HOW SOLAR WORKS ? . Solar panels produce electricity by converting the sun’s light energy (photons) into electricity using the principle known as photovoltaics or commonly known by the acronym PV. The root words of Photovoltaic originate from Greek for light “photo”. Voltaic comes from the electrical pioneer’s name Alessandro Volta where the term volt is a commonly known unit used to define electrical potential. Hence the term photovoltaic means “light electricity”. At the heart of a conventional solar panel are “solar cells” which are made of semiconducting material – crystalline silicon. The cells are fabricated using many similar techniques as computer chips (semiconductors) where the silicon is doped with other elements to conduct electricity. At the heart of the cell is the P/N junction or diode. Silicon has 4 electrons in it’s outer electron shell which are all bound to adjacent silicon atoms in the crystal lattice. For silicon to conduct electricity efficiently, it must be doped with an atom containing 5 or 3 electrons in its outer shell. This dopant atom then becomes part of the silicon atomic structure – bonding with adjacent silicon atoms leaving an extra electron or a vacancy – called a “hole”. Silicon doped with atoms containing 5 outer shell electrons is referred to as “N-type” due to a negative potential since it contains an abundance of electrons. The dopant for N-type is referred to as a donor atom as it “donates” an electron to the silicon lattice. Phosphorous is commonly used as the donor dopant atom. Silicon doped with atoms containing 3 outer shell electrons is referred to as “P-type” due to a positive potential since it contains an abundance of holes. The dopant for P-type is referred to as an acceptor atom as it “accepts” an electron from the silicon lattice. Boron is commonly used as the acceptor dopant atom. In N-type silicon, electrons are available for conducting. In P-type silicon, holes are available for conducting. Conventional crystalline silicon solar cells are fabricated using silicon substrates that are formed from P-type silicon. These substrates are subsequently doped with Phosphorus at the upper surface of the cell forming a very thin layer of N-type Silicon establishing the “P/N junction”. A thin layer of Anti-Reflective-Coating (ARC) is formed on the top surface. This film, typically silicon nitride, is deposited using techniques that target optical characteristics allowing specific wavelengths of the light spectrum to pass efficiently through the film and into the silicon substrate without reflecting from the surface. Metal contacts are printed and alloyed to the silicon on both sides of the cell (making contact to both the P-type and N-type sides of the junction) enabling electricity generated in the cell to flow into the panel’s circuit and ultimately working to run an electrical device. In the solar cell, when photons collide with a silicon atom, energy is transferred to an electron in the outer shell, electrons will flow across the P/N junction in one direction and holes in the other direction – establishing an electric current created by light energy. The “panel” is the last part of the fabrication process where the cells are soldered (wired) together in series to maximize voltage output. These cells are encapsulated into the panel using transparent Ethylene-vinyl acetate (EVA) film. The panel is assembled with a glass superstructure, aluminum frame work, back-sheet material typically made of PVA that are electrically insulating. Typical panel lifetimes are >25 years which places stringent requirements on these panel materials’ low rate of degradation and the panels sealing attributes which protect the cells and wiring from moisture and atmospheric contamination. A junction box is sealed to the back of the panel where the panels are connected together to form an array of panels. The number of panels in the array determine the total power output. Solar panels produce electricity in the form of direct current (DC). Most home appliances will require alternating current (AC). Typical solar panels array installations will incorporate an inverter which inverts the DC to AC current and matches the utility grid alternating current phase.
Posted on: Mon, 19 Aug 2013 05:11:52 +0000