Water Power

( Original Source : Wikipedia Encyclopedia, Photo : Google Images )

Energy in water (in the form of motive energy or temperature differences) can be harnessed and used. Since water is about a thousand times denser than air, even a slow flowing stream of water, or moderate sea swell, can yield considerable amounts of energy.

The reservoir created for hydroelectric dams may initially produce significant amounts of carbon dioxide and methane from rotting vegetation. Once this vegetation is gone, no additional greenhouse gases are produced. In some cases they may produce more of these greenhouse gases than power plants running on fossil fuels. They also affect water quality, creating large amounts of stagnant water without oxygen in the reservoir, and excessive air bubbles in the water downstream from the dam, both of which impact aquatic life. Failures of large dams, while rare, are potentially. Though the dams can be built stronger, at greater cost, they are still prone to sabotage and terrorism. Smaller dams and micro hydro facilities are less vulnerable to these threats. Wave and tidal stream power demonstration projects exist, but large scale development requires additional capital.

Wind Power

( Original Source : Wikipedia Encyclopedia, Photo : Google Image )

Wind power uses the naturally occurring energy of the wind for practical purposes like generating electricity, charging batteries, or pumping water. Wind turbines capture the kinetic energy in the wind, converting it into electrical energy. Utility-scale turbines are mounted on tall towers, usually 100 feet or more above the earth's surface where the wind is faster and less turbulent. In utility-scale power applications, anywhere from one or two to several hundred turbines are connected to the utility grid, providing electricity when the wind blows.

Kinetic energy in airflows can be used to run wind turbines; some are capable of producing 5 MW of power; turbines with rated output of 1.5-3 MW have become the most common for commercial use. The power output of a turbine is a function of the cube of the wind speed, so high-power output can be achieved as wind speed increases, though turbines must shut off at extreme wind speeds to prevent damage. Areas where winds are stronger and more constant, such as offshore and high altitude sites, are preferred locations for wind farms.

Nagarjuna Sagar Dam in India

( Original Source : Andhra Pradesh Tourism Website )

There would be very few modern constructions you will come across that evoke such a response. A feeling of awe and significance overcomes you when you lay eyes upon the Nagarjuna Sagar Dam for the first time. Its sheer size and magnitude leaves you breathless and astounded. As the tallest and largest masonry dam in the world, truly stands as one of the wonders of engineering excellence. Stretching across the mighty river Krishna, the barrage also has another distinction to its credit - it has created one of the world's largest man-made lake! The reservoir is a vital source of irrigation for vast tracts of the surroundings region. The two left and right canals, called Bahadur Canal and Jawahar canal respectively, cater to the watering needs of a very large area of the state. Successfully transforming a barren, thirsty land into a lush verdant landscape with acres and acres of green fields swaying in the breeze as far as the eye can see. Naturally, it has played a leading role in helping the state of Andhra Pradesh emerge as' the Rice Bowl of India'.

Significantly, the creation of this lake has submerged the excavations that were carried out here in 1926 which unearthed three historical sites- Dhanyakataka, capital of the Satavahanas; Sriparvata, Vijayapuri, capital of the Ikshvakus and a Buddist civilization that thrived here in the third and fourth centuries B.C. What is of special interest to historians is the fact that the excavations also revealed the existence of Brahmanical temples here which indicates that Hinduism and Buddhism flourished together in peaceful co-existence.

Solar Energy

Renewable energy sources Mass production of electricity from renewable energy flows requires technology that harnesses the power of natural phenomena such as sunlight, wind, tides and geothermal heat. Each of these sources has unique characteristics which influence how and where they are used.

The majority of renewable energy technologies are directly or indirectly powered by the Sun. The Earth-Atmosphere system is in equilibrium such that heat radiation into space is equal to incoming solar radiation, the resulting level of energy within the Earth-Atmosphere system can roughly be described as the Earth's "climate". The hydrosphere (water) absorbs a major fraction of the incoming radiation. Most radiation is absorbed at low latitudes around the equator, but this energy is dissipated around the globe in the form of winds and ocean currents. Wave motion may play a role in the process of transferring mechanical energy between the atmosphere and the ocean through wind stress (Sorensen, 2004). Solar energy is also responsible for the distribution of precipitation which is tapped by hydroelectric projects, and for the growth of plants used to create biofuels. In this context, "solar energy" refers to energy that is collected from sunlight. However, most fossil and renewable energy sources are ultimately derived from "solar energy," so some ascribe much broader meanings to the term.

Solar energy can be applied in many ways, including to : 1. Generate electricity using photovoltaic solar cells. 2. Generate electricity using concentrated solar power. 3. Generate electricity by heating trapped air which rotates turbines in a Solar updraft tower. 4. Heat buildings, directly. Careful positioning of windows and use of brises soleil can maximise inflow of light at the times it is most needed, heating the building while preventing overheating during midday and summer. 5. Heat foodstuffs, through solar ovens. 6. Heat water or air for domestic hot water and space heating needs using solar-thermal panels. 7. Heat and cool air through use of solar chimneys. 8. Generate electricity using Space Solar Power Satellite in geostationary orbit and beam it down via microwaves.

The sun does not provide constant energy to any spot on the Earth, so its uninterrupted use on Earth requires a means for energy storage. This is typically accomplished by battery storage. However, battery storage implies energy losses. Some homeowners use a grid-connected solar system that feeds energy to the grid during the day and draw energy from the grid at night; this way no energy is expended for storage. Batteries provide direct current (DC), whereas most household appliances run off alternating current (AC). Conversion from DC to AC leads to some energy loss.

Advantages from solar energy sources include the inexhaustible supply of energy and zero emissions of greenhouse gas and air pollutants. Shortcomings include, depending on application : 1. Economic competitiveness with conventional energy conversion 2. Intermittency; it is not available at night or during heavy cloud cover. 3. For photovoltaics (solar-electric), the current generated is only of DC type, and must be converted if transmission over the standard AC grid is needed. ( Original Source : Wikipedia Encyclopedia, Photo Source : Google Images )

Three Gorges Dam in China

World Water Council Director : Dams are necessary to solve "chronicle water scarcity" Daniel Zimmer was interviewed by the French daily Liberation on May 20, in an unusual position. The interviewer reminds that « many experts think that the fears about Three Gorges Dam or other large dams are rich countries fears. In the developing countries, ‘there are billions of people to feed it’s unthinkable to stop building large dams! If we do nothing, they will die out of hunger’ So explains one of the most famous French geologists, Ghislain de Marcilly. ‘If you take the Aswan dam, of course it had a disastrous environmental impact, but it enabled Egypt to double its population without famine.’” Here follows the interview Will the Three Gorges Dam be the last large dam of this type? Of course not! You just need to look at the situation in the developing countries to understand why. In Africa, for example, they store only between a few dozens and a few hundred of cubic meters per capita and per year. In the United States and in Europe, this figure is going up to 5000 cubic meters per year, when those regions need less water than Africa! There is a 1 to 100 proportion! We can therefore understand that developing countries want large dams and send us back to our own economic development when we talk about environmental risks! As for us, we have water for our consumption, for irrigation and even for leisure. Do the international institutions share this viewpoint? When the polemic began on large dams, the World Bank changed its infrastructural policy, refusing to launch other projects. Today, it recognizes this was an error. She renewed its estimation of the benefits from large dams and completely changed its strategy. For the Bank, if you want that the countries suffering from chronicle water scarcity get a minimum of water reserves to resist drought periods, it’s imperative to go back to those projects. On the condition, of course, that we take into account and we solve the social, human and environmental problems associated with them. Today, happily, we made big progresses on those points. But there are still very strong tensions around the Three Gorges Dam… Of course, there are always tensions around constructions like that. But once again, you need to keep in mind this colossal dissymmetry between the developing countries that need to store water to compensate for the hazards of climate, and the developed countries, where that need is less strong. That’s an injustice for which the countries from the South are reproaching us more and more and that we can no longer tolerate. Is there any alternative to large dams? In Western Africa, for example, we try to manage small reservoirs, more upstream, to delocalize water storage. Another possibility is underground storage rather than surface storage. That’s not always possible but if so, it is an interesting alternative.
(Original Source : ICOLD Official Site, Photo Source : upload.wikimedia.org/wikipedia/commons/a/ab/ThreeGorgesDam-China2009.jpg)

Bridges

Bridges have come a long way since ancient times, when people used logs or weaved vines to cross streams. In fact, they have become an art form.

The most common types of modern bridges include: beam, truss, arch, cantilever, cable-stay and suspension. A beam bridge, the simplest type of bridge, is made of long beams of wood, metal or concrete that are supported at each end by piers. In a truss bridge, the beams are arranged in a lattice pattern. Many railroad bridges are truss bridges.

Arch bridges feature roads built on top of arch curves. Arch bridges are made of steel, concrete or masonry. The Natchez Trace Bridge in Franklin, Tennessee, is an arch bridge. Suspension bridges are usually longer than other types of bridges. The road is suspended in the air on long cables that extend from one end of the bridge to the other. The cables sit atop tall towers and are secured on both sides by anchorages. The Golden Gate Bridge in San Francisco is a suspension bridge.

Cable-stayed bridges look a lot like suspension bridges, but the cables are attached directly to supporting towers and are secured to the roadway. Picture : The Meiko Bridges in Nagoya is an example of a cable-stayed bridge.

(Original Source : Fact Monster/Information Please® Database, © 2005 Pearson Education, Inc. All rights reserved, Photo Source : commons.wikimedia.org/wiki/File:Meiko_Central_Bridge_20170610A.jpg)