After crossing the 100-gigawatt mark in 2012, it took the world 10 years to deploy 1 terawatt of solar power. An additional 1 terawatt, enough to meet all of US power demand at its peak, took less than three years to build. Not even two years later in 2026 — the precise timing is subject to debate among analysts — the 3-terawatt threshold was reached.

No one really noticed.

That makes sense. For most people, the increased deployment of solar isn’t perceived in figures, but in other ways. “Take a train anywhere, say in the UK, and you’re likely to spot solar panels,” said Lara Hayim, head of solar research at BloombergNEF.  

The visual signal is only going to get stronger. Forecasters are so bullish about solar that, in just a few years, the 3-terawatt milestone will seem almost insignificant. BNEF expects the world to deploy more than 9 terawatts of solar by 2036.

But dig in a little deeper and you’ll find interesting stories. The first terawatt was mostly rich countries subsidizing the installation of solar, with China and poor countries still finding photovoltaics too expensive. That story changed going into the second and third terawatt, with China taking the baton from rich countries.

The result is that, even as the world has added solar power at an accelerated pace, the share of deployment going to poor countries has largely stalled since 2020. China has clearly been the main driver of the global story, said Hayim. But disaggregate the numbers, and “you can now see solar booms in other countries too.” 

In the past few years, countries like Pakistan, Nigeria and the Philippines have seen an extraordinary increase in the amount of solar power installed on rooftops. Some smaller markets, such as Cuba and Lebanon, have also seen rapid uptakes. It’s why the number of countries with at least 1 gigawatt of solar installed has grown to as many as 74 last year, up from 42 in 2020.

China’s solar deployment has been faster than the buildout of supporting infrastructure, such as transmission and batteries. That’s leading to more curtailment of solar production during peak hours, and thus a waste of resources. So analysts expect deployment in China to slow down. In its latest five-year plan, the country announced a series of measures to increase renewables consumption, rather than production, by more than 50%.

BloombergNEF expects that poor countries’ share of solar deployment will start growing again from this year onward. Most developing countries are starting with very low amounts of solar penetration in the grid and won’t hit the limits that China and other big adopters are facing now. By 2036, more than a quarter of all solar deployed will be in developing countries, with rich countries’ share falling to about 20%.

The boom in solar power has happened as countries have overcome local issues, from a lack of skilled workers to challenges of managing a grid with intermittent renewables. Still, Hayim says the main constraint for developing countries continues to be the lack of accessible financing. 

There is, however, a theoretical upper limit to how much solar can be added to the grid. That’s because, once solar power meets all the demand during the daytime, adding more is of no value. Countries such as Australia and regions like California, which have among the highest solar penetration, regularly set negative electricity prices during the daytime, signaling there’s too much solar power on the grid.

Lithium-ion batteries can help extend the solar boom for some time, absorbing excess power in the day and releasing it later in the evening. That’s what Australian policymakers have helped encourage through subsidies for home batteries. It’s also what’s starting to happen, regardless of policy support, in developing countries like Pakistan and the Philippines, where a battery boom is following a solar boom. 

Without battery energy storage, the solar revolution is unlikely to continue. “Without enough energy storage, you cannot maximize solar’s potential,” said Hayim.

To contact the author of this story:
Akshat Rathi in London at arathi39@bloomberg.net