Apart from rapid growth in China, clean energy investment in Japan soared 75 percent in 2012, thanks to national efforts to develop alternatives to nuclear energy after the Fukushima Daiichi nuclear disaster in 2011.

South Africa, meanwhile, emerged as the fastest-growing destination for clean energy investment among the G20 nations after attracting $5.5 billion, from less than $100 million in previous years.

"More money will be going into South Africa, as long as it keeps its policies in place," said Cuttino, who added that the country has put some ambitious targets and policies in place, such as its renewable energy tender program to encourage development of the sector.

Although worldwide investment in the sector fell last year, reached new generating capacity installed in 2012 hit a record 88 gigawatts, said the report.

China accounted for 30 percent of total clean energy investment in the G20 nations during the year, adding 23 gW of capacity, which accounted for 25 percent of the newly installed clean energy in the whole year, the report showed.

Cuttino said a sustained decline in the price of clean energy technologies and economies of scale had led to lower costs.

Lin Boqiang, director of the Center for Energy Economics Research at Xiamen University, said investment in clean energy often comes with a lag, and the record installed capacity might also be a delayed benefit of investments from previous years.