If you have ever noticed a straw in a cup of water appear “broken,” you have probably witnessed a universal principle at work. We encounter the same principle when driving home from work on a Friday evening: we seek the quickest route, not necessarily the shortest one. From tiny ants on the ground to distant galaxies, systems tend to follow the most efficient, namely, the fastest, path available.

Imagine you are running on a beach toward a friend in the water. Running on sand is faster than swimming, so the quickest route is not a straight diagonal line. Instead, you instinctively run along the beach for a distance before cutting into the water at an angle. Without knowing any physics, you naturally follow this principle: Fermat’s principle of least time.

The shortest path

In the 1600s, the French mathematician Pierre de Fermat proposed something radical: Light doesn’t always take the shortest path, but it does take the fastest one. At first, this seems odd. Why wouldn’t the straight-line path – the shortest possible route – always be the fastest? But the medium matters. Light moves at different speeds through different materials. It slows down in water, speeds up in air, and changes direction when moving between the two. Fermat’s insight was that light chooses the route that allows it to arrive in the least amount of time – even if this means curving or bending (refraction) along the way. Light bending through a glass prism or the formation of a rainbow are all results of this phenomenon.

Snell’s law

About thirty years before Fermat, the Dutch mathematician Willebrord Snell had already discovered a precise rule describing how light bends when it passes from one medium into another. This rule, now called Snell’s Law, tells us exactly at what angle the light will bend. But Snell’s Law is basically the mathematical expression of Fermat’s idea.

Amazingly, Fermat’s principle does not only apply to light. It is astonishing to see that the same logic that guides a ray of light also guides living creatures and physical systems. Fermat’s principle which initially described the behavior of light has now evolved to a broader idea in physics: systems tend to follow efficient paths, the ones that minimize time or energy. This theme appears throughout the natural world, from animal behavior to planetary motion.

The quickest path

It may be surprising to learn that ants – tiny, busy, seemingly chaotic – can mimic the path of a bending light ray. In certain experiments, scientists placed food on one side of a barrier and ant colonies on the other. The ants could walk across a smooth surface or move into a rougher, slower terrain. Over time, the ants collectively chose a route resembling the path light takes when moving between two media with different “speeds.” Their path looked like a refracted (bent) light ray obeying Fermat’s principle.

Much like light, the ant colony “searches” through many paths at first. Eventually, they figure the quickest route. The result is a collective behavior that finds almost the same solution a physicist would compute to predict how light bends. Ants obviously don’t do calculate equations, but they do choose the quickest path.

The most efficient path

Rivers carve their meandering routes over centuries, forming bends and curves. Flowing water tends to follow the easiest route downhill, not the straightest. It avoids obstacles and seeks out weaker soil, which means the river’s path is determined by minimizing energy loss. Though not exactly Fermat’s principle, the idea is remarkably similar: a physical system is finding the most “efficient” path.

The least amount of time

You might have experienced the illusion of water on the road on a hot day, or a pool of water in the middle of a desert (mirage). These are other examples of Fermat’s principle at work. On a hot day, sunlight bends as it travels through air layers of varying temperatures. Warm air is less dense, so light moves faster through it while cool air slows light down. These variations in speed cause light rays to bend as they travel through the layers, allowing the path from sky to eye to take the least amount of time and producing shimmering distortions, such as the illusion of water on a road. What looks mysterious is really optimization playing out in real time.

Minimizing travel time

If ants give us a small-scale analogy, galaxies give us a cosmic one. According to Einstein’s theory of general relativity, massive objects like galaxies bend the fabric of spacetime. Light traveling through this distorted space follows the “straightest possible” path—which looks curved to us. This effect, called gravitational lensing, can create rings, arcs, or stretched images of distant galaxies. Even here, at astronomical scales, the path of light still reflects an extremal principle: in curved spacetime, it follows a route that locally minimizes travel time (this specific line on a curved surface is called a “geodesic”).

If you dip wire frames into soapy water, the film that forms always stretches into a shape of minimal surface area, because that configuration requires the least energy. This is a different efficiency principle, but the connection remains: the resulting configurations minimize something – time or energy. Soap bubbles don’t consciously “choose” their shapes any more than light chooses its path. They simply obey this universal law of “efficiency.”

Dirt paths in the park

Even people unknowingly follow Fermat-style logic. Imagine walking across a city park: although paved walkways exist, people often cut diagonally across the grass if it is faster. Over time, these shortcuts become visible dirt paths. The same principle appears in GPS algorithms, which calculate routes that minimize travel time based on traffic conditions.

Economy over extravagance

Efficiency is baked into our decision-making, just as it is into light’s behavior. In this sense, Fermat’s idea feels almost philosophical: In the universe, “economy” is preferred over extravagance. What begins as a simple observation about light bending in water becomes a window into a deeper unity in nature. Fermat’s principle isn’t just a rule of optics – it’s a guiding thread woven throughout the natural world. Light bending at a glass surface, ants finding efficient routes, rivers snaking across landscapes, galaxies warping the paths of light, soap films forming perfect curves.

These are not random coincidences. They highlight a universal pattern. Fermat’s principle teaches us that even something as simple as a beam of light carries within it a profound law: the pursuit of the fastest path. What’s remarkable is that this principle doesn’t stop at optics but is in action at every scale. When we observe these systems side by side, we are reminded that the universe is not a collection of isolated phenomena but an interconnected framework of elegant principles. They have been in action since the beginning of the universe whether or not we have discovered them.

The next time you notice light bending in a glass of water or watch ants tracing a trail, you might see something deeper. You might be witnessing an invisible yet universal principle connecting the smallest creatures to the largest structures in the cosmos. Our universe is a book full of patterns. Fermat’s principle is one of its clearest, most beautiful expressions.

References

Oettler, Jan, Michael Kreuzer, and Jürgen Heinze. “Ants Follow Curved Routes to Minimize

Travel Time — A Potential Analogy to Fermat’s Principle.” PLOS ONE, vol. 8, no. 4, 2013,

e59772. https://doi.org/10.1371/journal.pone.0059772.

Original article: Czupryn, A. et al., Science 334, 1133 (2011).

Neurons are a highly specialized group of cells that transmit electrical stimuli to elicit responses in the body. This high specialization comes with a price: with few exceptions, neurons cannot divide to replace nonfunctional ones. Over the past decade, cell therapy, that is treatment of a disease by introducing new cells, has emerged as a new hope for neurological disorders such as spinal cord injury, Alzheimer’s disease, and Parkinson’s disease, albeit with numerous challenges. One of the major problems in the field is to make the newly-introduced cells integrate into the neural circuitry of the host organism. This proof-of-concept study showed that it is possible for transplanted neurons to functionally integrate into the host brain and cure obesity in a specific genetic mouse model. This genetic mouse model lacks the ability to sense leptin, a hormone that regulates body weight and metabolism. Thus, these mice are prone to obesity and diabetes. The authors transplanted progenitor neurons isolated from the hypothalamus-a part of the brain that regulates numerous functions including metabolism, hunger and body temperature-of normal embryonic mice to the hypothalami of newborn diseased mice. Twenty weeks after the transplantation, cells were shown to be functionally integrated into the native circuitry. Integrated neurons were able to create electrical stimuli, transmit signals and, unlike the native neurons, respond to the hormone, leptin. Amazingly, transplanted mice were 30% lower in body weight and diabetes-free compared to the obese non-transplanted counterparts. The results were dramatic, despite the fact that only a few of the transplanted neurons were actually converted to the neurons that play a role in energy metabolism and leptin response. The authors explain this phenomenon by stating that the transplanted neurons may work as “antennas” to sense leptin and regulate other neurons in the native circuitry. Although current research is far from human application, it is still an important step towards treatment of detrimental neurological diseases.

2- A new record in solar cell efficiency

Original Article: Yella, A. et al., Science 334, 629 (2011).

Since their discovery in 1991, dye-sensitized solar cells (also known as Grätzel cells) have offered great potential despite their low efficiency values. They consist of dye-soaked titania nanoparticles coupled to an iodide-based electrolyte that allows for absorption of light and its conversion to electricity through the fast transport of electrons. According to a report in Science, researchers from ecole Polytechnique Federale de Lausanne (EPFL) have substantially improved the efficiency values over 12%, making this type of solar cells a feasible contender to the incumbent silicon solar cells. To store the most sunlight, these cells absorb the colors of the light spectrum with the highest energies and reject the rest such as the green light. In addition to the increase in cell efficiency, Grätzel and coworkers have also reduced their cost by replacing expensive ruthenium dyes with a zinc-based dye. Finally, they have improved the voltage output by using a cobalt electrolyte, a redox system that is more compatible than the previous iodide systems. This new system with improved components has also increased the theoretical maximum efficiency to 30%, which will require further optimization in device design and engineering to achieve. The only major drawback is the use of organic solvents potentially limiting the efforts for large-scale fabrication.

3- IQ can still change in teenage years

Original Article: Ramsden S. et al., Nature 479, 113 (2011).

Intelligence quotient (IQ) is a standardized measure of human intellectual capacity that takes into account a wide range of cognitive skills. IQ is generally considered to be stable across the lifespan, with scores at one time point being used to predict educational achievement and employment prospects in later years. However Prof. Cathy Price and colleagues have found that verbal and non-verbal IQ can rise or fall in the teenage years. They tested 33 teenagers-19 boys and 14 girls-in 2004, when they were 12 to 16 years old, and again in 2008, when they were 16 to 20 years old. Each time, the teens took IQ tests that measured their verbal and nonverbal abilities. Then, using magnetic resonance imaging, the researchers scanned the teenagers’ brains while they performed verbal tasks, such as reading or naming objects, and nonverbal tasks, such as solving visual puzzles with their hands. The idea was to match their test scores with a picture of their brain structure and activity at each time. The test results revealed dramatic changes between their first testing and their second: verbal and nonverbal IQ scores of participants rose or fell by as many as 20 points (on a scale with an average score of 100). Some teens improved or declined in either their verbal or nonverbal skills, while others improved in one area and declined in the other. The brain scans mirrored the score differences. For example, in teens whose verbal IQ scores had increased, the scans showed increased gray matter density in a region of the brain activated by speech. Teens whose nonverbal skills had improved showed changes in a brain region associated with motor movements of the hand. The authors note that these were the largest changes observed, and that there might be many more that were not noticed.

4- A coordination path from an infant’s heart to the mother’s heart

Original Article: Feldman, R. et al., Infant Behavior and Development 34, 569 (2011).

A group of researchers sat 40 pairs of mothers and 3-month-old infants face-to-face, equipped with sticky skin electrodes on either side of their hearts. Beat for beat, mother and child’s hearts thumped together almost instantly as they shared loving looks or contented coos. This cardiac coupling worked only for moms with their own babies, and only when the duos synchronized smiles and other cheerful social behaviors. The researchers suspect that when humans mirror each other’s facial expressions, they may switch on specific areas in the brain that tell the heart when to thump. Melding with mom lasts longer than just a few beats, however. Babies who don’t tune in with their mothers are less empathetic as teenagers, according to previous work from the same group. Premature infants or those whose mothers have postpartum depression may be most at risk for losing this social skill because they miss out on early opportunities to interact with their mothers. The authors state that future research is required to examine the impact of interaction synchrony on other physiological processes, such as hormonal release or brain activation.

Our current source of energy is mostly fossil fuels such as oil, coal, and natural gas. Fossil fuels are nonrenewable. In other words, they are finite resources and they will diminish significantly in future; hence, they will be very expensive to use and environmentally harmful to recover. In contrast, solar, wind, biomass, hydrogen, geothermal, ocean, and hydro power are renewable energy resources, that is, they are constantly replenished and will not run out. Renewable energy is not only important for our energy needs but also has significant advantages over fossil-based energy resources in the protection of the environment. Besides, the environmental aspect of renewable energy also has a religious dimension, since preservation of the earth and its inhabitants is regarded as a duty for humankind.

Among these energy resources, solar energy is generally used for electricity generation or for hot water heating. It also finds uses in solar cooling, and in direct heating and lighting of buildings and homes. Solar panels are made of photovoltaic (PV) cells. The term “photovoltaic” means “converting light into electricity.” Solar energy technology has been around since the late nineteenth century. Yet, its share in energy production constitutes a very small fraction (less than 0.1%) of production around the world. This stems from the higher cost of electricity generation with solar panels in comparison to use of fossil fuels. In the US, electricity generated from PV cells costs $0.30 to $0.40 per kilowatt-hour while consumers pay only $0.10 per kilowatt-hour to the electric utility companies. Nonetheless, with recent advances in this technology, it will be possible in the near future to decrease the cost and make this technology viable for our energy needs as we face shrinkage in fossil fuels around the globe.

One of the factors that increases cost is the low power-conversion efficiency of current PV cells. The PV cells used in the market are mostly fabricated from silicon crystals and these cells show a power conversion efficiency of 15%. That means, 85% of photons go to waste when harvesting energy from sunlight. In fact, the theoretical limit of light harvesting in silicon-based solar panels is only 31% because of the low band gap of silicon, which only partially absorbs sunlight to form charge carriers in the device. To solve this problem, scientists have utilized three different crystals in a single PV cell to absorb more sunlight, and these studies have yielded a device efficiency of 37%. Just recently, scientists at the National Renewable Energy Laboratory (Golden, Colorado) and Boeing-Spectrolab have achieved a world-record conversion efficiency of 41% by using the same idea, establishing a new milestone in sunlight-to-electricity performance. Although such studies are very promising in this field, when it comes to production cost, these inorganic PV cells are still an expensive technology for power generation compared to fossil fuels.

Organic photovoltaics

An alternative solution to decrease the cost is to use devices with lower power efficiency but a very low cost of production. Organic-based PV materials offer such an alternative with easy and fast production techniques such as solution processing and printing. Conjugated polymers (polymers with alternating single and double bonds in their polymeric backbone) are especially important in this regard, since they exhibit semiconductor properties. The best organic PV cell efficiencies reported in recent years are around 5%. This number must double in order for the cells to be used in solar panels, assuming that the cell displays high photostability and conductivity. Many research groups are now focusing on organic-based solar systems as an alternative technology to their inorganic counterpart.

Although we are all familiar with solar energy, most of us do not know how electricity is produced from sunlight. To show the mechanism for photovoltaic activity, one first should look into an anatomy of a typical organic PV cell which is shown in Figure 1. This cell is based on an organic PV cell. The organic layer is sandwiched in between two electrodes where light absorption and charge separation occurs. Typically, glass is used for support but plastic materials can also be used as alternatives. The anode is usually indium tin oxide (ITO) and the cathode can be aluminum, calcium, gold, or magnesium. The electrodes must be semi-transparent to facilitate light absorption. Specifically designed conjugated polymers are utilized for sunlight absorption, where the wavelength range of absorbed light may vary from ultraviolet-visible to near infrared depending on the material used in the device. The efficiency of the device is determined by the extent of light absorption, efficiency of charge separation, and charge diffusion to the electrodes. The morphology of the organic layer has been found to be very important for device characteristics and cell efficiency. In an organic PV, an electron is promoted from the highest occupied molecular orbital (HOMO) level to the lowest unoccupied molecular orbital (LUMO) level upon light absorption (Figure 2). This transition results in an electron-hole pair which is then separated by the electric field formed by the different ionization energy of electrodes (Φ). Therefore, the electron moves to the cathode and the hole moves to the opposite side. This process causes charge flow between the electrodes and hence electricity is generated in the process.

Despite all the improvements in organic PV technology, current cell efficiencies are still low for electricity generation. The stability of organic PV materials must be improved as most of them are prone to degradation by oxygen and humidity in the air. The large-scale production of organic solar panels is possible, and yet the feasibility of current methods has not been investigated extensively so far.

Solar energy is a clean, renewable resource of energy and is projected to have significant role in the energy market in near future. Funding in the field of solar energy has been increasing in recent years due to the increasing need for energy and the likely reduction of fossil fuels towards the end of this century. Yet, our research efforts are still not sufficient for the advancement of this technology.

Importance of renewable energy for the environment: an Islamic perspective

Solar energy, like other renewable energy resources, is environmentally friendly. Its use should be promoted, as fossil fuels play a dominant role in the increase in greenhouse gases, which are believed to be responsible for the increased rate of global warming and hence climate change. Global warming may cause rises in sea level and changes in the amount and pattern of precipitation. These changes may in turn increase the frequency and intensity of extreme weather events, such as floods, droughts, heat waves, hurricanes, and tornados. Other consequences may include higher or lower agricultural yields, glacial retreat, reduced summer stream flows, and species extinctions. Warming is expected to affect the number and magnitude of the events mentioned above; however, it is difficult to connect particular occurrences to global warming.

In any case, focusing on renewable energy and energy-efficient technologies is one of the best options to secure the future of our planet and all existing forms of life on it. Our effort should not only be due to the expected shortage of fossil fuels in future. Rather, it must be seen as a duty and moral act to save the environment since use of renewable energy resources has little or no negative impact on nature. Religious awareness and guidance in this area is necessary so that each individual may take active part in the protection and development of the environment. Much environmental degradation is due to our ignorance of what our Creator requires of us. People should be educated to realize that the conservation of the environment is a religious duty demanded by God. This fact is expressed in Qur’an in a number of places such as, “Do good, even as God has done you good, and do not pursue corruption in the earth. Verily God does not love corrupters” (Qasas 28:77), “And do not follow the bidding of the excessive, who cause corruption in the earth and do not work good” (Shu’ara 26:151–152), “And do not cause corruption in the earth, when it has been set in order” (A’raf 7:56). Any deliberate damage to the natural environment and its resources is a kind of corruption which is forbidden by Islam.

As Muslims, we should protect and preserve the environment because by doing so we protect the creatures which pray to God and praise Him. Although we do not know how they praise God, the Qur’an clearly points this out: “The seven heavens and the earth, and all beings therein, declare His glory: There is not a thing but celebrates His praise, and yet you understand not how they declare His Glory!” (Isra 17:44). Islam is established on the concept of good (khayr). Since it is scientifically proven that protecting the environment is of great significance for all animals and plants on earth, Muslims should see it as khayr. In the last two verses of chapter Zalzalah (99:7–8), God says, “And whoever does good an atom’s weight will see it then. And whoever does ill an atom’s weight will see it then.”

Protecting God’s creatures and the environment is a duty of humankind because human beings are the “agents” of God on earth. This task cannot be performed by other creatures. Therefore, as the Muslim community we should all commit ourselves to the preservation and to the protection of the environment. Surely, investing in and promoting improvement of the technologies based on renewable energy is one way to go.

References

• http://www.nrel.gov/learning/re_basics.html
• http://www.islamonline.net
• http://lfw.pennnet.com/Articles/Article_Display.cfm?Section=ARTCL&ARTICLE_ID=257239&VERSION_NUM=3&p=12 (PHOTOVOLTAICS: Research targets more-efficient photovoltaics)
• http://lucy.mrs.org/publications/jmr/jmra/2005/dec/0407.html (Organic and nano-structured composite photovoltaics: An overview)
• http://www.orgchem.science.ru.nl/molmat/mm-web/education/caput-college/SolEnergMatCells-2004-83-125.pdf (A brief history of the development of organic and polymeric photovoltaics)
• http://en.wikipedia.org/wiki/Global_warming
• http://www.islamset.com/env/index.html

In recent years, we have realized that the world’s supplies of coal, gas and oil are limited. Nuclear power has been used as an alternative solution to fossil fuels. However, the use of nuclear power and fossil fuels incurred environmental problems so there is widespread public antipathy. As a result, the popularity of renewable energy has grown during the past twenty years. The World Energy Council estimated that renewable energy sources, such as solar, wind, hydro, wave and bio-mass, met 18% of the world’s energy needs in 1990 (World Energy Council, 1993). Their scenario is that the contribution from renewable energy could increase 30% by 2020.

One of the most promising of the renewable energy sources is the direct conversion of solar energy into electricity by photovoltaic generation. There are many reasons for growing popularity:

1. Photovoltaic generators do not pollute the air and do not leave waste products.

2. Photovoltaic generators are silent during operation.

3. They work effectively even in cloudy weather. They are more efficient at low temperatures.

4. As there are no moving parts, they work reliably for 20-30 years with little maintenance.

5. Solar energy is available everywhere so power can be generated anywhere it is needed. This makes photovoltaic generators attractive in the many places where there is no mains supply.

6. Photovoltaic generators can be planned and installed within a few months in contrast to conventional power stations which take at least five years to become operational.

7. Finally, photovoltaic generators can be located anywhere, such as in the roof or walls of an existing or already planned building, therefore they do no need to use up extra land.

The photovoltaic effect was first observed by Edmund Becquerel in 1839. Much later, in the 1930s, solid state researches developed the first photocells which were used in photographic exposure meters. In 1954, the Bell Telephone Laboratories made crystalline silicon solar cells with a conversion efficiency of 6% which was used in space programs. The market for photovoltaic modules has been growing steadily since; in 1991 it had reached about 50 MW per annum.

Solar Cell

The total radiant power from the sun falling on one square meter of a surface area can be as high as 1000W/m2 on a clear summer’s day and it can fall to 100W/m2 in cloudy conditions. In northern Europe, it seldom exceeds 850W/m2 (Treble F.C., 1993).

The inactive energy, solar energy, can be converted into electrical energy by solar cells. The absorption of light in semiconductors creates additional electrical charge carriers, both electrons and holes equally. If an electric field exists within the semiconductor, the negative electrons and positive holes move in opposite directions and this electrical charge separation results in the creation of a voltage. The movement of the electrical charges creates an electrical current and voltage so both current and voltage are generated simultaneously. This is the photovoltaic effect, the creation of a voltage by the action of light.

The basic way to establish an electric field in a semiconductor is to make a p-n junction. The electric field at the junction attracts electrons from the p-side and forces them to the n-side making it negatively charged. Similarly holes from the n-side are forced to the p-side, making this positively charged. Thus holes are creating a voltage. Figure 1 shows the basic features of a solar cell. The front contact grid is a thin metallic grid on the front surface and the back contact usually covers the whole of the back. This is called an n-on-p cell. Silicon is one of the popular semiconductor in the electronics industry so it is used for solar cells. Most commercial cells have a probable 20% efficiency which is the ratio of the maximum output power to the input power from the sun, but over 25% efficiency has been achieved in the laboratory. The theoretical limit for crystalline silicon cells is about 30% under 1000W/m2 irradiance and 25 °C operating temperature (Hill B., 1995). Solar cells which were made from gallium arsenate have achieved 34.2% efficiency.

Solar cells are fine objects which must be protected from any possible damage. The cells are usually connected in series, in parallel or a combination of both in order to produce necessary power and voltage. A photovoltaic module which is a collection of solar cells was bought about US$4/Wp (US$ per peak watt) in 1995. Modules must be capable of reliable operation for many years. The current target is a lifetimes of 30 years.

Photovoltaic applications

In 1994 the total world sales of photovoltaic modules reached 70 MWp per year. In recent years, photovoltaic modules have found many applications in various sectors. The main applications are given below:

1. Space applications: solar cells were first used to produce electricity for satellites in 1958. Since then, photovoltaic power generation has become an essential energy source in space. Solar cells can operate near or far from sun.

2. Telecommunication: transmitters and repeater stations are often located in distant places such us mountains, islands or deserts. Solar power has proved the cheapest and most reliable power for transmitters and repeater stations.

3. Electricity in villages: the majority of the population of the developing countries, approximately two billion people, live in small villages without electricity. As almost developing countries will find extending the mains grid to a few customers far removed from the mains supply lines too expensive, photovoltaic systems are the obvious, cheaper alternative. A small photovoltaic module with a battery can provide enough power for basic lighting, TV and a small refrigerator for a house. By 1993 more than 10,000 home systems had been installed in Indonesia. In addition, solar home systems had been installed in the Philippines, the Dominican Republic, Columbia, India, Kenya, Mexico, Morocco, Sri Lanka and Zimbabwe by 1993. The average price of a 50 Wp solar home system was about US$500 in 1993. Assume that a 50 Wp solar house system in future will cost about US$250, then 400 million solar home systems will be

installed in the world. The other applications of solar modules in villages are water pumping, irrigation, water purification, street lighting and TV receivers (Lysen E.H., 1994).

4. Grid connected buildings: the solar modules can be fixed on roofs or walls so no additional land is required. The most sensible use of photovoltaic cladding would be on commercial buildings because they need energy during working hours rather than at night. Photovoltaic cladding presently costs about 800m-2 in comparison with marble cladding cost around 1000m-2, granite cladding 800m-2. Photovoltaic cladding gives high-tech images for office blocks at lower cost than marble.

5. Central power stations: photovoltaic power stations have, so far, only been installed for purposes of research. Today, Austria, Germany, Italy, Spain and USA have small stations of this type.

The other applications of photovoltaic systems are pocket calculators, watches, clocks, torches, garden lights, portable radios, battery chargers for boats, caravans, electric cars, toys, railway signals, traffic warning lights, alarm systems, automatic weather stations, military equipment and so on.

Conclusion

The photovoltaic system cannot at present compete with mains electricity. However, early in the next century, when economies of scale are expected to bring about a reduction in manufacturing costs, solar power will be an important energy source.

References

• World Energy Council (1993) Energy for Tomorrow’s World, Kogan Page /St. Martin’s Press.
• Treble F. C. (1993) Solar Energy, The Solar Energy Society, Birmingham.
• Hill B. (1995) ‘Solar Power’, IEE Power Engineering Journal, (August 1995), pp. 175-80. Lysen E.H. (1994) ‘Photovolts for villages’, IEEE Spectrum, 31, (10), pp.34-9.