As you've probably found out the hard way, there's a difference between getting rich and getting rich quick. Anybody promising you riches that are both speedy and guaranteed is probably full of baloney. Investing in top stocks over the long term, on the other hand, can indeed make you very, very rich.

Three stocks that look like good candidates to make their investors wealthy include Clean Energy Fuels (NASDAQ:CLNE), NIO (NYSE:NIO), and Intuitive Surgical (NASDAQ:ISRG). Here's why they look like good buys now.

A young man and woman hold handfuls of $100 bills.

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A beaten-down renewable

After news networks called the election in President-elect Joe Biden's favor, shares of many renewable energy stocks soared. That included shares of natural gas fuel specialist Clean Energy Fuels. The company's primary business is selling natural gas fuel to trucks that have been specially outfitted to run on natural gas. Because natural gas is cheaper and cleaner-burning than oil, many companies have opted to convert their truck fleets from diesel to natural gas, which can save money and reduce emissions.

You might point out that even though natural gas may be cleaner than oil, it's still a fossil fuel. That's true, but Clean Energy is still a renewable stock by virtue of its hottest product: Redeem, a biofuel that's made from renewable natural gas. To make Redeem, Clean Energy collects methane -- a potent greenhouse gas -- from sources like farms, dairies, and landfills and processes it into usable fuel. When the methane is burned, it's turned into carbon dioxide, a much less potent greenhouse gas. So, using Redeem actually helps mitigate greenhouse gas emissions.

Redeem has supercharged Clean Energy's operations. According to CEO Andrew Littlefair on the most recent third-quarter earnings call, Redeem has grown to more than 60% of Clean Energy's overall fuel mix. Littlefair has set a goal of transitioning the company's fueling infrastructure entirely to Redeem by 2025.

Clean Energy's stock has risen more than 90% so far this year, but its current share price of about $4.50/share is nowhere near its all-time high of about $24/share. Its current price-to-book ratio of about 1.6 is higher than it was in all of 2019, but near the low end of the company's historical range of 0.4-5.2.

Even if electric car ownership surges, methane emissions from farms, dairies, and landfills will still be a problem. Clean Energy looks poised to provide the solution... and make investors rich in the process.

A bet on Chinese cars

The Chinese auto market -- the largest in the world -- has been a major source of revenue for plenty of U.S. car companies. That includes Tesla (NASDAQ:TSLA), which is the biggest player in the country's electric vehicle (EV) market, thanks to its Shanghai Gigafactory. However, a number of Chinese electric vehicle start-ups are poised to challenge Tesla for a slice of that market, including NIO. 

Compared to Tesla -- currently the largest automaker in the world by market cap -- NIO is small potatoes. The company just achieved the milestone of producing 5,000 cars in one month in October. Meanwhile, Tesla is delivering more than 48,000 vehicles per month worldwide. However, when it comes to China's EV market -- which is expected to be worth more than $800 billion by 2027 -- NIO may have some big advantages.

NIO has focused on full-size electric SUVs, an underserved market niche, but recently rolled out its EC6 "coupe SUV" (what we'd call a crossover). The EC6 is much cheaper than Tesla's comparable Model Y, and due to its lower cost, is eligible for Chinese government subsidies that Model Y buyers can't take advantage of.

There's certainly no guarantee that NIO will be a long-term success. But as the company grows, it's reasonable to assume that the Chinese government may tilt the playing field in favor of it and other domestic manufacturers. If NIO comes to dominate the Chinese electric vehicle market, an investment now will seem prescient indeed.

A temporary disruption

Robotic-assisted surgery may sound like something out of a sci-fi movie, but the technology is already here and already being used in hospitals around the world. The undisputed leader in the sector is Intuitive Surgical. The company's da Vinci system primarily performs minimally invasive elective surgeries, mostly in the fields of urology and gynecology. Guided by a human surgeon, the machine allows for more precise and less invasive surgeries, leading to faster recovery times and better patient outcomes. 

The coronavirus pandemic has been problematic for Intuitive. In the spring, as hospitals began to fill up with COVID-19 patients, many elective surgeries were deferred by hospitals or patients. Now, with cases again on the rise, deferrals are expected to skyrocket once more. And because Intuitive makes more than 70% of its money from recurring revenue like disposable instruments, accessories, and service contracts for its existing machines, a lack of elective surgeries hurts its bottom line. 

The good news for Intuitive -- and for all of us -- is that the rapid development of coronavirus vaccines seems on track to bring the pandemic to a conclusion sometime next year. At that point, robotic-assisted surgeries should resume their prior growth trajectory. In the meantime, Intuitive's shares seem attractively priced for a key player in a fast-growing industry.

Get rich quickish

While Clean Energy Fuels, NIO, and Intuitive Surgical could make you rich, it will probably take time. The industries in which they operate -- renewable fuels, electric vehicles, and robotic-assisted surgery -- will take some time to mature, and as with many developing industries, there's no guarantee that a rival won't steal their thunder. 

However, if you're an investor hoping to get rich and you don't mind a bit of risk in your portfolio, these three stocks are all worth a look.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.