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Solar cell

Increase efficiency of street-light solar panels using a maximum peak-power tracker

August 04, 2009 | Paul Buckley | 222900633
To run an HBLED-based street light from solar power, you need an efficient charging circuit, such as a Max Peak Power Tracker, to extract maximum solar energy and transfer it to the storage batteries.
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Street lighting in many municipalities accounts for nearly half of the electrical expenditure. In addition to the energy bills, the replacement and maintenance of low-pressure sodium or metal halide lamps pose additional costs and disruption of traffic. Solar-powered street lights using High Brightness LEDs (HBLED) do not depend on the grid for electric power and have the potential of saving billions of dollars in electricity and maintenance costs.

Despite their possibilities, solar street lights are not commonplace because of their price compared to conventional alternatives. Nevertheless, as the world looks for cleaner and greener alternatives, solar-powered street lights continue to benefit from advancements in the field of semiconductors, both in photovoltaics and integrated microcontrollers, to produce more cost-effective implementations.

While the sun radiates up to 1000 Watts per square meter, a typical panel can convert only 30% of irradiant energy to electricity. In most street lights, the energy harvested by day has to be stored in a battery, and using conventional charge controllers can lead to further conversion losses. As solar panels are p-n junctions, they do not operate as ideal power sources.

Instead, they have an operating point at which the power produced is at its maximum and any movement away from this point will progressively decrease the efficiency of the panel. In order to extract all the energy that a solar panel is capable of delivering, a fully electronic system called the Max Peak Power Tracker (MPPT) is required. The MPPT is a DC-to-DC converter that poses as an optimum load, allowing the panel to operate at its peak-power state. Since the Max Peak Power Point (MPP) is dependent on the amount of radiant sunlight and temperature of the panel, the MPPT must constantly adapt to maximize the energy conversion.

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