In recent years, few stocks have been as successful as Tesla Motors (NASDAQ:TSLA). At a time when the stock market was roaring ahead during its third strongest bull market in history, shares of Tesla have beaten the market by a stunning 101% per year since 2011. 

TSLA Chart
TSLA data by YCharts.

Tesla's remarkable share price growth is beaten only by its sales growth, which has enjoyed a remarkable 158% compound annual growth rate over the past three years. While that growth rate isn't sustainable, analysts are still expecting sales to increase 55% this year and 62% in 2015. 

Tesla Model S. Source: Tesla Motors

That growth is expected to come from Tesla's continued success with its Model S sedan, which is on track to meet the company's sales target of 35,000 for 2014, up 56% from 2013's figure of 22,450.

With next year's planned launch of Tesla's Model X crossover SUV, the company is planning on achieving a delivery rate of 100,000 vehicles by the end of 2015.

However, it's the launch of the Model 3 in 2017, with an expected base price of $35,000 and a range of 200 miles, that is usually viewed as Tesla's main growth engine.

Tesla Model X. Source: Tesla Motors.

After all, Tesla is building the $5 billion Gigafactory, the world's largest lithium-ion manufacturing plant in Nevada, to provide sufficient batteries for 500,000 vehicles per year. In fact the Gigafactory's planned output of 35 GWh per year is larger than the entire world's capacity in 2013.

Source: Tesla Motors.

However, this article isn't about Tesla's amazing cars and how they might drive long-term share price appreciation for investors -- at least not directly. Instead, I'd like to focus your attention on what I believe is Tesla's greatest asset and highlight a potential way it can drive the company's earnings growth in years to come. 

Optionality: The key to "unquantifiable greatness"
Last year my Motley Fool colleague Brendan Matthews highlighted seven principles to picking 10-bagger stocks, gleaned from years of studying the stock picks of Motley Fool co-founder David Gardner. One of those principles is "unquantifiable greatness": the ability to deliver products or services that customers adore.

However, perhaps the biggest aspect of this investing principle is the idea of optionality, a company's ability to successfully expand (and dominate) new products and services. In other words, optionality is the ability to find new worlds to conquer and then successfully conquer them.

The perfect example of this is (NASDAQ: AMZN), which David Gardner bought on Sept. 8, 1997, for a split-adjusted price of $3 per share. In his excellent summary of the reasons for the purchase, Gardner outlined his belief that Amazon was "about more than just books" a statement that proved very true, as Amazon branched out into selling every kind of product and many new services, such as cloud services and media streaming via Amazon Prime. 

Thanks to optionality, Amazon has grown into a 100-bagger with 2015 sales projected at $109 billion. 

I want to take that same concept and apply it to Tesla, to see where Elon Musk, the company's innovative CEO and co-founder, might take the company in the future.

Gigafactory: Cheaper batteries are just the beginning
When the Gigafactory opens in 2017, Tesla hopes it can cut battery costs by 30%, and by 50% when full capacity is reached in 2020.

Analysts believe that this means Tesla will be able to achieve a cost per KWh of $100 by 2020, 80%-85% less than EV batteries from 2010.

However, Tesla's big optionality opportunity doesn't lie in just batteries for electric cars, but energy storage in general, including renewable energy applications.

Energy storage: A $50 billion opportunity
According to analyst firm Lux Research, energy storage is expected to grow 8% annually and become a $50 billion market by 2020, the year the Gigafactory will achieve full production capacity. 

 ComponentProjected Market Size in 2020% of Energy Storage Market
Vehicle batteries $21 billion 42%
Electronics $27 billion 54%
Stationary Applications $2 billion 4%
Total $50 billion


Source: Lux Research.

Tesla, through its relationships with battery maker Panasonic (NASDAQOTH:PCRFY) and SolarCity (NASDAQ:SCTY.DL), is potentially setting itself up to play a major role in all three energy storage categories. 

For example, currently Tesla's battery packs are comprised of 8,000 individual battery cells, the same as used in conventional laptops.

This means that the Gigafactory may be able to manufacture batteries not only for Tesla's electric cars, but consumer electronics as well. Better yet, there's a very good chance that Tesla and Panasonic could manufacture these consumer electronic batteries at a cost that makes them ultra-competitive for use in laptops, smartphones, and tablets. 

A Tesla battery... in your smartphone?
Back in February, Gartner auto industry analyst Thilo Koslowski told Wired Magazine: "Depending on the capacity of the factory and who the other investors will be, Tesla could start selling its batteries for other products besides cars. ... This could actually mean Tesla might build batteries for Apple." However, potentially the largest long-term market for Tesla batteries isn't consumer electronics or electric cars, but renewable energy storage.

For example, Tesla recently began partnering with SolarCity to offer its customers energy storage systems to store power generated during the day. With the International Energy Agency projecting $6.4 trillion will be spent on renewable energy worldwide through 2035, this could prove to be a major growth catalyst for Tesla if the program can be scaled up and utilize recycled batteries from old Teslas. 

Optionality is an important idea for disruptive companies such as Tesla as it represents the potential of investing alongside an innovative, passionate corporate leader such as Elon Musk who could eventually take the company in new and profitable directions. However, Tesla investors today should remember that the possibilities of Tesla's future in the battery market, while real, represent a very long-term potential. Only invest in Tesla if you believe in the growth potential of their core business of great electric cars. Consider optionality only a growth "kicker" on top of an already great business and as always, own Tesla only as part of a diversified, well rounded portfolio. 

Adam Galas owns shares of Tesla Motors. The Motley Fool recommends and owns shares of, Apple, SolarCity, and Tesla Motors. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.