While the US reached 10 gigawatts of total installed solar PV last summer and should end 2013 a bit above that (official numbers aren't out yet), China has also had a very productive 2013 on the solar front. Depending on the source, China has installed between 9.5 and 12 gigawatt of solar panels during the year alone (this is not a cumulative number). This is more than has ever been installed by any country in a single year, and it's also more than the cumulative total of all previous years in China! That's truly remarkable, and it's only the beginning: the country expects to install 14 gigawatts in 2014.
This is a stark contrast to the country that for the longest time has been associated with solar power, Germany. During 2013, they only managed to add 3.3GW of solar capacity. Not bad, but not enough to be in a global solar leadership position.
China's performance is a good reminder that forecasts shouldn't always be trusted. Back in 2010, China set itself a target of 5GW of solar by 2015...
One of the reasons why solar power is growing so quickly is that prices have been steadily falling, making it a lot more affordable than even just a few years ago, and massively cheaper than a few decades ago:
More details on the falling price of solar power and why it will take over the world here.