SCIENCE & TECHNOLOGY

Power of the sun, sea and sand
By Paul Singh

Until now, generating electricity from solar energy has been a costly affair and it remained largely untapped. Any new energy technology must be economically more attractive than the existing sources. The high hidden environmental cost of existing fossil and nuclear energy sources has compelled scientists to find some alternatives like wind, geothermal, solar etc. The cost of these sources should match with the cheapest (US$0.04 per KWH) and most widely used fossil fuel i.e. coal.

Trends
The sun and a wind turbine is reflected at Renewables Energy Systems’ green technology and renewable energy site at Kings Langley in southeast England. Top executives from utilities, electric car, solar and wind power companies demanded that governments turn away from fossil fuels when they sign a new climate pact, expected in December. — Reuters

  • Identifying an easier way to high BP in kids

  • Scientists identify gene that may explain hair loss

Prof Yash Pal

Prof Yash Pal

 

THIS UNIVERSE
PROF YASH PAL

Liquid rises due to capillary action. It is against gravitational force. What is the maximum height to which any liquid can rise due to capillary action?
When you have some water in a glass, there is lot of drama going on. Molecules of water are moving randomly, colliding with each other. They attract each other and behave in a collectively responsible and democratic manner. They are subject to the force of gravity. 

 


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Power of the sun, sea and sand
By Paul Singh

Until now, generating electricity from solar energy has been a costly affair and it remained largely untapped. Any new energy technology must be economically more attractive than the existing sources. The high hidden environmental cost of existing fossil and nuclear energy sources has compelled scientists to find some alternatives like wind, geothermal, solar etc. The cost of these sources should match with the cheapest (US$0.04 per KWH) and most widely used fossil fuel i.e. coal.

Electricity from solar energy seems to have better long-term prospects. Already existing solar energy technologies such as thin film photo-voltaics (PV) technology from Interphases and very high efficiency concentrated photo-voltaics from Spectrolab and Emcore will probably take seven to 10 years to reach the cost target. The water based PV concentrator termed as Liquid Solar Array (LSA) system developed has all characteristics to meet the required cost target reliably and quickly. It utilises existing off-the-shelf technologies and makes use of relatively lightweight concentrators and operates in a pool of water to keep the concentrators cool, clean and efficient while providing protection from high winds and hail.

The system basically collects solar energy using sheets of durable plastic most economically within the band of + 35 degrees latitude. The PV concentrators are arranged in an array and placed on water rather than on land. This provides efficient cooling of the PV cells and allows a lighter structure to be used, resulting in cost cutting.

Each LSA has a tiny area of silicon photovoltaic cells at the water surface and a large plastic focusing lens to focus solar energy on the cells, converting the solar energy into electricity. The lens is just two millimeters thick but still strong enough to survive winds over 150 km per hour. A buoyant raft comprising moulded plastic members is used to support a tracking mechanism and a light weight lens. The plastic focusing lens rotates slowly above the water surface and tracks the direction of the sun. When wind speed exceeds 50 km per hour, the tracking system dips the collectors under the water for protection. It is a fantastic example of synergy of sun, sea (water) and sand (silicon) for harnessing the solar energy, where the water is the structural component of the system.

A land-based one square meter concentrator needs one square meter convection cooled aluminum fin area to dissipate 700 Watt radiation absorbed by the PV cells and not converted into electricity. It is achieved by forced cooling, which consumes additional electrical power to drive the cooling system. The substantial benefit of the LSA is that the surrounding water cools the silicon cells and creates a very low operating temperature at the PV cells to enhance their efficiency and resulting in longer life of cells. The beauty of LSA system is that energy here is collected using a plastic sheet and it produces more power from a given area than that of conventional flat PV systems and the power is more uniform over the day.

The LSA is best suited to large-scale distributed electricity generation in sunny areas where suitable water bodies are either available or even constructed. Most coastal areas and inland reservoirs within 35 degrees of the equator could be suitable for the LSA. The basic requirement is a protected area of water between one to ten meters deep. The places where suitable water bodies are already available and the sun shines over 2,000 hours per year, the LSA system could offer an extremely competitive source of raw electric power.

With good solar situations, custom built ponds may be economically feasible. In each case, the water itself is not consumed or changed at all. Therefore multiple use of water such as drinking, aquaculture etc is possible while the system is supplying power. A basic one square meter module of this system will generate about 120 Watt and is suitable for farm or village scale power systems of one to 20 KW. The LSA component would be most effective if broken into hundreds of systems each of about 10 to 100 MW for national power grid, as this would be least affected by local cloud. It is estimated that nearly four acres of water is needed to produce one MW electricity. The LSA is a combination of several existing technologies, which reduced the cost of raw solar electricity in the short term by a factor of four and in the longer term by a factor of eight.

With technology improvements and use of recently developed triple junction PV cells of 34 percent efficiency, the LSA system can deliver electricity even at lower costs. Thus, the LSA system opens the prospect for economically storing some of this energy in the form of hydrogen for use at times of cloud cover or night time use. This compressed hydrogen fuel can be used in motor vehicles making environment pollution free. In the medium term, the LSA system becomes attractive for industry to make use of the cheaper solar energy available through the day as much as possible and use fossil fuelled energy on sunset. As the cost of power from stored synthetic fuels is higher than solar energy, it is the need of the hour to make hay while the sun shines. The transition from conventional to renewable energy is just a matter of will power and it offers an economic way to make a rapid shift to a low emissions technology.
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Trends

The sun and a wind turbine is reflected at Renewables Energy Systems’ green technology and renewable energy site at Kings Langley in southeast England. Top executives from utilities, electric car, solar and wind power companies demanded that governments turn away from fossil fuels when they sign a new climate pact, expected in December. — Reuters

Identifying an easier way to high BP in kids

Washington: Paediatricians now have a simpler way to diagnose a serious problem facing children, hypertension. Research at the Case Western Reserve University School of Medicine has discovered that nearly 75 percent of hypertension and 90 percent of pre-hypertension cases in children and adolescents go undiagnosed. They felt that one of the main reasons may be the complex chart currently used to help physicians identify high BP in children. The researchers have simplified the chart - focussing solely on a child’s age and gender - eliminating the need for a height percentile and reducing the number of values in the blood pressure table from 476 to just 64. The revised chart and accompanying description will be published in the June issue of Paediatrics. — IANS

Scientists identify gene that may explain hair loss

HONG KONG: Researchers in Japan have identified a gene that appears to determine cyclical hair loss in mice and believe it may also be responsible for hair loss, or alopecia, in people. In a report published in the Proceedings of the National Academy of Sciences, the scientists described how they generated a line of mice that were lacking in the Sox21 gene. — Reuters
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THIS UNIVERSE
PROF YASH PAL

Liquid rises due to capillary action. It is against gravitational force. What is the maximum height to which any liquid can rise due to capillary action?

When you have some water in a glass, there is lot of drama going on. Molecules of water are moving randomly, colliding with each other. They attract each other and behave in a collectively responsible and democratic manner. They are subject to the force of gravity. There are no hills or valleys and the surface is flat. But some collective effects do manifest because the molecules at the surface are attracted only inwards, since there are no water molecules above them. This inward attraction produces a cohesion leading to something like a membrane on the surface — the ensemble of surface molecules belongs to a special population. This membrane has energy and tends to become as small as possible.

At the walls of the glass there is another force. This is the force of adhesion between the molecules of the glass and water; this adhesion is responsible for the fact that water wets the glass surface. This adhesion force tends to make the water rise along the wall of the glass. This can be seen from the fact that the level of the liquid next to the glass wall is slightly higher than in the middle. If there were no opposing forces, the water next to the wall will continue rising till it spills at the top. This does not occur because the consequent expansion of the surface is opposed by surface tension and, more importantly, because the rise of liquid in the vessel is opposed by gravity.

The contact length (around the edge) between the liquid and the tube is proportional to the diameter of the tube, while the weight of the liquid column is proportional to the square of the tube’s diameter. So a narrow tube will draw a liquid column higher than a wide tube. Height to which the liquid would rise in a tube increases inversely as the diameter of the tube. If we put in the appropriate values of surface tension, it turns out that this height would be about 1.5 cm if the diameter of the tube were 2 mm and 15 cm if the capillary diameter is reduced to 0.2 mm. Even narrower capillaries exist in nature.

It is worth wondering how some aspects of our world would change if surface tension of water were to disappear. Large number of insects and creatures that float on the surface of water would disappear. Without capillarity we would not have any trees or plants as they are nourished with water and juices rising up from the ground. There would be no forests. Water from rivers would not soak into the land around. Lakes and wells would become untenable. Irrigation would be impossible. Towels would not dry our skin after a bath. Cotton clothes would feel like skins of plastic. Fountain pens would not work. Finally, children will not be able to blow soap bubbles and the raindrops will not be round.
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