How Is Electricity Generated in Solar Power?
The conversion of solar energy into electricity is known as photovoltaic (PV) process. A few materials will absorb photons (discrete bundle of electromagnetic energy or basic unit of light) and emit electrons, a property known as the photoelectric effect. The capture of discharged electrons produces an electric current. Photovoltaic technology can convert light from the sun into power used for household lighting and appliances, electrical tools and computers.
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How It Works
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According to NASA Science, a photovoltaic or solar cell consists of two or more fine layers of silicon---a semiconductor commonly used in microelectronics---that forms a wafer. Specially treated, a cell has a positive side and a negative side, with conductors on both sides. This configuration forms a circuit, enabling the cell to create an electrical field. When light strikes silicon, the freed electrons generate a charge that can be conducted as direct current (DC).
Photovoltaic Modules
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A single cell produces a tiny charge. Multiple cells must be linked and wrapped in glass to form a module, reports The Electricity Forum. The design of each module will generate electricity at a specified voltage---for example, the 12 volts system. Wiring together several modules results in an array. Larger arrays produce direct-current electricity; however, their output depends on the amount of available sunlight. Given their flexible structure, arrays can be formed into either parallel or series arrangements to achieve the desired mix of current and voltage output.
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Source Issues
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Sunlight, or lack thereof, dramatically impacts the output of a solar cell. According to Gigaton Throwdown, if only part of the cell falls into shade, the electrical output drops due to electrons reversing course in the silicon, or short circuiting. Areas for PV installation should be clear of any objects---trees, towers, flags---that would cast a shadow. Tracking devices boost energy capture, but can be expensive.
Grid Connect Photovoltaic Systems
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PV systems that plug into a local electricity network are known as grid connected. In addition to an array and its mounting frame, these systems require an inverter to transform direct-current into alternating current electricity as well as a meter to track used and unused power. According to the National Renewable Energy Laboratory, consumers can either use power generated by the PV system or sell excess electricity to energy suppliers during daylight hours. At night, when the PV system lacks light, consumers can purchase energy from the network, thereby eliminating the need for storage. While PV modules are easily mounted on angled rooftops, photovoltaic roof tiles accommodate irregular surfaces. Technological advances in photovoltaics have led to the incorporation of PV systems into windows, canopies and actual building fabric.
Off-Grid Photovoltaic Systems
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Photovoltaic systems that are not connected to a power grid require storage, reports the IEA Photovoltaic Power Systems Programme. Rechargeable battery packs are typically sized to sustain household electricity for week of shady days. In developing countries or remote regions with few or unreliable power grids, standalone PV systems may pose the only option for energy. In developed countries, off-grid PV are often used to power street lights, outdoor waiting areas, telephone kiosks, boats, fountains and a wide range of electronic devices.
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References
- IEA Photovoltaic Power Systems Programme: Stand-alone PV power systems (off-grid)
- The Electricity Forum: Solar Electricity Explained
- NASA Science: How do Photovoltaics Work?
- Gigatown Throwdown: Solar Photovoltaics
- National Renewable Energy Laboratory: Very Large-Scale Deployment of Grid-Connected Solar Photovoltaics in the United States: Challenges and Opportunities
Resources
- Photo Credit moderne solarfassade image by Holger B. from Fotolia.com
