For an additional expense of less than $10, deployments that have a schoolserver, and a solar charging system for a lead acid battery, can make the SOC (State of Charge) easily visible, locally, and if they have an internet connection at the school, also visible to funders, and supporters worldwide.
This chart shows the battery as it is becoming fully charged early in the day by the solar panels — the controller is limiting the voltage and current so that the battery is not destroyed by overcharging. The SOC is hovering around the 95% level. In the middle of this graph, I left a load resistor connected overnight (the load wattage increased from 4 to 20 watts). It took a couple of days for the SOC to return to 100%. There is additional explanation of how to interpret the voltage, power, and percentage graphs.
In Haiti, I have helped to install solar controllers designed by Epsolar, a Chinese company. I bought one of these and installed it on my own test system, in California. The 20 Amp version I bought ($115), Tracer-2210RN, is one of a family which also includes 10A an 40A versions.
They all have available an MT-5 user interface with an LCD display, which the company sells separately.
This digital interface provides an opportunity for the Schoolserver to monitor, and publish the information which is vital for preserving the life and usefulness of the solar system, yet which is often difficult, for the school personnel to obtain.
$5.80 http://www.amazon.com/gp/product/B008AGDTA4 — for this USB to TTL dongle, green is transmit, white is receive, and black is ground. This must match up with the wiring of the Epsolar controller documented at https://github.com/xxv/tracer/blob/master/docs/Protocol-Tracer-MT-5.pdf
The code for integrating the Epsolar controller is available at https://github.com/georgejhunt/xsce/tree/tracer/roles/solar
The code can be downloaded by the following:
git clone https://github.com/georgejhunt/xsce –branch tracer –depth 1
The xsce/roles/solar/files path is where the code is burried.