Hydroelectric power supplies 16% of the world's electricity, making it a fantastic example of water as a renewable energy source. A testament to this remarkable power is China's Three Gorges Dam, the biggest dam on the planet, which is so mighty it can power an entire country. With a generating capacity of about 22,500 megawatts, this mega-engineering feat shows just how much energy a hydroelectric power plant can unleash. And if that isn’t cool enough, another impressive example is Brazil's Itaipu Dam, straddling the border of Brazil and Paraguay, which once held the word record of annual hydroelectric energy production, 103.1 million MWh in 2016,  further highlights the incredible potential of hydroelectric power and technology.

But there's more to these dams than just power; they help keep floods in check, manage water resources, and even support irrigation for local farms. Many hydroelectric systems are designed like a chain reaction, where water flows through a series of power plants along a river. This clever setup makes the most out of every drop of water while keeping the environmental impact low. In our quest to reduce reliance on fossil fuels and cut down greenhouse gas emissions, hydroelectric power stands out as a strong, sustainable solution, lighting the way toward a cleaner and more resilient future.

So, what makes this ancient yet ever-relevant source of energy tick? In this guide, we open the gates to everything you need to know about hydroelectric power. From the science behind the surge to the strengths that keep the water flowing strong, step into the current of knowledge that will take you on a thrilling water-powered race where every drop counts.

Hydroelectric power is electricity generated by harnessing the energy of flowing water. It captures water’s natural force - rushing rivers or cascading waterfalls to spin turbines connected to generators. Our journey with water energy began centuries ago with ancient water wheels used for grinding grain. By the late 19^th century, hydropower evolved into pioneering electric generation, laying the foundation for modern renewable energy through hydroelectric power plants. Today, hydropower remains one of the world's leading renewable sources, valued for its efficiency, reliability, and zero greenhouse gas emissions, sustainably powering both urban centers and small communities.

A hydroelectric power plant is a facility that converts the energy of flowing or falling water into electricity using turbines and generators. The amount of electricity generated depends on two main factors: the volume of water flow and the height from which the water falls (known as the “head”). Generally, increased water flow and a higher head allow a plant to produce more power.

1. Water intake:

Water from a river or reservoir (often stored behind a dam) is channeled into an intake and flows down through a large pipe called a penstock. The water at the top of the dam has potential energy due to its height.

2. Turbine spins

As the water rushes through the penstock, it pushes against the blades of a turbine, causing the turbine to spin in the hydroelectric power plant. This transforms the water’s energy into mechanical energy (the spinning turbine).

3. Generation of electricity:

The turbine is connected to a generator. When the turbine spins, it turns magnets inside the generator, converting the mechanical energy into electrical energy via electromagnetic induction. In essence, the generator produces electricity while the water continues through and out of the turbine.

4. Power output and transmission:

The electricity from the generator is then sent to a transformer, which raises the voltage for efficient transmission. Finally, the electricity is carried by power lines (the grid) from the hydroelectric power plant to homes, businesses, and other end-users. The water, having passed through the turbine, flows out downstream of the plant.

Thanks to the simplicity of this process, hydroelectric plants can reliably generate power whenever water is available.

Hydroelectric power plants can be categorized into a few types based on their design and how they harness water. The main types of hydroelectric power plant are:

- Impoundment (Dam) hydroelectric plant: This is the most common type of hydroelectric power plant. An impoundment facility uses a dam to create a large reservoir of water. Electricity is generated by releasing water from the reservoir through turbines in the dam. When more power is needed, more water is released to spin the turbines. Large impoundment dams provide the benefit of control: they can store water during wet periods and generate electricity during peak demand or drier times. Most big hydroelectric projects in India are of this dam-and-reservoir type.

- Run-of-River (Diversion) hydroelectric plant: A run-of-river plant generates energy from the natural flow of a river, usually without a large reservoir. Instead of a big dam, it may use a smaller structure called a weir to divert a portion of the river’s water through a channel or penstock to the turbines. The water is then returned to the river downstream. Run-of-river systems rely on the river’s continuous flow, so they produce a variable amount of power depending on seasonal water levels. They typically have minimal storage capacity, meaning they can’t hold much water in reserve. However, they have a smaller environmental footprint (no vast reservoirs) compared to large dams.

- Pumped storage hydroelectric plant: Pumped storage is a special type of hydroelectric facility that works like a giant battery for the electric grid. It has two water reservoirs – one at a higher elevation and one at a lower elevation. During times of low electricity demand, or excess power on the grid, the plant can use cheap or surplus electricity to pump water uphill from the lower reservoir to the upper reservoir. Later, during peak demand, that water is released back down through turbines to generate electricity. Pumped storage plants don’t produce new energy, but they are very useful for energy storage and grid balancing. For example, they can store extra energy from wind farms at night by pumping water uphill).

Hydroelectric power has many benefits, which is why it has been widely adopted around the world. Here are some advantages of hydroelectric power and hydroelectric power plants:

- Renewable and clean: Hydropower harnesses the water cycle. The water used for power is not consumed but returned to the river and can be used again and again. Generating electricity from water does not involve burning any fuel, so it produces virtually no air pollution or greenhouse gas emissions during operation. Hydroelectric power is one of the largest sources of emissions-free electricity globally. Unlike fossil fuel plants, hydroelectric plants do not emit carbon dioxide, sulfur dioxide, or other harmful gases while generating power, making advantages of hydroelectric power environmentally friendly.

- Reliable and flexible: Hydroelectric power is known for its reliability. A steady flow of water can provide a continuous baseload supply of electricity. At the same time, hydro plants are highly flexible – many can ramp their electricity output up and down very quickly to respond to changing demand. For example, a hydro turbine can go from zero to full power in a matter of minutes, which is much faster than most fossil fuel plants. This quick responsiveness means hydropower plants are excellent for providing power (meeting spikes in demand) and for emergency backup, establishing it as one of the advantages of a hydroelectric power plant. Modern hydro turbines can convert up to 90% of the available energy in water into electricity.

- Low operating costs and long lifespan: Once a hydroelectric power plant is constructed, it can run at relatively low cost. Water is free fuel – there is no purchase of coal, gas, or oil. Hydropower has provided low-cost electricity over decades. In many cases, hydro plants have extremely long lifespans – often 50 to 100 years or more – with periodic maintenance and upgrades. (For example, some of Tata Power’s own hydro stations in India have been running for over a century.) The long life and low operating cost mean that, over its lifetime, hydroelectric power is often one of the cheapest sources of electricity.

- Supports energy storage and grid stability: Hydroelectric plants with reservoirs can act as natural energy storage systems. When demand is low, water can be held back in the reservoir; when demand rises, the water is released to generate power. Moreover, as mentioned, pumped storage hydro plants explicitly store energy by pumping water uphill and later generating power, effectively functioning as large-scale batteries. This ability to store energy and rapidly inject power into the grid helps balance fluctuations. Hydropower’s flexibility and quick start-stop capability provide valuable grid stability services, like frequency regulation and reserve power. In essence, the presence of hydroelectric power plants can make the entire power system more resilient and responsive.

- Additional benefits (Flood Control, Irrigation, Recreation): Beyond electricity, hydroelectric projects often bring additional societal benefits. Dams and reservoirs can help with flood control by capturing heavy rain and releasing water in a controlled manner, protecting downstream areas. They also provide a reliable source of water for irrigation, supporting agriculture, especially during dry seasons. Many hydro reservoirs support fisheries and wildlife as well. All these side benefits mean hydroelectric power plants can contribute to regional development and environmental management.

Hydroelectric power plants are like nature’s helpers that work with technology to make electricity. They use flowing water from rivers or dams to turn big wheels, which then creates power for our homes and schools. These power plants work very well, last a long time, and are gentle on the Earth.

As more people want clean energy, using water to make power is becoming even more important. It helps keep our lights on and our cities running smoothly while protecting nature. Learning about how water makes energy is a great start to understanding renewable energy, because when water flows, the future glows!