No state has more electric vehicles on the road than California, where 46 percent of the nation's plug-ins have been sold since late 2010. Although it's the most robust EV market in the country, California is at risk of failing to meet its EV goals.

By 2025, 1.5 million zero-emissions vehicles should be on California roads, if Governor Jerry Brown's goals are realized. However, a recent analysis by the Natural Resources Defense Council suggests this goal may be too optimistic.

"The program is in dire need of a tuneup," Simon Mui, director of the NRDC's clean car efforts in California, told the San Francisco Chronicle. "It won't be delivering as many vehicles as the state wants." California will likely see just 1 million vehicles on the road by the deadline, the analysis estimates.

Meanwhile, the California Air Resources Board is thinking of making changes to the state's zero emissions program. It will discuss the program at a hearing scheduled for December. Until then, Tesla CEO Elon Musk has some critical words for the regulatory agency.

"The California Air Resources Board is being incredibly weak," Musk told Wall Street analysts on a conference call, adding the agency "should be damn well ashamed of themselves."

But CARB is keeping a cool head. "Elon Musk is working very hard to move a company forward," board spokesman Dave Clegern told the Chronicle. "CARB is working very hard to move the state of California forward. The moving parts are quite different."

An estimated 223,700 electric and plug-in hybrid vehicles have been sold in California since the end of 2010 when many EVs started hitting the market, according to data from the California Plug-In Electric Vehicle Collaborative. Still, the green vehicles account for less than 1 percent of cars registered in the state. Of course, part of the reason they have suffered is because of low gas prices.

But flaws in the state's EV credits program are also holding California back, some say. The report notes that because of Tesla's ambitious plans to produce 1 million cars at its Fremont factory by the end of the decade, it could receive enough EV credits to make it so other automakers would only need to sell relatively few EVs in the state. Under the California program, automakers can sell excess EV credits they earn to other automakers. Musk has said that so many credits are now available that they are worth just "pennies on the dollar." The program also offers more credits to EVs with greater ranges. Automakers are starting to greatly increase the range of their EVs, which means they can sell fewer of these vehicles to meet the requirements. Some, like Mui, say it's "an example of technology outpacing regulation."

Meanwhile, other critics, including John Bozzella, head of the lobbying group Global Automakers, say the state should work on expanding carpool lane stickers and rebates for EV drivers. The rebate program ran out of funding this June.