How a PV Cell Works

Sunlight is composed of photons, or particles of radiant solar energy. These photons contain various amounts of energy depending on the wavelength of the solar spectrum. When the photons strike a solar cell some are absorbed while others are reflected. When the material absorbs sufficient photon energy, electrons within the solar cell material dislodge from their atoms. The electrons migrate to the front surface of the solar cell, which is manufactured to be more receptive to the free electrons. When many electrons, each carrying a negative charge, travel toward the front surface of the cell, the resulting imbalance of charge between the cell's front and back surfaces creates a voltage potential like the negative and positive terminals of a battery. When the two surfaces are connected through an external load, electricity flows.

How a PV Cell Works

Individual solar cells vary in size from about 1 cm to about 10 cm across. A cell of this size can only produce 1 or 2 watts, which isn't enough power for most applications. To increase power output, cells are electrically connected into a module. Modules are connected to form an array. The term "array" refers to the entire generating plant, whether it is made up of one or several thousand modules.

The performance of a photovoltaic array is dependent upon sunlight. Climate (e.g. clouds, fog) has a significant effect on the amount of solar energy received by a PV array and, in turn, its performance. Most "commercial" photovoltaic modules are about 10 - 15% percent efficient in converting sunlight to electricity with further research being conducted to raise this efficiency. Experimental cells with conversion efficiencies in excess of 30 per cent are now possible.

Advantages of photovoltaic conversion for power generation are many and varied:

  • Conversion from sunlight to electricity is direct, so that bulky mechanical generator systems are unnecessary.
  • The modular characteristic of photovoltaic energy allows arrays to be installed quickly and in any size required or allowed.
  • Environmental impact of a photovoltaic system is minimal, requiring no water for system cooling and generating no by-products.
  • The siting of numerous small-scale generators in electric distribution feeders could improve the economics and reliability of the distribution system.
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