Power Electronics

Photovoltaics Make Radio System Truly Wireless

A digital radio transceiver from FreeWave, the FGRIO-S, can be powered with solar energy from a kit specially designed for that radio, making it truly wireless and virtually maintenance free."

The radio provides a wireless digital communications link for sensors and actuators. It has a nominal range of three kilometers with a unity-gain antenna, with a maximum range of dozens of miles with high gain antennas and clear line-of-sight conditions. The radio has power management features that reduce the capacity requirements of the solar cells, such as low power standby modes and the ability to activate and deactivate sensors.

The solar power kit for the radio consists of a solar panel and a weatherproof enclosure that contains a battery and a charge controller. Cables from the enclosure connect directly to the power supply input of the radio. A standard practice in the industry is to provide two weeks of holdup time in the event of a power failure. That same precaution is observed in this system, and the ability of the radio to monitor its input supply voltage would provide an indication of a fault in the solar power kit long before total failure of the radio.

Among the various components within the radio, the LEDs consume the most current, which is below 15 mA per LED. The LEDs are powered from a 3.3-V switching regulator.

According to Geoff Terrell, I/O Designer for FreeWave, the solar panel included with the kit provides 300 mA short-circuit current and 17 Vdc open-circuit voltage. The original battery charge controller in the kit was a Sunsaver 6 from Morningstar Corporation. This unit features PWM control and battery temperature compensation.

The Sunsaver 6 consumes 6 mA of current, which is equal to the standby current of the radio. A new version of the solar power kit uses a different charge controller from Rogue Engineering. This unit consumes 2 mA of working current, and features a 400-μA sleep mode. Rogue also supplies the solar cells for the kit, which are manufactured in China.

Colin Lippincott, CEO of FreeWave, said the solar power kit is designed to be a self-contained solution that delivers everything in one box to simplify the task of installation in the field. One of the main considerations of any solar system is the mounting of the solar cells. According to Ian Linn, Manufacturing Engineer at FreeWave, the kit is designed to simplify mounting while also providing flexibility to allow the optimum orientation of the solar panel for a particular site.

While the kit includes a compass to assist the installer with determining the direction the cell should face for maximum exposure to sunlight, the angle at which the cell is mounted is determined not only by the latitude of the site, but also geography and weather. For example, in certain solar energy systems in Canada, solar cells are often flush-mounted to poles, which allows the cells to receive sunlight reflected from snow, while also preventing snowfall from accumulating on the cells.

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