In 2013, Tesla Motors (NASDAQ:TSLA) sold 22,500 vehicles. The company expects that number to grow to 35,000 in 2014, up 55%. But it's in 2015 that Tesla's deliveries may really ramp up. In fact, it's reasonable to assume Tesla could sell 75,000 vehicles in 2015 -- more than double its 2014 deliveries.

Model S. Photo by Levi Sim, used with permission.

How Tesla gets to 75,000 annual deliveries
The logic is fairly simple.

First of all, it's crucial for Tesla investors to keep in mind that not only is Tesla limited by supply and not demand, but also that Tesla hasn't spent a dime on advertising for its Model S. Even more, Tesla says that it currently has no plans to initiate any paid advertising in the future, either. Obviously demand issues aren't a likely near-term issue for the company.

Second, investors should also note that Tesla is only just beginning its global rollout. About 20,000 of its 22,500 deliveries in 2013 were likely in North America. But Tesla's global ambitions shouldn't be underestimated. Its rapid Supercharger network expansion in Europe foreshadows Tesla's plans to deliver vehicles in large volumes overseas. Further, Tesla has said it will begin deliveries in China this spring. 

Given these assumptions, the path to 75,000 vehicles is straightforward. It begins with this excerpt from Tesla's fourth-quarter letter to shareholders.

For the year, Model S was the top selling vehicle in North America among comparably priced cars. Nonetheless, we believe there is room to improve in 2014 as we complete the Supercharger network and enable vehicle service almost anywhere in North America. The potential in Europe and Asia is even more significant. Towards the end of the year, we expect sales in those regions combined to be almost twice that of North America.

This means that Tesla's annual rate of deliveries in North America of 20,000 is likely to increase, and that sales in Europe and Asia combined should reach a rate of at least 40,000 vehicles per year by the end of 2014. That gets us to Tesla's annual rate of deliveries going into 2015 at 60,000 plus.

From here, we factor in the Model X 2015 potential. Tesla says it will begin volume deliveries of the SUV by the Spring of 2015. Assuming Tesla could match Tesla's 2013 Model S production levels for the Model X after volume deliveries begin, 15,000 Model X deliveries is a sensible number to latch on to.

Model X. Source: Tesla Motors.

Combining Model S potential with Model X, we arrive at our figure of 75,000.

Fast-growing companies are hard to value
If Tesla deliveries do follow this path, Tesla's 2015 year-over-year delivery growth rate will actually accelerate from the already robust rate Tesla has guided for in 2014. It's exponential patterns like these that make valuing stocks like Tesla so difficult. If Tesla can grow sales by 50% this year and more than double deliveries in 2015, what can investors expect in 2016 and beyond?

This impressive trajectory should keep Tesla investors holding onto shares despite a seemingly wild valuation. Tesla's monstrous growth likely won't be slowing soon. Two major catalysts for the company sit on the horizon: Tesla's third-generation lower-cost vehicle that Tesla intends to launch in 2017, and the company's planned Gigafactory for producing lithium-ion batteries at unprecedented scale.