Solar Power and the Raspberry Pi – 6 Months in the Sun

One of the critical subsystems of Project Curacao is the solar power system.  The original

solar cells have been exposed to the fierce sun for over 6 months.  I am happy to report that the Adafruit Solar Cells look absolutely perfect.  Talking with friends on other parts of Curacao, they have had nothing but problems with solar cells.  Traces pulling up because of heating, ocean spray coating cells to the point where they don’t even work, and warping in the bright sunlight.  The picture to the right is taken before cleaning and you can see the clouds reflected on the cells, they are so clean.

I have seen *none* of these problems with these Adafruit cells (made by Voltaic Systems, makers of fine solar-powered bags and packs).  These solar cells are expensive ($35 for one panel – $10/watt) but they clearly are tough enough for this environment.

There are two issues I was worried about.  One was salt spray from the ocean.  We put some solar powered lights down by the cliff (the house location is on a cliff 10 meters above the ocean) and they lasted less than six months.  The light solar cells were completely coated and inoperable.  Project Curacao and the solar panels were placed 10 meters back from the cliff edge and another 3 meters higher up and that fixed that problem completely.  They are clean!

I just took a reading from the panels (I can do all of this remotely using RasPiConnect) and I am getting  684ma @ 5.5V (3.7W) from two panels on the Raspberry Pi power system facing the sun at a pretty good angle.  Looking at the Battery Watchdog system, I am getting   187ma @ 5.2V (1.0W) in the full sun.  Note that these numbers are loaded and since the batteries are fully charged (you can tell because the solar panel voltages are > 5.0V) not much current is flowing out of the cells.  A better way of looking at the maximum power out of the solar cells will be just after night when the batteries are lowest.  I measure all the battery voltage and flows using the Raspberry Pi and display the graphs using RasPiConnect.  Data is good.

Solar Power Upgrades

I have added two more panels on the top of the Box, to give the system some extra margin.

I want the Battery Watchdog to run 24/7 and I found in the case of a cloudy week, the Arduino would run out of power and quit.  I fixed this in three ways:

• Adding a Watchdog board (soon to be a SwitchDoc Labs product) to reset the Arduino if it goes down
• Adding a new solar panel that should add 70% more power to the system
• Replacing the flaky DS1307 RTC with a more reliable DS3231 RTC

This is the inside of the box showing the new Watchdog board, the WeatherArduino board (with the DS3231 RTC in the foreground attached to the WeatherArduino board) along with the new Dual Watchdog Timer Board.

 

The box is going to be put in it’s new holder this afternoon.   I have one small problem to debug as I am not reading the power voltage to the Arduino.  Must be a loose wire.

It is already disconnected from the mains power.