(Bloomberg News) Demand for hybrid cars and electric vehicles may be more modest than advocates for those fuel-saving technologies expect, capturing only 7.3% of global sales by 2020, according to a forecast by J.D. Power & Associates.

Combined deliveries of hybrids, such as Toyota Motor Corp.'s Prius, and battery-powered cars including Nissan Motor Co.'s Leaf may reach 5.2 million units that year, out of an estimated 70.9 million passenger vehicle sales, J.D. Power said in the study released today. That falls short of Nissan-Renault Chief Executive Officer Carlos Ghosn's prediction that electric cars alone will be 10 percent of global sales by 2020.

"Consumers will ultimately decide whether these vehicles are commercially successful or not," said John Humphrey, senior vice president of automotive operations for J.D. Power. Given consumer attitudes toward such vehicles and "barring significant changes to public policy, including tax incentives and higher fuel-economy standards, we don't anticipate a mass migration to green vehicles in the coming decade."

Carmakers and governments in the U.S., Europe, Japan and China are spending billions of dollars to speed development of autos that use little or no petroleum to curb greenhouse gas emissions and reduce exposure to oil-price swings. The Obama administration committed at least $11 billion in taxpayer aid to help Nissan, Ford Motor Co., Tesla Motors Inc. and other car and battery makers get electric vehicles into production.

China Question

Demand may exceed 7.3% globally should China's government push electric-vehicle sales at a more aggressive pace, according to J.D. Power. Global hybrid and battery-electric vehicle sales may total 954,500 in 2010, or 2.2% of vehicles likely to be sold in 2010, the Westlake Village, California-based company said.

Hybrid and electric cars have been niche products in global markets so far, purchased mainly by people who are older, more educated and have higher incomes than the average consumer, J.D. Power said.

"Many consumers say they are concerned about the environment, but when they find out how much a green vehicle is going to cost, their altruistic inclination declines considerably," Humphrey said. In the U.S., the number of people who say they're interested in buying a hybrid drops 50% when they learn such vehicles typically cost about $5,000 more than equivalent models with gasoline engines only, he said.

Based on consumer interviews, J.D. Power said concerns about advanced vehicles include their looks and design, reliability, overall power and performance, range and time needed to recharge battery packs.

Prius, Leaf, Volt

Toyota's Prius is the world's best-selling alternative-fuel vehicle, with cumulative deliveries of more than 2 million units since it was introduced in Japan in 1997. Sales of the Leaf and General Motors Co.'s plug-in Volt sedan, likely to be the top- selling U.S. rechargeable models in 2011, begin late this year.