When energy sources are discussed, solar and wind often go together like a high school couple whose identities seem to have fused. Supporters hail them as the twin solutions to both the environmental crisis and the domination of fossil fuel markets by hostile countries, whereas opponents dismiss them as too variable, too expensive, and too diffuse to do any good. Now, however, it is becoming increasingly recognized that solar will likely be the world’s main source of energy in the next decade and probably thereafter. Meanwhile, wind power still provides more of the world’s electricity, and continues to grow, but at a much slower rate.

A sense of their divergence can be seen in the fact that last year at COP28 all nations committed to tripling renewable energy production capacity by 2030 in an effort to achieve the goals of the Paris Agreement. The latest projections from the International Energy Association foresees solar doing better than that, producing 6,500 TWh in 2030, more than four times 2023’s 1,600 TWh. Wind, the IEA projects, may barely double, from 2,300 TWh to 5,000 TWh. 

With the best hydropower sites already used, and nuclear power barely changed for 20 years, it looks like solar will have to do the heavy lifting if we’re to avoid climate catastrophe while keeping the benefits of industrialization. Note that every previous IEA projection has underestimated solar power’s subsequent growth.

Three major questions come out of this: Why the difference? Does it matter? What can be done? We will leave the last one to others, but decided to investigate the first two.

Renewable History

Aside from some ecosystems around hydrothermal vents and hydrogen-munching microbes, all life on Earth depends on the Sun – so humans have technically been using a type of solar power for warmth since before we were even humans. Efforts to make electricity from the Sun go back to before the First World War, and there’s even some evidence of rooftop solar panels over 100 years ago.

However, in 1973 when the oil crisis shocked much of the world into thinking it should look for alternative sources of energy, solar technology was very underdeveloped and immensely expensive. Meanwhile, wind power – drawing on more than a millennium of applications to grind grain and pump water – was far closer to being ready to fill the gap.

For decades, both wind and solar were overshadowed by nuclear power when it came to finding ways to power the world without relying on ancient trees and microbes. However, with nuclear power facing considerable opposition, enthusiasm for renewable energy remained. In the parts of the world where this attracted government support, it was wind that seized the initiative. 

In 2000, wind produced around thirty times as much electricity as solar, although between them they added up to much less than 1 percent of the global electricity supply. By 2010 wind made about 2 percent of global electricity, while solar was still a rounding error.

Even at that point, however, there were signs solar might eventually be the winner. The amount of solar capacity installed annually grew by around 40 percent a year from the late 70s to the middle of the last decade. The wonders of exponential growth meant the electricity produced increased a million-fold in that time. This wasn’t a coincidence. Advances in technology brought prices down, which spurred more use, which led to economies of scale that brought prices down further in a virtuous spiral.

Wind capacity installation grew at a rate of about 20 percent a year until 2010, which would still be impressive for most industries, were it not for the solar comparison. Nevertheless, having started so far ahead, it was still producing twice as much energy as solar in 2019.

Recent Trends

From 2010-2018, the amount of wind installed each year barely grew. It’s picked up again since, but in 2022, 86 GW of wind was added.

Meanwhile, 200 GW of solar were installed in 2022, and this year the figure is anticipated to approach 600 GW. If so, it will be almost five times wind.

Experts argue about whether solar power’s growth truly meets the definition of exponential, but it certainly looks like it to the untrained eye. On average, each year now sees 30 percent more solar installed than the previous one – a drop from the 40 percent growth of the 80s, 90s, and early 2000s, but nevertheless enough to strike fear into coal and gas producers’ hearts.

At that rate, it will take just eight more years of growth for solar to overtake coal as the world’s largest source of electricity. By that point wind, which seems to have shifted from exponential to arithmetic growth more than a decade ago, will probably be producing about three-quarters as much power, and falling further behind.

Why The Difference?

On the surface, solar and wind appear to have much the same strengths and weaknesses. Both have fallen in price dramatically over recent decades, and now, in most circumstances, it’s cheaper to build either than constructing and running new fossil fuel plants that will produce the same amount of annual electricity. In fact, in much of the world, it’s now cheaper to install solar or wind than it is to pay for the fuel and maintenance for coal or gas-fired planets that have already been built. Often this is the case even if you add in the costs of batteries to store the power for cloudy days or windless nights.

Yet despite both having a price advantage, it’s only solar that is growing at the rates the world needs. That is despite the fact that many of the countries most suited to solar, such as those located in Africa and the Caribbean, aren’t rich enough to be currently building a great deal of any sort of energy infrastructure at all.

IFLScience asked some experts in the field – some chose not to answer or expressed uncertainty. However, Dr Saul Griffith of Rewiring Australia, which promotes ways to replace fossil fuels with clean-sourced electricity, told IFLScience that “Wind is economic when giant and in the dozens or hundreds of installations, and therefore doesn’t have the consumer-led growth of small installations that are in the thousands…millions…billions!”

“Solar on the roof is so cheap now,” Griffith went on, “And with a battery included to make it a 24-hour resource, not only can you afford to install more than you need but the battery makes it an ‘always on’ energy source. Rooftop or community-installed solar – think the surf club, primary school, shopping centre, council building, along the train tracks – will be cheaper than wind per kilowatt hour once the wind generation finds its way across transmission grids and distribution grids and retailers who all take a cut and make it more expensive than local solar.”

Griffith previously founded Rewiring America as well as working for years on using kites to harvest the energy in high-altitude winds.

Even where wind is competitive with solar on price, only those with a lot of money can take advantage of it, whereas any homeowner can put solar on their roof. Small-scale solar farms are likely to be more economical than wind farms of the same size, allowing medium-level investors to get in on the act.

Professor Andrew Blakers of the Australian National University might be expected to have a bias in favor of solar, given that he was co-inventor of PERC cells, now the world’s most manufactured solar cell design. However, today he is more devoted to finding ways to store the energy from either source economically.

He told IFLScience that “80% of the global population lives in the sunbelt (+/- 40 degrees of latitude) where there is high and non-seasonal solar. Wind is not so good at lower latitudes.” 

Blakers also agreed with Griffith’s major point, noting. “Solar on rooftops took off. No equivalent market for wind.” The makers of small wind turbines, often with novel designs, sometimes attract publicity with claims they will disrupt power production in the same way rooftop solar has. So far, it’s only the giant windfarms that have proven economically viable outside small niches.

However, it’s not just about the technology. Blakers added that there is; “Less pushback against solar farms.” Delays caused by local objections, often whipped up by fossil fuel interests, have been far more effective in slowing wind construction, at least in democratic countries than large-scale solar. With the strange exception of American Home Owner Associations, such opposition has had almost no effect on rooftop solar.

Solar and wind together are best.

Professor Andrew Blakers

Some also argue that the wind industry has made strategic mistakes. Building larger and larger wind turbines, capable of harvesting stronger winds at higher altitudes, has helped bring costs down. Nevertheless, there is probably a limit to this, and some commentators have started arguing we’ve passed that, as manufacturers compete to have the biggest turbines on the market, risking the benefits of mass production in the process. 

Failures at wind farms, such as blades coming loose, seldom pose much risk to people or the environment, but are a gift to those opposed to the energy industry and the rush for size may be contributing.

Does It Matter?

As long as we find an affordable alternative to the polluting sources of energy, some might argue it’s irrelevant if there’s a balance, or one dominates. However, Blakers argued; “Solar and wind together are best.” That’s because, in much of the world, winds blow more reliably at night or in the evenings. Perhaps more importantly, wind production usually peaks in the winter months. 

Consequently, Blakers argued; “Offshore wind is really important for Europe, Japan and North-Eastern USA. Their winter solar is miserable.” That might be one reason why Donald Trump, among others, spread even more false claims about offshore than onshore wind.

The areas Blakers mentions are home to only a small portion of the world’s population, but consume a disproportionate amount of global energy. 

“Either [wind or solar] alone can still do the job,” Blakers added, “but at greater cost.” Often that’s a cost governments are reluctant to bear. It’s going to be hard to get poorer regions to adopt solar – which will eventually more than pay for itself but has high up-front costs – if they see some of the richest parts of the planet continuing to pollute.

Consequently, even if wind only ends up providing a much smaller portion of the power that replaces fossil fuels, its contribution to getting the world working together could be much larger.