Okay, so I actually looked it up, and your hunch is correct. According to the International Energy Agency's "World Energy Outlook 2012":
"A steady increase in hydropower and the rapid expansion of wind and solar power has cemented the position of renewables as an indispensable part of the global energy mix; by 2035, renewables account for almost one-third of total electricity output.", [1], page 6
Also, from their FAQ[2]:
> How much of the world's energy comes from renewable sources?
"In 2009, the world relied on renewable sources for around 13.1% of its primary energy supply, according to IEA statistics. Renewables accounted for 19.5% of global electricity generation and 3% of global energy consumption for road transport in the same year."
So it looks like the Slate article is grossly misleading.
[1] http://www.iea.org/publications/freepublications/publication...