If you ask 10 investors what an ultimate growth stock is (at any given time), they may present you with 10 different definitions and dozens of picks for what they consider an ultimate growth stock. The metrics they use to measure or identify these may range from performance history to future market forces.

While the choices may differ for every investor, few options are compelling enough that most investors can afford to ignore them. Ballard Power System (TSX:BLDP) has the potential to be that option, assuming the right catalysts are in place.

And if they are, buying the stock now at its brutally discounted state (94% down from its five-year peak) might be a brilliant thing to do. The stock is trading at $2.83 per share, so you can buy over 350 shares with $1,000.

Future of fuel cell

Ballard Power System specializes in fuel cells. These cells take hydrogen as fuel and convert it into electricity.

So, if we compare it to conventional electric vehicles (EVs), a fuel cell vehicle would have most of the same pieces (the power train and the rest of the car) but wouldn't require the massive batteries an EV requires to store electricity. It would have a fuel tank that could be filled with hydrogen and a fuel cell instead.

The trade-off has significant sustainability and practical implications, especially considering the massive and messy supply chain of batteries. So, it can also be considered one of the best ESG (environmental, social, and governance) stocks you can buy right now.

The future of fuel cells is bright mainly because of the level of practicality they offer. The problem is that hydrogen is quite volatile as a fuel, and it's challenging to store and transport. Also, generating hydrogen from water (through electrolysis) is still costly.

However, even a single breakthrough in the production, storage, or transmission of hydrogen that makes it cheaper and safer can position it as a more attractive green transportation solution compared to EVs.

The stock

One thing you need to understand about the stock is that it has already ridden the "sustainable investment" wave. It climbed over 1,400% in less than two years around the pandemic. Then it started slumping and has only recently started showing some positive activity.

The modest bull market phase that started mid-November last year has already pushed the stock up 58%. At this pace, it can easily double your capital in half a year if you buy now.

Despite lack of revenue, the company has adequate cash reserves to fund its operations. The company has received multiple orders recently, including six megawatts' worth of fuel cell production capacity in Europe alone (90 fuel cell engines).

The stock is already bullish, and its growth might accelerate amid positive news about its fuel source (hydrogen). The fact that EV growth is slowing and most countries are still way off from their emissions target might also favour fuel-cell companies like Ballard.

Foolish takeaway

The stock can more than double your money if it just hits $6 a share. The chances of the stock going back to its five-year peak (over $40 a share) are slim but if it happens, your 350 shares would be worth $14,000. Even if the stock doesn't achieve this lofty goal, the chances of it making you a solid amount of profit in a relatively short time-frame are quite decent.