Shared on September 05, 2012 written by Keith McRae
Operating Wireless Gateways & Cellular Routers Off-Grid with Solar PV Electric
Part 3:Solar Charge Controllers
These take the solar energy and provide it 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. At USAT Corp., when we are installing solar bundles into areas of low minimum solar radiation or with numerous pieces of equipment drawing on the solar system, we rely on MPPT controllers to contain the quantity of solar PV panels needed.
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.
USAT can also send over the Wireless WAN modem solar operation information, alerts, and state triggers when a smart charge controller is used. The controllers can also communicate on Modbus and other standards.
Keywords: Solar Charge Controllers, Solar PV Electric Operations