(Bloomberg) — The world’s green power goal has a wind problem.

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At the COP28 climate talks in Dubai last year, leaders from more than 130 nations agreed to triple renewable power capacity by the end of the decade. It was one of the few tangible agreements at the annual meeting and a goal that’s crucial to cut dependence on fossil fuels that cause climate change.

While the target remains achievable, current rates of clean power deployment aren’t sufficient and the rollout of wind turbines is lagging, according to the International Renewable Energy Agency.

“One of the big problems here is wind,” said Oliver Metcalfe, head of wind research at BloombergNEF. “The slow pace of wind progress is affecting the efficacy of that tripling renewables target.”

A decade ago annual solar and wind installations were neck and neck, then solar soared far ahead as massive investments in manufacturing capacity by the industry’s leaders in China has driven down the price of panels.

Though global wind capacity has nearly doubled in the past five years, solar has more than tripled. And the trend is set to continue. Solar installations are forecast to jump 34% in 2024, compared to a 5% increase for wind, according to BNEF. And outside China, by far the world’s biggest market, wind farm installations may actually fall slightly this year.

There are significant bottle necks in the wind industry, such as insufficient supplies of equipment, a lack of electric grid capacity and permitting issues, according to Sven Utermöhlen, head of the offshore wind business at Germany’s RWE AG.

“There are positive signs in terms of the offshore industry — the market is reacting — but the lead times are long in offshore wind and positive steps take several years to trickle down and have an effect,” Utermöhlen said in an interview.

By 2030, BNEF forecasts that solar will have reached over 90% of the capacity that’s required to put the world on track to reach net-zero emissions by 2050. Wind will only reach about 77% of the necessary total by the same date.

Politicians and clean energy proponents often group solar and wind together like twins, yet the two technologies are distinct. The differences can be complementary. Wind is often strongest during winter when sunshine is scarce, and turbines run for more hours of the year. That can help countries limit the need to revert back to natural gas or coal.

But other differences have helped give solar an edge. Solar equipment is typically small — a single module can weigh close to 50 pounds, light enough for a person or two to carry without equipment. And they can go basically anywhere: on a roof, in a field, in a parking lot. Sunshine mostly varies by latitude, making it easy to predict.

A wind turbine on the other hand is massive. And the bigger they are, the better the machines are at harnessing wind, making the electricity cheaper. But size is also a weakness: the machines have become so gigantic that specialized equipment is needed at every stage of production, including giant cranes, planes and ships to deliver and install them.

Solar’s growth has been supercharged by convenient installations on home and factory rooftops, including in densely populated cities. That’s not an option easily available for the wind sector, which has often faced public opposition to large onshore farms, and even complaints over turbines out at sea spoiling ocean views.

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And then there’s the cost. While soaring production of solar panels in China has helped slash costs to record-low levels, increasing prices of steel and other critical turbine components as well as supply chain bottlenecks and higher borrowing costs have driven up the cost of wind projects in recent years. By the end of last year, the cost of power from new onshore wind farms had risen dramatically in both the US and Germany, according to BNEF data on the levelized cost of energy. In the US, it was up about 40% from a record low reached in 2021. In Germany, Europe’s biggest wind market, there was a 35% increase from its all-time low in 2019.

Solar’s surge has kept the possibility alive that the world can reach its renewable target, though the slowdown in wind — which is more efficient — could mean a higher total capacity is needed to achieve the same reduction in power sector emissions. While electricity generation capacity is the most common way to measure power stations, it’s an imperfect one. To really understand a wind farm or solar park’s impact for the planet you also need to consider how sunny or windy it is in a given location. Analysts use what’s known as a capacity factor to essentially discount renewables for their variability.

In Germany, for example, a solar farm is expected to produce about 11% of the time. It’s about a third as productive as an onshore wind farm in that country, and less than a quarter as productive as turbines offshore, where wind speeds are stronger and more consistent. And while solar is an important part of Germany’s decarbonization pathway, it doesn’t produce during winter evenings when demand peaks.

Those issues underscore the need to speed up the development of wind projects and to continue to add more solar in order to meet the target to triple renewables capacity, according to IRENA.

There are positive signs. Solar installations have continued to exceed analysts’ expectations nearly every year. And wind has seen improvements as well. Inflation has come down, interest rates are starting to decline and governments are taking action to ease bottlenecks like permitting that have slowed expansion.

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