Upper Tatay: Cambodia’s Green ‘Battery’ in the Cardamom Mountains

On 10 April 2026, in the mountains of Koh Kong Province, a discreet yet historic ceremony marked the start of a construction project that could reshape Cambodia’s energy future. The first gigawatt‑scale pumped‑storage hydropower project in the country, Upper Tatay is also one of the most ambitious industrial bets in Southeast Asia.

A “green energy bank” in the Cardamoms

The Upper Tatay Pumped Storage Hydropower project, located in the Tatay River basin in Koh Kong Province in southwestern Cambodia, represents a total investment of around one billion dollars and an installed capacity of 1,000 megawatts.The facility will be equipped with four 250‑MW vertical‑shaft reversible pump‑turbine units, capable of operating alternately in pumping mode and turbine mode according to the needs of the national grid.

The principle of pumped‑storage hydropower is simple in design yet powerful in effect: during periods of low demand, surplus electricity is used to pump water from a lower reservoir up to an upper reservoir; during peak‑demand periods, the water is released back down through turbines to generate electricity.This technology turns the mountainous relief of the Cardamoms into a giant energy accumulator—a “green energy bank,” as the project’s promoters call it.

Designed for the Tatay River basin, the project is intended to perform core functions for Cambodia’s power system: energy storage, peak‑load regulation, smoothing demand troughs, and integrating new renewable‑energy sources.

A strategic turning point for Phnom Penh

Cambodia’s Minister of Mines and Energy, Keo Rottanak, described the project as “historical,” noting that it is the very first authorization granted by Cambodia for the construction of a pumped‑storage hydropower facility.The stakes go far beyond the technical. The minister emphasized that the initiative directly addresses the global hydrocarbon crisis by strengthening national energy security, and positioned the plant as a key driver of the national strategy to raise the share of clean energy from 63% in 2025 to over 70% by 2030.

Dependence on imported fuels is a structural vulnerability for Phnom Penh. Like other developing countries, Cambodia suffers from price and availability volatility in imported fuels stemming from Middle‑East disruptions and the absence of domestic refining capacity.A sign of this shift in course: the fuel‑import bill declined by about 11% in 2025 to 1.68 billion dollars, reflecting the growing share of renewables and the spread of electric vehicles.

Financially, the expected benefits are substantial. The plant is projected to generate more than 600 million dollars in tax revenues over a 40‑year BOT (Build‑Operate‑Transfer) period, providing a new source of national income for social development. The project is scheduled to be completed in 2029.

China, the quiet architect of a transforming grid

Behind the technical dossier lies a geopolitical and economic reality that no one seeks to hide. The Upper Tatay project is being developed by the China National Heavy Machinery Corporation (CHMC), a Chinese state‑owned enterprise. Its president, Xiao Ping, has described the plant as a key element of China–Cambodia industrial cooperation under the Belt and Road Initiative.

Chinese presence in Cambodia’s energy sector is nothing new. The Tatay hydropower plant, operated for ten years by the same CHMC, has produced more than 10.5 billion kWh of electricity, avoiding the emission of over 5.6 million tonnes of CO₂; it is now held up as a Belt‑and‑Road model of Sino‑Cambodian cooperation.More broadly, since 2010, Chinese investments have helped raise Cambodia’s electrification rate from 50% to close to 96%. Chinese investors have also built the Phnom Penh–Sihanoukville Expressway, a two‑billion‑dollar project, and a new airport inaugurated near the capital last year.

Ambassador Wang Wenbin of China to Cambodia reiterated at the opening ceremony that energy is “the flagship of pragmatic cooperation” between the two countries.

A technology on the rise across the region

The Cambodian project fits into a broader regional trend spanning all of Southeast Asia. As countries such as Vietnam, Thailand, and the Philippines push solar and wind power, managing intermittency has become a central challenge. Pumped‑storage hydropower appears as a proven response: by capturing excess renewable energy and releasing it on demand, it smooths fluctuations and contributes to grid stability.

The International Hydropower Association highlights the growing role of this technology: East Asia accounts for nearly half of the world’s installed pumped‑storage capacity, led by China, Japan, and South Korea, and hosts an even larger share of projects under construction or in planning.According to Rystad Energy, Southeast Asia could reach 18 GW of pumped‑storage hydropower capacity by 2033.

For Cambodia, Upper Tatay is not an isolated project but the centerpiece of a wider plan. In November 2024, the Cambodian government announced a target to increase the share of renewables in electricity generation to 70% by 2030, with 13 renewable projects totaling 1,275 MW already under construction and 23 additional projects approved for 2024–2029, including 12 solar parks, six wind farms, and two energy‑storage facilities.

Challenges of a transition under Chinese tutelage

Even if the stated ambitions are real, several questions deserve clear‑eyed examination.First, the concentration of investments in the hands of Chinese actors raises legitimate concerns about diversification of partnerships. China Huadian alone accounts for about 40% of Cambodia’s total electricity generation, and most of the major independent producers are owned by Chinese companies.While this dependence ensures accessible financing for a country with limited fiscal resources, it also raises questions about long‑term sovereignty over critical infrastructure.

Second, Cambodia’s historical reliance on coal remains a fact: in 2024, more than 40% of electricity consumption still rested on fossil‑fuel sources, mainly coal.Though Cambodia has decided not to invest in new coal‑fired plants after 2024, the effective transition will take time.

Finally, scholar Jayant Menon of the Singapore‑based think tank ISEAS‑Yusof Ishak Institute notes that the scale of this investment is considerable relative to the relatively modest size of Cambodia’s economy.The project’s profitability, underpinned by a 40‑year BOT concession, will depend heavily on sustained growth in national electricity demand.

Toward a “green battery” Cambodia in ASEAN?

The Upper Tatay Pumped Storage Hydropower Project is more than a civil‑engineering site in a remote valley of Koh Kong. It embodies a development‑model choice: that of a middle‑income country betting on storage infrastructure so as not to remain hostage to global hydrocarbon markets, while aligning itself with the regional push toward integrated power grids.

With a capacity of 1,000 MW, the facility is expected to become one of the largest renewable‑energy installations in Southeast Asia. Its commissioning, scheduled for 2029, will coincide with Cambodia’s 70% clean‑energy target—a tight window, yet carefully calibrated to show that the energy transition in developing countries can take unexpected forms, financed by non‑Western actors in regions long overlooked by major multilateral agencies.