What solar charge controller do I need to power a wireless modem?

The solar charge controller takes solar irradiance input and provides it as output to charge the battery storage in the system as well as provide electric to the system equipment (modems, cameras, meters, sensors, etc).
It is important to determine how critical array yield is, what the operating temperature requirement is, as well as if the controller will used in a hazardous location (Class 1, Division 2, Groups A-D, such as needed for oil & gas industry application).

Two major charge controller technologies are MPPT (maximum Power Point Tracking)and PWM (Pulse Width Modulation) charge controllers.
MPPT charge controllers maximize the yield from a panel by harvesting from the peak point of the PV array. The MPPT then convert the power to a charging voltage for the battery and boosts the power when needed. USAT often specs MPPT charge controllers that have a 97% or a 99% efficiency rating and a very low self-consumption rate. These are very useful when the yield from a one or two panels needs to be maximized—when adding another solar panel is not a practical option.

MPPT charge controlled benefit from using numerous power points during shading, sunrise and sunset, from very fast sweeping of the entire solar i-v curve, and from the strongest production during low solar insolation times. These often have temperature sensors that can adjust the charging temperature of the battery based on ambient temperature inside the enclosure. Solar sizing can be completes in watts since the panel will be fully utilized.

PWM charge controllers connects the array directly to the battery being charged, therefore operating the array at the battery voltage. The controller should have a 4 stage battery charging capability to maintain optimal battery life and charge state.

Array sizing must be done in amps as less power is available for charging the battery.

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