The exponential growth of solar PV

In his book The Switch, Chris Goodall confidently predicts that solar power will be the dominant form of energy for the 21st century. Many countries will be able to run entirely on solar power and storage, with only those colder and darker northern countries that will need extra energy sources.

That’s not a view shared by the International Energy Agency, the biggest forecaster of future energy. Year after year, they underestimate solar power. Analyst Auke Hoekstra has been tracking this failure, and updating a graph that illustrates it vividly. The coloured lines below show the IEA’s forecasts for solar PV, published in the World Energy Outlook. The black line shows reality.

Hoekstra explores his methodology and why solar is so consistently under-estimated here, but essentially it boils down to the fact that the IEA is forecasting incremental growth.  With solar PV, we’re looking at exponential growth. Installed capacity is doubling every two years, and current growth rates seem to confirm Goodall’s assertions. Others are noticing too. Here’s another analyst, Mike Shurtleff, showing how solar PV could be the dominant form of energy within a decade. Or you could look at the BNEF New Energy Outlook.

Looking at total global energy use, the contribution from solar has been vanishingly small and easily dismissed – less than one percent. How could it possibly compete with oil, coal and gas, let alone overtake them? But as Albert Bartlett said, “the greatest shortcoming of the human race is our inability to understand the exponential function.”

Perhaps a financial crisis or a resource crunch will knock it back, but the evidence is mounting that the future does lie with solar power. That will be a crisis for the fossil fuel industry, for the investors that have sunk their money into it, and for governments that depend on it for revenue. Money may already be tipping towards sustainable technologies, as Forbes were reporting this week. All of this won’t be enough to stop climate change on its own – we still need to reduce the use of fossil fuels, but the rapid rise of solar will still be very good news for the atmosphere, and for energy access and energy democracy.


  1. Unfortunately this according to my calculations using BP’s data is not true. The reason is that whilst growth in capacity is doubling every 2 years growth in output is not.

    1. That’s an important nuance, and I suspect those claiming it will be the dominant form of energy within a decade are making that mistake. There are competing projections and I don’t have the statistical nous to know which one’s most likely. The decline of oil is similarly difficult to project, but the takeaway is that it’s a matter of when, not if the world will run on solar power.

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