Hydropower is all about harnessing energy from water. It is a renewable source of energy as the water is continually replenished by precipitation through the water cycle.
Sometimes, energy from water may come naturally through the flow of a river or waves. Other times, energy comes from the force of water as it is released at height from a dam or other container. We are in essence ‘giving’ energy to the water here by gravity.
Hydropower produces no CO2. It can also be far less expensive as a form of electrical generation than fossil fuel powered plants and nuclear power plants. Once the hydropower system has been built, all it will require is maintenance and operation (much like any other power plant) as the ‘fuel’ is water which is naturally replenished for free, by the water cycle.
- Hydropower can be generated using four different methods:
- Hydroelectric Dams
- Rivers (Micro and Macro Schemes)
- Tidal Barrages
- Wave Power
Hydroelectric Dams have been around for over a century. They used to be, and in some cases still are, the main source of electrical generation for many countries. Nowadays, they tend not to be used as much as a primary source of energy (as fossil fuels tend to be). They are however generally used for generating electricity at peak demand, as they are quick to turn on and off (unlike a nuclear power plant). It is unlikely that more will be built in any large number, as any suitable sites often already have a dam built. It is more likely that refurbishments of existing dams will occur. The biggest dam construction in the world is in China on the Yangtze River, named the 3 gorges dam. It is not only the biggest hydroelectric energy generator but also the biggest energy generator in the world.
There are many rivers that are suitable for micro or larger scaled hydropower schemes. Water wheels have been around for centuries, and used initially to power an industry, such as textile or wheat. By temporarily siphoning off water from rivers and sending it through a turbine, electricity can be generated. There are different turbines, specifically designed for a certain nature of a water flow. Some are designed for fast flowing rivers with a small head, others, low flow with a high head.
Tidal Barrages work with turbines that can turn in both rotational directions. Water flows inland on a high tide and seaward on a low tide. As the water flows through a series of turbines, electrical energy is generated.
There are many different forms of Wave Power Devices still being researched and tested. Some are now being built in ‘arrays’ (groups of wave power devices). The ‘Pelamis’1 or ‘Wave Dragon’ is one such wave power device currently within its final stages of generating power as an array off of the coasts of Portugal and west coasts of Scotland. Wave power devices use the movement of the water in a variety of different ways. The ‘Pelamis’ works by generating energy through the movement between segments of its body. As one segment rises another one dips. The ‘forces’ created by hydraulic pressures between these segments generates the electricity through a hydraulic motor.
The following two articles on Hydropower will go into these concepts in more detail:
- Hydropower 1. Introduction
- Hydropower 2. Hydroelectricity and Micro Hydro Schemes
- Hydropower 3. Tidal Barrages and Wave Power Devices
Specific terminology useful for these three articles is below.
Terminology
h, Head
Example;
The hydraulic head here in the example is the distance between the water’s surface below (i.e. a river) and the outlet of the water from the reservoir.
Penstock
Is a water channel that nowadays leads into a turbine, transporting water through it.
Weir
A weir is a sort of dam that allows a river to ‘overflow’ over itself. The same terminology is used for large scale dams, where the crest of the dam allows water to overflow over itself, therefore maintaining a maximum water level within the reservoir.
Turbine
A turbine is a rotating mechanism (usually in the form of a series of blades) that extracts energy from a flowing fluid that is allowed to pass through the turbines path, and thus creates useful energy from the moving fluid.
Reservoir
An artificial lake used to store a quantity of water.
Ρ, Fluid Density
In Physics, this means Mass divided by Volume. All that is needed to be considered here is that freshwater and seawater have different densities. Sea water is 1025 kg/m3, whereas freshwater is 1000kg/m3.
Φ, Fluid Flow
Fluid flow is a volume of fluid that passes through a given area per unit of time, e.g. m3 per second.
G, Gravity
Measured as 9.81 m/s2
1. Pelamis Website. Available [Online] at: http://www.pelamiswave.com/
