Tesla (TSLA) - Get Report got a love letter of sorts from its billionaire co-founder and CEO, Elon Musk, who on Valentine's Day laid out $10 million for additional shares in the electric-car giant.

Musk on Feb. 14 snapped up 13,037 shares at $767 each, raising his stake in Tesla to 18.5%, or 34.1 million shares, Bloomberg reported, citing a Securities and Exchange Commission filing.

The executive has done well with the purchase. Shares of the EV maker at last check were trading at $907.82, off 1.1%. Tesla shares have more than doubled this year.

An unexpected third-quarter profit helped trigger the epic runup, with Tesla's market value now having raced past such established auto makers as General Motors  (GM) - Get Report, Fiat Chrysler  (FCAU) - Get Report and Volkswagen  (VWAGY) .

Analyst upgrades have helped keep Tesla shares moving higher, with short-selling activity having dropped.

Tesla's stock price surged on Wednesday after analysts at Piper Sandler hiked their price target nearly $200 to $928 a share from $729.

In their research note, Piper Sandler analysts Alexander Potter and Winnie Dong attributed their confidence in the Palo Alto, Calif., company to its development of solar-based systems to charge its cars.

The analysts did a first-hand test of Tesla's developing technology, installing a solar-based system to charge a Model X SUV. 

The results, the Piper Sandler analysts wrote, were "illuminating."