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Solar Photovoltaic Technology

HOW DOES SOLAR PHOTOVOLTAICS WORK?

Photovoltaic (PV) systems use cells to convert solar radiation into electricity. The cell consists of layers of a semi-conducting material. When light shines on the cell it creates an electric field across the layers, causing electricity to flow. 
The greater the intensity of the light, the greater the flow of electricity. However, a PV system can also generate electricity on cloudy days; it does not need bright sunlight to operate.

The performance of a solar cell is measured in terms of efficiency at turning sunlight into electricity. A typical commercial solar module has an efficiency of 16.5% - in other words, over one-sixth of the sunlight striking the module is converted into electricity. Improving solar module efficiencies while holding down the cost per cell is an important goal of the PV industry.

PHOTOVOLTAIC TECHNOLOGIES

Crystalline silicon (monocrystalline or polycrystalline) and Thin Film are the two main photovoltaic technologies.
  • Crystalline silicon
    Made from thin slices cut from a single crystal of silicon (monocrystalline) or from a block of silicon crystals (polycrystalline), with an efficiency ranging between 16% and 19%. This technology represents about 87% of the market today
  • Thin Film
    Made by depositing extremely thin layers of photosensitive materials onto a low-cost backing such as glass, stainless steel or plastic. Lower production costs counterbalance this technology’s lower efficiency rates (from 10% to 15% average)
  • Other cell types
    Several other types of PV technologies are being developed today or are starting to be commercialised, including concentrated photovoltaics (operates with concentrated sunlight, using a lens to focus the sunlight onto the cells) and flexible cells (similar production process to thin film cells, their flexibility opens the range of applications)

PHOTOVOLTAIC APPLICATIONS

Solar photovoltaic systems can be installed on rooftops, integrated to a building's envelope, or ground-mounted. Photovoltaic applications include residential systems, larger industrial/commercial systems and utility-scale power plants, but also consumer goods. A solar photovoltaic system can be either connected to the grid or off-grid.

  • Grid-connected residential systems
    Can be rooftop, integrated in the building’s envelope (used as a building component for insulation, roofing tile, shading, etc.) or mounted directly on the ground (in the garden). Connection to the local electricity network allows any excess power produced to feed the electricity grid and to sell it to the utility. Electricity is imported from the network when there is no sun  
  • Grid-connected power plants
    Can be ground-mounted, or located on large industrial/commercial buildings such as shopping malls, airport terminals or railways stations. These produce a large quantity of PV electricity at a single point, and make use of already available space providing a part of the electricity needed by these energy-intensive consumers (in the case of industrial/commercial buildings)
  • Off-grid systems for rural electrification
    Can be a small solar PV system covering the basic electricity needs of a household, or a larger solar mini-plant, providing enough power for several homes. These systems bring access to electricity to remote areas (mountain huts, developing countries, small islands). More information is available at www.ruralelec.org 
  • Off-grid industrial applications
    Very frequent in the telecommunications and transport fields: Repeater stations for mobile phones, traffic signals, marine navigation aids, security phones, remote lighting, highway signs, etc. These bring cost-effective power in areas far away from the electricity grid, avoiding the high cost of installing cabled networks
  • Consumer goods
    Many everyday electrical appliances use PV cells: watches, calculators, toys, battery chargers, water sprinklers, lighting, etc.

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