Sirindhorn Dam was opened in 1971. It’s now being upgraded to produce a mix of hydro and solar energy EGAT

When people imagine world-saving energy technology – the kinds of gadgets that can usher humanity into some futuristic, zero-carbon age – they’re generally going for something more inspirational than hydropower and solar panels. After all, both of those have been around for at least a century, and yet they haven’t fixed climate change. But just because something is slow, it doesn’t mean it’s boring.

"Last month, Thailand laid out plans to add a 45-megawatt solar array to Sirindhorn Dam, a dam nearly five decades old, by next year. That’s not a great amount of megawatts, but this “hybrid” setup would be the largest of its kind anywhere in the world.


Thailand has high hopes for it. The idea is that hydro and solar balance each other out, working better as a team. If the Sirindhorn project is a technical success then Thailand intends to follow it with 15 more projects at dams around the country. In total they would add up to 2.7 gigawatts - or about the size of four mid-weight coal plants.

“Basically, what you do is put the solar modules on rafts on the water and then you feed the power into the grid. That’s all it is. It’s like solar panels on a boat,” says Jenny Chase, a solar analyst at Bloomberg New Energy Finance, a research firm. “Solar’s so cheap now that you want to put it pretty much everywhere you can.”

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Thailand is in the same position as a lot of emerging countries. It relies heavily on fossil fuels, which represent some two-thirds of its energy consumption. The fuel is mostly imported, which is inefficient and expensive. Fossil fuels also worsen pollution, an issue that has reached crisis levels in many parts of the country. Particulate-matter levels in Bangkok have repeatedly spiked past the level deemed safe by World Health Organisation guidelines. Children are often being kept home from school and in many stores there’s a recurring shortage of breathing masks.

All of this has the Thai government motivated to jack up renewable energy over the next two decades. Handily, Thailand is blessed with long, bright, hot days. By 2036, according to the government’s plan, the amount of solar capacity in the country needs to nearly quintuple to about six gigawatts.


The challenge: figuring out where to put it. Thailand is a large country, with plenty of room for solar farms, but arable land is precious. Thailand was the world’s largest rice exporter until recently, with a third of its workforce in agriculture, according to UN’s Food and Agriculture Organisation. And what’s the next best thing to land? Water.

And particularly the reservoirs next to dams. Solar units have become so cheap that these mini-lakes are increasingly suitable for what are called “floatovoltaics” – solar panels, but on a boat.

How does it work? Dams run, day and night, by saving up water and then releasing it through turbines as needed. But in this “hybrid” design, there’s a solar array floating next to the dam. It generates power by day, which allows the dam to save up water and run harder in the evening.

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Alone solar and hydro are inconstant; together, they’re reliable. “From this combined plant, there wouldn’t be ups and downs. It would be almost like a constant dispatch,” says Nirmal Nair, an electrical-engineering professor at the University of Auckland, New Zealand. “Solar without this kind of a structure would be looking for a battery. Here the water is acting as a battery."


It does cost extra to put solar on a boat; these aren’t dinghies, but precision-engineered mounting devices. But in principle, solar-on-a-boat makes itself valuable in other ways. For one, it shares power infrastructure with the dam, so no need for costly new wires. Secondly, solar reduces evaporation from the reservoir, which preserves more water for energy and human use.

Most importantly, it saves land for growing food. But are these “hybrid” concepts just a Thai curiosity, or a potential solution in a world that needs renewable energy any way it comes?

When solar is this cheap, the latter isn’t quite so laughable. According to research released last year, there are dams on every continent that could theoretically host hundreds of megawatts, or even gigawatts, of solar: think Ghana, Venezuela, India. “The concept can be replicable in many countries based on the design type of turbines used in the hydro power plant,” says a spokesperson of the Solar Energy Research Institute of Singapore that prepared the research last year for the World Bank.

Compared to cold fusion, solar and hydro combo might sound kind of dull. But one thing is for sure: solar-on-a-boat looks like it might just work.

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