It's the middle of summer. You are trudging along the dusty road that seems to stretch endlessly before your eyes. The enormous bag-pack on your back weighs you down as if it is filled with lead. It's been two hours since you've run out of water, and already you feel the thirst overwhelm you with giddiness. The road is so hot that you could fry your scrambled egg on it. You wonder, how on Earth could it be so hot? And then you look at the sun up above. If the sun's energy is so powerful enough to sizzle your very self, could not the energy be harnessed to our use?

 

You're dead on. Welcome to Solar Power.

 

 

Let There Be Light!

 

Recounting the history of the human use of the sun as a specific energy source is almost impossible – almost all the energy existing on the Earth comes and came from the sun. Our sun produces 400,000,000,000,000,000,000,000,000 watts of energy every second, and the belief is that it will last for another 5 billion years. The sun's light provides light for the day, and gives warmth to all that lives on Earth (if there was no sun, nothing could live on Earth).  Consequentially, at least 95 % of all the reactions and phenomena occurring on our planet is the cause of the sun (one of the few exceptions would be everything pulled towards the centre of the Earth, which is caused by the Earth's gravity), from cross-continental meteorological activities to the growing of an apple tree. Wind is created by the temperature differences of air in different areas, which is the cause of sunlight. Your breakfast cereal was created by processing grains, which was grown thanks to sunlight. Thus, it would not be entirely wrong to say that all of the energy sources we are discussing in these articles are in some way or another related to the sun's energy. That means there are about as many as millions of ways of turning sunlight into useful energy for us.

 

But sunlight as a singular, unique and specific source of energy – sun's energy 'straight from the sun,' not after going through a number of processes – reduces photo-energetic physics to a far narrower subject. That will be the principle focus of today's article.

 

 

How does Sunlight Produce Electricity?

 

Let's first learn the nature of light itself. Surprisingly, the light that comes from the sun is more or less the same as the light coming from a gourmet restaurant's chandelier, or that from emitted by a campfire. They are all the same in respecting the fact that they are all electromagnetic radiation. Although electromagnetic radiation is similar to mechanical waves (i.e. sounds), it has a very important difference: it consists of a changing electric field and changing magnetic field. It's a complicated story about the wave physics of light, so we'll skip that.

 

When discussing the energy of light, scientists tend to embrace the concept of photons. This was first proposed in 1905 by the famous scientist Albert Einstein, who suggested that all electromagnetic radiation, including light, consists of many packets of energy that release the energy upon colliding with matter. According to this theory, these photons are what transfer the sun's energy from the sun to the Earth. The means of turning sunlight into useful energy, then, is really the means of turning photons into useful energy. There are a number of ways to do this I will talk about the main three.

 

 

1.     The first method uses Photovoltaic Cells (better known to us as solar cells), which generate energy in a way surprisingly similar to photosynthesis. A PV Cell is an array of very thin silicon semiconductor strips that, when hit by photons, produces an electric current. This electrical current can then be connected to a circuit, and used to light homes, boil water, ect.

 

PV Cells are used widely in the modern world, from calculators to satellites. They are cheap and compact, and have an acceptable efficiency. Though the output isn't always large, PV Cells are often used where weight and mass needs to be minimized, i.e. when batteries cannot be used. This comes in very important in aerospace technology, where 'every kilogram counts,' literally.

 

When compared to loading a satellite module with a ready-charged battery, PV Cells would give a continuous supply of electricity with far better efficiency (and of course normal batteries last only for a certain amount of time, after which they need to be replaced). Many homeowners also plant PV Cells onto their roofs or on the lawn. This contributes to saving a few bucks from the monthly energy bills, which can be a big difference on the long run.

 

 

2.     The second method, compared to the first, is less efficient and technical, but sometimes more applicable. This method uses a parabolic, light-reflecting surface (i.e. mirrors) to focus sunlight on a single point. This single point will accumulate heat this heat energy can be used to do various things. Often the heat is used boil water and turn it into steam, which then turns a turbine and runs a generator, producing electricity. This energy is called Solar Thermal Energy.

 

Unlike PV Cells, this Solar Thermal System isn't that compact, and actually requires considerable area to produce the sufficient energy. Besides, it can't be used as effectively in colder areas (e.g. Siberia) because the cold wind will cool everything as soon as the focused light rays are converted into heat. Nevertheless, this system is used widely throughout the world, particularly in less developed countries that lack technology, capital, and infrastructures to produce PV Cells. In remote villages where electricity supplies go through the floor, domestic hot water is frequently prepared using this method (the pot containing water is placed on the focal point of the light the pot will heat up, and so will the water).

 

 

Advantages & Disadvantages

 

I am very happy to announce this: The Sun is free! All we need to do is collect the sunlight coming down onto the Earth. The sun is not only free, but will last for billions of year more. And unlike wind or water, which is unpredictable, sunlight is almost always consistent (that is, at least during the day), and shines equally throughout the world (except the poles, which don't receive as much sunlight). It goes without saying that sunlight is obviously sustainable and pollution-free.

 

Now for the bad news. Solar energy can only be used during daytime (at night there's no light, there's a rhyme for you), and then again is only effective during a relatively short span of time – usually from 10 a.m. to 4 a.m.. The PV Cells and mirrors, that receive and reflect light respectively, inevitably take up considerable amounts of area, and this area is often not available. Finally, the output is also a problem. With current technology, output from either PV Cells or any other means of solar energy conversion is quite low. This means that solar energy is, to this date, not a significant source of energy.

 

 

Cast Study

 

The countries most suited for solar energy production would probably be desert countries in Africa and Middle East. Both PV Cells and Solar Thermal Systems are seeing wide usage in nations such as Egypt, Saudi Arabia, Jordan, UAE, Morocco, and Libya. These countries receive sunlight intense enough for solar power to be feasible, and have sufficient technology and capita for installing solar farms nationwide. In some non-tropical countries such USA or China, some areas are partially sunny enough for solar farms to be installed (in USA, the Mojave Desert in China, the Taklimakan Desert).

 

Even in countries where nationwide solar power generation is unfeasible, many gadgets, from household items to vehicles, are run by solar panels. Calculators, lawn and street lamps, remote-controlled toy cars, clocks and watches are a few examples. And finally, as mentioned before, individual home owners can install solar panels on their roof to supply a little electricity to the mains circuit, and save some of their monthly energy bills.

 

 

Areas of Research in the Future

 

The biggest problem we have with solar energy is the low output compared to the large area generation facilities take up this often precludes solar power from being a meritorious energy source. Given that semiconductor technology is already highly advanced, further research probably won't make PV Cells significantly more efficient.

 

Currently, scientists are planning a mean of shooting up solar energy plant modules into outer space, on Earth orbit. This module, similar to a satellite in appearance, will have a gigantic wafer-like wing, covered with PV Cells, which will receive sunlight straight from the sun, turn it into electricity, and transfer it onto the surface of the Earth. This idea, compared to building solar farms on the surface of the Earth, has two advantages: there will be unlimited area, and energy production will be more efficient (the sunlight doesn't have to pass through the atmosphere). A way of transferring the electricity from outer space to Earth needs to be devised (clearly we can't connect all that way with electric cables) – this may perhaps be done via a laser beam regularly shot into a receiver.

 

At least what we do know for certain is, someday, when we humans finally venture to settle other planets, solar energy will come in very handy.

Citation of Images:

Buemi, Dave. DoD Energy - "We Have the Land & the Demand" Digital image.Buy American Act Compliant PV Modules – How to Know? The PV Advocate, 20 Feb. 2010. Web. 4 Aug. 2014. <http://davebuemi.com/page/2/>.

Buemi, Dave. Solar Module Packaging. Digital image. Buy American Act Compliant PV Modules – How to Know? The PV Advocate, 20 Feb. 2010. Web. 4 Aug. 2014. <http://davebuemi.com/page/2/>.

Abengoa's PS10 Project in Seville, Spain. Digital image. Solar Thermal Energy on an Industrial Scale. Solar Thermal Energy, 2008. Web. 4 Aug. 2014. <http://www.solar-thermal.com/>.

PV Cells on Rooftop. Digital image. Solar Thermal Energy Freely Available Heat For Our Use! Alternative Energy Action Now, n.d. Web. 4 Aug. 2014. <http://www.alternative-energy-action-now.com/solar-thermal-energy.html>.

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