Model S.

Tesla Motors (NASDAQ:TSLA) stock finished the week about 4% lower, underperforming the S&P 500's small loss of just 0.6%. Investors watching Tesla's stock, however, shouldn't stress over short-term volatility. Trading at about 10 times sales, erratic movements in the stock price are basically inevitable.

Looking back at the week, here are the most notable stories related to Tesla stock.

Plug-in sales soar
In 2013, sales of plug-in cars in the U.S. (including hybrids) nearly doubled over 2012 figures. This trend expands on rapid growth that occurred in 2012, too.

Plug In Ev Sales

Source: Data retrieved from Green Car Reports.

Notably, Tesla's sudden leap into the EV scene meant that Tesla U.S. deliveries accounted for an estimated 18.8% of total plug-in sales in the U.S. in 2013. Without accounting for Tesla's Model S sales, in fact, the nice year-over-year increase in plug-in sales of 81% would have turned out to be a much smaller 47% gain.

Either way, soaring sales of EVs suggest they are officially here to stay.

Ford and SunPower team up
Though the innovation isn't exactly very helpful, Ford's announcement that it will unveil a concept car with a solar-charging roof using SunPower's technology does have meaningful implications. Most notably, it highlights the inevitable connection between solar power and electric cars -- whether the solar panels are built into a car's roof or providing electricity for homes and charging networks. Though Tesla may never user solar panels in its roofs, the company will undoubtedly work closely with solar companies in the future as both solar and battery innovations make new things possible. In fact, Tesla is already working with SolarCity by providing batteries to store backup energy and offset peak energy usage.

Just barely scratching the surface in solar power potential, investors in the electric vehicles space should keep an eye on the solar industry developments to see how they will impact the outlook for EVs.

Invest in Tesla? Not yet, says one analyst
Fool contributor David Kretzmann made an excellent case for why investors should look for an opportunity to buy Tesla stock -- just not at today's prices.

Kretzmann advises that Tesla is priced for perfection today. Though Tesla stock could prove him wrong, he admits, a bet on the stock at today's prices is simply speculative. Acknowledging the company's incredible performance, he suggests investors should wait for the stock to "take a sizable hit" buying any shares.

Meaningful news?
Though the week had several interesting stories, none were big enough to alter an investor's existing investment thesis for the stock.

Going forward, the two biggest stories at 10,000-foot levels for Tesla investors to keep an eye on are Tesla's ability to ramp up production and management's plans for 2014.

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Fool contributor Daniel Sparks owns shares of SolarCity and Tesla Motors. The Motley Fool recommends and owns shares of Ford, SolarCity, and Tesla Motors. Try any of our Foolish newsletter services free for 30 days. We Fools don't 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.