How solar cells work:
Solar energy is radiant energy from the sun. Solar energy in the form of heat and light sustains life on earth. Solar energy can also be collected, stored and put to work by converting it to pollution-free thermal energy and electricity. However, less than 1% of the world’s total electricity production comes from solar power.
Solar cells called Photovoltaic (PV) cells convert sunlight directly into electricity. they rely on the photoelectric effect which is the emission of electrons when a light is shone on it.
Semi-conductor materials, such as silicon is the key property of these solar panels as the share some properties of metals and also properties of an electrical insulator. The solar cells are made up of two types of semiconductors, called p-type and n-type silicon. The p-type of silicon is made my adding atoms, like boron or gallium as they have one less electron in their outer energy level than silicon does. Because the elements boron and gallium have one less electron, an electron hole is created. The n-type silicon is produced by including atoms that have one more electron in their outer level than silicon does, the most common is phosphorus. Because phosphorus has one more electron than silicon, one electron just moves inside the silicon structure without being bonded.
The p-type silicon and the n-type silicon are placed next to each other, as shown in the diagram. Due to the fact that in the n-type layer, there is an excess of electrons, and in the p-type layer, there is an excess of positively charged ‘holes’, the electrons from the n-type layer travel over to the p-type layer. This causes the p-type silicon to contains negatively charged ions and the n-type silicon contains positively charged ions. This creates an electric field.
As photons, which are miniscule particles that radiate from the sun, hit the silicon atoms of the solar cell, they transfer their energy to lose electrons. This knocks the electrons off the atoms, creating an electric current, which can then be captured to create electricity.
Energy Output and Efficiency
The amount of energy a solar cell can produce depends on the efficiency of the solar cell, the size of the solar panel and the amount of sunlight hitting the solar panel size. The average of sun light power or solar power covering all the spectrum is about 1KW/m2. Solar cells made of 1 m2, produce about 140-170 W.
The efficiency of the solar cell is the percentage of the solar energy shining on the cell that can be converted into useable electricity. This can be effected by the different wavelengths of sunlight that reach the earth’s surface and only some photons pass through the earth’s atmosphere, it can also be effected by the temperature, reflection (if you minimize the amount of light that is reflected away than it can increase the cells efficiency). The average cell efficiency of a solar panel is between 11 – 22%. The higher the efficiency of a solar panel, the more solar power it will produce per square meter. However, the efficiency of a solar panel is constantly increasing due to constant research in having a developed a cell that converts sunlight to electricity at 34.5%. The original efficiency of a solar panel (in 1954) was about 6%.
Resources needed to make solar panel:
- Sunlight – Used to knock the electrons off the silicon
- Silicon – which is used as a semi-conductor as when light form the sun hits the solar cell, electrons from the material are knocked loose from the atoms in the semiconductor material
- Glass – Which allows light to pass through yet provides enough protection to withstand outdoor temperatures and rough weather
- Metal – To create a backing material which the silicon can be placed onto, it can also be used as a frame
- Copper – To create the cell ribbons inside of the solar cells
- Boron/Gallium – To create positively charged holes in the silicon
- Phosphorus – To create an excess of electrons
Renewable energy is generally clean and non-polluting. Given that solar energy is from the sun and it doesn’t emit carbon dioxide, it is classified as renewable energy. In order for energy to be renewable energy to be sustainable it has to be obtained from resources that are inexhaustible, unlike fossil fuels. Solar energy is a sustainable form of energy because the resource (sunlight) required to produce electricity is an inexhaustible resource as it take less than a human lifetime to replenish. The Earth receives an average of 250 watts of energy from the sun per square meter so the resource will never run out as energy from the sun will continue to reach the Earth’s surface for centuries to come. However, even though the sun itself is eco-friendly, to manufacture the panels requires the use of chemicals such as sodium hydroxide and hydrofluoric acid, the production of which emits greenhouse gases and produces waste. So, the actual manufacturing process produces waste even though the energy source is sustainable. Also, the waste created from the solar panels also has an environmental impact. Recyling is important as the panels have silver, tellurium and indium which are precious metals which, if the panels are not recycled, they will become a scarce resource, making the disposal of solar panels unsustainable. However, solar companies are now producing sustainability reports to help fix this problem.
Advantages
Solar power is a clean source of energy and it doesn’t emit any carbon dioxide in the atmosphere while it is running, unlike fossil fuels. This means that it doesn’t contribute to global warming. Another advantage is that the sun is a renewable energy resource so you will never run out power coming from solar panels. It can be used to produce electricity as long as the sun exists and the sun is expected to last for 5 billion years. The sun is an incredibly powerful energy source and because solar panels are becoming increasingly efficient, we can always utilise enough energy from the sunlight. Another benefit of solar panels is the little maintenance required. Unlike wind energy, there are no moving parts, so the inverter only needs to be changed every 5-10 years and the cables also need minimal maintenance. Solar panels also have a long 25-30 years lifespan, which is long lasting compared to other renewable energy resources. Solar energy is accessible in areas without access to power cables and works efficiently in remote locations where running power lines would be difficult or costly. Solar panels can be set up to produce solar energy wherever sunlight is received. Solar power can create jobs for example, solar panel manufacturers, solar installers and this grows the economy. A U.S report found that the solar energy industry provided 373,807 direct jobs distributed across manufacturing, installation, distribution, and support services in America. The solar energy industry grew 24.5 percent between November 2015 and November 2016 giving solar power the largest number of workers in the energy industry compared to other renewable energy resources.
Disadvantages
The supply of solar panels cannot keep pace with demand. Unlike fossil fuels, another disadvantage of solar power, like wind power, is that it cannot be transported. The best locations are often located a great distance from the solar load centres which makes the storage and connecting costs of solar energy a lot more expensive. The availability of the sunlight is only predicable a few days in advance. This means that the energy generated fluctuates according to the real availability of the sunlight.
Solar power also only would be effective in continuous sun. Some places (like the Amazon rainforest which receives very little sun and the Arctic which receives 6 months with absolutely no sun) would struggle to get power from solar panels. Solar panels cannot create energy when it is dark or cloudy, therefore it would be hard to rely fully on solar panels unless you have batteries that could store a lot of the energy. In fact, cloud cover can reduce the solar output by 70% in 1 minute. Another disadvantage is the waste generated from old solar panels due to very limited places to recycle solar panels. This is a major concern because the resources required to make these panels are often rare resources that are becoming scarce. Solar panels are also having a negative impact on the environment when people build solar energy power plants as habitats are destroyed to place rows of solar panels. Solar panels are also expensive to install, compared to fossil fuels which are quite cheap.