World solar and wind electricity production data for 2019 have just been released, and they appear to confirm the trend we discerned in our June 9 post, How fast can solar push out fossil fuels?. Exponential growth appears to be finished for both of these pillars of renewable energy.
In this post we show that the linear growth pattern into which solar and wind have apparently settled, while impressive on many counts, isn’t steep enough to displace fossil fuels fast enough to avert climate catastrophe.
There’s no question that solar and wind have grown rapidly worldwide, stimulating hopes that these technologies represent a transformational juggernaut that can carry us into a fossil fuel-free future. Between 2000 and 2016 global solar electricity production grew at an average rate of 44% per year while wind electricity production, starting from a larger base, grew at 25% per year, according to the BP Statistical Review of World Energy, 2020.
A consistent increase by a constant percentage represents exponential growth. Continuation of the 2000-2016 percentage growth rates would lead to enough energy production to blow fossil fuels out of the picture within several decades. But a closer look reveals that solar and wind’s worldwide percentage growth rates have recently been declining. Figures 1 and 2 above show actual growth to 2016. Figures 3 and 4 add production that would have been expected through 2019 and this year as well if exponential growth had persisted, with the yearly growth percentages to 2016 remaining constant.
The takeaway from Figures 3 and 4 is that solar and wind appear to be transitioning from their early, exciting, exponential growth phase into a more settled linear pattern. In each year from 2016 to 2019 global solar electricity grew only by approximately the same absolute amount per year, not by over 40% per year as it had earlier. A straight line fits this recent trend well, indicating a linear (i.e., additive), not exponential (i.e., percentage) rate of increase. The same applies to wind.
That solar and wind growth should transition from exponential to linear shouldn’t come as a surprise. As I noted in my June 9 post, maintaining exponential growth over long periods of time is extremely challenging. Most technologies, after an initial exponential growth spurt, tend to grow in a linear manner, adding a more-or-less constant increment each period. This pattern fits U.S. automobile ownership, railroad track mileage and electricity production — despite consistent technological improvements — to name just a few technologies, and natural systems as well.
If the solar and wind transition to linear growth is confirmed over the next few years, how much electricity production are they likely to contribute by 2040? Linear growth would represent more-or-less steady production of a constant amount of new capacity each year, with the amount being a function of manufacturing capacity and other constraints such as siting and financing. Based on their 2016-2019 growth, the upper limits of future annual growth are 161 TWh/y for solar and 216 TWh/y for wind. (These are upper limits, at the 95% confidence level; mean growth rates for 2016-2019 were 132 TWh/y for solar and 153 TWh/y for wind.) Solar would then provide about 4,000 TWh to world electricity supply in 2040, and wind approximately 6,000 TWh, as Figures 5 and 6 show.
To put these future productions levels in context, we need to look at how much electricity production will be required. World electricity production last year totaled about 27,000 terawatt hours. That figure will almost certainly grow not only to spread prosperity to the one to two billion people who currently use little or no electricity, but to shift provision of transportation, heating and factory production to electricity from petroleum fuels on account of climate concerns.
In a recent report, Global Energy Outlook, the U.S. NGO Resources for the Future (RFF) reviewed and compared projections from some of the world’s leading energy institutions. Because many of the projections used different assumptions, RFF “harmonized” them to bring them into an apples-to-apples alignment. An approximate average of these projections is that world production of electricity will grow by 2040 to about 40,000 TWh. I myself derived a considerably higher figure for the same year, around 70,000 TWh, when I used the En-ROADS simulation tool developed by Climate Interactive, Ventana Systems and MIT Sloan School and set electrification of transportation, buildings, and industry to a maximum level. (Projections this far into the future are fraught with uncertainty but are nevertheless useful in framing the discussion.)
In a non-climate-challenged world, steady linear growth leading to a total 10,000 TWh of production from these two renewable sources by 2040 would be a worthy achievement. But it’s barely a third of today’s electricity consumption, and just one-fourth or less of the expanded generation that’s likely to be needed in that year. Without major changes that significantly accelerate development of low- and zero-carbon power sources, or that drastically reduce the need for energy, the “missing” electricity will come from fossil fuels, exacerbating the already ominous impacts of climate change.
Such major changes could include emergence of one or more disruptive new technologies, such as utility-scale storage cheap enough to ameliorate wind’s and solar’s intermittency, more efficient methods of harnessing solar, wind, and geothermal energy, a radically different, easily deployable version of nuclear power, or something else not yet above the horizon. The need for new low-carbon tech was underscored this week by the International Energy Agency, whose new Clean Energy Innovation report concluded that “Without a major acceleration in clean energy innovation, net-zero emissions targets will not be achievable.”
Another major change could be a revolutionary policy that dramatically accelerates progress in energy efficiency and funnels significantly more funding to R&D of new power sources. One policy that could catalyze that is a steadily increasing fee on emissions of carbon dioxide. Pricing carbon emissions so that uses of fossil fuels include their true climate costs would incentivize development of low- and zero-carbon power sources and encourage the full gamut of low-carbon alternatives from energy efficiency and conservation to more-efficient and less-carbon intensive factories, transport and electricity. This could be done in an income-progressive, revenue-neutral fashion, as in proposed legislation H.R. 763, the Energy Innovation and Carbon Dividend Act, introduced early last year by Representative Ted Deutch (D-FL).
But the time left to phase out fossil fuels and avoid the worst effects of climate change is dwindling fast. After three consecutive years of incontrovertibly linear (additive) growth — extrapolation of which leads to scenarios falling far short of what’s needed to meet the twin imperatives of prosperity and decarbonization — the onus should be on renewables advocates to demonstrate why the world’s hopes should continue to be placed largely on solar and wind.