Not that long ago, the plunge in oil prices that has occurred over the past year would have been to renewables what kryptonite was to Superman, as the Financial Times put it. Not anymore. Yes, it’s true that American investors would have been better off putting their money into the S&P 500 from April 2014 to April 2015 than in clean-tech funds. That was the period that saw oil prices drop from almost $100 to less than $50 a barrel, before recovering a bit. But in the first quarter of 2015, many clean-tech funds handily outperformed the S&P. Moreover, the sector did not see a wave of bankruptcies and pullbacks like the one that scarred it a decade ago, when a glut of Chinese manufacturing drove dozens of solar companies into oblivion. In fact, global clean-energy investments increased 17 percent in 2014, reaching $270 billion, reversing two years of declines. While government-policy support remains crucial, renewable companies also did well raising money in the markets; equity investment rose 54 percent in 2014.

There are other reasons for optimism. One is that deployment of renewable technologies continues to rise. The United States is on course to install 12 gigawatts of renewable capacity this year, more than all conventional sources combined. Wind capacity grew by 8.1 percent in 2014, and based on its analysis of projects in the works, the US Energy Information Administration (EIA) estimates capacity will grow another 13.1 percent in 2015 and 10.9 percent in 2016. Solar is growing even faster, though from a smaller base. Between now and 2022, the EIA predicts that renewables will account for the majority of new power; by 2040, its US market share could be 18 percent, up from 13 percent in 2013.

Globally, 2014 saw a record 95 gigawatts of new wind and solar, and the International Energy Agency (IEA) expects renewables to account for 25 percent of power generation in 2018, up from 20 percent in 2011. In 2014, nonhydro renewables accounted for almost half (48 percent) of net new power capacity. This was the third year in a row the figure was above 40 percent. Solar, in particular, is hitting its stride and has grown an average of almost 30 percent a year for the past decade.