Electric-car maker Tesla Motors (NASDAQ:TSLA) remained a hot topic in automotive commentary during 2015. But despite all the attention the company received during the year, the stock price at the time of this writing -- at around $217 -- implies a slight decline in the share price for the full year of around 2%. Could 2016 reinvigorate an upward climb in the stock price?

Tesla Model X Delivery

Model X. Image source: Tesla Motors.

A key catalyst
Measured by incremental growth in vehicle sales, 2016 could very well be Tesla's best year yet. During the second half of 2015, Tesla put into place two key drivers for sales growth: a new production line and its first new vehicle since 2012. These drivers are positioned to make a meaningful impact on sales as early as the first quarter of the 2016.

With Tesla's third-quarter guidance calling for a total of $1.7 billion in capital expenditures during 2015, this was a huge year of spending for the company -- particularly spending related to growth plans. Reviewing Tesla's financial statements reveals that it's likely that investments in production capacity expansion and manufacturing equipment and tooling for its September-launched Model X together represent the majority of this spending.

Looking ahead to Tesla's fourth quarter, capacity expansion and Model X manufacturing appear to remain a key focus of its planned $500 million in capex.

"The increase in spending is primarily due to accelerated investments in the Gigafactory, further vertical integration of seat assembly, and other manufacturing activities, as well as faster milestone execution by certain suppliers for Model X manufacturing equipment and tooling," management said in its Q2 shareholder letter.

Looking ahead
To bet that Tesla's spending won't produce a handsome payoff as production ramps up, investors would have to both ignore the company's excellent history of converting capex into significant growth and an interesting and important heads-up from management in its shareholder letter: "We have historically been frugal with our capital spending, and our most recent capital spend per unit of incremental capacity is significantly more efficient than even our prior performance." (Emphasis added.)

Pair huge and apparently efficient investments in manufacturing capacity with Tesla's launch of a fully electric SUV late in 2015 (a move which essentially doubles its addressable market), and Tesla's sales are set to soar in 2016.

Tesla Vehicle Sales Estimate

Data in chart based on quarterly shareholder letters. Years marked by asterisks indicate estimates based on Tesla management commentary and outlook. Chart source: author.

No wonder Tesla is predicting it can produce and deliver significantly more vehicles in 2016 than it will deliver this year. The electric-car maker believes vehicle sales can jump by around 38,000 units between 2015 and 2016, according to management outlined in Q3. This would more than double the company's estimated vehicle sales growth between 2014 and 2015 of 18,400 units, and it would be Tesla's best sales growth ever when measured in absolute vehicle deliveries.

Of course, sales growth doesn't translate to investor returns. The market has essentially priced in considerable growth for Tesla, going forward. But if it can grow its sales this meaningfully in 2016, shareholders can be more confident in the company's ability to execute on its ambitious longer-term growth plans to deliver 500,000 vehicles per year by 2020.

Daniel Sparks owns shares of Tesla Motors. The Motley Fool owns shares of and recommends 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.