
WilliamsRDM, Inc. 8 | P a g e
Table 1: Basic Solar Test Parameters
Symbol Definition Description Value
Vo Open Circuit Voltage Open Circuit Voltage that would be
measured from solar panel with a
multimeter
19.4V
Is Short Circuit Current Short Circuit Current that would be
measured from a solar panel with a
multimeter
168mA
Vm Maximum Power Point Voltage The voltage at which the solar panel
produces its maximum output power
17.7V
Im Maximum Power Point Current The current at which the solar panel
produces its maximum output power
139mA
Pm Maximum Power Point power The maximum power the solar panel can
produce if loaded at its maximum power
point voltage and current
2.4W
From a user perspective the most important parameter to consider is the Pm (Maximum Power) parameter
which measures the maximum power that the solar panel can output when properly loaded in a particular
lighting condition. The output power in full sun with the sun directly overhead should be close to the rating of
the solar panel that is being tested otherwise the panel may not be working properly. For example, if a 5W solar
rock is being tested in full sun and only producing 0.2W then the solar panel may not be working properly.
If multiple solar devices are connected in parallel with a Y-Adapter, then the measured output power should be
approximately the sum of each individual solar device.
8 Smart 12V Test
The Smart 12V Test is used to test the WilliamsRDM Covert Smart Solar Devices which incorporate a Maximum
Power Point Tracking (MPPT) Solar Charger, Partial Shading technology and are designed to charge 12V lead acid
batteries. This test should be performed outside on a sunny day to measure the maximum power from the Smart
Solar Device. The Smart 12V Test provides information on the battery charging voltage, current, power as well
as a pass/fail indicator for the smart solar device. Table 2 shows and example of the test parameters provided
by the solar tester for the Smart 12V Test as well as their definitions and a brief description of their meaning.