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5.1: Introduction

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    84792
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    The oldest “green power” harnessed of by humans (even before they had become humans!) is direct solar power. They used it to get warm in the morning, to make dried berries, meat, or fish... The second oldest is biofuel power, until modern times all fires needed wood, or fuels extracted from animals, live or dead:: burning animal fat in primitive lamps was a method of making light, and dried cow’s dung burned in simple furnaces was used for cooking food, or for keeping people’s dwellings warm at nights.

    In chronological order, Hydro-power and wind power probably share the position of the third-oldest methods of extracting energy from natural sources. Which one should we discuss first? Well, as patriotic Oregonians, let’s give the priority to hydro-, because most of electric power generated in our State comes from hydro-power plants.

    We don’t know when exactly our ancestors learned how to harness the energy of flowing waters for doing usable work – but certainly, it was a long time ago. Archaeological findings reveal that quite sophisticated water wheel machines were already used in ancient Egypt for lifting river water to irrigation systems in the 4th century BC. Ancient Romans at the end of the BC Era and the beginning of modern Era used waterwheels for powering various types of machinery, such as, e.g., sawmills. An excellent overview of the history of the waterwheel up to the modern days is given in this Wikipedia article.

    clipboard_ea4815354ebefb841ca11ae12217321dd.png
    Figure \(\PageIndex{1}\):An old waterwheel, probably from the XIX Century (source: Wikimedia Commons).

    The old charming waterwheel shown in the Fig. \(\PageIndex{1}\). could generate perhaps 1 or 2 kiloWatts of power, at the most. Things has changed dramatically when people started using hydro-power for generating electricity – which happened shortly after the discovery of electromagnetic induction by Michael Faraday, shortly afterwards followed by the invention of electric generator (also known as “dynamo”) based on the Faraday Law. Combining a dynamo with a waterwheel was a “no-brainer”. After the first hydro-power plant was built – reportedly, in 1878 – new hydropower plants started rapidly emerging. Due to the ever-growing worldwide demand for electric power, the hydropower plants were also growing, so that more and more Mega-, and later Giga-Watts of power could be supplied by them. Today the record-keeper, the “Dam of Three Gorges” hydro-power plant, generates 24 GigaWatts of power, some 20 milion times more than an ancient waterwheel. The power of the largest American hydro-power plants are not as spectacular as that of the Chinese and Brazilian supermonsters but they are by no means small. The largest American – the Grand Coule Dam – is, by the way (or by the FREEway, you may see it from I-86) on the Columbia River, not very far from us. Note that the famous Hoover Dam is not the largest American hydro-power plant as far as the power generated is concerned contrary to what many people think, it’s perhaps “the best known”, because of the height of the dam and the spectacular surroundings.

    clipboard_eff169b49177da88740b00dd1ba254d82.png
    Figure \(\PageIndex{2}\): The dam of Three Gorges in China, the largest hydropower plant in the world, delivering 24 000 MW of power (source: Wikimedia Commons).
    clipboard_e198eebb673f9df5a56470dfbfbf2678a.png
    Figure \(\PageIndex{3}\): The 14 000 MW Itaipu Power Plant, until recently the largest in the world. It’s owned jointly by Brazil and Paraguay (the Itaipu Riveris the borderline between the two countries; source:Wikimedia Commons).
    clipboard_eb7ebfa8caf53d3ae93cfebdde368b8bb.png
    Figure \(\PageIndex{4}\): Left image: the largest US 6800 MW hydro-power plant, at the Grand Coule Dam on Columbia River. Right Image: the 2080 MW Hoover Dam hydro-power plant at Colorado River (source: Wikimedia Commons).

    The power of the largest US hydropower plant, the Grand Coule, is listed as 6800 MW, and its energy output per one year as 22.6 Tera-Watt-hours. But if you divide this number by the number of hours in a year (365 24), we get the average power of only 2580 MW. How comes? Well, this is something normal for most hydropower plants in the world. Usually, the power listed is the maximum power they can generate. But there is not enough water in the river to allow them to run at maximum power all the time. So why to install machinery with the output power 21 times larger than the power of the water flow in the river? The answer is simple: namely, the demand for electricity is not constant, it significantly varies over the 24 hour period, with two huge peaks during the morning and the evening rush-hours. Therefore, at other times the plants run at power lower than the average, using less water than flows into the reservoir – in other words, water is being stored behind the dam. And then, at rush hours, the water stored may be used for running at full power to help the grid to deal with the huge demand. For Hoover Dam (2080 MW maximum power, and 4 TW annually) the difference is even more pronounced:

    \[ \dfrac{4\;TW}{365 \times 24 \; hours}= 457\;MW \notag \]

    it is, 4.5 times less than the maximum power.

    The ability to store energy is an important advantage of the hydropower plants. In addition, they can react very quickly for sudden increase in the demand for power – they can switch from a low-power output to high-power output in a few minutes. Much faster than the “number two” on the list, the turbines fueled by natural gas, for which the “start-up time” is usually given as 25-30 minutes (for plants using steam turbines – which provide most of the electric power in the US – the start-up time may be as long as several hours).


    5.1: Introduction is shared under a CC BY 1.3 license and was authored, remixed, and/or curated by Tom Giebultowicz.

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