The shift away from fossil fuels towards a low-carbon world is more a very gradual steering correction than a simple u-turn, but the latest report from the International Energy Agency (IEA) suggests we are changing direction faster than expected. Renewables have now overtaken coal as the world's largest source of installed power capacity, and the agency's projections over the next five or so years paint a pretty promising picture for the industry indeed.

With wind and solar leading the charge, renewables added a record 153 GW of power capacity in 2015, which represents more than half of the world's new power capacity for that year and a 15 percent increase on 2014. A record wind power addition of 66 GW and a record solar photovoltaic addition of 49 GW had a huge part to play. This was illustrated by the half-million solar panels installed around the world every day, and the two wind turbines installed in China every hour across 2015.

The reasons for this unprecedented growth are varied, the agency says, listing advancing technologies, more accommodating policy and growing competition as key factors. The need to cut carbon emissions is a big motivator, but improving air quality and a desire to diversify energy sources to improve energy security also contributed to what is billed as a "turning point" for renewable energy.

But capacity is one thing, and when you're relying on the sun to shine and the wind to blow, actual power generation is very much another.

"Renewable power capacity becoming the largest installed power capacity in the world is a very important milestone on the journey to transition to a sustainable economy and to mitigate the climate change," Emre Gençer, Postdoctoral Associate at the MIT Energy Initiative, tells New Atlas. "However, due to the variability and intermittency in availability of renewable energy sources, the installed capacity does not always reflect the production capacity."

Because coal generation doesn't operate at the mercy of the elements and can be fired up and turned off as needed, it has a higher output than energy gleaned from the sun and the wind. Jeff Logan, Senior Energy Analyst at the US' National Renewable Energy Lab, tells us that IEA figures indicate coal generation exceeded renewable generation by 40 percent in 2014.

"While coal plants generally operate at full output about 60 percent of the time in most markets, wind plants generate power at their full potential about 35 to 40 percent of the time, and solar plants about 20 to 25 percent of the time," he tells New Atlas. "This explains why renewables have more generating capacity than coal, but less overall generation."

In its 2015 World Energy Outlook, the IEA predicted that renewable generation will overtake coal generation in 2030, but the latest report may instil its experts with a little more optimism. The agency now expects renewables to account for more than 60 percent of the growth in global power capacity over the next five years and exceed 7,600 TWh (terawatt hours) by 2021, equal to the combined electricity generation of the US and Europe today.

This is a 13 percent increase on its predictions from the year previous, a change it attributes mostly to more renewable-friendly policy in key markets: the US, China, India and Mexico. Over the same period, it expects costs to become lower, 25 percent for photovoltaic solar and 15 percent for onshore wind.

And with policy starting to push the pieces into place, it is possible that near-term research advances in energy storage might allow us to squeeze more out of these resources during the transition period. Gençer tells us that backup power plants installed and managed in the right way can help address some of the immediate drawbacks of wind and solar energy, giving our journey down the renewables road another healthy nudge along.

"For example, a more stable power output can be achieved by having both wind and solar in power generation portfolio," he explains. "Integration of energy storage systems at different scales is critical to ensure continuous power supply from renewable sources. During the periods of renewable energy availability excessive energy is harnessed and stored. Stored energy is then used when renewable energy sources are not available."

Source: International Energy Agency