The stock market had an amazing performance in 2020. Major market benchmarks clawed back from the depths of the coronavirus bear market to end the year with solid gains. Many individual stocks did far better, posting amazing returns.

One group of three high-growth stocks  stood out from the crowd. If you'd taken $10,000 and invested in each of those stocks at the beginning of 2020, your three positions would've grown to more than $200,000 by the end of the year.

If you thought the good times for those stocks ended last year, you would've been wrong. In just the first few weeks of January, that $200,000 portfolio would've gotten even more valuable, weighing in at more than $450,000 currently.

So which stocks are they, and what does the future hold for them?  

PLUG Chart

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1. Plug Power

Plug Power (PLUG -6.95%) went on an amazing run in 2020, climbing more than 1,000%. The stock has gone on to double again since the beginning of January. Add that up, and $10,000 invested in Plug just 13 months ago would now be worth more than $220,000.

Plug Power specializes in hydrogen fuel cell technology. The company has worked in the industry for years, most notably in providing lift trucks for materials handling. More recently, Plug Power has aimed at the on-road electric vehicle market, where it offers modular fuel cell engines that are allowing early adopters to add hydrogen-fueled technology to their businesses.

The growing popularity of electric vehicles has been instrumental in pushing Plug Power higher, as have efforts toward promoting renewable energy more generally. But Plug has also had business successes, partnering with companies like Walmart and Renault in efforts to grow faster and open up opportunities in new markets.

For long-term investors, Plug Power has had a long and storied history -- and the results haven't been all that good. But this time around, shareholders hope that the hydrogen concept has more staying power and that Plug will hold a growing group of competitors at bay.

2. Kopin

Many investors have probably never heard of Kopin (KOPN -10.93%). However, the stock has done particularly well, rising sixfold in 2020 and doubling again in 2021. A $10,000 investment from January 2020 would be worth over $130,000 now.

Kopin focuses on making microdisplays and headset solutions for various consumer, commercial, and military applications. That's been an up-and-down business over the years, but recently, Kopin's prospects have picked up considerably. That's because the company's products are increasingly finding their way into virtual reality devices.

For instance, earlier this month, investors learned that Kopin is providing the microdisplays for new VR glasses made by Panasonic. That followed earlier news that it would produce similar microdisplays for a Chinese company.

Even after its big gains, Kopin is still a small company, with a market capitalization of less than $450 million. That gives it more room for growth if it can keep landing lucrative contracts, but shareholders should watch closely to see if Kopin can get closer to profitability in the near future as well.

Bundles of cash in a pile.

Image source: Getty Images.

3. Aqua Metals

Finally, Aqua Metals (AQMS -6.93%) has been a recent winner. The stock was stagnant during most of 2020, but a late-year surge gave investors a nearly 300% return. A further doubling in January has turned $10,000 into $95,000 for those who bought at the beginning of 2020.

Aqua Metals is in the business of recycling lead, which it then refines and provides to its customers. Lead is a key component in the vast majority of rechargeable batteries, so Aqua Metals delivers a few layers of sustainability in its operations. Its proprietary approach helps to boost the yield from lead recycling efforts while avoiding toxic processes.

The company primarily spent 2020 working on its V1.25 AquaRefining electrolyzer. By the last few months of the year, Aqua Metals was debt-free and ready to move forward. 2021 has gotten off to a fast start, with the company landing a huge agreement with chemical conglomerate BASF that should help it accelerate its plans moving forward.

Aqua Metals is also a small company even after its rise, with a similar market cap to Kopin of around $440 million. If it can sell customers on the benefits of eco-friendly recycled lead for battery use, then Aqua Metals could have more upside.

What to look for going forward

Plug Power has grown into a large-cap stock, with a market cap of nearly $35 billion. That potentially limits its future growth, unless it can successfully realize the full vision of its hydrogen business model.

For Aqua Metals and Kopin, however, investors can foresee much greater upside potential in the long run. That's not to say that they'll remain on their fast-paced ascent throughout 2021 and beyond, but they're in interesting niches of fast-growing industries that warrant a closer look.