Drop in haze, pollution contributes to China’s solar generation in July

In a new weekly update for pv magazine, Solcast, a DNV company, reports that reduced atmospheric haze helped solar irradiance surge to around 40% above the July average in Northeast China.

Asia in July delivered a mixed bag for solar producers, with extremes at both ends of the irradiance spectrum. The northeast of China once again recorded unusually high solar irradiance, boosted by clearer-than-usual skies, while the tropics transitioned into an active weather phase that limited solar potential across Southeast Asia and the northern Philippines. Meanwhile, suppressed weather activity in parts of North Asia, including South Korea and Japan, created favourable PV generation conditions, according to analysis using the Solcast API.

A large part of Northern Asia saw significant positive irradiance anomalies, with Japan and South Korea hitting 30% above average in some places. Northeast China saw the largest benefit, with irradiance surging to approximately 40% above the July average, particularly inland from Shanghai and Beijing. A key cause was reduced atmospheric haze, which allowed more sunlight to pass through the atmosphere. Solcast data shows clear sky Global Horizontal Irradiance (GHI) – i.e. irradiance before cloud impacts – was 7% above average in this region, an unusual pattern for July when haze typically acts as a limiting factor.

The haze reduction extended into South Korea, where clearsky GHI was up to 4% above average. Suppressed cloud cover due to positioning on the northern flank of tropical weather activity further contributed to increased irradiance across the broader North Asia region. To quantify the impact of this anomaly, the Solcast data science team have modelled the power impacts of this irradiance anomaly below, highlighting the expected impact for reference 1 MW sites in Jinan. Power modelling for 1 MW fixed-tilt and single-axis tracking installations shows a notable generation benefit in July 2025 compared to recent years.

Further south, the situation was starkly different. The tropical storm season in the northwest Pacific shifted gears in July, bringing a sharp uptick in storm frequency and associated cloud cover. After a subdued start to the 2025 season with just two named storms in June, July saw three named tropical storms and three typhoons. These systems brought extensive cloudiness to tropical areas, reducing irradiance by up to 25% in the northern Philippines and Taiwan and by 10-20% across southern China, Vietnam, Laos and northern Thailand.

One of the most impactful systems, Severe Tropical Storm Wipha, brought deadly flooding and landslides across a swathe of Asia including the Philippines, Taiwan, Hong Kong, Vietnam, and Myanmar.

The storm caused widespread power outages and is believed to have resulted in at least 57 fatalities. As these systems passed, irradiance dropped sharply, as shown in Solcast estimates such as the 19 July decline when Wipha moved from the northern Philippines toward China.

Solcast produces these figures by tracking clouds and aerosols at 1-2km resolution globally, using satellite data and proprietary AI/ML algorithms. This data is used to drive irradiance models, enabling Solcast to calculate irradiance at high resolution, with typical bias of less than 2%, and also cloud-tracking forecasts. This data is used by more than 350 companies managing over 300 GW of solar assets globally.