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Photovoltaic: electricity from light. Photo = light; voltaic = volts, a measure of electricity.
Solar energy systems are composed of PV (photovoltaic) modules or panels, an inverter, and a digital electric meter that connects to the utility grid.
• PV modules convert light into DC (direct current) electricity, the same kind of power provided by auto and flashlight batteries.
• The DC is changed by the inverter into AC (alternating current), like the power supplied by the electric utility.
• The AC is distributed through the building or home electric panel and flows to outlets, lights and switches.
• The inverter also sends surplus energy through the electric meter out to the grid.
• The meter keeps track of the energy flowing out for credit with the local utility. This credit applies to the electric bill and helps pay down the cost of the solar system.
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Solar PV modules are made of silicon, just like computer chips. Silicon generates an electrical current when exposed to light. PV modules are made of two extremely thin slices of silicon, one with a positive charge (p) and the other with a negative charge (n), sandwiched under a protective sheet of glass. An electrical field forms at the boundary where the two silicon layers meet, called the P-N Boundary. Sunlight reaches earth in the form of energy packets called photons, which have the ability to knock an electron free from a silicon atom. Free electrons, which have a negative charge, are attracted to holes in silicon atoms where other electrons have been knocked free. The holes have a positive charge. As the negative free electrons move towards positive holes in silicon atoms, they are captured by the electrical field that forms at the P-N Boundary where the positive and negative silicon layers are joined. Fine wires on the surface of the silicon capture the free moving electrons, and when they are connected in a circuit, direct current electricity flows from the PV module. The DC flows to an inverter, which changes 96% of the electricity generated by the solar modules to AC. The AC from the inverters flows to the electrical distribution panel for use in the home or building. Solar needs no maintenance except to spray dust off with a hose during dry periods. Usually rain washes away the dust. Solar energy systems are solid state and have no moving parts, never wear out, and don’t heat up or smoke, shake, vibrate, buzz, chug or whistle.


PV modules generate electricity when they’re exposed to sunlight. The more sunlight they collect, the more electricity they produce. In countries located on the equator, PV modules collect the most sunlight when they’re mounted flat, because at the equator the sun rises in the morning and follows a trajectory straight overhead, 365 days a year. Throughout the day the flat PV panels receive the maximum sunlight possible. In the northern hemisphere, the sun moves across the sky at an angle to the earth and dramatically changes position in the sky between summer and winter. Flat-mounted PV modules lose much of the sunlight they could potentially collect because it reaches the panels at a sharp angle. Much of the light simply bounces off the glass surface of flat panels. U.S. solar installers typically tilt PV modules to the sun at the average angle that collects the most sunlight year-round. Unless the PV system is located on the equator, it doesn’t make sense to have flat-mounted solar panels.


Dust in the air gathers on PV modules just like it does on a car. The fine coating of dust that dulls a car’s finish also reflects sunlight off the surface of a PV module—preventing light from penetrating to the module to thus generate electricity. Dirty PV modules produce less electricity than clean modules. Rain washes airborne dust off tilted PV modules. Flat-mounted PV modules gather more dust, and when it rains dirt puddles on the surface of each module. It’s recommended in dry periods to spray dust off PV modules with a hose. If they’re mounted flat, there’s nowhere to spray the accumulated dirt—like trying to spray dirt off a large, flat driveway. Tilted modules are more productive because they shed dust and stay cleaner.


In the same way that a computer has fans to cool the silicon chips, solar modules are mounted in a tilted position to allow cooling air flow across their front and back surfaces. Flat-mounted PV modules have no air flow across the back, run hotter and are less productive. Like computer chips, PV modules are primarily made of silicon, and like microchips they operate most efficiently when they’re cool. Heat causes electrical resistance in a silicon chip or PV module, which slows productivity. PV modules generate electricity from light, not heat, and heat reduces electric production because of resistance. Heat gain from the sun is radiated from the front and back of a tilted module, cooling the panel, lowering resistance and raising productivity.