When certain solids come into contact with the light it sets negative and positive charges free within them which in turn creates electrical activity i.e., electric current in them. The famous scientist, Albert Einstein received the Nobel prize in physics for analyzing this phenomenon which came to be known as 'the Photoelectric Effect'. The following section explains, in brief, how this phenomenon is implemented in the form of photovoltaic cells (solar cells) for electricity generation. It is estimated that 20-30% of energy in every household is used to heat water. If it is coming from electricity or by burning fossil fuels then it better be generated by using solar panels. These panels, once installed, can last up to 25 years and there is almost no expenditure in maintaining them.
Solar Panels are Made With...
A typical solar panel for generation of electricity contains 36 solar cells of different sizes, depending on the wattage or amperage of the panel. A strong aluminum panel serves as a rest for the solar panels and is mounted in a tough frame. The yield of the electricity depends on the type of material that goes in making the solar cells. Monocrystalline or polycrystalline solar cells are used to make rigid solar panels.
Monocrystalline or Polycrystalline Solar Cells
Monocrystalline solar cells are made of 1 millimeter thick wafers of silicon that has been grown from a single silicon crystal. The yield of electricity from the solar panel made using these efficient solar cells is more than polycrystalline solar cells.
Thin wafers of multifaceted silicon crystals are used to make polycrystalline cells. These are less efficient than monocrystalline ones. However, polycrystalline solar cells used in rigid solar panels are cheaper than monocrystalline solar cells.
How Does a Solar Panel Make Electricity
Solar cells make use of the photoelectric effect for the production of electricity. Pure crystalline silicon is not a good conductor of electricity. Its electrons are not free to move about and carry an electrical charge. So atoms of other elements are added to 99.999% pure silicon. Elements such as boron, when added to silicon, turns it into the P-type silicon, which readily accepts electrons. On the other hand, elements such as phosphorus when added to silicon, convert it to the N-type silicon, which readily supplies electrons.
Solar cells, which are also known as photovoltaic cells, are made using a P-type silicon layer, a N-type silicon layer and a transparent and electrically conductive layer. It also has metal contact layer and a P-N junction. When sunlight falls on both the silicon layers of the solar cell, electrons and positive charges (protons) get excited and start moving within the layers (where N-type gives and P-type receives). This flow of electrons is known as electric current. These moving charges are then channelized through the electrical contacts laid on the solar cells to the junction box and emerge as direct current (DC) which can be used to charge batteries. The DC is fed to an inverter which converts it to alternating current that can be used to power electrical equipment.
Solar Panel's Efficiency
In the northern hemisphere, solar panels must face south and those in the southern hemisphere, must face north to take the maximum advantage of the available sunlight. The electricity production is measured in the units of kilowatts, wherein one kilowatt is equal to 1,000 watts. On a clear day, the solar energy (sunlight) hitting 1 square meter of the earth's surface, has the potential of producing 1,000 watts of electricity. The efficiency of solar panels ranges from 5-18 percent and mainly, depends on the type of solar cells used in it. Under laboratory conditions, multi-junction solar cells have achieved 40% of efficiency. The intensity of sunlight, cloud cover, rain and snow are major factors, that can affect a solar panel's electricity production.
Advances in Solar Cells Technology
Thin-film Solar Panels
They are made by laying a layer of silicon on either side of thin and transparent sheets of various materials. The sheet is layered with solar cells of P-type silicon on one side and the corresponding N-type silicon layer on the other side. The sheet is arranged in such a way that the sunlight falling on it passes through the N-type silicon layer, transparent sheet and then it reaches the P-type silicon layer. This excites electrons and protons, and generates electrical activity which creates an electrical field around the middle sheet. Electric current starts flowing through the sheet which is electrically conductive. Solar panels made using this technology are light and easy to handle. The method used to make these solar cells is inexpensive and does not waste precious silicon while making them. Amorphous silicon is used to manufacture these solar cells.
Solar Cells Made with Carbon Nanotubes
Scientists at New Jersey Institute of Technology (NJIT) have developed a technology to make solar cells using carbon nanotubes that can be painted or printed on flexible plastic sheets. They believe that the walls or roofs of houses painted with these inexpensive solar cells can be used as solar panels to produce electricity which then can be stored in the rechargeable batteries for one's personal use.
Solar Thermophotovoltaic (TPV) Devices
Scientists at Massachusetts Institute of Technology (MIT) have developed a new approach to generate electricity from the Sun's energy. Thermophotovoltaics (TPV) are solid-state devices that employ two layers to convert radiant heat from the source such as the Sun. Mirrors are used to collect and concentrate sunlight on the top layer of TPVs. The top layer consists of photonic crystals which are designed to prevent the absorbed energy from escaping into the atmosphere, however it allows it to escape to the (photovoltaic) layer underneath. The trapped heat is emitted as light of wavelength most suitable for photovoltaic conversion. Solar TPV devices are efficient than the traditional photovoltaic solar cells and are claimed to convert as much as 36 percent of incident solar energy into electricity. Though these devices are a recent development and not yet mass-produced or in commercial use, they represent a mighty achievement in use of solar energy.
Additional Facts Related to Photovoltaic Power Generation
- Germany is the leader in the solar panel based electricity production.
- Solar Energy Generating Systems (SEGS), the biggest solar power farm in the world, is installed in the United States. It consists of 9 solar power plants, erected in California's Mojave Desert and has combined capacity of generating 354 Megawatts of electricity.
- Blythe Solar Power Project is another farm, under construction, in California, at Riverside County which is expected to produce 968 megawatts of electricity.
- There is a huge demand for solar panels in Asian countries due the abundance of sunlight.
- Some of the governments are offering to buy the electricity produced using the solar panels. The German government is paying as high as 4 times the normal rates to buy this type of electricity.
Commercial Use of Solar Panels for Generating Electricity
|List of Photovoltaic Power Stations|
|Golmud Solar Project||Qinghai Province, China||200 MW|
|Montalto di Castro Photovoltaic Power Station||Montalto di Castro, Viterbo, Italy||84.2 MW|
|Finsterwalde Solar Park||Finsterwalde, Germany||80.7 MW|
|Ohotnikovo Solar Park||Okhotnykovo, Crimea, Ukraine||80 MW|
|Sarnia Photovoltaic Power Plant||Sarnia, Ontario, Canada||80 MW|
|Solarpark Senftenberg, Germany||Senftenberg, Brandenburg, Germany||78 MW|
|Lieberose Photovoltaic Park||Lieberose, Brandenburg, Germany||71.8 MW|
|Rovigo Photovoltaic Power Plant||Rovigo, Italy||70 MW|
|Le Gabardan Solar Park||Gabardan, France||67.2 MW|
|Sault Ste Marie Solar Park||Sault Ste Marie Solar Park, Canada||60 MW|
|Perovo Solar Park||Perovo, Ukraine||60 MW|
|Olmedilla Photovoltaic Park, Spain||Olmedilla de Alarcón, Spain||60 MW|
|Olmedilla Photovoltaic Park||La Mancha, Spain||60 MW|
|Strasskirchen Solar Park||Straßkirchen, Germany||54 MW|
|Strasskirchen Solar Park, Germany||Bavaria, Germany||54 MW|
|Lieberose Photovoltaic Park||Brandenburg, Germany||53 MW|
|Tutow Solar Park, Germany||Tutow, Mecklenburg-Western Pomerania, Germany||52 MW|
|Copper Mountain Solar Facility||Boulder City, Nevada, USA||48 MW|
|Puertollano Photovoltaic Park||Castila-La Mancha, Spain||48 MW|
|Moura Photovoltaic Power Station||Amareleja, Portugal||46 MW|
Once solar energy was a hi-tech field. The space vehicle Vanguard-1, launched on March 17, 1958, was the first to utilize the solar panels. Now, scientists are experimenting with consumer vehicles. They are trying to convert roofs of these vehicles in solar panels, by painting them with solar cells made with the carbon nanotubes. The whole world is gearing to convert as much of safe and free solar energy into the electricity as possible.