Tuesday, June 8, 2010

Fathomless sun!

As a source of energy, nothing matches the Sun. It out-powers anything that human technology could ever produce. Only a small fraction of the sun’s power output strikes the Earth, but even that provides 10,000 times as much as all the commercial energy that humans use on the planet. If one believes the big bang theory, then the sun has been around at least as long as the Earth has been and its been that way for around 4-1/2 billion years approximately. Also ever since humans stepped on to this planet, they have been witness to the daily cycle of days and nights. Sun has been accepted as a great source of energy since ancient times and still as yet it has been glowing away to glory to showcase the human limitations in harnessing that energy. There is limited success alright but largely there are only gaps in the technological solution.

Let us look at this in perspective. The earth receives 174 peta Watts (1 energy unit = 1KWh, 1PWh = 10^12 units) of solar radiation at the upper layer of the atmosphere. Of this, approximately, 30 percent is reflected back into the space, whereas the rest is absorbed by the clouds, oceans and land masses. So there is plenty to harness, but technological limitations are brought to the fore and to me, in essence, they bring to the fore the limitations of the otherwise celebrated human brain. Sure, there are many achievements that the human race can be proud of, but the bar is set by the Sun. The problem is there and known, resources in the form of solar energy are there and plenty, but the solution in the form of harnessing them are far fewer. The solar power has the potential to provide over 1,000 times total world energy consumption, though today it provides only around 0.02% of the total.

India's power sector has a total installed capacity of approximately 1,46,753 Megawatt (MW) of which 54% is coal-based, 25% hydro, 8% is renewables and the balance is the gas and nuclear-based. Power shortages are estimated at about 11% of total energy and 15% of peak capacity requirements and are likely to increase in the coming years. In the next 10 years, another 10,000 MW of capacity and investment of about Rs. 24 lakh crore are required.

Fortunately, India lies in sunny regions of the world. Most parts of India receive 4-7 kWh of Solar radiation per square metre per day with 250-300 sunny days in a year. India has abundant Solar resources, as it receives about 3000 hours of sunshine every year, equivalent to over 5,000 trillion kWh. India can easily utilize the Solar energy or Solar Power. Today the contribution of Solar power with an installed capacity of 9.84 MW, is a fraction (< 0.1 percent) of the total renewable energy installed 13, 242.41(as on 31st October 2008 by MNRE - the Ministry of New Renewables Energy). Solar power generation has lagged behind other sources like wind, small hydropower, biomass etc. By the way, India is only an example. The scenario is no different world-wide. In the US, this percentage is only around 1 %.

Solar power, is a term largely related to the generation of electricity from sunlight. This can be direct as with photovoltaics or indirect as with concentrated solar power (CSP), where the sun's energy is used to boil water, which is then used to generate electricity. Photovoltaic materials convert light energy to electricity using semiconductor materials like Silicon. When certain semiconducting materials, such as certain kinds of silicon, are exposed to sunlight, they release small amounts of electricity. This process is known as the photoelectric effect. The photoelectric effect refers to the emission, or ejection, of electrons from the surface of a metal in response to light. It is the basic physical process in which a solar electric or photovoltaic (PV) cell converts sunlight to electricity.

A typical PV system is made up of different components. These include PV modules (groups of PV cells), which are commonly called PV panels; one or more batteries; a charge regulator or controller for a stand-alone system; an inverter for a utility-grid-connected system and when alternating current (ac) rather than direct current (dc) is required; wiring; and mounting hardware or a framework.

Concentrated Solar Power, on the other hand, uses the concept of focused sunlight. CSP plants generate electric power by using mirrors to concentrate (focus) the sun's energy and convert it into high-temperature heat. That heat is then channeled through a conventional generator. The plants consist of two parts: one that collects solar energy and converts it to heat, and another that converts the heat energy to electricity. Within the United States, over 350MW of CSP capacity exists and these plants have been operating reliably for more than 15 years. The amount of power generated by a concentrating solar power plant depends on the amount of direct sunlight at the site. CSP technologies make use of only direct-beam (rather than diffuse) sunlight.

CSP can use the conventional and ubiquitously available flat solar panels, or parabolic troughs, or even power towers for concentrating the solar light.

The problem with human technology in harnessing the solar energy has been in the area of efficiency of conversion. Typically it is no better than 10-20%. Given their manufacturing costs, modules of today’s cells incorporated in the power grid would produce electricity at a cost roughly 3 to 6 times higher than current prices, or 18-30 cents per kilowatt hour. To make solar economically competitive, engineers must find ways to improve the efficiency of the cells and to lower their manufacturing costs.

Prospects for improving solar efficiency are promising. Current standard cells have a theoretical maximum efficiency of aroud 30 percent because of the electronic properties of the silicon material. But new materials, arranged in novel ways, can evade that limit, with some multilayer cells reaching 34 percent efficiency. Experimental cells have exceeded 40 percent efficiency.

Another idea for enhancing efficiency involves developments in nanotechnology, the engineering of structures on sizes comparable to those of atoms and molecules, measured in nanometers (one nanometer is a billionth of a meter). Recent experiments have reported intriguing advances in the use of nanocrystals made from the elements lead and selenium. In standard cells, the impact of a particle of light (a photon) releases an electron to carry electric charge, but it also produces some useless excess heat. Lead-selenium nanocrystals enhance the chance of releasing a second electron rather than the heat, boosting the electric current output. Other experiments suggest this phenomenon can occur in silicon as well.

Theoretically the nanocrystal approach could reach efficiencies of 60 percent or higher, though it may be smaller in practice. To the core, lies the problem of engineering advances and in turn human inability to harness the Sun. These advances will be required to find ways of integrating such nanocrystal cells into a system that can transmit the energy into a circuit.

Even if the engineering challenges are overcome and advanced solar cells become available for generating electricity cheaply and efficiently, a major barrier to widespread use of the sun’s energy remains the need for storage. While there is sunlight roughly 50% of the time in a daily cycle, its usage in night hours requires us to store all the energy captured during the day. Then, there is the cloudy weather that interrupts solar energy’s availability. At times and locations where sunlight is plentiful, its energy must be captured and stored for use at other times and places.

Many technologies offer mass-storage opportunities, but none perfected yet. Pumping water (for recovery as hydroelectric power) or large banks of batteries are proven methods of energy storage, but they face serious problems when scaled up to power-grid proportions. New materials could greatly enhance the effectiveness of capacitors, superconducting magnets, or flyweels, all of which could provide convenient power storage in many applications.

Another possible solution to the storage problem would mimic the biological capture of sunshine by photosynthesis in plants, which stores the sun’s energy in the chemical bonds of molecules that can be used as food. The plant’s way of using sunlight to produce food could be duplicated by people to produce fuel.

For example, sunlight could power the electrolysis of water, generating hydrogen as a fuel. Hydrogen could then power fuel cells, electricity-generating devices that produce virtually no polluting byproducts, as the hydrogen combines with oxygen to produce water again. But splitting water efficiently will require advances in chemical reaction efficiencies, perhaps through engineering new catalysts. Nature’s catalysts, enzymes, can produce hydrogen from water with a much higher efficiency than current industrial catalysts. Developing catalysts that can match those found in living cells would dramatically enhance the attractiveness of a solar production-fuel cell storage system for a solar energy economy.

Fuel cells have other advantages. They could be distributed widely, avoiding the vulnerabilities of centralized power generation.

If the engineering challenges can be met for improving solar cells, reducing their costs, and providing efficient ways to use their electricity to create storable fuel, solar power will assert its superiority to fossil fuels as a sustainable motive force for civilization’s continued prosperity.

So what I have outlined above are the challenges for harnessing. solar energy Generally, the technological innovation is required while tapping scarce resources. But here is a case of plentiful. There is so much to tap and unfortunately it only exposes the brazen limitations of human mind.

It is possible, that historically where the technological innovations happened most, that is in the western world, there may not have been focus on this subject much as they dont get much of sunlight and the sun - but temperate countries like India are offered with an opportunity on the platter.

There is a need, the reserves of coal are limited, nuclear energy can only generate that much but the demand will never cease. In times of increased pressures on deploying green technologies, what better opportunity, than tapping the Sun and meeting all of the requirements? Here is an opportunity for India and similar countries to showcase her innovation capabilities in coming up with solutions that the world can then follow!

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