Hydroelectric power

Wow! Look at the force of that river. Let's put it to use. A waterwheel can capture the energy of moving water. The energy is then transferred to the saw, splitting heavy logs into planks - a sawmill.

The waterwheel is connected to a shaft, and that shaft can be connected to all sorts of industries that need mechanical power. It starts to get crowded by the river bank. What if there was some other way of transferring power rather than using a shaft and belts? Instead of using the rotating motion from the waterwheel directly, how about a device that converts the kinetic energy into electrical energy - a generator. Electricity is more practical and flexible.

More and more people want to use the new power source. To capture more of the mechanical energy of the water, the water in the river is guided to a pipe where a more advanced waterwheel - a turbine - is placed. Now, more of the mechanical energy is converted to electricity. This is a basic hydroelectric power plant. Hydro means water.

As more people want more power, the engineers at the hydroelectric power plant start thinking, and then start building. In order to generate more electrical power, the blades of the turbine need to be pushed with more force. To do that, we need higher pressure. And to get higher pressure, the water needs greater depth. So they clear the valley above the plant and build a dam-wall.

The water builds up behind the dam, forming a reservoir. The dam wall keeps the water in the reservoir. When an intake-gate is opened at the bottom, water flows through a tunnel and spins the turbine. The higher the dam, the higher the pressure, and more pressure means more power. Water in the reservoir can be replenished by mountain streams from melting snow or by rainfall.

That means that the fuel that hydroelectric power plants use is replenished by nature. That's what it means to be a renewable energy source. In a modern hydroelectric power plant, most of the mechanical energy is converted to electric energy - 90% or so. That's a high efficiency compared to other energy sources. In a coal-fired power plant, only about one-third of the heat is converted to electricity.

Another great advantage of hydropower is that no harmful gases like carbon dioxide are produced. In that sense, it's also a zero emission energy source. But there are downsides too. During the construction of the dam, water levels rose. That meant people living close to the river had to move away.

When the fish in the stream tried to migrate back to their breeding pools, the dam wall was stopping them. The river's water level shifts dramatically, which can cause entire ecosystems to die out. And despite their efficiency, hydropower plants are very expensive to build. So it only makes sense to establish hydropower in the best locations. There are two things a hydropower plant needs: a large and steady inflow of water, and that water being at a high enough point in the landscape that allows for a deep dam, since with great depth comes great pressure, and with great pressure, more electrical power.

Countries like Norway, Paraguay and Ethiopia are blessed with these features, which is why over 85% of their electricity supply comes from hydroelectric power. Around the world, hydroelectric power is by far the most used renewable source of electrical energy. It accounts for 19% of the world's electricity supply. That's nearly one-fifth of the world's electricity generated from moving water.