Hydropower

Can you power entire cities just by using water?

There's a renewable source that's the most powerful of all and generates far more electricity than either wind or solar ^[1,2,3]. It's called hydroelectric power, and uses the movement of water to generate enormous amounts of energy.

With the energy transition well underway, hydropower has huge potential ^[3,4,5]. As wind and solar energy race ahead, reaching net zero by 2050 requires a similar acceleration in hydropower development ^[5-9].

So, what are the latest advancements in this technology, and how can its real power be unleashed?

Since the dawn of civilization, humans have realized that water is power. If you look back 2,000 years to ancient Greece, you will see that among beautiful mountains and sunny prairies, the Greeks were already using water wheels to grind wheat into flour ^[10,11,12].

Later, the Romans industrialized the process, creating an incredible production factory at Barbegal in southern France ^[13-18]. Archaeologists believe it ground out up to 25 metric tons ^[16,17] of flour every day using 16 water-powered mills, enough to feed all the inhabitants of the nearby city of Arles ^[11,16,18].

Over the centuries, humanity continued to find new ways to harness the power of water. Nowadays, hydropower supplies about 14% of global electricity generation ^[1,2], placing it right after coal and fossil gas.

But how does it work? There are three main types of hydropower plants ^[19]:

Type 1: a reservoir.

The most common type uses a large dam across a river to create a reservoir that's higher than the rest of the river. Whenever energy is needed, water from the reservoir above gets released to flow downstream. Thanks to the elevation difference, the flowing water spins a series of turbines that are placed at the lower level and connected to generators ^[19]. Et voilà, the generators create electricity.

However, building a reservoir is a big project that floods the land and cuts off the natural flow of the river ^[20]. But there is another option…

Type 2: run-of-river.

Widely used around the world, this simple system can work with or without a dam. Basically, when a river is naturally going downhill, you create a small diversion - this way, a portion of the river is channeled through a canal. Then the water in the canal passes down a pipe, spins the turbines and bingo: electricity! ^[19,20]

But is hydropower even possible without a river nearby? Yes it is…

Type 3: pumped storage.

Here, we have two reservoirs, one at a lower level and one that's higher. This can be combined with another renewable energy source, like solar power.

During the day when the sun is shining, solar panels can overproduce electricity. Normally this spare electricity would be wasted, but if you can divert it to run a pump, you can push water uphill to the higher reservoir ^[19-23].

At night, when the sun isn’t shining and electricity demand is typically higher, the water can be released from the higher reservoir to run the turbines and generate electricity on demand.

It's like a giant rechargeable water battery. In fact, these pumped hydro systems account for over 90% of global long-term energy storage ^[5,22].

Hydropower systems don’t necessarily require massive construction. They can be much smaller and even fit in your backyard. All you need is elevation and access to a sufficient amount of falling water ^[24]. And don't let the size fool you! A tiny local system can provide enough power for a small village ^[19,25,26].

So can hydropower help lead the way to net zero?

Unfortunately, hydropower is not all smooth sailing: it faces some hurdles ^[27,28].

The first problem is social: these construction projects can lead to the displacement of communities. In fact, for a large reservoir dam, hundreds of thousands of people may need to leave their homes and relocate elsewhere ^[29-32].

The second problem is environmental: if not planned properly, dams can cause enormous damage to the surrounding environment and the wildlife that inhabits it ^[33-36].

But with the right approach and innovation, hydropower can play a vital role in reducing CO₂ emissions ^[27,37]. Solutions are being proposed: ^[38,39]

For example, consulting local communities gives them a say in decisions so that they can directly benefit from the project ^[40,41].

Environmental Impact Assessments, or EIAs, must also be put into action to minimize the harm to the surrounding environment ^[42,43,44].

Experts are also striving to develop better technology, such as fish ladders and fish-safe turbines ^[45,46,47].

The world seems to have forgotten about hydropower, but it’s like a sleeping giant, with most of its global potential still untapped. Just as well. It’s estimated that doubling worldwide hydropower capacity will be needed to achieve net zero by the year 2050 ^[5,6].

As wind and solar grow, expanding pumped hydro energy storage will also be essential to support these intermittent energy supplies ^[5,22,23].

Planned responsibly, hydropower can lead the transition away from fossil fuels because it’s powerful, reliable, and on-demand.