Massive hydropower projects are frequently criticised for causing more harm than good. What role should they really be playing in the clean energy transition and the future of hydropower?

Hydropower is by far the largest source of renewable electricity globally and is projected to grow further in the coming decades. However, some researchers have questioned the future of hydropower, concerned it could have a larger climate impact than is often acknowledged.

Studies show some hydropower plants can have emissions comparable to fossil fuel plants, adding to a long list of other problems associated with the technology, from impacts on river flow and ecosystems, to the displacement of local people. Many countries and institutions promote the expansion of hydro as a low-carbon way of meeting the world’s growing electricity demand, but can it shed its image as the dirty man of renewables?

The third renewable pillar

Water has been used as a source of energy for thousands of years, and hydro was one of the earliest forms of mechanical energy used in factories.


“Hydro has been the renewable energy technology from the purely mechanical days of grain grinding and textile mills of the mid and late-1800s,” says Robi Robichaud, a renewables expert at the World Resources Institute, a non-profit organisation based in the US. “Even as we [began] to generate electricity, hydropower was a leader in the 1890s [to] 1940s where it was available. It competed primarily against coal.”

Hydropower remains by far the largest source of renewable electricity, supplying around 16% of global power in 2019 – roughly three times the generation of wind power and six times that of solar. (It is worth noting that many environmental groups do not consider large hydropower a truly “renewable” resource due to its negative ecological impacts.)

Electricity production from hydro has increased by around two-thirds since 2000, and is expected to remain the largest source of renewable power for decades. Around 1,000 dams are under construction, largely in Asia, and the International Energy Agency (IEA) expects hydropower generation to rise another 50% by 2040. However, the recent rapid increase in wind and solar power means hydro’s share of the renewable electricity mix will drop below 50% for the first time by 2024, says the IEA.

In short, while solar and wind are the renewable superstars of the 21st century due to their rapid cost reduction and growth, hydro remains by far the largest overall source of renewable power, and will for some time. The IEA expects it will still account for 16% of the world’s electricity generation in 2025.

“They are still installing new [hydro], but they’re not going gangbusters,” says Robichaud, underlining that the best places for hydro are already taken.

China leads the world in hydro generation, followed by Canada, Brazil, the US, Russia, India and Norway which are all large producers. Hydropower is different in many ways from solar and wind, not least in its geographical distribution. The majority of dams are also not used for hydropower, but for storing water or as flood protection.

This storage ability is a key difference between hydro, and wind and solar.

Hydropower is like a big battery, you can store power in the form of water,” says Mark Mulligan, a hydro expert from Kings College London. “And then you can release the water when you want and generate your electricity on demand.”

Advocates of hydro say this storage ability makes it the ideal partner to more variable wind and solar power: water can be pumped up a dam into the reservoir when excess electricity is available and released when needed. Such pumped storage hydropower provides 94% of the world’s battery storage, even if this proportion is steadily shrinking with the rising capacity of lithium ion batteries.

There is significant interest in whether large hydropower plants could play a smaller role in global energy production. One study found that replacing all hydropower generation in the US with solar PV would use just 13% of the space of existing reservoirs.

The cost of hydropower overall remains slightly below wind and solar, shows the latest report on renewable power generation costs from the International Renewable Energy Agency (IRENA). The report found that the global weighted-average cost of newly commissioned hydropower projects in 2019 sat at $0.047 per kilowatt-hour (kWh), compared with $0.053/kWh for onshore wind, $0.115/kWh for offshore wind and $.068/kWh for solar PV.

However, while wind and solar costs are coming down year by year, globally, hydropower costs went up by 27% between 2000 and 2019 due to rising installed costs, especially in Asia. The IRENA report said this was likely due to projects being in more challenging sites, noting that nine-tenths of hydro capacity commissioned in 2019 was cheaper than the cheapest new fossil fuel-fired cost option.

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