Musk's holdings in solar panel installer SolarCity and electric car maker Tesla are down a staggering $US3.3 billion ($4.64 billion) since the start of the year. Musk is the largest single owner of both companies - which together have handed their investors total market value losses of $US14.8 billion this year.

Both Musk's companies have been falling out of favour with investors as the market punishes companies that are thin on profit but high on valuation. Falling oil prices have also taken out the urgency and enthusiasm over alternative energy plays.

Musk is now down $US666 million in his shares of SolarCity on the year. The stock plunged 25 per cent on Wednesday to $US19.56 after the company that installs and leases solar panels told investors late on Tuesday it was likely to lose up to $US2.65 a share in the current quarter. That's deeper than the $US2.49 a share loss investors were expecting, according to data from S&P Global Market Intelligence. The negative outlook completely overshadowed the fact that during the fourth quarter the company reported a smaller-than-expected quarterly loss of an adjusted $US2.37 a share. Shares of SolarCity were already down 48 per cent this year - before Wednesday's drop.

Next, all eyes are on Musk's big investment: Tesla. Musk's massive $US4.3 billion stake in the electric car maker makes his $US419 million position in SolarCity look small fry. Shares of Tesla have slid 37 per cent this year - serving up a nearly $US12 billion loss to investors, of which Musk has suffered $US2.6 billion.

After the market closed on Wednesday, the Silicon Valley electric car maker reported a quarterly loss for the eleventh straight quarter as higher sales of its Model S sedans failed to offset rising costs. Tesla said its net loss nearly tripled to $US320.4 million, or $US2.44 per share, in the December quarter, from $US107.6 million, or US86¢ per share, a year earlier. Revenue rose nearly 27 per cent to $US1.21 billion.

Investors had predicted the company to turn a profit of an adjusted 12 US cents a share, reversing its quarterly losses. Revenue for the quarter was expected to rise 65 per cent to $US1.8 billion.

Still, it's too soon to feel bad for Musk. His stakes in SolarCity and Tesla are still valued at $US4.8 billion. That doesn't even include his stake in space flight pioneer SpaceX, which is privately held.

And Tesla forecast higher-than expected  deliveries of Model S sedans and Model X SUVs and surprised the market saying it expects to turn in a profit in 2016, sending its shares 15 percent higher in after-hours trading.

So not all is lost for Musk: perhaps Tesla is turning on the turbo now and blowing away the negative investor sentiment that got him hammered this year.

​MCT, Reuters