First of all we need a way to simulate the Raspberry Pi "load" toward the system.
Browsing around the net I found the perfect tool for that, an USB load capable to be set to draw from few mA up to 3A.
Another nice thing to have is an USB voltmeter/current meter like this one :
Then the idea is to use the Raspberry Pi itself, powered externally, to run a monitor program to capture the battery charge/discharge and other conditions, like full sun/night to determine the solar power supply under different conditions.
Here a block schematic about the test environment.
The goal is to have the system set to draw about 300-350 mA from the solar power, simulating the average load of a Raspberry Pi, and see how the system behave in few week run, monitoring the battery charge/discharge via the Raspberry Pi.
MonitoringAs mentioned, the monitoring is done using a Raspberry Pi with the groove system.
At least we need to monitor the battery charge and the amount of light (used to determine if there is sun enough to charge the battery.
The monitoring program, in python, running on the Raspberry Pi is quite simple.
It just open a log file and every 60 seconds reads the value of the voltage and the value of the light.
The data collected in a file are then displayed on a graph using gnuplot.