Thursday, 14 August 2014

Rejuvination of Solar Power

One of the greatest challenges scientists face today is finding renewable energy sources that are efficient and have successful practical applications. It has become more and more common to see houses with solar panels on their roofs and the cost of these panels have fallen over the years, making them more accessible to people.

Why are renewable energy sources needed?

Most people still rely on traditional sources of energy, fossil fuels. Global Warming is caused by the release of greenhouse gases and carbon dioxide is the primary cause. It is estimated that CO2 makes up 72% of the total emitted greenhouse gases, followed by methane and nitrous oxide. The largest source of carbon dioxide emissions comes from the burning of fossil fuels, which we all rely on for electricity, light and gas.

Fossil fuels are technically a renewable energy source as they are continually being made underground. The problem is that humans are consuming the fuels at an alarming rate, far faster than the rate of production of fuel. Therefore to reduce the emissions of greenhouse gases and reduce the effects of Global warming on the Earth, scientists and Governments across the world are moving towards the production of new renewable energy sources with reduced emissions of carbon dioxide.

This is where solar panels come in. Solar power uses photovoltaic cells to convert sunlight into electricity which can then be used to power a home. Electricity is produced in the cell by something called the 'photovoltaic effect'. Simplified, the photovoltaic effect relies on a property called the 'photoelectric effect' which is exhibited by some substances. In essence, the photoelectric effect means that when the substance is faced with light, it absorbs photons and emits electrons. These freed electrons then go into the circuit to generate an electric current and hence electricity that can be harvested.

What are solar panels?

The crystalline structure of silicon
Solar panels are made from cells of silicon, a semi-conducting material, which are interconnected and join to form a circuit whereby electricity can be produced. Silicon is a semi-conductor due to its atomic properties and is in group 4 of the periodic table, meaning it has 4 valence electrons. Although preceded by Aluminium and above Germanium in the periodic table, Silicon is not a metal, so the 4 valence electrons are not free to move and hence are held in place by 4 strong covalent bonds with four neighbouring silicon atoms. This forms a lattice, a diamond cubic crystal structure. Because of this property, pure silicon is basically an insulator, although it can be made into a semiconductor by adding impurities. Solar cells require semi-conductors instead of simply conductors, due to the fact that one of the properties of a semi-conductor is that their conductivity changes with varying conditions such as temperature. 

Many people have solar cells installed to reduce their carbon footprint as the only greenhouse gas emissions involved in the process is the production of the cells themselves. No fuel is required for the solar panels to work and hence no carbon dioxide is released.

How efficient are they?

The downside to solar panels is their efficiency, with only around 15% of the suns energy being converted into electricity, however work is being done to increase efficiency by looking at the use of new materials. I was recently reading an article on Popular Science, found here and discovered Perovskites.

Perovskites are set to replace silicon in solar panels as they are easier to manufacture due to the fact that a conducting layer is not required. They are also readily-available, cheap and have a greater efficiency when it comes to generating electricity. It is predicted that Perovskite solar power could reach efficiencies of around 50% as scientists have recently done more work on the structure of the crystal and how electrons are transported. Also the polymers made from these crystals have the property of being translucent meaning maybe some time in the future, we might not have solar panels on our roofs, but in our windows.

It's extremely exciting to see new ideas come together and watch people take steps closer towards an age of renewable energy sources. Who knows, maybe Perovskites are the answer we have been searching for?

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