18. 06.
Nanocrystalline photovoltaic devices have become viable contenders for large-scale future solar-energy-conversion systems.
olar cells that copy nature’s very own energy-conversion process could constitute the next generation of green energy-generating sources. Based on photosynthesis, in which plants transform the sun’s rays into stored energy, mesoscopic injection solar cells offer credible and attractive alternatives to solid-state p-n junction devices (explained below). These relatively new nanocrystalline photovoltaic devices, which were invented in the early 1990s, promise viable solutions to future large-scale solar-energy conversion issues on the bases of cost, efficiency, stability, availability, and environmental compatibility.
Operational Principles
Mesoscopic injection solar cells operate in an entirely different manner from conventional solar p-n junction devices. Mimicking the principles of solar-energy conversion that natural photosynthesis has successfully adopted over the last 3.5 billion years, they separate light harvesting from charge-carrier transport. The semiconductors that conventional cells use assume both functions simultaneously, imposing stringent demands on purity and entailing high material and production costs.
In contrast, an injection solar cell has a molecular sensitiser or semiconductor quantum dot located at the junction between an electron (n) and a hole-conducting (p) semiconductor or an electrolyte (Figure 1), which absorbs the solar light. Upon excitation, the absorber injects an electron and a hole into the n- and the p-type materials, respectively, resulting in the photo-generation of charge carriers, collected at the front and back of the device. The photovoltage developed by the cell corresponds to the difference in the electrical potentials of the two materials under illumination.
This cell configuration has the great advantage that the solar-energy-conversion process involves only majority charge carriers. Electrons and holes are generated in different phases, and the presence of the sensitiser significantly blocks their recombination across the interface. A flat junction, however, allows absorption of a few percent at most of incident sunlight, entailing very small conversion efficiencies since the optical cross-section of a dye or quantum dot is much smaller than the area it occupies. The introduction of a nanocrystalline titania (TiO2) film to support the sensitiser has overcome this fundamental problem of harvesting solar light efficiently.
Mesoscopic morphology produces an interface with a huge area endowing these systems with intriguing optoelectronic properties. The Laboratory for Photonics and Interfaces at the Ecole Polytechnique Fédérale de Lausanne in Switzerland has invented a prototype of this family - the dye-sensitised solar cell (DSC). Figure 2 shows a schematic of the cell along with a scanning electron microscope picture of a typical nanocrystalline TiO2 film.
Photovoltaic Performance
The DSC currently reaches 11.2% energy conversion efficiencies under standard reporting conditions in liquid-junction devices. Figure 3 shows typical photovoltaic performance data. Solid-state equivalents using organic hole-conductors have exceeded 5% efficiency whereas nano-composite films comprising only inorganic materials, such as TiO2 and CuInS2, have achieved efficiencies of between 5 and 6%. New dyes showing increased optical cross-section and capable of absorbing longer wavelengths are currently under development. Similarly, scientists expect nanomaterial research to improve cell performance. Other current research focuses on solid-state hole conductors and tandem cell structures as well as quantum dot sensitisers to boost the conversion efficiency further.
Contrary to amorphous silicon, which suffers from degradation owing to light-induced defect generation (known as Stabler-Wronski effect), extensive accelerated light soaking tests carried out over the last decade have confirmed the intrinsic stability of the DSC. Recent high-temperature stabilisation has allowed the DSC to meet for the first time the specifications laid out for outdoor applications of silicon photovoltaic cells. Researchers have developed new amphiphilic (water-soluble group connected to a non-polar water-insoluble hydrocarbon chain) sensitisers that demonstrate strikingly stable performance under both prolonged thermal stress and light soaking.
Industrial Application
The Australian company Dyesol Inc, the first in the world to manufacture DSC modules commercially, organised a conference in February 2006 in Canberra on the Industrialization of Dye-Sensitised Solar Cells, which presented an impressive demonstration of how far this new photovoltaic contender has progressed in less than 16 years after the author’s first scientific publication on this topic. The enthusiastic and upbeat mood of the meeting revealed a consensus among the numerous international participants that the DSC has reached the end of its gestation period and moved forward with its first commercial applications. Building integrated photovoltaic and lightweight flexible applications offers particularly attractive near-term opportunities. Figure 4 exemplifies the possibilities of multicolour modules and see-through power-producing windows using DSC technology.
The walls of the Toyota Dream House have installed DSC panels (Figure 5), offering a building-integrated source of solar power to the inhabitants. Dyesol has started pilot production of DSCs in Australia, while British company G24I has built a 20MW plant for flexible DSC fabrication in Cardiff, Wales.
Mesoscopic solar cells suit a whole realm of applications ranging from the lightweight low-power market to large-scale applications. Their excellent performance in diffuse light gives them a competitive edge over silicon in providing electric power for both indoor and outdoor standalone electronic equipment. Application of the DSC in building-integrated photovoltaic has already started and will become a rich field for future commercial development.
18. 06.
This is project on Tidal Energy as part of Renewable Energy Systems Course in Fall 2009.
19. 10.
For billions of year since beginning of universe and later formation of our solar system the sun (Stars) has been the prime source of energy. In other words there are no other source of energy which is inexhaustible and available free.
Solar energy is the radiant light and heat from the Sun that has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation along with secondary solar resources such as wind and wave power, hydroelectricity and biomass account for most of the available renewable energy on Earth. Only a minuscule fraction of the available solar energy is used.
Whatever fuel we are using in today’s developed world is only a byproducts of solar energy, be it coal, oil, hydro or any other from or energy. Since it is only the sun which has provided the initial energy and power in the process of transformation and storage or energy in different forms. Can you imagine a day without sun?
Today we are depending on other sources of energy like oil, coal, gas simply because we humans have always been looking for a easy way of life. As a result of thoughtless use of these polluting energy sources which emit harmful green house gases we have now endangered the existence of life on Earth. And if we do not take proper measures now it may be too late and we would be giving our new generation the worst place in the universe.
Time has come and we need to change our thinking for betterment of our coming generations. At least we can make our planet a clean place by using Renewable Energy sources.
The Solar Energy intercepted by earth in one day is enough to power whole world for couple of years. But still we do not have any technology which can harvest this huge amount of energy and store it for future use. In fact we even do not need to store this energy if the whole world is interconnected with power transmission lines then half of the world which lies facing the sun in a given time can power rest of the world. This may be possible in future but right now it is next to impossible. May be some day it happens!
Here is what we can do right now to cut down emission of green house gases.
- Using Solar Power systems (PV Panels)to generate Electricity.
- Solar Water Heaters can be used to get hot water for both domestic and industrialuse.
- Solar thermal energy can be used for cooking using solar cookers. It can also be used for power generation.
- Proper planning while building construction can ensure maximum day light isavailable so that artificial lighting use is minimized.
- Selective shading and proper thermal mass utilization can result in well lit space at
comfortable temperature.
1. 10.
Renewable Energy Technologies (Wind and Solar) have an important role to play in World’s Energy sector. With right approach the Renewable Energy Industry can become a major player in world’s energy sector, and meet the energy needs of a significant proportion of population by using Wind and Solar Systems.
Renewable energy technologies can play a major role in national developmentin terms of job creation and income generation as well as providing and environmentally sound energy service. Renewable energy technologies can play complementary roles to large scale conventional energy technologies.
Renewable energy can be important alternatives for power generation in many drought prone countries when conventional electricity sector (mainly Hydro based) experiences deficits.
Other factor is due to continous use of fossil fuels we are facing threath in form of global warming and if the trend continues the outcome may be devastating destroying the environ ment of our mother Earth. Whole world acknowledges this fact and is taking action to reduce dependancy on fossil fuel.
