Floating Solar Thailand: Sirindhorn and Ubol Ratana Performance

Thailand’s floating solar program has moved from experiment to proven infrastructure. The Sirindhorn Dam project, operational since 2021, has already cut its payback period to just five years while offsetting 47,000 tonnes of CO₂ annually (Power Technology, 2024). Its successor at Ubol Ratana Dam, which began commercial operation in March 2024, is reporting 5–8% higher energy yield than equivalent ground-mounted systems thanks to the cooling effect of water (EGAT, 2024). Together, these two projects anchor a national pipeline of 2,725 MW that could make Thailand one of Southeast Asia’s largest floating solar markets by 2030.

For anyone tracking the country’s clean energy transition, these dams are the proof points. They show whether floating solar can survive tropical heat, monsoon seasons, and the technical challenge of merging two very different generation technologies into one continuous power stream.

TL;DR: Thailand’s Sirindhorn (58.5 MW) and Ubol Ratana (24 MW) floating solar projects generate 24-hour clean power by pairing daytime solar with nighttime hydropower. Sirindhorn has cut its payback period to five years and saved 500 million m³ of water from evaporation, while Ubol Ratana reports 5–8% higher yields than ground-mounted systems due to water cooling (EGAT, 2024; Power Technology, 2024).

How Does a Hydro-Floating Solar Hybrid System Work?

A hydro-floating solar hybrid isn’t simply a solar farm on water. It’s an integrated power plant that uses the same reservoir for two distinct generation cycles. During daylight, 144,400 solar modules at Sirindhorn Dam and a 24 MW array at Ubol Ratana Dam capture sunlight from the water’s surface. When the sun sets, the existing hydropower turbines at each dam — 36 MW at Sirindhorn and 25.2 MW at Ubol Ratana — take over (Power Technology, 2024; EGAT, 2024). This pairing solves the single biggest weakness of solar energy: intermittency.

The system doesn’t stop at pairing two sources. Ubol Ratana adds a Battery Energy Storage System (BESS) and an Energy Management System with weather forecasting to smooth the transition between solar and hydro output (EGAT, 2024). Think of the battery as a shock absorber. When a cloud bank rolls over the reservoir and solar output drops, the BESS releases stored power for minutes until the hydropower plant can ramp up. Without this buffer, the grid would see sudden voltage swings every time weather changes.

The floating platforms themselves are engineered for tropical conditions. EGAT specifies environmentally friendly materials and panel tilt angles designed to let sunlight penetrate the water column, minimizing impact on aquatic ecosystems (EGAT, 2024). At Ubol Ratana, the entire solar array covers less than 1% of the reservoir surface — a deliberate design choice to protect fisheries and water quality.

A key insight from EGAT’s design is that the water itself boosts performance. Solar panels lose efficiency as they heat up. Ground-mounted panels in Thailand’s tropical climate can reach surface temperatures above 65°C, cutting output by 10–15%. Water-cooled floating panels stay closer to ambient temperature, which is why Ubol Ratana sees 5–8% higher yield than equivalent land-based systems (EGAT, 2024).

According to EGAT’s hybrid design, the shared transmission infrastructure at each dam site cuts capital costs by roughly 15–20% compared to building separate solar and hydro plants. The dam already has switchyards, grid connections, and access roads. The floating solar array simply plugs into existing infrastructure.

Sirindhorn Dam: How Did Thailand’s First Floating Solar Giant Perform?

Sirindhorn Dam in Ubon Ratchathani Province became the world’s largest hydro-floating solar hybrid project when it entered commercial operation in September 2021 (SEI Press Room, 2021). With 58.5 MW of solar capacity spread across 121 hectares of reservoir surface and 144,400 individual modules, the project cost $59.6 million and was expected to offset 47,000 tonnes of CO₂ every year (Power Technology, 2024).

The real story is what happened after the panels started generating. By October 2024, EGAT reported that the plant was “consistently producing more electricity than originally expected” at a technical conference in Ubon Ratchathani. Strong performance had compressed the estimated payback period from an initial projection of roughly eight years down to just five years.

Our finding: The 500 million m³ of water evaporation prevented by Sirindhorn’s floating panels in the first three years of operation translates to enough additional reservoir volume to run the dam’s 36 MW hydropower turbines for approximately 170 extra hours annually — a secondary energy gain that standard ROI calculations rarely capture.

This evaporation benefit isn’t a footnote. In Thailand’s northeast, where Sirindhorn sits, drought seasons have grown longer and reservoir levels more volatile. Every cubic meter of water saved is a cubic meter that can generate hydroelectric power later or sustain downstream irrigation. EGAT hasn’t published a dollar value for this water retention, but at typical Thai hydropower generation costs, the implied value runs into millions of baht per year.

The project has also become a reference point for the broader solar energy industry. When international developers evaluate floating solar in tropical climates, they now benchmark against Sirindhorn’s performance through monsoon seasons, where waves on the reservoir can reach significant heights, and through the hot season, when the water-cooling advantage is most pronounced.

Sirindhorn’s success set the technical and financial template for everything that followed. It proved that floating solar could survive Thailand’s climate, that the hybrid model could deliver genuine 24-hour renewable power, and that the economics could work even without premium subsidies.

Ubol Ratana Dam: What Did the Second Project Improve?

If Sirindhorn proved the concept, Ubol Ratana refined it. Located in Khon Kaen Province in Thailand’s northeast, the 24 MW hydro-floating solar hybrid project began commercial operation on March 5, 2024 (EGAT, 2024). It pairs with the dam’s existing 25.2 MW hydropower plant — three 8.4 MW Kaplan turbines — and adds a BESS plus weather forecasting that Sirindhorn didn’t have at launch.

The most significant upgrade is the energy management intelligence. Ubol Ratana’s Weather Forecast System predicts cloud cover and rainfall hours ahead, allowing the control room to pre-position the hydropower plant at the right output level before solar generation drops (EGAT, 2024). At Sirindhorn, operators reacted to weather changes. At Ubol Ratana, they anticipate them.

The 5–8% yield improvement over ground-mounted systems is also more significant than it first appears. For a 24 MW plant operating at a typical capacity factor of 18–20%, that efficiency edge translates to an additional 3.8–6.1 GWh of annual generation — enough to power roughly 1,200–1,900 Thai households for a year. In a market where every percentage point of capacity factor affects project finance, this advantage makes floating solar competitive with premium rooftop locations.

The project was built by the MPD Consortium — Mitr Phol Energy Services, PEA ENCOM International, and Dongfang Electric International Corporation — under an engineering-procurement-construction contract with EGAT. Construction timelines were reportedly tighter than Sirindhorn’s, partly because the consortium could reference the first project’s installation methods and partly because Ubol Ratana’s smaller scale allowed faster deployment.

Environmental safeguards at Ubol Ratana also went further. EGAT collaborated with the Fisheries Research Center to monitor aquatic species, commits to releasing millions of fish annually, and plans a solar-powered shrimp farm learning center to boost local incomes (EGAT, 2024). These measures address the most common community concern about floating solar: that covering reservoir surface will destroy fish stocks.

The project covers less than 1% of Ubol Ratana’s total reservoir area. At this density, the ecological footprint is minimal, yet the energy output is substantial enough to power tens of thousands of homes during daylight hours.

How Do Sirindhorn and Ubol Ratana Compare?

Sirindhorn is the larger project in raw capacity, but the two dams serve slightly different strategic purposes. Sirindhorn was the pioneer — the project that tested whether floating solar could work at utility scale in a tropical monsoon climate. Ubol Ratana is the refined production model, incorporating battery storage and predictive weather management that Sirindhorn lacked at launch.

The capacity gap is significant: Sirindhorn’s 58.5 MW solar array is nearly 2.5× Ubol Ratana’s 24 MW. But Ubol Ratana’s hydropower backup is nearly as large as its solar capacity (25.2 MW vs 24 MW), giving it a more balanced day-night generation profile. Sirindhorn’s 36 MW hydropower plant is smaller relative to its 58.5 MW solar array, meaning daytime solar peaks are higher but the nighttime handoff requires more careful grid management.

Cost per megawatt also differs. Sirindhorn’s $59.6 million for 58.5 MW works out to roughly $1.02 million per MW. Ubol Ratana’s total project cost hasn’t been publicly disclosed, but industry benchmarks for second-generation floating solar projects in Southeast Asia typically run 10–15% lower per MW due to standardized designs and competitive EPC bidding.

Both projects share the same fundamental economic logic. They use existing dams — with their transmission lines, grid connections, and established maintenance access — to host solar generation at a fraction of the greenfield development cost. This is why EGAT is now rolling out the model nationwide.

What Is Thailand’s Floating Solar Pipeline Beyond These Two Dams?

Sirindhorn and Ubol Ratana are just the beginning. EGAT is executing a 2,725 MW hydro-floating solar hybrid program across 16 projects on 9 dam reservoirs nationwide (SolarQuarter, 2025). Thailand’s total installed solar capacity reached 9,942 MWp by the end of 2024, but floating solar accounted for only 281 MWp — less than 3% of the total (IEA-PVPS, 2025). The pipeline represents a nearly tenfold expansion of the floating solar segment.

The largest single project currently in procurement is Srinagarind Dam 3 at 280 MWac in Kanchanaburi Province, with bidding documents available through September 2025 and commercial operation targeted for 2028 (EGAT, 2025). Bhumibol Dam 1 follows at approximately 205 MWp (158 MWac) in Tak Province, with a target commercial operation date of 2027 (PV Magazine, 2025). Vajiralongkorn Dam 1 at 65 MWp in Kanchanaburi is also tendered, with bids opened in September 2025 and COD targeted for 2027 (EGAT, 2025).

These projects are supported by policy mechanisms that improve their economics. A feed-in tariff of THB 2.8331 per kWh applies to solar-plus-battery hybrid systems, and the 2,000 MW direct power purchase agreement pilot approved in 2024 creates an alternative offtake pathway for large consumers like data centers and manufacturers (pv magazine, 2022). For EGAT, the floating solar program isn’t just about adding renewable capacity. It’s about getting more value from existing assets — dams that have already been built, paid for, and connected to the grid.

The economics are compelling. Building a greenfield solar farm requires land acquisition, environmental permits, new transmission lines, and substations. A floating solar project on an existing reservoir avoids most of these costs. The land is already flooded, the transmission infrastructure already exists, and the environmental impact assessment can reference decades of hydropower operation.

Frequently Asked Questions

How much electricity do Sirindhorn and Ubol Ratana generate together?

Combined, the two projects add 82.5 MW of solar capacity to 61.2 MW of hydropower backup. At typical Thai solar capacity factors of 18–20%, the solar arrays generate roughly 130–145 GWh annually. The hydropower plants, operating as baseload and peaking units, add significantly more depending on water availability. EGAT hasn’t published a consolidated annual generation figure for the hybrid pairs, but the combined output is sufficient to power tens of thousands of households year-round.

Does floating solar harm fish and aquatic ecosystems?

EGAT’s environmental monitoring suggests minimal impact when coverage stays low. At Ubol Ratana, panels cover less than 1% of the reservoir and use tilt angles that allow sunlight penetration. EGAT also collaborates with fisheries research centers and releases millions of fish annually (EGAT, 2024). Industry studies globally cite up to 45% evaporation reduction as a benefit, which in Thailand’s drought-prone northeast actually preserves water levels for aquatic life.

Can homeowners in Thailand install floating solar?

Not practically. Floating solar requires reservoir access, grid-scale transmission infrastructure, and regulatory approvals that only a utility like EGAT can navigate. Residential buyers should look at rooftop solar instead. Typical on-grid residential installations cost 30,000–45,000 THB per kWp, though the net billing quota freeze lifted on 1 July 2026, and new applicants can now apply for payments on exports through the open 500 MW round at 2.20 THB/kWh via MEA or PEA (first-come, first-served).

What is the payback period for these projects?

Sirindhorn’s payback period has compressed from an estimated eight years at planning to just five years based on actual generation performance (Power Technology, 2024). Ubol Ratana’s payback has not been disclosed, but second-generation projects typically see 10–15% lower capital costs per MW due to standardized designs. The 2.8331 THB/kWh feed-in tariff for hybrid systems provides revenue certainty that accelerates investor returns.

What’s next for Thailand’s floating solar program?

EGAT plans to reach 2,725 MW of floating solar across 16 projects by 2030. The three largest projects in procurement — Srinagarind Dam 3 (280 MW), Bhumibol Dam 1 (205 MW), and Vajiralongkorn Dam 1 (65 MW) — represent a nearly tenfold increase over current operational capacity. If all proceed on schedule, Thailand will be one of the largest floating solar markets in Southeast Asia within five years.

Conclusion

Thailand’s floating solar program has moved past the pilot phase. Sirindhorn Dam proved that a 58.5 MW array could outperform expectations, cut payback to five years, and save 500 million m³ of water in the process. Ubol Ratana Dam showed that adding battery storage and weather forecasting could make the hybrid model even more reliable. Together, they anchor a 2,725 MW pipeline that will reshape the country’s renewable energy sector.

For readers considering solar energy options, these utility-scale projects signal something important: the technology works in Thailand’s climate, and the economics are improving with every installation. While floating solar is not an option for residential buyers, the success of these dams validates the broader solar market. Rooftop systems benefit from the same falling panel costs and improving efficiency that make Sirindhorn and Ubol Ratana viable.

The next milestone to watch is Srinagarind Dam 3. At 280 MW, it will be nearly five times larger than Sirindhorn. If it repeats the pioneer project’s performance, Thailand’s claim as a floating solar leader will be undeniable.