Posted tagged ‘place’

HOW FUEL CELL WORK?

August 23, 2011

An electrochemical reaction occurs between hydrogen and oxygen that converts chemical energy into electrical energy.

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Think of them as big batteries, but ones that only operate when fuel—in this case, pure hydrogen—is supplied to them. When it is, an electrochemical reaction takes place between the hydrogen and oxygen that directly converts chemical energy into electrical energy. Various types of fuel cells exist, but the one automakers are primarily focusing on for fuel cell cars is one that relies on a proton-exchange membrane, or PEM. In the generic PEM fuel cell pictured here, the membrane lies sandwiched between a positively charged electrode (the cathode) and a negatively charged electrode (the anode). In the simple reaction that occurs here rests the hope of engineers, policymakers, and ordinary citizens that someday we’ll drive entirely pollution-free cars.

Here’s what happens in the fuel cell: When hydrogen gas pumped from the fuel tanks arrives at the anode, which is made of platinum, the platinum catalyzes a reaction that ionizes the gas. Ionization breaks the hydrogen atom down into its positive ions (hydrogen protons) and negative ions (electrons). Both types of ions are naturally drawn to the cathode situated on the other side of the membrane, but only the protons can pass through the membrane (hence the name “proton-exchange”). The electrons are forced to go around the PEM, and along the way they are shunted through a circuit, generating the electricity that runs the car’s systems.

Using the two different routes, the hydrogen protons and the electrons quickly reach the cathode. While hydrogen is fed to the anode, oxygen is fed to the cathode, where a catalyst creates oxygen ions. The arriving hydrogen protons and electrons bond with these oxygen ions, creating the two “waste products” of the reaction—water vapor and heat. Some of the water vapor gets recycled for use in humidification, and the rest drips out of the tailpipe as “exhaust.” This cycle proceeds continuously as long as the car is powered up and in motion; when it’s idling, output from the fuel cell is shut off to conserve fuel, and the ultra capacitor takes over to power air conditioning and other components.

A single hydrogen fuel cell delivers a low voltage, so manufacturers “stack” fuel cells together in a series, as in a dry-cell battery. The more layers, the higher the voltage. Electrical current, meanwhile, has to do with surface area. The greater the surface area of the electrodes, the greater the current. One of the great challenges automakers face is how to increase electrical output (voltage times current) to the point where consumers get the power and distance they’re accustomed to while also economizing space in the tight confines of an automobile.

PRODUCE ELECTRICITY FROM SOLAR HEAT

August 22, 2011

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The principles of solar thermal power conversion have been known for more than a century; its commercial scale-up and exploitation, however, has only taken place since the mid 1980s. With these first large-scale 30-80 MW parabolic trough power stations, built in the California Mojave desert, the technology has impressively demonstrated its technological and economic promise. With few adverse environmental impacts and a massive resource, the sun, it offers an opportunity to the countries in the sun belt of the world comparable to that currently being offered by offshore wind farms to European and other nations with the windiest shorelines.

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Solar thermal power can only use direct sunlight, called ‘beam radiation’ or Direct Normal Irradiation (DNI), i.e. that fraction of sunlight which is not deviated by clouds, fumes or dust in the atmosphere and that reaches the earth’s surface in parallel beams for concentration. Hence, it must be sited in regions with high direct solar radiation. Suitable sites should receive at least 2,000 kilowatt hours (kWh) of sunlight radiation per m2annually, whilst best site locations receive more than 2,800 kWh/m2/year.

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In many regions of the world, one square kilometer of land is enough to generate as much as 100-130 Giga watt hours (GWh) of solar electricity per year using solar thermal technology. This is equivalent to the annual production of a 50 MW conventional coal- or gas-fired mid-load power plants. Over the total life cycle of a solar thermal power system, its output would be equivalent to the energy contained in more than    5 million barrels of oil2).

TURNING SOLAR HEAT INTO ELECTRICITY

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Producing electricity from the energy in the sun’s rays is a straightforward process: direct solar radiation can be concentrated and collected by a range of Concentrating Solar Power (CSP) technologies to provide medium- to high temperature heat.


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This heat is then used to operate a conventional power cycle, for example through a steam turbine or a Stirling engine. Solar heat collected during the day can also be stored in liquid or solid media such as molten salts, ceramics, concrete or, in the future, phase-changing salt mixtures. At night, it can be extracted from the storage medium thereby continuing turbine operation.