Originally published September 27, 2017. Updated September 28, 2026.
The world added 452 gigawatts of new solar in 2024, and the International Energy Agency has undercounted solar growth at that pace for more than a decade. If you’re trying to guess when solar and batteries get cheap enough to matter for your own roof or your town’s grid, the agency’s own numbers have run behind reality the whole time. Its 2025 outlook lowered its five-year forecast by 5% instead of raising it, the first downward move in years, and it points to policy shifts in the US and China as the reason.
How much solar the world built in 2023 and 2024
By the numbers that matter, solar’s growth kept accelerating while the forecasts were catching up. Global solar capacity additions reached 345.5 gigawatts in 2023, based on IRENA data reported by pv magazine, then climbed to roughly 452 gigawatts in 2024, according to IRENA’s own tally. Total renewable capacity added in 2024, across solar and every other renewable technology combined, came to 585 gigawatts. Cumulative installed solar capacity crossed 1 terawatt in 2022 and then doubled to 2 terawatts two years later, according to Ember’s Global Electricity Review.
Generation is a different measure than capacity, since how much of it converts to electricity depends on average capacity factor. Output grew 474 terawatt-hours in 2024, up 29% year over year, which Ember called the largest source of new electricity generation worldwide for the third year running. If your utility added new generating capacity that year, solar was probably most of it. Growth kept climbing in 2025, when solar output rose a record 636 terawatt-hours, up 30%, enough on its own to meet 75% of the world’s increase in electricity demand that year.
What the IEA expects for 2025 through 2030
The IEA’s Renewables 2025 outlook projects 4,600 gigawatts of new renewable capacity worldwide between 2025 and 2030, with solar PV accounting for about 80% of that, or roughly 3,680 gigawatts. In the US, the lower number reflects an earlier phase-out of federal tax credits and new restrictions on solar and wind permitting on federal land. If you live in the US, those policy changes are likely to slow how fast new solar reaches your state’s grid over the next five years.
Al Jazeera covered the same revision under a sharper headline, calling it a sharp fall in the outlook for renewable power.
How far short the early forecasts fell
Adam Whitmore, an energy policy analyst who has tracked IEA forecasts since 2013, laid out the scale of the early miss in a 2019 post. The 2013 outlook expected around 28 gigawatts of solar installed per year by 2018, while actual installations that year were already running at 100 to 110 gigawatts annually. A 2025 academic review of IEA World Energy Outlooks published between 1993 and 2022 found that renewable energy growth was underestimated across nearly all of them, in an analysis by LUT University researchers reported by pv magazine.
| IEA forecast | What it projected | What happened |
|---|---|---|
| 2013 World Energy Outlook, for 2018 | About 28 GW of solar added per year | 100 to 110 GW added per year |
| 2020 World Energy Outlook, five-year total for 2022 to 2026 | 1,092 GW of new renewable capacity | Revised up to 1,920 GW two editions later, while solar alone added 345 GW in 2023 and 452 GW in 2024 |
| 2025 World Energy Outlook (Renewables 2025), for 2025 to 2030 | About 3,680 GW of new solar capacity | Revised down slightly from the prior year’s forecast |
Source: Adam Whitmore (2019). Carbon Brief. IRENA. IEA, Renewables 2025.
Why the models kept missing solar’s growth
Part of the miss came down to price. In his 2013 analysis, Adam Whitmore argued that the IEA had been slow to recognize solar’s falling costs, with cost assumptions in its own outlooks running well above the prices solar was selling at. The agency’s models also leaned on linear extrapolation of national plans at a time when solar costs and installations were both moving on an exponential curve.
That gap between what’s affordable and what the models expect still shows up in long-range scenarios. The IEA’s own 2022 net-zero pathway projects 15.5 terawatts of solar by 2050, while a LUT University analysis reported by pv magazine put what’s technically and economically feasible at 63.4 terawatts, about four times higher. If you’re weighing a solar or battery quote against a year-old projection, the agency’s own long-range scenarios still run understated by a similar margin.
Has the agency fixed the problem, or changed direction
The IEA did correct course for a while. Between 2020 and 2022, it raised its own five-year renewable capacity forecast in three consecutive editions, from 1,092 gigawatts to 1,496 gigawatts to 1,920 gigawatts. That’s a 76% increase in two years, according to Carbon Brief’s analysis of the agency’s own reports. Solar installers kept beating even those newly raised numbers in the years that followed, adding 345 gigawatts in 2023 and 452 gigawatts in 2024.
The 2025 outlook breaks that pattern. The IEA’s five-year forecast moved down for once, and it points to policy retrenchment in the US and China as the cause. That’s a different kind of miss than the one Whitmore and the LUT researchers described.
What the forecast gap has meant for policy and investment
Whitmore’s argument went beyond accuracy for its own sake. His case was that cost assumptions running well above real market prices produced projections that made solar growth look more dependent on subsidy than it was. Actual installations kept accelerating through the years that followed regardless, as the capacity and generation numbers above show.
Grid operators now face a question the original pieces didn’t have to answer in the same way. They have to manage power generated when demand is low and the sun is still out, largely through battery storage, and that balancing act is now as much a part of the growth story as the installation totals themselves. For you, it shows up as new batteries going up next to substations and solar farms, built to hold your afternoon’s cheap solar power until demand picks back up after dark.
Why 2025 already looks like every year before it
The first year of the IEA’s newly lowered five-year window is already in the books. Solar generation grew a record 636 terawatt-hours in 2025, 33% above the previous record year. China alone built 336 terawatt-hours of that growth, more than half the global total. That’s the same shape as 2013, 2020 and every outlook since, with real installations outrunning the agency’s own numbers before the forecast period is even a fifth over.
