To capture the maximum amount of solar radiation throughout the year, mount a fixed solar panel to optimize the sun's
energy throughout the year. For the northern hemisphere, face the panel true south. For the southern hemisphere, face
the panel true north. If you are using a compass to orientate the panels, compensate for the difference between true north
and magnetic north. Magnetic declination varies across the globe.
A solar panel's average tilt from horizontal is at an angle equal to the latitude of the site location. For optimum
performance, adjust the tilt by plus 15 degrees in the winter or minus 15 degrees in the summer. For a fixed panel with a
consistent power requirement throughout the year, adjust the tilt angle to optimize for the winter months: latitude plus 15
degrees. Although in the summer months the angle may not be the most efficient, there are more hours of solar energy
available.
For sites with snow in the winter months, the increased angle helps to shed snow. A solar panel covered in snow produces
little or no power.
5.3.3 Recommended Solar Configurations
These solar panel and battery combinations assume direct sunlight for two to three hours a day. Solar insolation maps
provide approximate sun energy for various locations. The depth of battery discharge is assumed to be 50 percent.
Solar panel and battery combinations for a DXM Controller system
Solar Panel
Battery Capacity2
Days of Autonomy
DXM mA
DXM Controller
5 watt
10 Ahr
10 days
25 mA
DXM Slave Controller - ISM radio and I/O base board
20 watt
14 Ahr
10 days
30 mA
DXM Controller with ISM radio
20 watt
20 Ahr
10 days
35 mA
DXM Controller with ISM radio and Cellular Modem
5.3.4 Monitoring Solar Operation
The DXM solar controller provides Modbus registers that allow the user to monitor the state of the solar panel input
voltage, the battery voltage, the charging current, and the temperature in °C. The DXM Controller can be configured to
monitor the health of the charging system as well as send an alert message when the battery is too low.
The charts show a typical charging cycle, with each vertical grid representing about eight hours. The chart shows three
days of charging.
Figure 1. Solar Panel Voltage (mV) -- Cloudy First Day
Figure 2. Battery Voltage (mV) - Cloudy First Day
2 Battery capacity (amp hour) is standard amp rating taken for 20 hours. Battery capacity should be monitored for reliable system power and may
need to be increased for cold weather locations.
DXM100-Bx Wireless Controller Instruction Manual
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