What solar panel do I need for a solar powered wireless modem?
Designing a photovoltaic solar system destined to supply the energy needs of a transmitting and receive wireless radio modem involved elements very different than a system designed as grid-tied, or to connect to AC power devices. The attached devices have low energy demands, energy remains in DC (no inverter is used to create AC power), panel-mounting space is minimal, and environmental conditions can be harsh.
Choosing A Solar PV Panel
The Solar PV or photovoltaic panel harvests electricity from the sun. Quality and efficiency vary widely from manufacturer to manufacturer. Panels often use polycrystalline silicon, monocrystalline silicon, amorphous silicon, cadmium telluride, and copper indium (di)selenide/sulfide (CIGS). CIGS has the highest absorption coefficient of solar modules and is useful in harvesting energy in sub-optimal conditions such as on cloudy and overcast days and has high efficiency and carries a high cost per watt. Monocrystalline thin-film solar cells are often more expensive than multi-crystalline or polycrystalline based cells, but have a greater efficiency which is useful for wireless off-grid installations and provide a balanced price to performance.
While researching ratings be mindful of whether the wattage is rated as PTC or STC. PTC or PVUSA Test Conditions uses a known constant developed by NREL (National Renewable Energy Labs). STC, or Standard Test Conditions, uses a methodology that produces higher results. Generally, PTC is held to be more reflective of real-world solar and climatic conditions.
Understand the efficiency of the panel. On a pole-mounted system, an efficient panel should be used to ensure that the system can be powered by one or two panels.
The panel must have its performance characteristics available, and these should follow a known standard such as PTC mentioned above.
The panel needs to be paired with a proper solar charge controller. USAT technical service engineers can help differentiate the balance between panel productivity and charge controller efficiency. If you are limited on panel space and have a heavy demand, then we need to maximize panel yield along with using a highly efficient Maximum Power Point Tracking charge controller. On a recent deployment, USAT leveraged these performance attributes along with an optimal battery array to meet a DOT requirement of 10 days runtime, without the sun.
Along with the panel size, the power demand must be taken into account. USAT has demand requirements in varying loads on transmitting and receives wireless radios such as those in the Sierra Wireless AirLink® Raven, Sierra Wireless AirLink® PinPoint, Sierra Wireless AirLink® GX-400 and GX-440, Encore Bandit, Cradlepoint MBR and COR, Digi Connect, Digi WR, and Digi Transport, CalAmps, Multitech and Red Lion Sixnet Bluetree.