In the year 2000, the entire world had roughly four Gigawatts of solar power capacity installed, and it didn’t seem to be going anywhere fast. In 2002, the International Energy Agency forecast suggested that, by 2020, global solar capacity would still be hovering at around 10GW, and still barely register on the global energy markets.

How things change. Over the 15 years that followed, solar energy capacity expanded by 5,700 percent, reaching 227GW. The International Energy Agency revised its solar estimates upwards three times over that span, but its most recent estimate—over 400GW of installed capacity by 2020—is already falling behind the curve of solar’s growth. In 2015, the most recent year that numbers are available, 57GW worth of solar panels were shipped. That’s enough to add 400GW of new capacity in seven years, under the completely unrealistic assumption that our manufacturing capacity won’t expand in the mean time.

If most projections have been wrong, is there anything we can say about the future? An international team of energy experts makes an attempt to figure out where solar might be going out to the 2030s, when they expect we’ll have Terawatts worth of photovoltaics on our grids.