A Live Green, Live SmartTM Briefing 
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A lot of consumer technology starts its life in more exotic settings. The little photovoltaic cells, or PVs, that power inexpensive calculators and gadgets were first developed by researchers at Bell labs experimenting with silicon wafers that turned out to be sensitive to sunlight. By the 1950s this knowledge led to the development of photovoltaic cells that could capture sunlight to power orbiting satellites; orbiting satellites led to those gadgets, wristwatches, calculators – and eventually, to commercial and home production of electricity.
A photovoltaic cell gathers photons, particles that are the largest portion of sunlight, as fuel to generate electricity. The photovoltaic cell itself combines elements of conventional batteries: a cell structure containing a semiconductor element between the top and bottom surfaces absorbs sunlight and releases electrons through the top surface. The bottom surface is less receptive to electrons, which causes an imbalance in the electrical charge between the two sides of the cell (like the positive and negative ends of a conventional battery) creating voltage that can flow through as direct current to be used as electrical power.
A PV system combines individual cells in modules of two to thousands of PV cells to form an array that collects sunlight and converts it into an electricity-generating system.
Small PV systems may power a single appliance for immediate use, larger ones can meet the needs of entire homes or commercial buildings. Home PV systems are familiar to most of us as the flat-plate collectors observed on houses since the mid-1970s, used mainly for small electrical needs, heating water, and for space heating. Commercial arrays may involve many rows of photovoltaic mirrors, and can be configured to suit the design of large structures’ roofs and walls, and are usually unseen by the casual observer.
So what happens when the sun goes down? Photovoltaic systems can be engineered to store energy for later use when there isn’t enough sunlight to directly generate power.
Today’s PV systems are usually combined with connection to conventional energy systems as back-up when conditions – weather, maintenance, damage – require. Even in consistently cloudy climates, some PV energy can be produced. In sunnier settings, PV users can even collect enough sun-generated energy to sell their excess back to the main utility grid for use elsewhere. Some systems may generate more electricity than the owner uses, resulting in photovoltaics not just saving money, but making money in some cases.
Once installed, solar energy is clean and non-polluting: they produce zero emissions and their operation uses zero nonrenewable energy. The pollution from manufacturing the cells is more than offset by the energy and pollution saved in their application: users of PV systems decrease the need to burn coal and other dirty fossil fuels for heating and electricity.
Photovoltaic systems are an overall positive for individual users and the environment, allowing users to control costs and countries to support energy independence (the sun is locally available); reduction of pollutants from burning and transporting other fuels helps reduce greenhouse emissions and other environmental degradation. Solar energy is one energy source we can indulge in without guilt.