hydropower

Hydropower, also known as hydroelectric power is the power derived from the energy of falling or fast-running water, which may be harnessed for useful purposes. Hydropower from many kinds of watermills has been used a number of times as a renewable source of energy for irrigation and operation of different mechanical devices, such as sawmills.

In the 19^th century, hydropower became a source of generating electricity. Cragside in Northumberland, England was the first house powered by hydroelectricity in 1878 and the first commercial hydroelectric power plant was built at Niagara Falls in 1879. In 1881, street lamps in the city of Niagara Falls were powered by hydropower.

 LEARNING OBJECTIVES

• Define hydropower.
• Describe water flow through a power station.
• Describe different forms of energy.
• Explain basic hydro energy schemes and how they harness energy.
• Discuss the environmental effects of hydropower installation.

GENERATION OF HYDROPOWER

In the generation of hydroelectric power, water is collected or stored at a higher elevation and led downward through larger pipes or tunnels to a lower elevation. The difference in these two elevations is known as the head. At the end of its passage down the pipes, the falling water causes turbines to rotate. The turbines, in turn, drive generators, which convert the turbines’ mechanical energy into electricity. Transformers are then used to convert the alternating voltage suitable for the generators to a higher voltage suitable for long-distance transmission. The structure that houses the turbines and generators, and into which the pipes or penstocks feed, is called the powerhouse.

LOCATION

Hydroelectric power plants are usually located in dams that impound rivers, thereby raising the level of the water behind the dam and creating as high a head as is feasible. The potential power that can be derived from a volume of water is directly proportional to the working head. To produce an equal amount of power, a low working head installation will require more volume of water than a high working head installation.

STORAGE OF HYDROPOWER

The demand for electric power varies considerably at different times of the day. In order to even the load on generators, pumped-storage hydroelectric stations are occasionally built. During off-peak periods, some of the extra power available is supplied to the generator operating as a motor, driving the turbine to pump water into an elevated reservoir. Pumped-storage systems are efficient and provide an economical way to meet peak loads.

In certain coastal areas, hydroelectric power plants have been constructed to take advantage of the rise and fall of tides. When the tides come in, water is impounded in one or more reservoirs is released to drive hydraulic turbines and their coupled electric generators.

Falling water is one of the three principal sources of energy used to generate electric power, the other two being fossil fuels and nuclear fuels. Hydroelectric power has certain advantages over other sources since it is continually renewable owing to the recurring nature of the hydrologic cycle and does not produce thermal pollution.

Hydroelectric power is a preferred source of energy in areas with heavy rainfall and with hilly or mountainous regions that are in reasonably close proximity to the main load centers.

Many of the negative environmental impacts of hydroelectric power come from the associated dams, which can interrupt the migration of spawning fish, such as salmon, and permanently displace ecological and human communities as the reservoirs fill.

A thermionic power converter also called a thermionic generator is a device that converts heat directly into electricity using thermionic emission rather than first changing it to some other form of energy.

A thermionic power converter has two electrodes, one of these raised to sufficiently high temperatures to become a thermionic electron emitter, and the other electrode called a collector, because it receives the emitted electrons, is operated at a significantly lower temperature. The space between the electrodes is sometimes a vacuum but is normally filled with gas or vapor at low pressure. Thermionic converters are solid-state devices with no moving parts and exhibit a relatively large power-to-weight ratio, they are well suited for some applications in spacecraft.

A thermionic power converter can be viewed as an electronic diode that converters heat to electrical energy via thermionic emission. It can also be regarded in terms of thermodynamics as a heat engine that utilizes an electron-rich gas as its working fluid.

TYPES OF THERMIONIC CONVERTERS

The major types of thermionic converters are:

• Vacuum converters. The efficiency and the available power of a thermionic converter is limited greatly by the buildup of space charge in between the electrodes. Vacuum converters use a small gap between its collector and emitter. The gap is 0.025 to 0.038mm or 0.001 to 0.0015 inch. This is so in order to minimize effects caused by electronic space charge. At a temperature of about 800 Degrees or 1500 Fahrenheit, electric power is converted at a rate of 0.1 to 1 watt per centimeter squared of emitter surface. The manufacture of converters with such small spacings is difficult.
• Gas-filled or plasma converters. The design of these converters is such that it supports a continuous generation of positively charged ions, and mixing with the negatively charged electrons, between the collector and emitter. This is to provide the plasma with a neutral space charge. This reduces the electrostatic resistance force that a liberated electron encounters when passing to the collector from the emitter.
• Auxiliary discharge converters. In this type of converters, an inert gas (such as: xenon, neon or argon), is used between the electrodes. The application of voltage to a third electrode leads to the production of positive ions. The main advantage of this type of converters is that they operate at a low temperature. This allows the use of several fossil fuels.

ADVANTAGES OF HYDROPOWER

Advantages of using hydroelectric power include;

• Minimal pollution as there is no fuel being burned.
• It is a free source of power, as water that runs turbines is free from nature.
• Hydropower prevents the emission of greenhouse gases, therefore, conserving the environment.
• Hydropower has low maintenance and operation cost.
• It is a renewable source of energy. Rainfall is free and it is responsible for re-filling the reservoir. Therefore, the fuel is almost always there.

DISADVANTAGES OF HYDROPOWER

Disadvantages of hydropower include;

• High cost of investment.
• It is dependent on rainfall.
• It interferes with the diversity in water, for example, fish.

SUMMARY

• Hydropower is the power derived from the energy of falling or fast-running water
• The generation of hydropower is done by raising water, and then letting it down through tunnels. As the water flows in high pressure, it turns turbines
• Mechanical energy from turbines is converted into electrical energy by drive generators
• Transformers help electricity to be transmitted over long distances
• Hydropower is a renewable source of energy