Green Power Hub in Canyon

A great dam stands on the Lancang River in a canyon located between the counties of Nanjian and Fengqing in Yunnan province, southwest China. This is the Xiaowan Hydropower Plant, a key power source for China's west-to-east power transmission program and a flagship project in the cascade hydropower development of the Lancang River Basin.

The Xiaowan Hydropower Plant has been advancing on a path of innovation, from the excavation of a 700-meter-high slope to the independent development of the core control system of the 700 MW hydropower unit.

Tackling complex geology

When the first group of builders walked into the unfrequented canyon, they were met by nearly vertical cliffs, a rapid river and complex geology. Excavating a 700-meter-high slope was unprecedented in global hydropower history.

Soon after construction began, Slope No.2 developed dangerous creep deformation. It created the risk of a landslide that could block the river and form a landslide-dammed lake, threatening the safety of the arch dam and the underground powerhouse.

The situation was traced to three main factors: the excavation disrupted the slope's original stability, the blasts during construction caused vibrations, affecting the slope, and the rainfall softened the soil. In addition, delays in implementing support and drainage measures aggravated the situation.

Although some experts thought the site would be extremely difficult and risky to stabilize, the building team ultimately settled on a comprehensive treatment plan. It meant using prestressed anchor cables, with anti-slide piles as a supplementary measure.

More than 1,380 bundles of anchor cables, 15 anti-slide piles and retaining walls, 10 steel-frame anti-slide piles, and a three-dimensional drainage tunnel system comprising nine levels with a total length of 3,750 meters were all completed within just over a year.

"The anchor cables stabilize the accumulated mass by pulling it from above, while the anti-slide piles act like a row of supporting columns to hold the bottom in place, and the drainage system promptly alleviates the impact of rainfall," Sun Yamin, a hydraulic engineering technician, said. Through these intensive, comprehensive stabilization measures, the deformation was brought under control in about six months and reached long-term stability after one year.

Developing a domestic control system

For a long time, the key hardware and software of the core control system and supporting system in large hydropower plants used imported equipment, which meant expensive purchases and maintenance, according to Wang Yuanhong, deputy director of the Xiaowan Hydropower Plant.

The computer-based supervisory and control system is like the nerve center of a hydropower plant. It is also one of the Xiaowan Hydropower Plant's key areas of focus. Two development paths lay ahead: the mature distributed control system used in thermal power plants and the centralized control architecture for hydropower plants that is safer and more reliable, but more challenging.

After repeated discussions, technical reviews and analyses, the project leader made the final decision: building a fast, efficient, compatible and open centralized control system that uses international communications standards for power system automation, supported by hardware terminals integrating automatic generation control and automatic voltage control functions.

The first communications test was unsuccessful, but the team did not give up. After countless rounds of testing, troubleshooting and optimization, indexes such as the timeliness, accuracy and speed of control and response of the system's data transmission all met the requirements of national and industrial regulations. Some of the indexes are even higher than current standards.

In September 2025, the Xiaowan Hydropower Plant became China's first hydropower plant with generating units boasting an individual capacity of 700 MW and a 100-percent domestically managed control system.

A hydro-solar complementary model

There are several photovoltaic (PV) stations around Xiaowan. PV power generation, dependent on weather conditions, varies strongly and can be intermittent. Large-scale integration of solar power into the power grid can cause safety issues. Zhang Xiaodong, deputy director of the Xiaowan Hydropower Plant's new energy construction and management department, said they envisioned a hydro-solar complementary model that leverages the rapid startup and shutdown capabilities of hydropower to smooth out fluctuations in solar power output and ensure grid stability.

With a reservoir capacity of 15 billion cubic meters, the Xiaowan Hydropower Plant is essentially a giant "power bank" with excellent regulating capabilities. When there is surplus electricity, PV power can be used to pump water into the reservoir for storage and release it when needed. This can significantly improve the utilization of PV power, Zhang said.

The key to realizing this vision is to optimize how PV power is connected to the hydropower plant. The project team conducted a detailed assessment of the conditions at each PV station and proposed an innovative hydro-solar interconnection model. A dedicated collection station was proposed to aggregate power from the dispersed PV resources for transmission, complemented by grid-forming synchronous condensers.

Following this model, the Xiaowan Hydropower Plant gathers 1.23 GW of clean energy from 16 PV stations in the region with a total installed capacity of 5.43 GW. The annual power generated can meet the need of about seven million households, and cut about 16 million tonnes of CO2 emissions per year.

Source: Science and Technology Daily