* Investment down $600 million to $80.3 billion
* Capacity reached 318 GW in late 2013
* Growth expected to rebound in coming years
LONDON, April 9 (Reuters) - Growth in the wind energy market slowed in 2013 for the first time in more than 20 years led by a fall in U.S. projects while investments fell $600 million to $80.3 billion, the annual Global Wind Report said on Wednesday.
New capacity of around 35 gigawatts (GW) came on line, down from more than 45 GW added the previous year.
The world's installed capacity stood at around 318 GW in late 2013.
"The annual global market for wind energy shrank in 2013. We knew that this was likely to be the case... but we didn't expect the drop in the United States to be as dramatic as it was - going from 13 GW in 2012 to just 1 GW in 2013," the report said.
For 2014, it said there could be a record amount of wind power facilities built.
"Partly because of the drop in the U.S. in 2013, 2014 promises to be a record year," the report said. "The U.S. had an all-time high of more than 12,000 megawatt (12 GW) under construction in December of 2013, and... 2014 and 2015 will be solid and productive years for U.S. installations as a result."
German engineering firm Siemens said in the report that renewables, including onshore and offshore wind, will generate a quarter of global electricity within the next two decades.
"By our calculations, by 2035, renewables will be generating more than 25 percent of world's electricity, with a quarter of this coming from wind," said Markus Tacke, chief executive of the wind power division of Siemens Energy.
Siemens said that this growth would be driven by improving cost competitiveness of wind power.
"If you look at the overall costs to the economy, then wind power - onshore as well as offshore - has long been on an equal footing with conventional fuels, if not actually superior to them," the company said.
The report said that most growth was expected in emerging markets in Latin America and Africa, while Europe would see most growth in Germany and Britain, which together would make up almost 50 percent of the continent's wind energy expansion.
Public anger in China at the choking smog engulfing major cities would also trigger renewed growth for wind power, it said.
Europe remains the world's biggest wind market, with 121.5 GW of installed capacity.
Asia has 116 GW, North America 70.8 GW, there is 4.8 GW in Latin America and the Caribbean, 3.9 GW in the Pacific Region, and 1.3 GW in Africa and the Middle East. (Reporting by Henning Gloystein; editing by Jason Neely)