2015, the largest annual increase ever, while renewable heat capacity increased by around 38 gigawattsthermal (GWth), and total biofuels production also rose."

The report encompasses wind, solar and geothermal energy, as well as biofuels. A major driver behind the record increase is the falling cost of solar and wind power, as the technology becomes more advanced and efficient. The growing interest of private equity firms and venture capital funds is another tailwind for renewables. The report states that investment in renewables reached $286 billion in 2015, up from $273 billion in 2014. A similar rate of growth is expected this year, which makes renewable energy a must for your long-term wealth building strategy.

Solar and wind projects accounted for the majority of new renewable energy projects. Solar power is one of the biggest investment opportunities available, with tremendous growth potential. In 2015, solar capacity enjoyed the largest yearly gain in its history.

Attesting to its staying power, renewable energy also has generated a lot of new jobs. More than 8 million "green" jobs were created last year, a 5% increase from 2014, with most of them in the solar and wind industries.

One of the surest ways to make big money over the long haul is to buy the stocks of companies that are tapped into unstoppable trends. Few trends are as sure and swift as the growth in renewable energy. But which stocks? Many companies in the industry are volatile small-caps or overextended large-caps. The recent bankruptcy of indebted solar developer SunEdison is a stark case in point.

An appealing solar stock now is Canadian Solar (CSIQ - Get Report) , a mid-cap maker of solar cells and wafers that's stable and positioned for strong capital appreciation. With Canadian Solar shares now trading at $18.11, the consensus 12-month price target from analysts who cover the stock is $28.69, which suggests shares can gain a whopping 58% in the next year.

But if you want an investment that's more diversified and a play on the entire renewable industry (and not just on solar), a smart buy now is the First Trust NASDAQ Clean Edge Green Energy Index Fund (QCLN - Get Report) . With net assets of $63.41 million, the exchange traded fund's top holdings include Tesla, First Solar, SolarCity, Hexcel, ON Semiconductor and Linear Technology. The expense ratio is a low 0.60%.

The First Trust NASDAQ Clean Edge Green Energy Index Fund has racked up a three-year total return of 8.30%, and this ETF is poised for greater gains in 2016 and beyond, as renewables increasingly join the mainstream of energy production.

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John Persinos is an editorial manager and investment analyst at Investing Daily. At the time of publication, the author held no positions in the stocks mentioned.