Basics of solar power-Part III

We’ve covered the workings of a solar cell in the first two parts of this series – Basics of solar power Part I and Basics of solar power Part II. In part three of this series and as mentioned in the previous post, we’ll now find out what new materials have been discovered/invented in order to boost the solar cell efficiency. It is important to know that it is not only the characteristics of the materials that boost efficiency of the solar cells but other factors too and will be discussed in this post.

History of solar cell materials:

The history of solar cell materials can be traced back to 1873, when Willoughby Smith discovered the photoconductivity of selenium. Later in 1953, a mere 4.5% efficiency was achieved by Bell Laboratory when they fabricated the first crystalline silicon solar cells.

Factors affecting solar cell efficiency:

After 140 years since the discovery of photoconductivity of selenium, the world record for solar cell efficiency has rose to 44.7%. The reason why we haven’t reached a 100% are plenty. One apparent reason is dust. As dust accumulates on the cell’s surface, it blocks the sunlight that is available to it. Rovers in the space that study planets run on solar power. These too require frequent cleaning in order to work efficiently day in and day out. Rovers thus must dust themselves off and start all over again. A self-cleaning technology that has been developed to help rovers do this can also be applied to the panels here on the deserts of the Earth. It uses the principle of repelling dust particles using electrostatic forces. As you can see, even if deserts provide us with maximum sunlight, dust can stifle all our efforts of putting it into use. To add to the problem is lack of water. Water is scarce in such arid regions, hence water-cleaning is not a feasible option. NOMADD is an automated and mechanical technology that claims to solve these woes.

Next to dust is the problem of reflection of light off the surfaces of the solar panels. We require the light to be absorbed and not reflected. Anti-reflection coatings are hence applied.

Other factors influencing solar panel efficiency are rather inconspicuous. These are related to the intrinsic properties of materials such as band gap. Band gap energy is the minimum amount of energy required by the incoming photons to kick loose the electrons in the material (kicking the electrons by the photons is scientifically called as photoexcitation). Band gap is the gap between the valence band of the material and its conduction band. Conduction band is where the electrons flow freely. Please know that when the electrons start flowing, not all of these electrons constitute the electricity generated. This is because some of these electrons recombine with nearby holes. Hence, not all electrons are ‘collected’. The band gap energy is different for different materials. Any less, no electrons move. Any more, light energy is converted into heat energy instead of electrical energy. To overcome these energy-efficiency limits, scientists have devised several ways.

How were scientists able to increase photovoltaic efficiency?

Structure of the solar cell: Take the example of the world record beater solar cell. It employed a procedure called wafer bonding in which two desired semiconductor crystals can be connected together without loss of crystal quality. Also, multi-junction cells (more than one sandwich) are reported to have higher efficiency as compared to single junction cells. Multi-junction cells overcome the Shockley–Queisser limit over the single-junction cells.

New  materials: Ferroelectric ceramic material – perovskite crystals made with a combination of potassium niobate and barium nickel niobate, was developed by the team at the University of Pennsylvania and Drexel University. The additional materials in the crystals were inserted to alter the energy band gap. The magic of these being ferroelectric is in the fact that they are able to channel the haphazard movement of kicked electrons in a much better way. In other words, consistent polarity is maintained in a much better way without much loss.

Better cooling: IBM’s developed a liquid metal cooling system for concentrated photovoltaic cells so that they can endure highly focused solar energy without overheating.

Using up all the sunlight: Sunlight is made of a range of wavelengths of lights – the electromagnetic spectrum. Silicon absorbs light of wavelengths close to the visible range. Photovoltaic response curve – solar cell output plotted against wavelength, will show the wavelengths absorbed. In order to harness the entire spectrum, scientists have to engineer new materials. New nanomaterials can now do just that.

Upping the existing materials: Semiconductor materials do not absorb light all that well when they are made thinner. To improve this without compensating on the thickness of the material, scientists have identified a concept called ‘nanocavity’. With this, we can have thinner yet better solar cells.

Biomimicry: Bio-inspired materials’ best example will be one that has taken after the process of photosynthesis. This gave rise to dye-sensitized solar cells. On the other hand, bio-inspired mechanisms such as moving solar cells are inspired from sunflowers that track the sun.

Reported timeline of solar cell energy conversion efficiencies (from National Renewable Energy Laboratory (USA)) is shown below.

This ends the third part of the series of Basics of Solar Power.

This blog post was first published at GreenHatters on March 18, 2014. Version edited for minor corrections. It’s a part of a series on solar power fundamentals.

GreenHatters is a not-for-profit initiative that cares for the environment and promotes sustainability, strives to create awareness on Energy conservation and Carbon footprint responsibility.

Basics of solar power-Part II

I hope you found the Basics of Solar power – Part I useful. Please feel free to pop in and leave a comment or a question – here on this blog or let’s talk on Google+, Facebook or Twitter. In this part of the series, we are going to see what solar cells are made of.


(Image of Silicon: Wikimedia)

What is solar cell made of?

Solar cells are made of a semiconductor material, typically silicon. Silicon is the second most abundant element on earth, first one being oxygen. It is a metalloid, an element which displays properties that are both like a metal and a non-metal. Pure silicon however can neither conduct well nor insulate well, hence it needs to be doped.

What is doping?

Doping is a process in which impurities are added to increase or decrease the number of electrons. In other words, doping is a process of adding elements which can either donate or withdraw electrons from silicon. This process causes either excess of electrons or electron deficiency in the silicon material. When an element with 5 valence electrons is added to a silicon that naturally has 4 valence electrons, it becomes n-type (more electrons). When an element with 3 valence electrons is added to it, it becomes p-type (less electrons or more holes). These are known as pentavalent and trivalent impurities respectively.

Is silicon the only material used for making solar cells?

Apart from silicon, gallium arsenide (GaAs); cadmium telluride (CdTe) and copper indium gallium selenide (CIGS) are also used. One also needs to know that solar panels are wrapped in a safety glass and given an anti-reflection coating for better and longer performance. So, these materials too are a crucial part of the entire solar panel system. A hunt for new materials continues to achieve greater efficiencies. Not just for solar cells but also for anti-reflection coatings.

Let us now focus on silicon as the material of construction.

Kinds of silicon:

Solar cells are made of three kinds of silicon:

  • Monocrystalline
  • Polycrystalline
  • Amorphous

How do I know which one is the best?

The choice for the kind of silicon depends on various factors such as:

Geography: The place you are going to assemble the solar panels at determines the choice of the panel. This is because each of these materials reacts differently to climatic conditions.

Type of application: Will it be placed on a building or your car? Amorphous panels take up a lot of space and hence cannot be used on a car. These are the ones you can see on calculators.

Efficiency: Monocrystalline panels have the highest efficiency of them all.

Durability: Monocrystalline panels live longest.

Budget: Monocrystalline panels are the most expensive.

Researchers are trying to discover and invent new materials that are cheaper and more efficient. They are also working on engineering techniques for modulating existing materials because each one of them has its own beauty. Keep an eye on the third part of this series to know more about new findings!

See you soon!

This blog post was first published at GreenHatters on March 6, 2014. Version edited for minor corrections. It’s a part of a series on solar power fundamentals.

GreenHatters is a not-for-profit initiative that cares for the environment and promotes sustainability, strives to create awareness on Energy conservation and Carbon footprint responsibility.

Basics of solar power-Part I

openclip(Image: Openclipart)

Sunlight is the energy source that drives our planet. Each and every thing on this planet is a receptor of sunlight. Each species uses sunlight in its own way. Plants cannot move around in search for food and hence they rely on sunlight for cooking their own food. Without the UV rays in the sunlight, humans could suffer from a disease called rickets, because it is these rays that are necessary for human bodies to produce Vitamin D which in turn allows our bodies to absorb calcium. But there’s another way we can harness this energy. It’s by converting sunlight directly into electricity or by using its thermal energy to convert water into steam, which is indirectly converted into electricity.

On an average, earth receives 164 Watts per square meter for an entire day (24 hours). Multiply that with the surface area of the earth and it receives a whooping 84 Terawatts of Power. (Earth is called Terra in Latin, different from ‘tera’ watts.) Here’s a picture of the dynamics of solar radiation reaching our planet.


(Image: University of Oregon)

How do we collect sunlight?

We collect sunlight (solar energy) with solar panels. Solar panels are a collection or an array of photovoltaic modules. (photo = Greek phōs = “light” and “volt” = the unit of electro-motive force = last name of the Italian physicist Alessandro Volta) Photovoltaic modules are a collection of solar cells.

When particles of light aka quanta of light or photons hit these panels, they are absorbed by the semiconducting material of the panel. Example of a semiconducting material is silicon. A solar cell is made up of two types of semiconducting materials – p-type (more positive charges/holes) and n-type (more negative charges/electrons). They are sandwiched together to form a p-n junction and due to such a configuration, current flows only in one direction.

When I say photons hit this material, it means that the photons kick the electrons out of the n-type layer. The photons kick them out of their usual place and let them loose. The kicked electrons are all excited now and start moving into the p-type layer. But now they want to go back home, so they return back in a loop. This is what constitutes a flow.

In school, we’ve learnt that when electrons flow, we get electric current. This is due to difference in electric potential. Any system wants to go back to its stable state. Hence, to counteract this difference, the electrons move in a way to regain balance again (electrons get homesick).

The sandwich of p-type and n-type layers of semiconductor materials caused the electrons to flow in one direction. This kind of a flow of current is known as direct current (DC). But this is not what the appliances at our home use, do they? The appliances run on AC: alternating current. DC can be converted into AC with an inverter.

This is all for now. I’ll leave you with this song until I get back to you with the Part-II section of this blog post.

This blog post was first published at GreenHatters on February 14, 2014. Version edited for minor corrections. It’s a part of a series on solar power fundamentals.

GreenHatters is a not-for-profit initiative that cares for the environment and promotes sustainability, strives to create awareness on Energy conservation and Carbon footprint responsibility.

Energy efficient buildings

(Image: Wikimedia)

What does a hut, an igloo and a bamboo shack have in common? They are primitive and are green buildings. Back then, that was all the material that was available to build shelters. Such dwellings still exist on this planet. People didn’t know they were building ‘green buildings’ because they didn’t have to bother. But now considering the rate at which buildings are made, it is a necessity to keep a check on its side effects.

Keeping a check on the consequences of constructing innumerable dwellings is just one side of the coin. The other side of the coin represents learning from nature. Mick Pearce, an African architect was inspired by the ingenuity of termite homes. These homes always have their internal temperature maintained. They are strong and durable. How is this possible? The answer lies in its engineered structure – the shape and the way air flows (convection) inside; the application of which now stands tall in Zimbabwe – The Eastgate Centre.

Are our current buildings green? Not all. But people have studied these buildings and put together a few things to make them greener. When judging the greenness of an existing building or when we have to build a new one, one has to consider an entire life cycle of the building. This life cycle assessment (LCA) includes:

  • Materials needed for constructing the entire building
  • How the materials were procured
  • Design of the building
  • Operation and how it responds to atmospheric conditions
  • Maintenance
  • Renovation
  • Demolition

During this life cycle analysis, one can measure:

  • carbon dioxide emissions
  • energy consumption
  • waste produced
  • resource consumption such as water
  • pollution caused

To give an example, we can think of net-zero energy buildings. Net-zero energy buildings (aka zero-energy building, zero net energy (ZNE) building, net-zero energy building (NZEB), or net zero building), wherein zero signifies no carbon emissions. Although initial costs of these buildings are higher, ZNE buildings are sustainable and hence a wise long term strategy. But where do carbon emissions come from in a construction industry? An entire life cycle of this industry shows that GHG emissions come from the following areas of the process:

  • Materials of construction (The manufacture of which depends on energy and energy comes from fossil fuels on a large part.)
  • Construction on-site processes (This would need energy.)
  • Associated transport/ Distribution (Transport means fuel, simple.)
  • In-Use operations that is use of lighting, air conditioning: heating or cooling.
  • Demolition and waste handling (When everything is done, even demolishing it requires energy.)

These areas are common to both commercial as well as residential buildings. What can be done to countermeasure the effect of such consumption? One way is to adopt solar power. Buildings can be fitted with solar panels for in-use operations that account for the largest proportion, over 80%, of total CO2 emissions in this industry. To the rescue now smartphone apps that homeowners can use to energy audit their homes on their own. Existing buildings can be fitted with solar panels or can be provided with an external insulation depending on the local climate conditions.

To regulate this entire process, standards have been laid down and vary from country to country. In the USA, for instance, LEED (Leadership in Energy and Environmental Design) provides ratings which help builders and owners construct a green building.

This blog post was first published at GreenHatters on February 15, 2014. Version edited for minor corrections.

GreenHatters is a not-for-profit initiative that cares for the environment and promotes sustainability, strives to create awareness on Energy conservation and Carbon footprint responsibility.

Worth a thousand words

11,000 trees planted by 11,000 people from all over the world in Finland, as part of a massive earthwork and land reclamation project by environmental artist Agnes Denes, one of the pioneers of Environmental Art. Read more about Agnes, here, best known for her Wheatfield project in Manhattan.

Landfill reclamation project, 1992

Source: Agnes Denes Studio

Will we be wearing these hazmat suits and masks in the future? Hope not.

Hazmat surfing


Indoor air quality can be and is enhanced through indoor plants. How about when you are out there? When the air pollution gets worse, will you take the plants with you?

Upfest 2015 - Urban Festival in Bristol
Street Art

Source: Dr. Love

Not so subtle project that spreads awareness on paper consumption and recycling.

PaperBridge - visualisation
Paper Bridge

Source: Steve Messam

No blind spot for this trash bag. Makes me want to sing ‘But then I just smile, I go ahead and smile…..‘ (flip-flops) flip-flops-163577_640

Seeing trash differently

Source: Trash Project

Reminiscence of our ways of material consumption. Where are our patterns of consumption taking us?

Becoming aerosolar

Source: Tomas Saraceno

Before and After. Daesung Lee has found a way to show what it will be like if we don’t act now.

Futuristic archaeology

Source: Daesung Lee

Permanently etched on my mind. I so want to see this all over.

Green roof

Source: May 19, 2014, New Yorker Magazine Cover

One of the winning entries of DEP’s Water Resources Art and Poetry program, out of 1,350 2-12 grade students from New York city. A total of 1,400 pieces of Artwork and Poetry were created by these young artists for the 29th Annual Water Resources Art and Poetry Contest.

By Adrianny Estevez
By Adrianny Estevez

Source: Department of Environmental Protection, NY

Mario Miranda’s 1987 cartoon captured the suddenness of environmental degradation and the Goan artist’s inability to process the altered landscape before him.

Source: The  Caravan


  • Goan Art taken from The Caravan, 16.07.2015